Please read thoroughly, it will not be all in order but I think I have covered most points!
Health and Safety
Wear safety glasses at all times, nitrile/latex gloves are also useful as lime dries out skin. If lime does make contact with your eyes use eye wash, if this doesn’t solve it go to A&E. It’s advisable to wear gloves as lime dries your skin
When to Use Cold Mortar
Do not use cold mortar during winter months – Mid September till early May. Cold mortar pointing should be done from May till end of August and will not need a pozzolan. I would recommend using it hot after this time and adding a pozzolan.
Do not use if scorching hot sun as you do not want the mortar to dry too quickly. The slower it dries/cures the better.
The lime mortar must be more feeble than the stone. Cement and a lot of the NHL limes are proving to be far too hard, this is why houses are becoming wet.
Preparation of the wall:
Remove all old pointing from wall, do this at the earliest chance possible. A lot of walls will have a vast amount of water in them. Some people are even taking the cement out the previous year, and sheeting them up over the winter months, just to help them dry.
Before repointing wash down thoroughly with hosepipe to makes sure all debris/dust is out. #
Hot lime mortar 2.5:1 mix sets/cures by carbonation. A pozzolan can be added to the mortar to give an initial hydraulic set. We provide Argical M1000 and terracotta brick dust. A maximum of 5-10% can be added to the mortar.
If you are pointing a soft stone wall, soak the walls the day before pointing and again on the day of pointing. Once the glaze has gone off the stone pointing can then begin.
Generally, builders find it easier to use a finger trowel (if larger gaps a small bullheaded trowel) to push the mortar into the joints. Make sure it is in as far as possible, it needs to be attached to all the stones as firm as possible.
Some DIY men use a mortar gun, but it is very rare to see a good builder with a mortar gun. It doesn’t push the mortar in strong enough to make sure all the voids are filled.
The mortar wants to be proud of the stone by approx 5-8mm. This will be needed if the mortar shrinks and when the mortar has to be knocked in. Do not keep smoothing it off with the finger trowel, this will only draw the lime to the front and make the mortar weaker.
If there are any gaps above the width of a finger, galleting stones need to be put into the centre of the gap, ideally no gaps should be wider than 15mm to help stop shrinkage. Lime needs to be attached to a stone. Any large lumps of lime will fall out in the first 2 years. It’s very important to have the mortar pushed in as hard as possible into the gaps and put as many galleting stones into the mortar.
If the mortar is setting too quickly a garden misting spray should be used to slow the drying process down, put the hessian up and bring it down the wall as much as practically possible ie coffee time, lunch time. Do not start wetting the hessian until the mortar has turned “leathery”. Once it gets to that stage wet the hessian but not with a jetted hosepipe.
If working over the spring/autumn/winter months, it should not be necessary to wet the hessian as there will be enough humidity in the air and more of chance of a frost.
Check the pointing approximately 4 hours later to make sure there hasn’t been any shrinkage by trying to push the mortar in further. When you cannot make an impression in the mortar with your finger (this could be the same day with hydraulic mortar, or it could be 2, 3, or 4 days later with hot mortar), use a pointing brush to hit against the mortar, this will help to push the mortar in further and take the mortar back in line with the front of the stone, in an ideal world you do not want the water to sit on the wall.
At the end of the day, spray with sprinkler again and cover over with a hessian sheet, damp the hessian sheet down with water once in place.
Extra care should be taken on the corner of buildings, a vertical board should be used to try and protect the corners from the wind, this way the board takes the brunt of the wind, and hopefully the corner will be protected.
Next day dependant on weather/humidity, if it is still soft, check it has not shrunk by pushing in to make sure it is compact, if it is dry damp with sprayer again. Keep the mortar covered over for 2 weeks and keep the sheet damp if in hot/windy conditions.
In certain situations, the bottom 500mm of wall will contain a great deal of water. The new lime mortar will keep finding this water and will take a long time to cure, it is therefore possible that the frost can deteriorate this mortar. If this does happen, it is not a difficult job to replace the flaked mortar the following year.
If pointing indoors the hessian is not needed, but it does need misting a few times.