Hi,

I'm about to lay my Devi UFH on Hardibacker 250 and then was planning to level/fill with SLC before tiling (Travertine, Keraquick white).

Do I need to use a primer on Hardibacker?

If so should I prime the whole floor before laying the UFH or just the areas that don't have the heating mat on them afterwards?

Thanks

Giles

HI Giles and welcome...

Usually a wipe over with a clean sponge is sufficient, Hardi do not recommend to prime.. but also check instructions on the SLC..

No you shouldn't need to prime the boards for the tile adhesive to bond to them. The problem I find is that the boards can be really dusty and this makes it hard to stick the ufh down. I prime the boards before taping the UFH mats down, seems to make a world of difference.

To add to my above post, I use a different brand of backer board and they recommend priming before laying UFH, if Hardie dont, then it is always best to follow their instructions.

Giles.. How big an are is it..?

You could bed the UFH into a 3mm bed of flexi adhesive, this will hold the mat in-situ , then you can SLC over the top.

Hi Dave,

Its about 7 sq M. I was hoping to minimise height build-up so i'm happy to prime if it's necessary either before or after laying the UFH but is it overkill given that I've installed a backer board anyway?

Forgot to mention that the next layer is a membrane bedded in Kera if that makes any difference.

Should I be looking for a branded SLC e.g. Mapei or will something like Wickes Ultra do just as well? The Wickes one recommends priming but I assume they are thinking of rough dusty renovation surfaces rather than newly laid backerboard

I use 2 brands at present and use depends on where tiles come from

One is Mapei renovation screed SLC and the other is Weber floor flex... both are fibre modified SLC's..

Priming will help the Devi matt stick down better

When it comes to choosing your SLC, I dont think that you can go far wrong with Mapei but whichever one you choose the important thing is that you make sure that it is suitable for UFH, you would be amazed at how many people make that mistake. Have a really good read through all the bumpf on the bag, it should tell you if it is suitable

Thanks all for the advice!

As I'm covering with Keraflex it seems sensible to go with the Mapei and their primer! Just got to find somewhere that stocks it now!

Originally Posted by jay

Priming will help the Devi matt stick down better

I must agree with Jay, the self adhesive Devi mat does stick well to a primed surface. But as Dave says you are better going with the board manufacturers recommendations.

Originally Posted by Phil Hobson

I must agree with Jay, the self adhesive Devi mat does stick well to a primed surface. But as Dave says you are better going with the board manufacturers recommendations.

Makes you wonder just how long Hardie have been producing all the tile adhesive on the market these days