Recommendation: Tiling a damp concrete floor - best method with limited high available

[gmt1981]

Hello everyone.
Now, please bear with me as I may take some time to get my point across being a compete newcomer to DIY.

I have also receive so much contradicting info from so called "tradesmen" it's unbelievable, so I would really appreciate the some advice on the following situation.

Well, basically the house is circa 1870 standard end terrace Victorian. It has had an extension about 50 years ago and that is the problem room as the flooring was laid without any DPM under the existing concrete floor, so there are some rising damp issues (I think).

To add to this, when we bought the house about 6 months ago the existing felt roof (on the extension) had a gaping hole that was letting rain water run down the inside of the walls and then on to the floor. At the time there was a engineered solid wood nailed to batons.

As you will see from the below photo, the room is all but finished with the exception of the floor. The room was actually a bare shell (back to brick) and after consulting various people, we were advised to run a DPM sheet up the walls to about 1m, and then the walls were battened and celotexed accordingly. The DPM also covered the floor so that it acted like a type of bath, but to keep the water from getting to the walls and floors.



Our intention was to lay a floating engineered wood floor (on top of underlay) but after the flooring guy came round, he said there was a lot of moisture under the sheet as it was making the floor sweat. He wasn't keen on laying a floor as it was, and even said that if we laid a liquid DPM with an additional plastic DPM on top, then the water would probably pass through both DPM layers.

The moisture readings taken at the time were 120 and 85, although the 120 reading was due to fresh concrete having recently been laid to level part of the room out.
Clearly I would like to have wooden floors but I have been recommended to lay tiles instead. So out comes the tiling man.....

The tiling man, although recommended by a family friend, hasn't had much experience on damp floors so doesn't know if he can get an adhesive to stick to a liquid DPM. He has got back to me tonight and confirmed that he isn't aware of such a product.

So this leaves me in a bit of a bother, especially as I can't lay another screed as there is only just over an inch to the bottom of the door frame.

So what are my options with regards to laying tiles? The existing floor is fairly even although has a few nail holes in it and an occasional small chunk out here and there. So my thoughts are:

1) Arcrylic SLC, then liquid DPM, then SLC. If this option is chosen, how much room would I need under the door to take into account 8mm tile and adhesive?

2) fill all the little holes with a bit of filler, then just DPM first, then SLC. I'm just worried that the floor will suck up all the DPM and cost me a fortune.

3) Final option is to SLC then DPM, but my limited understanding is that you won't be able to get the tile adhesive to stick to the DPM.

Oh, and can someone recommend the exact products I should be buying. The room is 2.3mx3.6m if this is of any use.

I really hope someone can help me out on this!
Many thanks in advance
Graham

[Dave]

Hello Graham and welcome..

First of all, which liquid DPM are you intending to use..?

Oh and yes you can tile to liquid DPM's with an S2 adhesive..

[Ajax123]

Don't use an acrylic leveling compound direct to the concrete. These will end to emulsify in the presence of high moisture levels.

My own thoughts are

1 Ensure the concrete surface is clean and free from dust
2 apply 1 coat of a suitable epoxy damp proof membrane - there are loads of these about but if you ned names let me know
3 apply a second coat of DPM and into this broadcast some coarse dry silica sand.
Allow the whole thing to set and then vacuum up any remaining loose sand
Use a cement based smoothing compound if you need to level the floor
allow this to set and dry (perhaps 48 hours) then lay your underlay and wooden floor

If there is really lots of rising moisture then you may want to consider speaking to one of the moisture membrane specialists like John Newton Mebranes or someone like that but unless you are in a flooded flood plane I doubt there will be that much.

[gmt1981]

Hello Graham and welcome..

First of all, which liquid DPM are you intending to use..?

Oh and yes you can tile to liquid DPM's with an S2 adhesive..

Hi Dave,

I'm not sure about what DPM I would use. I suppose Mapei or stopgap 75 or 76 is what people seem to recommend, but it seems pretty expensive stuff, although I don't really need that much (10 sq m).

What is the S2 adhesive you are referring to?

Is it ok to put the dpm straight on the old floor, or is there a big risk of the floor sucking it up and I will have to use 3 times as much?
Thanks again for the help

[gmt1981]

Don't use an acrylic leveling compound direct to the concrete. These will end to emulsify in the presence of high moisture levels.

My own thoughts are

1 Ensure the concrete surface is clean and free from dust
2 apply 1 coat of a suitable epoxy damp proof membrane - there are loads of these about but if you ned names let me know
3 apply a second coat of DPM and into this broadcast some coarse dry silica sand.
Allow the whole thing to set and then vacuum up any remaining loose sand
Use a cement based smoothing compound if you need to level the floor
allow this to set and dry (perhaps 48 hours) then lay your underlay and wooden floor

If there is really lots of rising moisture then you may want to consider speaking to one of the moisture membrane specialists like John Newton Mebranes or someone like that but unless you are in a flooded flood plane I doubt there will be that much.

That's one option I haven't considered, but it sounds like a good one. I have decided to go for the tile option as I feel this will be let suceptable to moisture, so I do have question though. As space is really tight under my door, do you see any issues just tiling on top of the dpm? If the SLC will stick then i suppose the tile adhesive would too.

I have about 15mm under the door to play with, so assuming 2mm for the dpm, 8mm for tile and say 5mm for adhesive, that doesn't really leave me with any space for self levelling, although I doubt this would be so much of an issue if I'm laying tiles.

What DPM would you recommend I use?
Many thanks for all your help

[martifee]

after the flooring guy came round, he said there was a lot of moisture under the sheet as it was making the floor sweat. He wasn't keen on laying a floor as it was, and even said that if we laid a liquid DPM with an additional plastic DPM on top, then the water would probably pass through both DPM layers.

Hi Graham,
If the floor is sweating, it suggests the surface of the floor is much colder than the air in the room, so the air is condensing on the surface of the concrete. Try to get some insulation into the equation.
As suggested by Ajax, make the concrete clean and dust free. Fit an insulated tile backerboard (which come as thin as 6mm) with a rapid setting tile adhesive (floor can be levelled during this process). Tape the joints in the boards, then roller on liquid membrane. Then once dry tile onto directly.
Since you ask for product names, Tile adhesive - PCI Nanolight Rapid, Boards - PCI Pecidur (I'd use 10mm if you can trim door a bit, 10mm meets european U value for insulation standards) and membrane - PCI lastogum. Link for specifications.
http://http://www.pci.uk.com/EN/Pages/default.aspx

Hope this helps
Regards,
Martin

[Ajax123]

The DPM's I am most familiar with are Universal one coat from Tremco. Same name product from Laybond/Bostik and Merlin Coatings Barrier Coat. All are good products. If you want to tile direct to the DPM you might need to reprime it as you go using an epoxy primer and tile onto this whilst still tacky. Have never seen tiles direct to the DPM but have seen levelling compounds galore so on that basis I agee it should be possible. I would tend to ask the manufacturers for advice on this specifically though.

Alternatively you could just trim the bottom of the door.

[tfs]

Stopgap is good stuff mate.

I would prime the liguid dpm once dry and then use a slc over the liquid dpm before tiling.