How do I tank a cellar?
Question:I've dug out 8" and now have a level about 10" beow finished floor level. Its' a bit lumpy and bumpy but fairly level, and even the highest points are sufficiently low enough. I'm intending to use a bitumous plastic sheeting and then what? Do I need insulation, and what are the differnt layers that make up the finished floor, and in what order?
Answers:
You will need to put down a plastic dpc sheet on the floor of the cellar and put over a concrete screed and damp proofer.
The walls will have to be battened with a dpc sheet behind, making sure that any nails or screws do not carry through any damp to the timber by using sleaving or plastic washers. When the wall is covered and the noggins in place you can plaster board with a foil backed board.
If you are just asking re the floor, the main thing is to have sufficient head height as a finished level.If the floor has been newly dug up , level it as much as possible then get a hard core such as type one to form a base ,use about four inch of depth, hire a whacker and whack the floor down as hard and as level as you can.This done then apply alight dry bed of screed to smooth the floor.On top of this now you can put a heavy membrane which should cover the floor and also rise up along the wall edges by about a foot.At this stage you can add insulation such as kingspan (50ml) min in depth. Over this you now pour concrete (100ml) depth .The concrete is to be levelled and smoothed over.. If also you are doing the walls in the cellar ,you have to prepare by filling in large holes etc.Tanking is normally a three coat process but can be four.I normally use a three coat one.The first coat I do is a splatter coat which is a sloppy consistency made up of sand/cement with a ratio of 0ne to one sand/cement mixed with water/sika ratio ten to one water/sika.This is applied by spattering it on to the wall covering the entire wall.When this coat pulls in a bit a second coat mixed at a ratio of sand/cement 1.5 to 1 and water/ sika ten to one.This is applied by trowel and hawk method , again the entire wall gets covered and the plaster is scooped into the floor to curve the meeting point of wall and ceiling.When this coat dries , a splatter coat of sand/cement with water only mixed at ratio of sand/cement 2 to one which is of a wet consistency is splattered on to form a key. the third coat is applied the next day ,its mixed sand/cement ratio 3/1 with water /sika 10/1.This again covers the wall entirely and is smooth floated and again scooped into the floor to round the floor/wall joint..Keep this wet for 7 days or so to prevent fast drying...
sinthaproof, painted on in two layers, on the third pepper sand on to bond the render. always plaster if you nail into it it defeats the object of tanking,
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