Edinburgh:
Masons Mortar Ltd
77 Salamander Street
Edinburgh EH6 7JZ

Tel: 0131 555 0503
Fax: 0131 553 7158

Glasgow:
Masons Mortar Ltd
Unit I, Woodville Court,
Woodville Street
Glasgow G51 2RL

Tel: 0141 445 4812
Fax: 0141 445 8898

Fife:
Masons Mortar Ltd
Block 2
Woodend Industrial Estate
Cowdenbeath, Fife
KY4 8HW

Tel: 01383 514 460

Newcastle:
Masons Mortar Ltd
Unit 11
Brough Park Trading Estate
Fossway, Newcastle upon Tyne
NE6 2YF

Tel: 0191 908 9234

Practical Guides

Why Lime Mortars

Our historic buildings are entrusted to generation upon generation to preserve our heritage. We have a duty of care to ensure that whatever repair or conservation strategy we employ, however well intentioned does not impact upon that duty. Masonry walls are predominantly masonry and lime mortar, they have been shown by virtue of their durability to work well together for thousands of years. Recent repairs that have employed modern materials and concepts have been disastrous often resulting in rapid and irreversible loss and decay of build fabric. We have been producing traditional mortars and building materials since 1989. Our Price List and Product Guide is intended to provide as wide a choice of materials possible to meet the many requirements of building conservation, restoration and repair and where applicable New Build projects. With the benefit of more than 20 years of experience, we have brought together technical information to make the building professional and conscientious owner aware of material performance, characteristics and what they need to consider when deciding whether a specific mortar is fit for the purpose. This is a price list and a product guide it does not provide specifications. We have a wide range of materials, for plastering, rendering and finishing traditional surfaces. Please take a few moments to read the relevant sections they are there for your guidance. We have also introduced a range of lime based materials suitable for new build projects. These include: coloured one coat renders and backing coat renders and multi use binders for building and pointing. We can colour match our materials to suit most requirements and offer this as a service to our customers. Should you require any assistance with any aspect of our products please do not hesitate to call us and discuss your needs.

Choosing The Approprite Mortar

One important rule of thumb is that the mortar should not be stronger than the host masonry and be at least as vapour permeable. With this basic rule in mind applied to the case of historic traditional solid wall construction, two further criteria stand out.   First is the background. In a new build situation a designer has a choice of matching materials to suit the environment, detailing etc; this is not always the case with existing buildings. Secondly exposure, the location, environment and exposure to wind driven rain. Water, particularly in the form of wind driven rain is possibly the greatest threat to buildings, minor failures, slight cracks, inadequate joints and small detailing defects are cruelly exposed in strong wind driven rain. Internal timbers, imbedded in walls pick up moisture from wet masonry and mould and rot proliferate at an alarming rate, often unseen until the damage is beyond repair. In addition, damp walls require higher energy in the form of heating to maintain comfortable living conditions.   The primary dilemma comes when say for instance the background condition is such that only a relatively weak mortar would be appropriate, but the environment is such that a weak mortar would be unlikely to cure properly before the onset of winter, thereby leaving the walls exposed to even greater risk of saturation. Knowing the correct balance between background, mortar choice and mortar performance is therefore all-important.  

Our Pre Mixed Dry Bagged Range will match or exceed the general performance figures shown on the table opposite.
Although the exposure classification would suggest that the higher the number the better the mortar, this is based on current design criteria. A mortar class 1-4 can be successful in high exposure ratings provide it has been fully and properly cured, the difficulty comes in relation to the time it can take to achieve full curing and how proper detailing acts to protect areas of a building, both during initial curing and thereafter. Pre Mixed Dry Bagged Mortars will generally exceed these performance figures especially in relation to early freeze thaw resistance.
Much is made of Freeze Thaw resistance, however if something is not wet, it can’t freeze, and ultimate freeze thaw resistance is closely linked to pore structure and vapour permeability.
The use of Capillary rise figures in isolation does not mean that a mortar is vapour permeable.
Vapour permeability comes in most mortars at full carbonation, where the pore structure is such that ice crystals that form within the matrix of the wet mortar are large enough and well enough linked to allow the ice to expand harmlessly across the matrix of the mortar.
Full carbonation; can take many months, usually 10-12 in good curing conditions for a 20mm thick render. Partial carbonation in a hydraulic lime mortar is often adequate to resist freeze thaw depending on the strength achieved through the hydraulic set (Normally 1.8-2Nmm2) but this will depend on location and exposure.
In the majority of cases mortar joints are far less susceptible to initial or early freeze thaw action, with the exception of joints in dense impermeable masonry units, (examples would be Granite, Basalt, Slate, some sandstones, lime stones and some types of brick) This is due to a cascade effect where water that is not absorbed into the face of the masonry, flows freely down the wall face, any wind pressure then concentrates the water, exposing weak or defective joint finishing, leading to early saturation and a higher risk of freeze thaw, particularly relevant to parapets, copes, sills and chimneys.
Saturated masonry has the potential to trigger
Sulphate reactions, either from air borne pollutants or from soluble Sulphates in the host masonry or sands or through capillary action from ground water.
Road salts, de-icing, water thrown up by vehicle spray all affect the performance of walls. Apart from design requirements for early initial and final compressive strength, such as thin wall construction, lime mortars, specified and used properly, have performance characteristic that are superior to Portland Cement mortars for every aspect of traditional building repair.
 
Lithomex

Stone repair and restoration mortar
Specially formulated mortar based on Natural Hydraulic Lime and aggregates for the repair or simulation of masonry, brick or stone. Lithomex is a custom coloured mortar supplied in 25KG bags to which only mixing water is added.
Lithomex has high vapour permeability, low modulus of elasticity, excellent bond characteristics and achieves early freeze thaw resistance. Lithomex develops early strength but not such that it becomes stronger than the background. It is not suitable for repairs to stair treads.
Applied at minimum thickness of 5mm (can be dressed or cut back to a feather edge). The maximum recommended unsupported thickness is 80 - 100mm. (Not projecting work) In cases where a thickness greater than 100mm is required some anchorages may be required. In the case of full depth projecting work anchorage is advised.

Simulation of stone / brick features, rough finishes, false joints etc. can be made approximately 5 hours from application (in damp cold weather leave up to 24 hours).
Shaping and forming of details, corners and such can be carried out with the edge of a trowel or steel float and carved details with small tools as the work proceeds or using chisels once the material is fully hardened. Fine polished finishes are achieved either by troweling after initial set has begun or by fine carborundum paper after the material is sufficiently hard. Its unique qualities allow it to be tooled, shaped and sculpted even weeks after the final set has taken place. This affords sufficient time to achieve the very highest standard of work with the best quality reproduction. Where ashlar masonry or very finely jointed masonry has suffered damage to the arises, flush finishing in Lithomex with a tucked joint is the ideal solution. Lithomex can be lime washed.


Ashlar: Bedding and Pointing mortar

Traditional ashlar jointing and bedding mortars were made with fine sieved lime, either non-hydraulic or feebly hydraulic lime and crushed chalk, with or without a small amount of crushed stone or sand added for bulk where joints required.   This was mixed on a marble slab with just enough linseed oil to grease the tools, it was made up into a consistency similar to stiff glazing putty. Where non-hydraulic lime was used, this could be stored in a damp or oiled cloth to prevent drying, where feebly hydraulic or moderately hydraulic lime was used, it would be mixed and used on the day or within 24 hours depending on the type of hydraulic lime used.
Material.
Non-hydraulic: Supplied as a fine sieved pre-mixed putty mortar in 20 or 10 Litre plastic buckets with re-usable airtight lids.
Ready for use with additional on site mixing to increase workability (without the addition of water)
Feebly hydraulic NHL 2 or Moderately Hydraulic NHL 3.5: Supplied as a premixed dry powder mortar for mixing on site with the minimum amount of clean potable water to produce a stiff putty to which a small amount of linseed oil may be added if required.
Background.
Generally, natural stone (Ashlar blocks) or rubbing bricks, for building, or existing masonry for re-pointing. The background should be clean and free from loose or friable material, well washed to remove dust. Dampen high suction units. (Do not dampen very low suction materials such as granite)

Application.

Laying sawn six sided blocks or rubbing bricks.(Joints not exceeding 3mm )

Butter beds and perpendicular ends a full bed of mortar, firmly pressed into place to slightly more than the desired bed thickness, lay next block in place to line and level by tapping firmly and repeatedly such that a slight excess of mortar is squeezed out when the correct joint size is achieved.(this indicates full face contact with the units) Leave excess in place for several hours.

Laying single faced masonry units.(Traditionally hewn ashlar masonry dressed only on the face)

Lay a ribbon of ashlar mortar (approximately 25mm in width on the leading edge of the ashlar faced unit and a bed or normal coarse stuff to bed the irregular meeting faces. Tap down the stone to line and level and correct joint size, excess ashlar mortar will squeeze out. Leave excess in place for several hours or longer before trimming back.

Re-Pointing Existing Masonry  

Joints should be properly raked out using appropriate tools, avoiding damage to the arises of masonry units. Joint depth should be consistent and the back of the joint squared, with masonry faces being free of loose or friable materials and dust free.

Protection of the masonry with tape avoids staining. Joints must be thoroughly washed clean before applying new mortar and remain damp enough to control suction during application and initial curing.

Cleaning excess mortar from the face of masonry may cause the lime binder to spread over the surrounding units and may lead to unsightly staining.

Tape on either side of the masonry, carefully placed to accurately follow the open line of the joint will provide protection against staining. In addition, it will allow very narrow joints to be filled with a small flat spatula such as the square end of a trowel and square and allow the mortar to be firmly pressed into the joint. Excess mortar can be left over the taped edges until the mortar stiffens sufficiently for it to be struck to flush when the tape is removed, usually within 24 hours.

Where the edges of the masonry are worn or damaged from previous repair, carefully cutting of the stiffened mortar to the weathered edge will create a fine shadow gap and minimise the visual impact of a white mortar filling irregular features in the masonry.

Joints over 3-5mm are not true ashlar joints and a mix with a higher sand content   should be used. (see fine jointing mortars guidance sheet)

Deep or open joints particularly at cornices and projections may be impossible to fully and adequately fill, leading to tip pointing, in these instances, consideration to the Clay Cup method should be given.

Mixing Hydraulic Ashlar Mortars:
The materials are supplied dry, ensure all components are fully combined. Add just sufficient water   to make the material into a dough like consistency, If required a good double handful size lump of the mortar add a tablespoon of boiled linseed oil   and knead into the mix until it leaves the hands clean and is fully plastic. (Disposable or rubber gloves are usually worn for this process).   Feebly hydraulic mortars NHL 2 should be used within 24 hours. Moderately hydraulic mortars NHL 3.5 should be used within 4-6 hours. Keep all mixed hydraulic mortars covered in sealed containers once mixed.

Moderately hydraulic lime mortars will require re-working.

Mixing Non-Hydraulic Ashlar Mortars:

Supplied as a ready mixed wet plastic mortar complete with Linseed oil, the mortar may be stored indefinitely in airtight sealed close covered frost free conditions. The mortar may stiffen (loose initial workability) in storage or transit, but will with re-working without additional water return  to a fully plastic putty, a gloved hand will provide the quickest method of re-working. Only ever add water to a non-hydraulic ashlar mix where there is a need to soften the putty consistency for specific applications, such as very tight joints (less than 1-2mm)

Consumption:

1000 linear metres of bed joints, at 2mm thick, and 100 mm on bed requires 200 litres of mixed mortar. Re-pointing 1000 linear metres of 2mm thick joints at a depth of 10mm: 20 litres of mixed mortar are required.

  Health and Safety:

Dry bagged materials contain fine powders and fillers: Use suitable PPE.

Always wear properly fitting dust masks appropriate for the hazard classification; See separate COSHH sheet for lime and fine silica sand or titrated chalk fillers.

Avoid ingestion, contact with skin and eyes.

Lime is an alkaline material in wet and dry conditions and poses a risk in contact with, the eyes and exposed skin.

Burnt Sand Mastic 
 
Traditional sash and case windows and door frames

Traditional windows and door frames were not and should not be fixed in any way to the outside masonry rather they are wedged and held from the inside by battens for lath or plaster or the window shutter casing or on the hard with plaster tight up to the frame. They were face bedded around the frames with hairy lime plaster to ensure full contact with the rebated masonry detail, and subsequently pointed up externally with Burnt Sand Mastic to form a long lasting, completely wind and water tight flexible joint between the outside masonry and the timber frame. This method of fitting timber frames to openings in traditional masonry buildings has never been surpassed and should not be altered.  Traditional Burnt Sand Mastic

Made by roasting sand on a hot plate or in a kiln and was originally mixed with lead based driers and crushed chalk. However for many decades now, alternative natural driers have replaced the lead products. Available in a limited number of colours by request.

Burnt sand mastic as supplied contains no lead products.

Preparing the joint.

New installations should follow traditional practice. Repair work may have to take account of erosion of masonry, movement, poorly fitted previous replacement windows or doors or poorly executed repair work including non hardening modern mastics which require replacement.

Eroded, defective masonry should be repaired to form a neat edge where practicable to maintain the burnt san mastic joint at a consistent size (approximately 20mm). Burnt sand mastic is not a masonry repair material: Joints that have lost their lime backing and where there is clear space between the frame and the masonry must be packed, either with well haired lime mortar or a rot proof compressible filler such as Flexcell, in all events the gap must be filled to within 10mm of the plane of the ingo.

Sash and case windows have weight pockets and when filling the gap, care should be taken to ensure nothing enters the weight pocket and affects the free running of the window. For this reason expanding foam should be avoided.

The timber frame should have loose flaking paint removed and be fully primed and undercoated before applying the finished mastic. Check the absorbency of the masonry, repair or render with water as the mastic is oil bound and high absorbency may occasionally result in bleeding from the mastic into the surrounding masonry .

If the masonry has a high surface absorbency, use tape to protect and mask the masonry to prevent undue surface spread. (Trail samples should be carried out) Although oil stains usually do evaporate over time, avoidance is the best option .

Using a small painters fitch, neatly apply a small quantity of the oil drier directly onto the frame and masonry to prime the surface ready to receive the mastic. Keep the primer to the line of the mastic avoid over priming. This can be done up to 1 hour before applying the mastic (weather dependant). Do not allow the oil primer to dry, apply the mastic while it is still feels oily or tacky to the touch.

Mixing.

As supplied Burnt Sand Mastic is a two part product, the burnt sand, in a tub and the two part oil and drier in a plastic bottle. For each Ltr of burnt sand add approximately 200mls total of oil hardener is added a little at a time, mixing carefully at each addition until the mastic is worked into a thick putty like consistency and comes cleanly of the mixing trowel. It should be possible to turn virtually all the material into a large ball with a single flip or the trowel. Allow to stand in a covered container for approximately 2 hours prior to use to ensure that all the oil and hardener has fully integrated with the burnt sand. Remix immediately before application.

Application.

Using a mastic trowel and box, press the mastic into shape in the box and lift with the trowel, filling from the bottom of the joint and work up, always lay mastic on mastic, do not work to an open face as this will result in poor compaction, flush the mastic with the face of the ingo tight to the frame. Where the joint to be filled is less than 10mm it may be necessary to form a neat angled fillet of mastic, not exceeding a 45 degree angle. It is important to maintain a consistent margin on the timber frame. Keep tools wiped with an oiled cloth during the application.

After filling, starting from a corner, press the mastic trowel tightly against the face of the timber frame and masonry jamb and carefully press and draw the trowel to create a neat regular flush or angled fillet.

Clean away any excess mastic and wipe the finished timber edges on completion. Where tape has been applied to minimize soiling with oil on absorbent surfaces, after finishing the mastic, remove the tape immediately, taking care to ensure that the mastic does not pull away with the tape. There should be no visible lips at the mastic edge on removal of tape.

Mastic should not be over painted, paint deteriorates relatively quickly and requires constant maintenance.

Once mixed with the oil drier and re-mixed prior to use, mastic will begin to harden, therefore mix only that which can be used within 4 hours. In normal weather conditions a noticeable hardening will take place within 24 hours.

 

Terminology.

 

Oil Drier:               Oils containing a drying agent that will cause hardening over time

 

Mastic Trowel:     Long rectangular trowel square sides approximately 18-20mm wide.

 

Mastic Box:          Open ended three sided wooden box with handle to hold mastic while
                                 working150mm x150mm x 50mm deep (a harling trowel can also be used)
 

Ingo:                       Inband return from face of wall to window or door frame

 

Fitch:                      Thin angled paint brush used for cutting in angles and corners.

 
Lime Paints – User recommendations 
 
Vibrant and beautiful, the St Astier lime paint range is the perfect compliment to lime rendering and harling, suitable for most backgrounds. Can be applied to gypsum plasters, lining paper, cement and lime backgrounds, bricks, blocks and untreated timber. Some backgrounds may require a primer to reduce suction.

Mixing. The general ratio is 1 volume of powder to 2 volumes of clean water. Further dilution might be necessary on porous backgrounds.

Unadulterated lime paint is supplied in tubs as a powder for mixing on site with water. The tub has a fill line for normal use. Proper mixing is essential. The lime paint should be completely free of lumps or fine particles. Check the bottom and sides of the mixing tub to ensure all the powder is fully combined.

When supplied with Uni Protect (an additive to improve adhesion) the product will be supplied ready mixed in a wet state for final stirring on site immediately prior to use.

In all instances when using lime paint, regular stirring is essential to ensure a consistent application.

Application. Do not work in temperatures below 8C or above 30C or in visibly humid conditions, ie. Mist or Fog. Protect painted areas from direct sun, drying wind and rain for 3 to 4 days (longer in damp weather conditions). Do not use warm air dryers.

Apply with a good quality bristle or hair brush in short strokes, evenly and thinly spread the lime paint on the surface, work into any small hollows or cracks. Do not overload the brush, use only the bottom third of the bristles, do not apply unevenly. Generally 2 coats are sufficient. Wait 12 - 24 hours between coats.

On large areas of work, always keep the working edge damp, do not allow the lime paint to dry out and form a dry joint. Inadequate protection of the working area will exacerbate drying. Dampen with a light mist sprayer if necessary. Sufficient personnel should be used to complete large areas without forming dry joints.

Always finish whole walls or elevations into details, angles, corners, down pipes or the like in one operation to avoid colour banding.

St. Astier Lime Paints can be sprayed with an airless sprayer.

Background.

Ensure that background is dry, clean and sound. Do not apply lime paints on waterproofed surfaces, distempers, existing glossy and waterproofed paints, dirty or polluted surfaces.

Remove any loose or flaking paints and repair defective plasters or renders. Test the background for suction by lightly flicking clean water from a brush on to the surface of the wall.   Rapid suction into the background means that dampening with clean water will be required. In this cases thin the first coat out with 30% additional water. If thinning is required mix as normal then take out with a measured container the quantity you require to be thinned, place it in a separate container and add the extra water. A low suction background does not require pre wetting or additional thinning for the first coat, but may require the addition of UniProtect (an additive to improve adhesion)

All new rendered or plaster surfaces should be properly dry before applying lime paints.

Lime paints can react with some modern gypsum premixed plasters due to their additives content.

Wallpaper joints are often smeared with adhesive during hanging. Make sure that the adhesive paste used is water-soluble. Clean the joint before applying lime paint, as excess adhesive residues on the face of the paper will cause the lime paint to dry out a different colour. Always conduct a test in a small area.

Suitable backgrounds.
Can be applied to most normal external or internal plastered surfaces (see background) including gypsum and cement, previously painted surfaces and untreated timbers.

Always carry out a test sample if in doubt.

Unsuitable backgrounds.

Not to be used on backgrounds that contain waterproofing agents, oil paints, grease or cement paints which have water repellent agents.

Protection.

Do not use below 8C or above 30C. Avoid working in foggy/ damp weather.

Protect from rain, strong direct sunlight and drying winds for at least 24 hours.

Technical data:

Made from pure high calcium hydrated lime. Acrylic addition: max. 5%.

Pigments: mineral or earth oxides.

Shelf life:

Powders: 6 months from production date

In water : 12 months

Normal dilution ratio -1 vol. powder : 2 vol. water (1kg. Powder : 4 litres water)

Health and Safety

Irritant. To the eyes and skin. Wash affected areas abundantly with clean water (do not use soap).   Do not ingest or inhale dust. Wear adequate protection (mask/goggles/gloves) during handling and mixing.


Managing rendering
 
Rendering should only be carried out by skilled crafts people with experience in the type of work proposed.
Before the work starts:
Planning for render work is an essential part of any contract programme and should at the outset be planned and co-ordinated with other aspects of the work.
The installation of services, completion of roofs, drainage, ground levels, window and door installations, scaffolding, storage and mixing areas and a programme that allows the work to be carried out in a sensible time frame and at an appropriate time of the year or with adequate protection are all factors which must be given full consideration 
Rendering can often be the largest visible finished work element of a building, and apart from the aesthetics, its primary function is to maintain the wind and watertight integrity of the building so the workmanship, planning and execution is of utmost importance.
New work should never be repaired because someone forgot to put in an overflow pipe, or missed an external light fitting.
The finish should be discussed, agreed and provided for inspection for approval by all concerned. This is always best achieved by ensuring a suitably sized sample panel is carried out in full, sufficiently well in advance and accordance with the application method approved (including adequate curing between coats) in a location that it can be retained until the work is complete and handed over. Agreed sample panels should never be covered up or removed until all work has been completed and passed as fit for purpose.
 
Background preparation:
The background should be clean and free of deleterious materials that may affect bonding.
Repairs to masonry and joints should be carried out in suitable materials, fit for purpose.
Beads, construction joints, stop ends should be fixed in advance of the render work and checked to ensure they are plumb, level and straight.
The positioning of beads relative to distance from the wall should be inspected to ensure the specified thickness of the render can be achieved.
Where the distances between beads and stops is such that running screeds, dots and dabs or rules are required, these should be identified and a course of action set in place to ensure they can be carried out in a workmanlike manner.
Efflorescence should be brushed off surfaces and checked again for re-occurrence.
 
Background suction should be checked and allowances made for dampening prior to commencement of render.
 
Material Storage:
Sand, sufficient to carry out all the work should be delivered to site and stored such that it will be kept clean and free of deleterious materials, open necked tone bags should be stored off the ground on pallets and covered to prevent saturation either from the ground or rainfall. Bulk deliveries should be stored on tarpaulins or a clean free draining hard standing.
All sand and aggregates must be covered to prevent drying out or saturation from rainfall or loss of fines from strong winds.
Sands should be checked for bulking on delivery and allowances made in the mix gauging.
Dry bagged or ready mixed mortars, bags or tubs of lime must be stored on pallets in dry frost free conditions.
Water should be clean free potable water.

Mixing:
As per the manufacturers recommendations or where separate ingredients are being used, in accordance with the specification.
 
Equipment:
Mixers should be Pan, paddle, force action or roll pan mixers. Free fall/ concrete mixers are generally not suitable for mixing lime mortars.
 
Scaffolding:
Working scaffolding for rendering should be free standing detached from the wall or tied only where it will not interfere with completion of the work.
Where necessary, a two or three board internal run with hop upswill be required – i.e. Hand casting or mechanical spray harling.
Free standing independent scaffolding capable of supporting temporary covers and shading are essential to ensure the work is finished to a high standard without putlog ties but sufficiently robust to provide adequate protection for the newly applied materials.

Lime Plaster
This is not a specification or a set of instructions. It is for information only. The sole purpose of which is to provide the reader with general information related to the use of products supplied by us.
Mortar.
Plastering in ordinary mortar normally consists of three-coat work, using traditional materials. Lime plaster was generally made with non: or feebly hydraulic lime and sand and this is the basis for this guide. This type of lime sets and hardens predominantly by slow evaporation of water from the mix and re-absorption of Carbon Dioxide from the air. By its nature the drying: absorption process is slow, therefore lime plaster curing can be a lengthy process, and should not be hurried.
 
Background.
For plastering on the hard, the background will normally be brick or stone.   The surface should be clean, free from dust and any organic materials such as lichens etc. Test the surface of masonry backgrounds for dust by applying a piece of masking tape to the background and immediately remove, examine the sticky side for traces materials that may affect the bond between the plaster and the wall
Internal walls can be uneven and rough, often with areas that have been altered. Different background conditions are therefore common and this needs to be addressed before plastering. Deep holes, wide joints or pockets should be dubbed out in thin layers of mortar with pinnings (bits of brick or stone) tightly bedded in mortar and left to cure.   The aim of preparing the background should be to achieve a surface that can take a first coat of consistent thickness, and to provide an adequate key for this first coat. The quality of preparation work is vital to the quality of the finished job. Suction between the first coat and the wall (and between all subsequent coats) is the primary means of bonding although a physical is also important. Different materials have different levels of suction, so for instance where a door way has been knocked through a stone wall and the edges built in brick, the brick may well have a different level of suction to the stone. Understanding and controlling suction is important for successful work.
 
For lath and plaster work, laths should be fixed by butt and break joints to joists or battens securely fixed back to wall or ceiling, with gaps between the laths of approx, 8 - 10mm. The support battens or ceiling joists should be spaced such that the lath does not give unduly in the centre. Wide spacing of battens or joists may require intermediate support or thicker laths used. Laths, sawn or riven (traditionally hand made) should be thoroughly damp before fixing. Dry laths swell when wet mortar is applied to them, sometimes causing the laths to bow, in or out. Nails for fixing lath should be thin shank to avoid splitting the ends. Building paper and insulation is occasionaly placed between laths and outside walls to comply with current building control requirement’s, this will have a dramatic effect on the drying rate and prevent proper rivet formation when fixed hard against the back of the lath. If building paper and insulation are essential, use moderately or eminently hydraulic lime for the first coat as it has a natural set and does not depend on slow drying, maintain at least a 20mm gap between the paper and the lath.
 
First coat, Render coat.
Coarse stuff is knocked up immediately before use by beating the coarse stuff to increase the workability.   It may be necessary to add water to the mix at this stage. Immediately prior to use, hair is teased into the mortar and repeatedly chopped and turned until a good even distribution is achieved. The hair should be long and strong, free from lumps and clumps. It should be clearly visible as a beard around the edge of an inverted trowel full of mortar. The hairs should be at approximately 1mm centres.
 
When working on the hard the first coat of mortar should be applied by throwing (a spray gun can be used) or with a laying-on trowel on to a dampened but not wet background at approximately 9 - 12mm thick.  
For application onto laths it should be trowel applied as evenly as possible and pressed home to form rivets    between and behind the laths.   The render coat should not be straightened.  
As initial shrinkage takes place in the drying out phase, tighten the entire surface in with a cross grained wood float, closing back by further dampening and tightening in a close circling motion.
Key the surface with a comb, or with a lath scratcher for plaster on laths, taking care not too score to deeply, which will cut the hairs and may cause a loss of integrity in the coat. In the case of lath work ensure that scratching is across; not in line with the lath. Thereafter if necessary control the rate of drying out by misting the surface with clean water or lime water, until all shrinkage has stopped and the mortar has hardened sufficiently to receive the second coat.    Do not over- wet the surface. (When beads of water appear on the surface it is over-wet.)   Plastering on laths may take longer to dry as there is no suction of moisture into the background.
 
Second coat . Floating coat.   (This is the straightening coat)                  
Using the same coarse stuff as the render coat and following the same method of knocking up and introducing hair, apply with a laying-on trowel to a dampened background. At this stage if straightening is necessary then fill out deepening’s in thin layers and apply the floating coat to the desired line using rules or dabs.   Maximum thickness should be 12mm in one pass.   Tighten in as before with a cross grained wood float and key lightly with a devil float to receive the finish.
 
This coat should be finished to a high standard, straight and true, ready to accept the finishing coat (setting stuff)
 
Setting Stuff. Third coat. (Finishing coat. Hair is not required)
Apply with a laying-on trowel in two passes to an overall thickness of about 3mm maximum, less is better and tighten in with a cross grained wooden float, dampening as necessary as the set takes up. Setting stuff sets by suction from the background.   The final finish is produce by troweling the surface with a steel float and dampening as necessary.
Patching finished lime plaster into a repair requires care. The finish is sand based and will abrade and degrade existing edges leading to dull open surfaces around the repair.   A clean break of a few mm is necessary around the patch that can be filled later with lime putty when the patch is fully hardened
 
Decoration.
Wallpaper or paint finishes should only be applied to fully dry and set work. Lime wash, distemper and casein paints are traditional finishes for new work. Laitance reduces suction of new plaster and will prevent lime wash adhering to the surface. In these instances and only when the work has fully dried out, a fine abrasive paper can be used to improve suction. The surface should never be abraded such that the finish is damaged.
 
Protection.
Work should never be undertaken in frosty conditions or where the temperature is likely to fall below 5 0 C during the execution of the works or until the mortar has hardened. Protection should remain in place for as long as possible. Ensure that the rate of drying is consistent and that strong draughts are excluded from the working area. This is particularly important where a building has windows removed or doors open. Never force the drying by introducing heaters, heating in the building should be background only and should be consistent. If heating is required to maintain a proper working temperature, use Propane heating, this has the effect of producing both moisture and heat simultaneously. Ensure the temperature is adequately controlled. (Any heating appliance should be used strictly in accordance with manufacturers recommendations)
 
Good working practice.
Adequate preparation and protection are essential. Due care and attention should be applied to all the works. Sample panels should always be carried out in accordance with the specification. Three-coat work will require sufficient time to allow for properly executed and finished samples.

Introducing: The Render gun
 
Render, stucco, external plaster, call it what you will, it’s one of the most common forms of mortar application to buildings, old and new.
 
What range of materials can be applied using a render gun?
Almost anything, cement and sand mixes, even with fibre reinforcing, lime mortars, hairy lime plaster, gypsum plasters, Artex and Tyrolean.
In fact from very fine finishing mortars through to wet dash harling coats with gravel up to 6-8mm can be applied with a render gun.
 
Why should I use a render gun
There are many reasons to choose a render gun over hawk and trowel application, but the simple fact remains that any rendering or plastering material has a high water demand for hand application allied to finer sands for workability, these principle needs can and often do result in high shrinkage in the finished work.
A render gun uses air pressure to drive the materials on to the wall and provides a consistent even distribution of materials that stick extraordinarily well on impact.
The grade of sand and water requirements for mixes is significantly better than can be achieved by trowel application.
Everyone knows that sharp concrete sand has lower shrinkage than plastering sands, lower water demand and much lower overall shrinkage, that’s why dryer, sharper concrete sand mixes are used for floor screeds.
 
So what are the main advantages of a render gun over hand application?
Lower water content
Sharper, grittier sands for base coat applications
High bond contact with the background
Lower risk of shrinkage
Consistent even application pressure
Speed of application
What are the downsides?
A redundant tool box full of hawks and floats
 
How hard is it to use? How long will it take me to be able to use it with confidence?  
Its ridiculously easy, and few hours and your set; Most of that time will be getting the mix consistency, actually using the render gun is about as simple as it gets.
 
Will a render gun make me a better tradesman?
No but it will make you more efficient, productive, reduce reworking, add greater flexibility, instil more confident and add immeasurably to you range of work, you will discover a whole new range of application and finishing techniques you probably would not try before, become obvious, clear and simplified.

General guide: for re-pointing masonry.
 
Mortars.
Before deciding to re-point a basic understanding of the function of mortars is required.  
Mortar is used for jointing individual units in a mass of masonry. The final structure must have certain characteristics to function satisfactorily. It must carry the load for which it was designed it must be durable and it must give protection against wind, rain and frost.
Mortars should develop sufficient strength and at such a rate as to be capable of withstanding the stresses to which they will be subjected during the construction of the building and subsequently when the structure is fully loaded. It should not however set and harden so quickly that it becomes inflexible at any stage and cannot accommodate the slight movement, which will inevitably occur during and after the completion of the building.
Mortar should be permeable in itself, both so that the quantity of free water on the face of the building is reduced, thus reducing the possibility of wind-driven water penetration, and so that moisture evaporation is not concentrated in the masonry, which may then be vulnerable to accelerated breakdown in the vicinity of the joints. Mortar should bond firmly to the units so that a tight joint is obtained through which rain will find it difficult to penetrate.
Mortar should be workable, so that the material may be applied easily and to ensure that the vertical as well as the horizontal joints can be adequately filled. Masonry buildings rely on their mass and the interlocking of individual units for their stability, and the mortar in a masonry building serves in the main to provide a bedding medium for often very irregular components, filling the voids and maintaining the wind and watertight integrity of the building. There is normally no requirement for significant structural strength in the mortar of traditional masonry buildings, particularly in re-pointing work.
 
Protection, good working practice.
Current codes of practice for working with cement-gauged mortars are also relevant when working with lime mortars and cover most of the basic requirements for good working practice in the use of traditional mortars, (although these practices are seldom if ever carried out correctly, despite being included in every contract document.) The basic difference is that traditional lime mortars are more delicate and some times require to be protected for considerably longer periods of time against the effects of drying winds, strong sunlight, rain and frost.
Where scaffolding is in place to carry out the works, fine mesh debris netting can fixed to the outside of the scaffold. This gives basic protection to the working area, slowing down strong wind, whilst still allowing good light for the works. (Current Codes of Practice require adequate lighting for the execution of the works)   Securely fixed haps or thin plywood sheeting fixed over polythene should cover the top of the scaffold onto the wall heads or to just below the gutters to ensure that rain does not wash down then face of the walls. (Scaffolding should always be erected in such a manner as to allow the highest point of the building to be protected.  Within the confines of the external protection, the work should be protected up close by covering it with hessian sheets or polythene or both. (Polythene should never come in contact with the work.) Accurate records of the minimum and maximum temperatures below the covers should be taken daily, with provision to record these over weekends and holiday breaks. If during any period, the temperature inside the covers falls below the requirements and frost damage occurs, that area of work should be removed and re-done.  
All work should be kept damp, not wet, by repeatedly dampening with a fine mist spray, with limewater or clean drinking water for at least 3-4 days when using Natural Hydraulic Lime Mortars and for 5-7 days for Non-hydraulic Lime Mortars. These are minimum requirements which may need to be extended depending on prevailing conditions.
 
Re-pointing.
Before any re-pointing work is undertaken; a complete survey of the building: should be carried out by the supervising officer, and the contractor, to determine the precise areas to be re-pointed.
 
Often much of the old lime mortar raked out on site is sound and could, with advantage, have been left in place. The builder of the second half of the 20th century expects mortar to be strong, hard, and dense and cement rich.   Strength is perceived to be a prerequisite and upon encountering soft lime mortars, they will remove them in the belief that the softness is a sign of failure. In other instances, entire elevations are re-pointed to provide a uniform colour, rather than re-pointing defective joints with a suitable and compatible mortar.
It is essential that all pointing is carried out to match previously approved samples. This will remove any tendency for artistic licence on the part of the builder. The finish achieved on mortar joints can have a dramatic effect on the visual appearance of the completed work, although this is often not immediately apparent, sometimes only being condemned after the scaffold has been taken down.
Joints should be thoroughly cleaned out, from top to bottom, the joints should be washed out to remove all loose materials and dust, this is important as the mortar will adhere to dust which is left in the joints and deplete the bond.   Mortar should be plastic and workable but as stiff as possible. It should be pushed into the back of the joints in layers, avoiding large volumes of deep filling at all times. On rubble elevations, pinning stones should be used to fill wide and deep joints in the same style as the original build. This will reduce the volume of mortar required and will assist the process of setting and final full carbonation.
A “well filled” joint is at least flush with the surrounding stone, or to the weathered edge.
Random rubble should be fully flush pointed, often partially over the face to produce a flatter appearance. It was commonly lined out to look like coursed masonry. Recessed joints define the masonry components and detract from the aesthetic of the wall, becoming a feature in them selves.
To ensure good compaction and adhesion within the joint, the mortar can be tamped firmly back with a stiff bristle brush as it starts to firm up. The timing of this is critical, if it is carried out to soon after placing, fines in the mix will be drawn to the surface and will form a dense skin, inhibiting the proper curing of the mortar. Once the surface of the mortar is firm (usually the next day in the case of simple lime mortars) lightly brushing the surface to expose the aggregate can improve the appearance of the mortar and make the joints less visible. This process should not be undertaken before the surface has stiffened or mortar will be smeared onto the face of the stone. Brickwork has a number of specific joint finishes to numerous to go into in this short guide, but the principles of timing of the finishing of the joint still apply.
The final colour of mortar joints is influenced by choice of aggregate. The fines in the mix will control the finished colour, a wide range of colours are possible.
 
Re-pointing, Ashlar masonry.
Ashlar masonry should not be re-pointed unless there is evidence of water penetration. It is very difficult to re-point ashlar masonry without causing unsightly damage.
Protective tape should be applied to the joints of fine ashlar work before mortar is pushed into place. The vertical joints almost always require greater amounts of filling than the bed joints, due to the lack of compaction and filling when building. Loose mortar should be carefully raked out of fine joints using a tool such as a hand-held hacksaw blade.
Mechanical removal of defective mortar can be particularly damaging, and is too risky to be used in most situations. Mechanical tools should not be used on historic masonry except in very experienced hands and the use of bolsters or quirks for cutting out mortar joints should be avoided on ashlar work.
When re-pointing ashlar masonry the mortar should be brought out to the edge of the masonry, taking care not to smear the face. Mortar is normally inserted into fine joints by pressing it into place with a flexible blade or spatula. The mortar needs to be inserted to an adequate depth and it will be necessary to push it back into place with the thin edge of a blade when working on very fine joints. Where possible the full depth of the joint should be filled with mortar, however in some situations, (where the joint gets wider away from the face) it may be necessary to provide a backing strip such as twisted waxed twine to provide a firm support to ensure proper compaction of the mortar.
Pointing deep joints should be done in layers of 15 - 20mm at a time, allowing the preceding layer to take up before applying the next.
For ashlar masonry, a well-filled joint is one that is flush with the face, or very slightly recessed.
 
Finishing   joints.
Almost without exception the method of finishing the joint will have the most profound effect on the final appearance of the work, joints should not highlight the masonry they should be simple, uncomplicated and have minimum impact on the aesthetic appearance. It is often better to simply fill a joint and then when it has cured sufficiently to scrape it back to the plane of the wall. This opens the surface and allows best possible curing conditions, minimises the visual impact and removes any tendency for overworked, mannered finishes which become a feature them selves. Samples should always be carried out. Work should never proceed until the sample has been approved and the sample should remain for reference throughout the entire works.
 
Choosing an appropriate re-pointing mortar.
Analysis of original bedding material is usually a good first step in determining the correct materials to use in the repair of historic masonry. Mortar can and does change with time, it is better that analysis is carried out by a suitably experienced person or laboratory.
It will not always be the case that simple matching will be sufficient. The exposure and condition of the building today may well be different from its original construction. Ruins and monuments require a different approach, as they seldom have roofs or copings too wall heads.
Buildings that were once surrounded by trees and woodland, may well now sit in very exposed conditions and any repair mortar will have to reflect current exposure.
There are a range of different types of lime mortars available that will suit almost all environments but not necessarily all masonry types, always consult a competent specialist before determining the final mortar specification for the works .
 
This is a general guide only and not intended to be a specification.

Super Fine Lime Wash – User recommendations
 
Vibrant and beautiful, Masons Mortar Super Fine Lime Wash range is the perfect compliment to lime rendering and harling, suitable for most traditional masonry backgrounds. Can be applied to any background which exhibits a degree of suction: Lime wash adheres to the background by penetration of the substrate, it is not film forming.
 
Mixing.
 As supplied the materials may have settled, so thorough stirring is required each day before use and occasionally during the working day. The best method is by an electric whisk or paint stirrer attached to a drill. Further dilution might be necessary on porous backgrounds.
Unadulterated lime wash is supplied in tubs as a plain white or pre-pigmented liquid.  Proper mixing is essential whether the material is pigmented on not. The lime wash should be completely free of lumps. Check the bottom and sides of the mixing tub to ensure the lime wash is properly stirred.
In instances where difficult backgrounds are encountered and when requested the lime wash will be supplied with Uni Protect (an additive to improve adhesion) this will be clearly marked on the label.
In all instances when using lime wash, regular stirring is essential to ensure a consistent application.
  Application. Do not work in temperatures below 8oC or above 30oC or in visibly humid conditions, ie. Mist or Fog. Protect painted areas from direct sun, drying wind and rain for 3 to 4 days (longer in damp weather conditions). Do not use warm air dryers.
 
Apply with a good quality broad bristle or hair brush in short strokes, evenly and thinly spread the lime wash on the surface, work into any small hollows or cracks. Do not overload the brush, use only the bottom third of the bristles, do not apply unevenly. Generally 3-4 coats are sufficient. Wait 12 - 24 hours between coats.
On large areas of work, always keep the working edge damp, do not allow the lime wash to dry out and form a dry joint. Inadequate protection of the working area will exacerbate drying. Dampen with a light mist sprayer if necessary. Sufficient personnel should be used to complete large areas without forming dry joints.
Always finish whole walls or elevations into details, angles, corners, down pipes or the like in one operation to avoid colour banding.
Superfine lime wash can be sprayed with an airless sprayer.
 
Background.
Ensure that background is dry, clean and sound. Do not apply lime wash on waterproofed surfaces, distempers, existing glossy and waterproofed paints, dirty or polluted surfaces.
Remove any loose or flaking paints and repair defective plasters or renders. Test the background for suction by lightly flicking clean water from a brush on to the surface of the wall.   Rapid suction into the background means that dampening with clean water will be required. In this cases thin the first coat out with 30% additional water. If thinning is required mix as normal then take out with a measured container the quantity you require to be thinned, place it in a separate container and add the extra water. A low suction background does not require pre wetting or additional thinning for the first coat, but may require the addition of Uni Protect (an additive to improve adhesion)
All new rendered or plaster surfaces should be properly dry before applying lime wash.
 
Lime wash is a wet application material and can react with some modern gypsum premixed plasters due to their additives content. Generally for internal use, distemper was most commonly used, but if lime wash is chosen, take care to properly check the background.
 
Suitable backgrounds.
Can be applied to most normal external or internal plastered surfaces (see background) including gypsum and cement and untreated timbers. (Uni Protect may be required to improve adhesion on some backgrounds.
Always carry out a test sample if in doubt.          
 
Unsuitable backgrounds.
Not to be used on backgrounds that contain waterproofing agents, oil paints, grease or cement paints which have water repellent agents.
 
Protection.
Do not use below 8 C or above 30 C. Avoid working in foggy/ damp weather.
Protect from rain, strong direct sunlight and drying winds for at least 24 hours.
 
Technical data:
Made from specially selected pure high calcium quicklime.
Pigments: mineral or earth oxides.
Shelf life: Unlimited if stored in airtight tubs and protected from frost.
 
Health and Safety
Irritant. To the eyes and skin. Wash affected areas abundantly with clean water (do not use soap).   Do not ingest or inhale dust. Wear adequate protection (mask/goggles/gloves) during handling and mixing.