Before any re-pointing work is undertaken a survey of the building should be carried out by the supervising officer and the contractor to determine the precise areas to be re-pointed, and the nature and style of finish to be achieved.
Often much of the old lime mortar raked out is sound and could, with advantage, have been left in place. Todays builder expects mortar to be strong, hard, dense and cement rich. Strength is perceived to be a prerequisite and soft lime mortars are often removed in the belief that the softness is a sign of failure. In other instances, entire elevations are re-pointed to provide a uniform color, 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 performance and visual appearance of the completed work, although this is often not immediately realised, sometimes only being condemned after the scaffold has been taken down and the full visual impact becomes apparent. Preparation:
Starting from the top of the building, defective joints should be carefully cut out with appropriate tools and the joint thoroughly cleaned out, ensuring the inside upper and lower edges of the masonry are properly scraped clean of old mortar. In brickwork the joint should be raked out to 11/2 times the width of the joint or a minimum 3/4 of an inch. Ensure the back of the joint is square. The joints can be cleaned with a vacuum, low pressure compressed air and/or rinsed out with a garden hose to remove
all loose materials: this is important as the mortar will adhere to dust which is left in the joints and deplete the bond. This is normally done form the top of the building down as the old lime in the mortar can stain the masonry if it is not properly washed of, working from the top down avoids unnecessary wetting of previously finished work. Prior to any re-pointing, controlling the absorption rate of the background is essential.Application:
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 good yardstick is to keep the joint thickness to no more than a finger thick, if the joints are wider than this they should be pinned with compatible matching masonry.Finishing:
In natural stone masonry, 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 too 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) lightly scraping 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. A well filled joint is close to or flush with the surrounding masonry or to the weathered edge. Recessed joints define the masonry components and detract from the appearance of the wall, becoming a feature in themselves. Historically the common practice was to fully flush point and line out rubblework. Brickwork has a number of specific joint finishes too numerous to go into in this general guide, but the principles of timing the finishing of the joint still apply.
The fines in the mix will determine the finished color, therefore a wide range of natural colors is achievable without pigmentation. The whiteness of St Astier limes ensures the best color reproduction of the chosen aggregate.
Re-pointing dense impervious masonry.
Some masonries, such as granite, basalt etc. and dense impervious bricks require special consideration. Due to their very nature these materials have little, if any, moisture absorption and therefore moisture is transferred to the joints.
In these circumstances the choice of mortar and method of application and finishing is very important.
The joints are more vulnerable to the effects of wetting during placing and immediately afterwards until a full set and carbonation has taken place. Using St. Astier NHL mortars will ensure setting without having to rely completely on carbonation. The stiffest mix possible should be used, avoiding free water in the joint cavity and consequent de-bonding effect. The vapor permeability
Joints should be filled to flush, never recessed. Recessed joints will leave ledges for the accumulation of water that will keep the mortar joint wet for longer periods and accelerate the decay process. while feebly hydraulic limes were often used for the building of walls with impervious masonry the construction period usually left sufficient time for the joints to set up and cure before exposure to rain. Re-pointing is a much quicker process and more hydraulic materials are almost always a better option.
Joints should be raked back to approximately 1″, thoroughly cleaned, including the top and bottom faces of the beds, ready for the new mortar. Pinning stones should not be removed, but if they are loose, they should be removed and put back during the re-pointing. Where a wall has previously been re-pointed and the pinning stones have been lost, suitable replacements should be used. The walls should be well washed to remove any dust and loose friable material making sure that the entire elevation is cleaned down to prevent staining on the walls. Impervious masonry should be dry when the work commences, however the original backing mortar should be kept damp.
Re-pointing ashlar masonry.
Protective tape should be applied to the joints of fine ashlar work before
Mechanical removal of defective mortar can be particularly damaging and
Ashlar joints are usually no more than 1/32″- 1/8″ wide. It has
When re-pointing ashlar masonry the mortar should be brought out to the
Pointing deep joints should be done in layers of 3/4″- 1″ at a
Very badly worn or damaged edges may require surface repair (see stone