porch

[wayne]

customer has had upvc porch put on side of house to use as utility room. floor is existing outside concrete. they want it tiling and im just wondering does it need a liquid dpm before tiling?

 

[Rob Z]

Hi Wayne I've always used Ditra over slabs for that reason. Ditra allows for the movement of vapor under the sheet and off the the perimeter of the installation.

The only thing that I know of that is truly vapor proof are the epoxy coatings that will seal the surface of the concrete and reduce vapor transmission to a very low level. These epoxy coatings are really $$$$$$$.

 

[White Room]

Is it a concrete or screed floor

 

[Ajax123]

Hi Wayne I've always used Ditra over slabs for that reason. Ditra allows for the movement of vapor under the sheet and off the the perimeter of the installation.

The only thing that I know of that is truly vapor proof are the epoxy coatings that will seal the surface of the concrete and reduce vapor transmission to a very low level. These epoxy coatings are really $$$$$$$.

I wouldn't think an epoxy DPM is anymore expensive than an uncoupling membrane really. If you use ditra the moisture can move around. If you use a DPM it can't. Not sure which would be safer in all honesty.

I think for tiles I would tend to use Ditra though as there is likely to be quite a bit of thermal gain in this type of porch so expansion and contraction a potential issue as well as damp and the Ditra will help dal with both.

If you decide the DPM route have a look at Tremco Universal One Coat. I got this on my convervatory floor and did it myself - was really easy. If you going to tile on top I think you will need to overcoat it with epoxy primer as yo will need a tacky top coat for the addy to grab.

 

[White Room]

Would'nt you need to dpm up the walls slightly,say 150mm

 

[Ajax123]

Would'nt you need to dpm up the walls slightly,say 150mm

I was assuming it was UPVC to the floor but you could be right cos if the walls will draw they might get damp.

 

[White Room]

I have seen where they do a few courses of bricks to raise up but if the upvc is laid directly to the floor then no need for a dpm

 

[Rob Z]

I wouldn't think an epoxy DPM is anymore expensive than an uncoupling membrane really. If you use ditra the moisture can move around. If you use a DPM it can't. Not sure which would be safer in all honesty.

I think for tiles I would tend to use Ditra though as there is likely to be quite a bit of thermal gain in this type of porch so expansion and contraction a potential issue as well as damp and the Ditra will help dal with both.

If you decide the DPM route have a look at Tremco Universal One Coat. I got this on my convervatory floor and did it myself - was really easy. If you going to tile on top I think you will need to overcoat it with epoxy primer as yo will need a tacky top coat for the addy to grab.

The only one I know about that is sold here and suitable for tile is Laticrete 312. My cost for the material alone is more than Ditra + thinset, and the prep on the slab is a bit more work (needs to be ground down to bare concrete for the epoxy paint).

I used to have a local dealer for Tremco products, and I never asked them for tile-suitable coatings for slabs. I'll look into that because we have a basement slab to do sometime in the next month or so. I'm glad you reminded me about the Tremco line.

 

[DHTiling]

If it is an exisiting slab,,, then i will breath as normal..

As long as it is dry then tile as you wouls an out side slab.. frost resistand addy and grout..

don't over spec it..