Pointing is what stops the ingress of water through the gaps in between the brick or stone of a wall. Old pointing breaks down over time and allows rainwater to penetrate through to the inside and cause damp patches and so should be repaired or completely re-pointed to keep the rain out.
There are many different kinds of pointing the gap between bricks and stone with raised pointing being the most time consuming and expensive and flat pointing the easiest.
With any pointing there has to be enough of a groove for the cement or lime mix to be pushed in enough so that it will stay in for longer than a few months or a season.
A good depth would be a half inch but at least a centimetre is needed for it to bed in and hold.
Re-pointing old pointing that has weathered means raking out the joints. If the joints are loose and crumbling then using a tool such as an flat screwdriver or a raking-out tool will be enough, but if the joints are too hard then a joint chisel and hammer will be needed to tap out a groove for the new pointing to push into.
Wire brushing the joints will clean them up and then brushing with a soft haired brush will remove most of the dust so that the cement will adhere. Wetting the joints with water before cementing will stop the mix drying out too fast.
Before cement came along, lime was used, and lime, unlike cement absorbs water when it’s raining and then allows the moisture to escape again.
Damp can occur when the hard impervious pointing of cement breaks down and lets water in that then can’t evaporate back out as lime pointing would do, so it’s important to keep cement pointing in good condition.
When using lime allow a few days for it to become hard because lime takes longer than cement to go off.
If pointing in lime in a hot spell then spray water over the work and keep it covered with a damp sheet until it’s hard enough to work and clean up. In most cases this will be a short space of time, usually after one or two days. Keep an eye on it, and testing is necessary to catch it before it becomes too hard to work.
Lime takes some skill to use properly and so a little bit of training would go a long way especially if restoring listed buildings where like for like materials have to be used.
There are places around that teach how to use lime and the different sand involved and where to source it.
Different sands make different coloured mixes, and dyes can be used to make bold coloured pointing.
Cement will go off quicker than lime and so can be finished on the day. Usually a three in one mix of sand and cement is sufficient for most pointing; but if it’s too hard it can crack and too soft will weather too fast.
Depending on how warm it is, doing a square metre at a time is best to keep on top of it and not have it go off before you can tidy it up.
For raised pointing, put enough mix on a hawk and using a long flat pointing-in tool press the mix well into the joint, and then forming a finger of mix push that onto the joint and square off and work your way along.
A mix too dry won’t stick well if at all, and a mix too runny will droop so getting the mix right at the start is best and then keep to that formula.
When it has dried enough, excess can be scraped off and a soft but firm paint brush can be used to rub the joint down to round it off to make it neat.
On walls that are exposed to a lot of rain the joint is tapered downwards so the rain runs off of it. A thin three inch trowel is best for most pointing jobs, the rounded edge one is the most usable but the pointed one also has its uses.
To keep it neat looking, try to keep cement or lime from discolouring the face of the brick or stone, but if any mix does get on the face then it can be wire brushed when dry enough, usually the next day when it is dry and crumbly but certainly before three days when it will start to become hard.
Flat pointing where the joint is filled to no more than the surface of the wall is the easiest and quickest. The cement is pushed in from off the hawk and a trowel is run along it to firm it in and even it off and as it starts to go off a brush is run over the joint to clean it up and make it neat.
Make sure there are no gaps in the cement pointing for water to get in or you could find a damp patch on the inside.
Pointing can be done by anyone keen enough to have a go at it but some hands-on tuition could save a lot of trial and error.
When mixing lime, wear a mask and eye protection.
Cement can burn if exposed to it long enough so wearing protective gear is advisable such as gloves and knee pads if kneeling on it.
Clean up any dropped mix on the ground and hose down to leave it a clean and tidy job well done.
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