Tanking on existing concrete floor - basic questions

[d000hg]

I've a concrete floor which is damp and I don't want to break it up to re-lay, it's also cold and hard. I have come across the idea of tanking, where you effectively build a water-tight box inside your room - a room within a room almost?

Could one lay a plastic sheet on such a floor and then just lay a new floor on top - tiles or MDF sheets, etc?

I can't see any way to do that without putting holes through the plastic liner if you want the new floor firmly fixed - is that a problem or are a few small holes unimportant? I was picturing adding sealant when screwing wooden planks into the concrete so the liner is still watertight, or similar. Is that right... or maybe you need a floor that is heavy enough to just sit on the plastic without being fixed, like a thin concrete slab you just pour on the old concrete, sandwiching the plastic?

Is plastic sheeting what is used as the basis of such systems or can/do you paint/spray a membrane on existing walls and floors?

And finally - does the 'tank' need to be as complete as possible, including the ceiling? Or only as high as the damp reaches or is expected to reach - e.g. if you had rising damp you could stop at chest height?

Anyone got a link to a proper guide on what tanking is and how it is done, or able to share the basics?

 

[nuzuki]

Ive used tanking slurry (cementone brand from toolstation) on a outbuilding with a substructure. The instructions say to put on 2-3 layers from memory. You must apply the layers before the last applied layer fully dries. I used it on a wall but did a very light mix on the floor also just as I had a load leftover.

I have another outbuilding that has damp issues and I think its to do with no DPM put under the slab so as an afterthought I was going to add tanking slurry.

Im no expert but I would probably avoid using a plastic sheet unless the concrete your putting on top of the old concrete is going to be thicker than 2-3inches. You could look into a latex floor or just apply the tanking slurry to the floor, add a little to the walls 1 or 2 courses up (depending on how much tanking slurry is leftover after doing the floor). Then just lay the new slab over the top of that. It should cure your problem unless the damp is coming from somewhere else like the roof or poor ventilation.

You can also buy products made by everbuild that can harden the concrete and waterproof it. In some cases it is just dilute PVA.

If you do use the tanking slurry just apply it with a broom and wash afterwards. Saves you buying an extra brush and bending down to apply it.

 

[d000hg]

Thanks... I'd never heard of tanking slurry so I'll have to research it.
PVA is something I've come across though with mixed results.

 

[d000hg]

I came across this guide (http://www.diydoctor.org.uk/projects/tanking.htm)

Which covered the approach I was familiar with as well as the slurry version. I assume the slurry is basically just a kind of render with waterproofing built in - I hadn't realised until watching a video how thin the layer is. Can I also use this in small localised damp areas - I have one small section of wall which was not treated with damp-proof injections and has some rising damp so I was wondering if I could just apply some of this on the inside.

 

[^woody^]

Coat it with a two part surface DPM such as Ball Stopgap F75 or F77.