Re-pointing ashlar masonry.
Ashlar masonry should not be re-pointed unless there is evidence of open joints. It is very difficult to re-point ashlar masonry where cement pointing has been applied previously, removal often causes more damage than doing nothing. However where it is necessary, mechanical removal of fine cement joints between ashlar blocks is achievable with blades now being available as thin as 1 – 1.2mm.
Removal by any other means is fraught with risk and a hammer and chisel should never be used its simply asking for trouble
Ashlar joints are usually no more than 1-3mm wide. It has become common practice to “pare point” or “ribbon point” these joints because they are so difficult to fill. Should re-pointing be necessary, joints should be carefully removed to a depth of 10-20mm and re-pointed using a feebly or moderately hydraulic ashlar pointing mix available form St Astier distributors (see Ashlar Joints). Where the arises of the stone have become rounded or damaged from previous repairs the weathered edge or a very slightly recessed joint produces a visually more acceptable finish.
Protective tape can 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 full depth of the joints joints using a tool such as a hand-held hacksaw blade to help grip the loose materials, vacuum cleaners are a very simple, reliable method of removing fine dust and the best option of all is a light air jet with or without water. The vacuum can be used to control dust when using fine air jets, wet or dry
The mortar should be brought out flush edge of the masonry or where tape has been applied it should overlap the tape. If the work is being done without tape using the three wipe method, then the pre-wetting (dampening process) is vital to avoid staining.
Mortar is normally inserted into fine joints by pressing it into place with a fine wire key or on a taped background 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 grout very deep joints (see Ashlar Clay Cup Grouting).
Pointing deep joints – more than 20mm but less than 40mm should be done in a single pass to full depth. joint depths greater than 40mm are done far more quickly if they are grouted
Worn or damaged edges where the arisses have been completely lost and the joint is at least 20mm wider than original may require surface repair (see Lithomex)
It is possible to reduce the visual impact of the traditionally very white ashlar mortars where movement has created wider joints – often and particularly the perpendicular joints, may have moved creating joints up to 10mm, in these instances, the addition of a specific see the section – (Beefing up Ashlar Mortars on site)new joint lines struck and pointed.