The Preparation, this is just as important as the pointing it’s self.
Using a plugging chisel or picking hammer to ensure the stone or bricks are not forced apart, rake out existing pointing that is defective to a depth usually equal to twice the width of the joint, and not less than 20mm.
Damping down the joints.
Joints should be first dampened down to reduce the suction and prevent the lime drying down to fast this will also reduce cracking and shrinkage. Leave enough time for the stone or brick face to dry to prevent smearing. Mortar mix should be as dry as practicable to allow maximum compaction in the joint.
Gauging of the mix.
Normally a good mix is 3/1 mix of good quality, coarse sharp sand to mature lime putty for internal and external pointing.
Normally you start pointing at the top and work down to allow for cleaning up and spraying of the wall to continue. Use a pointing key or metal spatula and force mortar into joints from a hawk. If joints are deeper than 20mm, they will need to be dubbed out first to avoid shrinkage. Pointing can either be finished flush or rebated a little, depending on the width of the joints.
Once the mortar is ‘green hard’ i.e. firm enough to brush without smearing but still malleable) brush or tamp the joints with a churn brush. This will enhance the aggregate and give a coarser texture to the pointing.
The drying rate of the mortar is important, to control the rate of drying, external pointing should be mist sprayed. It should also be protected from the direct sun, wind, and frost in the winter time. We normally recommend a sheeted scaffold and hessian cloth to provide a more controlled environment.
Lime is a caustic substance so it is imperative that operatives wear eye protection protective gloves and clothing including dust masks when mixing and always follow the safety instructions listed on our labels.
Owners of listed buildings can, in some cases, get grants or loans to help them with repairs and maintenance.
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First let’s look at the building material of a typical traditional constructed property in the Oldham – Saddleworth area.
The walls of these properties are typically constructed of two leafs of sand stone with a rubble infill the original mortar being of a lime base, and the internal plaster if applied also being lime. Through stones were installed to tie the two wall structures together and improve stability.
In the photograph on the left the stonework has been damaged due to the incorrect use of a hard cement based strap pointing. The pointing should be considered as sacrificial to the stone and should therefor always be softer, in this situation lime pointing should be have been used.
Lime pointing is more vapour permeable (Porous) and more flexible, so allowing faster evaporation and drying of the structure, it also has the ability to some extent to reseal small cracks, so preventing water ingress, which results in frost damage.
The photograph on the right shows a close up of damage to the stone, the stone has been eroded away by the effects of the weather leaving the hard cement still in place, this will result in water ingress and further damage to the stone.
The photograph to the left shows how cement render applied to a solid brick wall with lime mortar can result is serious damage to the brickwork the render will needs to be stripped away and the wall area repointed using a 3/1 mix of good quality, coarse sharp sand to mature lime putty pointing.
The photograph on the left shows the wall area striped of the cement render and repointed with lime pointing around a week later after some good drying weather, which is very important when undertaking lime pointing work the wall surface has dried down extensively.
All works undertaken by Olympic Construction are undertaken by fully trained and experienced craftsman, our stone masons being registered with English Heritage.
See our information and guidance sheets for more information on lime pointing.
If you have any questions please call us on 0161 633 9860 and we will be happy to answer any of your question.