Tiles on the floor slab

[hairypete]

Hi,

I have a 1940s house on a ground slab, i.e., clay, gravel, concrete slab.

I want to lay insulation, gypsum, and tiles, but NO underfloor heating.

Question number 1: Is there any point in laying 20-30 mm of foam board?

Question number 2: Should I lay Platon underneath if I'm going to use foam board, or should I use boardfix directly on the slab with the foam board?

Question number 3: Is there a complete good solution for this, or is it all a matter of compromise?

I know I should break up the slab, add insulation, and pour new, but that's not an option.

Hoping for an answer,
Peter

P.S I have searched forums, asked the expert, and googled all possible combinations on the topic.

 

[Daniel_Lundqvist]

Hello, what is the purpose of the Styrofoam?
I could imagine that a ventilated floor with platon and possibly a fan could be good in your case. How thick is the slab? Is it below ground level, i.e. a basement?
Not an expert on the subject, but the only thing I know is that basements can often have some moisture problems.

/me

 

[anaitis]

Lay the tiles directly on the concrete.
You should have neither plasterboard nor insulation.
NOT platon. Any moisture should be able to rise through the tile joints.

 

[Mikael_L]

Hello, what is the purpose of the foam plastic?
/me

The purpose might be to avoid heating up Mother Earth with the underfloor heating. It's quite often recommended to have insulation under the underfloor heating so not too much energy escapes that way...

But the problem hairypete might encounter is a lot of moisture beneath the foam plastic (between concrete and foam plastic). It might attack the sill later on... :-/

 

[Snailman]

Villavarm uses platon and insulation on top of the slab, check out this image

http://www.villavarm.com/bilder/konstruktioner/golv_big.jpg

 

[Mikael_L]

The purpose could be thought to be not to heat up mother earth with the help of underfloor heating. It is often suggested to have insulation under the underfloor heating so not too much energy escapes that way... But the problem that hairypete might have is a huge amount of moisture under the cellular plastic (between concrete and cellular plastic). It might attack the sill later... :-/

Damn, I've started reading carelessly, now I've missed several times... OK, it would not be underfloor heating... !!! What I wrote I think can still apply, in principle. However, heat losses downward due to a lack of insulation are not at all as significant unless it is underfloor heating. Insulation under the floor can be good; the floors will certainly be warmer then. The problem is the moisture you can get under the insulation, which can attack the sill and all other organic material in contact with the slab. If your floor has previously been directly on the slab, you've probably had some thermal leakage downwards, which has ensured that the moisture level on the slab's surface has remained reasonably low; the floor may also have been able to breathe and thereby ventilate away moisture. If you insulate, the slab will probably become cooler and "ventilation" poorer, so the risk of increased moisture levels cannot be ruled out. Increased moisture does not damage cellular plastic, for example, but it is likely that you also have some wooden structures in contact with the slab underneath, and they could be in danger. I can't give you any advice on what to do...

 

[Mikael_L]

As previously mentioned, tiling directly on the concrete without a moisture barrier, gypsum, or anything else is probably a fairly safe approach. However, there is a risk of having really cold floors.