Tiling above UFH using 18mm chipboard - Tile Advice

[Hazel]

Hi,

I have recently installed wet UFH, and put biscuit sand and cement screed on top of this in between joists. Covered this with 18mm toungue and groove chipboard, which is glued and screwed.
Plan was to now put down a decoupling membrane, then flexible grout and adhesive tiles.
I am looking for confirmation this is the best route, and for any advice!!
Thanks!

 

[Flintstone]

Hello hazel. I would overboard with 6mm cement board such as hardie backer then tile. Make sure the underfloor heating has been commissioned before you do anything.

 

[Hazel]

Hello hazel. I would overboard with 6mm cement board such as hardie backer then tile. Make sure the underfloor heating has been commissioned before you do anything.

Thank you for replying!
So you wouldn’t use a decoupling membrane at all?

Why is the hardiebacker better? Does it need fixed every 6cm? This wouldn’t be possible as the pipes are under the floor so screws would go in?

I thought the movement would be stopped from cracking floor above with the decoupling membrane?

Sorry if these are silly questions!!!

 

[Old Mod]

There are no silly questions Hazel, only silly answers.
In essence your method is perfectly ok.
However, NO particle board is a good substrate.
Depending on the type of chipboard it may require a particular type of preparation before you can even fix Ditra 25 to it, some are resin faced for example.

To split hairs, ANY material placed between the substrate, in this case chipboard, and the finished floor surface will decouple the floor, as long as it’s only fixed to the chipboard and not through to the joist.
Basically the role of the decoupler is to separate it from the main structure. (Your home)
That way the building can move and your floor, will in theory, stay in tact.
That is the primary role of a decoupler.
In the case of a cement board, it will still act as a decoupler, as it’s placed between substrate and tile.
What a cement board would have over a membrane is the fact that it’s not only stuck with tile cement, it’s mechanically fixed too. (Screwed down)
That would eliminate any special preparation techniques that may be required for the particle board.
Whilst a cement board overlay is an inert material, not effected by temperature fluctuations or moisture, the chipboard isn’t as stable.
The ultimate choice for your install would be an inert structural material.
There are two such materials that meet that requirement.
1. GIFA board, a gypsum based material, &
2. 22mm No More Ply. A cement board.

If you were to chose the former, you would need to use their primer for the GIFA board, and follow the instructions carefully.
As gypsum and cement based adhesives are not friends unless primed correctly.
But both are excellent products.

 

[Just Rizzle]

why do builders put any wooden materials over ufh. wood is an insulator why do you put wooden handles on pans because they dont get hot.
i would rip up your chip board and over lay with 2 layers of 12 mm hardy backer board layed 90 degrees to each other.this will allow the heat from your floor to pass through more effectively and probably half your future heating bills. by over lapping the hbb you can do away with the decoupling mat. i would stick the hbb over the in fill between the joists and also screew to the joists any voids beneath the substrate and your uht will reduce heat transfer costing you money.

several years ago i tiled several large houses which used this method using a similar product to hbb and the heat transfer was amazing.
if you want to test my advice do you have a hot plate put a piece of chip board on it at full heat and see how long it takes to get hot do the same with hbb