Tanking - what is it and when to apply

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Tanking is, as its name suggest a method of sealing a wall to prevent water ingress (think 'water tank)
often mis-specified as a cure for damp problems it is basically a waterproof cementious slurry (wet mix) that is applied to a surface to prevent water penetrating the internal surface of a building..
The idea is almost like coating the bottom of a pond to keep the water in but in reverse... it keeps water out..
example... an extreme one..
lets just say the ground (not floor, ground is external) level of your house is above the dpc level by about 3 feet, and the soil is against the outside of your building. The wall is of 9" solid construction.
Now, the water draining into the soil is also soaking into your wall (its porous, see suction) and its coming through on the inside making your internal plasterwork bubble and bringing with it hygroscopic salts (that white fluff you see manifesting itself on the inside of damp buildings)
there are 4 ways of solving this..
1) lower the ground level below dpc. Problem solved.
2) install a membrane between the soil and the wall that allows water to drain away from the building. Expensive but technically possible, the membrane has an air gap allowing the wall to breathe.
3) move the soil away and paint a bitumen waterproof solution on the external and put the soil back. Doesnt let it breathe externally, whatevers in the wall is coming inside.
4) tank it.
you'd coat the internal wall with a tanking solution up to and beyond the height of the ground level, this would stop water ingress wherever the tanking is applied..
you also kill all the suction so a basic render on top is gonna be hard work.
What you dont do is stop the water thats already in the wall soaking upwards (capillary action, similar to what happens with a failed dpc) and manifesting itself above the tanked area.
So, basically, tanking is NOT really a solution to a problem though in some cases its the only thing that will work e.g. differing FLOOR levels throughout a building, the lower level needing to be tanked up to the upper level where there is a dpc installed to stop moisture going any higher..


I'll just add to this before i get shot at by the damp proofers..
Dp companies do use tanking quite regular BUT its almost always used in conjunction with other treatments/methods to reinforce the job..
e.g. trimol applied to a floor without a membrane, tanking applied to the lower 6" of the wall, down over a bottle cove at the junction between wall and floor onto the floor - solves the joint problem..


also 2 types of tanking theres negative tanking and positive tanking ... positive is like a swimming pool water pushing against the walls ( and is easiest to sustain ) and negative ie basement where water is trying to push render/plaster etc off of wall from reverse side ( this is wear many problems can arise if not done properly).
Lots of different types of tanking systems available Epoxy, paint membrane,plastic membrane, bitchamine seal etc ..the list is endless ( well nearly ) but all are no good if u break the seal either it be by a nail/ screw hole in the wall thtas not been sealed properly or not doing the floor as well. Most companies who are Guaranteeing all these types of tanking systems , guarantee materials and products normally, and any guarantees on workmanship normally has to be brought forward by customer within a 30 day period of completion......due to the nature of this trade
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