Damp Proof Membrane for Concrete Floor

[Ptostevin]

Hi

 

Earlier this year we had a french builder renew our roof  and also put in a concrete floor in a room where the timbers had rotten because the ground was so damp . With the heavy downpours in August we found that damp was coming up through the concrete floor. We contacted the builder and were left speechless when he said that he hadn't put in a membrane "it was not in the devis"! We had automatically  assumed that one would be installed - to us its like saying that he didn't nail the roof timbers together as nails were not explicitly mentioned in the quote! Part of the room already had a concrete floor and the dampproof membrane was clearly visible here. I don't suppose we have any come back on this? As we do not want to break up and re-lay the floor can anyone recommend a solution??

 

Paul

[Washy]

We found it difficult 8 years ago to even buy membrane and polystyrene to put under our concrete floor.  It is not usual for the polystyrene to be put underneath and we had several local passing hunters comment about this and saying it would not be stable on the membrane, and that the concrete should be 'direct' onto the rubble and stone.  We imported the membraqne from the UK and found some polystyrene panels abandonned at a local builder's merchant by someone who had ordered them some months previsouly.

[Martinemj]

if you dont want to kango up your floor then the only solution is to apply a membrane coating on top of the floor.

this can be in the form of either a thoroseal type of

waterproofer(as used in basement tanking,looks like cement )

brushed on in two coats (thickness of double cream ish)

then apply a self leveling compound over the top(to give a smooth finish)

or

apply synthaproof(blackjack) type of coating at least 3mm per coat.2 coats to be sure .

blind with a little sand to aid adhesion and apply self leveling compound to finish.

i would however think about redoing the whole floor with the membrane included as it should have been first time.

thats my opinion on the job but ime sure someone will come up with other ideas.

reguards

martin

[Piprob]

It is very hard to understand the mentality of your builder. Normally advice comes thick and fast, particularly as every recommendation comes with its price.

Anton Redman, who used to post regularly on the site, would have an opinion worth hearing. For my part, while there are some liquid proofer treatments for concrete around, I am very much afraid the floor needs to be taken up and re-laid. You are desribing a floor that seems to get quite wet in certain conditions, so even if you manage to seal the surface of the new work, water will still find its way up at the intersection of the old floor with the new.

I will guess that the total cost of the floor, including digging it up again and re-laying, will be minor compared to the potential costs and risks of serious damage to your walls and footings.

Take courage and bite the bullet. You might be poorer, but you'll sleep better.

 

[Caterham7]

If you can afford to lose the headroom and incorporate a step into the room,you could build a floating floor above the existing.

Either DPM +concrete or screed,with optional insulation between.

Or DPM + insulation + timber floating floor.

I would also suggest you investigate the cause of the excessive damp as it may be beneficial to reduce this if possible.

Regards Tony

 

[Ptostevin]

...one of the reasons for the damp in the room is that the ground level in the stable next to the room and the garden level beyond that is a lot higher (about 2 feet in the stable). The stable floor is earth at the moment but I (not a builder this time!) will eventually lay a concrete floor with dpc here. I was wondering if digging down in the stable next to the house wall and putting some sort of damp barrier here would help? Also perhaps some drainage at the rear to take away some of the water that is perhaps coming from the garden.

We may have to wait and see what the floor is like after the winter - hopefully if its not too bad we can some how avoid having to dig it up....but when we bought it last Oct. and lifted the rotten wooden floor there was surface water underneath!! Last week when we were there I put guttering on the garage behind the house and routed this to a drain so thats a slight reduction in the ground water which may help...

I still can't get over the fact that a reputable builder didn't put a dpc in - especially at 45.73euros/m2 - originally I thought the only reaon I could not see any visible dpc at the edges of the room was that he had bridged it with the screed.... C'est la vie...

Thanks for the advice so far.

Paul

[Caterham7]

If it is feasable a french drain in both the stable and garden,below the internal floor level should help to reduce the amount of water accumulating under the floor.A vertical damp-proofing barrier could be installed at the same time on the stable side of the wall.

Regards Tony

[Cassy0110]

I'm very sorry that you got a poor quality specialist

[Harnser]

We had part of our large barn dirt floor concreted 10 years ago, not for living in,  but as a workshop, garage and storage. Dug out, blinded and levelled with 0/30, rolled and wackered flat. Then 1000 gauge polythene* laid with steel mesh on stools 25 mm higher than the polythene. Self-levelling sloppy concrete poured through one of the windows from a mixer truck and then the usual tamping with a plank on edge.

*https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-membrane-black-1000ga-25-x-4m/88322

The ground outside was up to half a metre higher on two sides but there has been no damp coming up in 10 years.

The terassement contractor who did it said that part of the reason for laying the polythene under the concrete is to stop the water in the concrete being sucked out of the wet concrete by the dry floor underneath and curing too quickly causing cracking, which seems to have worked.  We kept off the floor for 3 weeks and sprayed it with water every day to let it cure before putting any weight on it - It was November when it was done.

[Hectorsdad]

I notice that your quoted price is given in £ and not €. Is all this about a house in France or UK? maybe I missed that information.

I would have expected a price similar to that quoted assuming your rooms are of typical sizes. One of my great regrets is that I chose the cheap, easy option when it came to dealing with our large, lounge floor in France. I should have carried out a full renewal following the scheme you have described. The insulation is vital to a successful result. I think you would be getting good value but it is always advisable to get at least one more quotation.