Hello I’m Colin Braithwaite and this is my son Philip we’re from Braith-Heritage Supplies. We’re working with sustainablebuild.co.uk and we are going to give you a short demonstration on lime plastering.
First of all we will just damp the wall down. Obviously this is a random, rough, rubber wall, get plenty of water on there, to stop the wall sucking the water out of the lime mortar. When you are doing a wall like this the first course you need to fill all the large voids.
Lime mortar is quite a heavy product, so you can’t put masses on at any one time. We’re looking at usually for coats of a maximum of 12mm thick. If you go past 12mm you will find it drops off.
Now you would leave that now for 3-4 days, the air will dry it out. Then you would come back and wet it down again. If you where going to do this yourself for the first time we recommend that you try no more than a metre. Do a metre section from start to finish, until you become confident and happy with the work you are turning out.
Now when you have your lime mortar on the wall you need a straight edge, you could use a piece of wood like Philip is doing. The idea is to scrap it off gently away, to get the wall as flat as you can. Do it horizontally and vertically, and you can see where it has left a hole in the middle there. If you leave that how it is, that’s an ideal surface for the next surface to key onto.
This wall is one that we did 4 days ago, and Philip is now going to put another coat of plastering on here. The idea of this coat is to get the finish better still.
Obviously Philip has laid that on; we will now leave this for about 2 hours just to let it go off slightly. Then he will rub it down with a Urethane Float. The idea of this is to flatten it to get the lime mortar even flatter. It leaves us a very nice surface for laying the plaster it’s self.
Philip is now going to put the finishing plaster on top of that. Obviously it will be dried out so you need to damp it down well in advance. Otherwise if you don’t wet it down the water and lime finish will just be sucked straight out of it and you won’t have any workability what so ever.
Usually we would leave that for an hour and a half to two hours, just to let it go off. Really you just need to touch it or if need be you float it up again to get those lines out. Just touch it gently, and when it is firm, just to get it ready for the lime wash you would just sponge the lime in very, very gently and that just opens it up slightly to allow the lime wash to key into the lime plaster.