need advice on rising damp with a concrete floor

[newman650]

Hi. wonder if anyone can give me advice on rising damp with a concrete floor.

I need to find a way of damp proofing a floor before insulating with a thin polystyrene layer and then covering with lino it but it will not be possible to put in a damp proof membrane and then lay more concrete on top. Is there some kind of product that i can put directly onto the existing floor that will prevent the rising damp but also is durable enough to park a car on? I have heard about a product that you mix with water and simply pour over the concrete and it then dries to form a hard rubber barrier (on witch insulator and lino can be laid on top) but despite looking on the net i cant find a thing. What about using something like wicks liquids damp proof membrane..

Would that be durable enough once dry if i was to throw a 3mm thick a thin polystyrene layer and then lino directly on top of it to park the car on?. As you have guessed i know nothing much at all on this so and would welcome advice. Thanks, Mat

[ransley]

I think you are out of luck if its real damp, your water table is high if its wet even in the middle.

[The Medway Handyman]

Whats going to happen to the polystyrene when you park a car on it? 3mm of polystyrene won't insulate anything, too thin.

[stuart noble]

that or SBR

most BMs stock.

[meow2222]

Would that be durable enough once dry if i was to throw a 3mm thick

polystyrene wont last a moment with a car on it. Yes one can paint dp membranes on, but that approach tends to exacerbate rising damp rather than stop it, since water can no longer evaporate of the slab surface, leaving it even wetter - and of course an aftermarket coating doesnt keep the water from the walls where it can rise.

Best if you tell us what sort of building it is, incl age, and what youre wanting to do with it

NT

[The Natural Philosopher]

Oh it will be a lot better than nothing at all.

[stuart noble]

SBR is very low viscosity, and penetrates well into concrete, so it tends not to form a film on the surface.

[Rod]

They do make roads out of expanded polystyrene - and, sometimes, about all they put on top is an asphalt layer. That polystyrene is probably a bit stronger/stiffer than ordinary insulating boards.

[The Natural Philosopher]

You can certainly run a car over floor grade (extruded) polysterene without it completely criushing.

With a bit of load spread on top..maybe 3/4" ply - it wold probably be OK.

It is its own vapor barrier/DPM.

[Bruce]

Almost true, but not quite. It is normal to put at least 300mm of compacted fill material over the polystyrene, which is protected with a membrane. The asphalt construction is then done over the top of the compacted fill.

There is no need for the polystyrene to be either stronger or stiffer than ordinary insulating boards.

[Rod]

Thanks. I saw film of it being done many years ago - very likely they have learned a lot since then. Pretty sure they sprayed liquid tar onto it, then asphalt. But I could have blinked... :-)

[meow2222]

To stop rising damp it would need to penetrate 9" horizontally under the walls. That strikes me as unlikely, though I'm open to evidence to the contrary.

NT

[newman650]

Ok....Thanks for the advice. It might help if i give a clearer picture of the problem.

I live in London and own an old classic car which i am keeping stored in the garage. The problem is that the garage is getting damp. There are a few air bricks that help air flow but still condensation seems to build up. The floor is always 'cold and damp' The garage is made of thick concrete slabs (walls and roof) and is located where i cant possibly get power to it for a dehumidifier/fan etc. i don't own it and i am not allowed to put in more air bricks.

It seems as if the concrete 'soaks' up the moisture in the atmosphere and then retains it so it seems to always keep it damp.

I wonder if ever a damp course was ever laid on the floor when the garage was built. The floor itself sits a good few inches from the ground but is still damp.

It is not possible (i am not allowed) to put in a whole new concrete floor because it will add 4 inches on top of the current floor level.

I can however raise the floor by one inch. I thought about DP membrane and then a inch of cerement, but was told that would be useless as it would just break up in no time.

I realise that it will be impossible to make it as dry as a bone baring in mind all the circumstances..but will try to do as much as i can to reduce the dampness/condensation in there. I have coated the floors and the roof with 1) a damp proof 'rubberised' membrane and 2) coated floors / roof with i inch thick polystyrene in the hope it will help bring down the otherall dampness and condensation. I have also sprayed the exterior walls with 'clear spray damp proof stuff' that claims to help stop water penetration but still allowes the concrete to ' breath'

The problem is the floor. I need to find a way to stop A) the damp coming up and adding to the overall dampness and b) try to find a way of reducing surface condensation... As i said earlier the ventilation is not brilliant, but there is at least some.

I was wondering as i said in my original post would it work if i used the same stuff of the walls as the floor? A couple of millimetres of that paint on damp proof membrane., a couple of mill of polystyrene sheeting (like the stuff you would line a uneven wall with when wall papering) and then on top of all that lino just to stop it all scuffing up. I should point out that although the car is parked on it it will not get a lot of heavy use. It just sits there. At the end if the day i am just trying to prevent the car rusting. Its in concourse condition but parts for it are hard to get for it now. Any advice that anyone can give on how to make it dryer in there would be welcome.

Thanks Mat

[meow2222]

Sounds like you cant put right the design shortcomings that are causing the problem. Lino on the floor - no need for 2x DPMs - will block slab evaporation to the interior, but it will make the wall situation worse. Painting things on the exterior is only going to make matters worse too.

It sounds insoluble given the restraints. You could maybe bodge it to improve things some, but I'd not be too fast to do work until you've talked it thru..

One approach that might work is intelligent forced ventilation. A unit measures temp and rh indoor and out, and turns the fan on when water content is lower in the exterior air. Could be run off a solar panel & battery, and fitted onto existing vents. However I dont know any such ready made unit, and it can only do so much.

I would put lino down, sealing it down round the edges. It'll make the lower walls damp but you should still see less interior evaporation.

NT

[stuart noble]

SBR is usually the latex in latex screed. No substitute for a proper dpm but it seems to do the job under lino and vinyl flooring. As we know, rising damp is unusual anyway :-)