Hardiebacker under Insulation boards?

[Bathfix Bob]

Hi Guys, in my current bathroom job its been a late decision to have an electric underfloor heating mat.

Its 18mm chipboard well screwed down and I've bought, cut and laid 6mm Hardiebacker but not fixed or glued it yet.

Shall i do away with the Hardie and just screw and glue 6mm insulation boards down or shall I glue and screw hardie as normal and then insulation board on top? I want to keep the hardie really but I suppose I can use it on my next job.

Tiles will be porcelain.

 

[hmtiling]

Get rid of the Hardie if the floor is sound.

 

[Stef]

It will be fine to fit ufh on top of Hardie, not ideal as you would be better with thermal.
Might not perform as efficiently but it will be pennies of an extra cost.

 

[Flintstone]

Personally I would go over the hardie with the ufh

 

[hmtiling]

I was under the impression Hardie was a terrible insulator hence it being specified for overboarding wet ufh sometimes

 

[Bathfix Bob]

Thanks guys,

It's seems some people love insulation boards and some hate them, my local independent tile shop dosnt sell them and whenever I ask they say theres no call for them as everyone tiles on Hardie.
I have to go to the tile Giant in the next town if I need them.
Can someone explain why it's okay to tile on something so soft like foam cored boards when we do everything we can to make floors rigid?
The smaller the tiles the more likely they would 'sink' into the board.

 

[Ttt1601]

You've kind of answer your own question there, it's about point loading those thermal boards are are bloody solid if you've got a large surface area on them, but hit them with a hammer you'll go through it

 

[Dumbo]

If I'm correct most insulation board manufacturers are happy with a tile size down to 50mmx50mm although one of the ones that marmox make are happy to go slightly smaller I believe but you would have to check with them .

 

[hmtiling]

If I'm correct most insulation board manufacturers are happy with a tile size down to 50mmx50mm although one of the ones that marmox make are happy to go slightly smaller I believe but you would have to check with them .

Agree, although that may not be the case once latexed

 

[Dumbo]

Agree, although that may not be the case once latexed

Please educate as to why