tilers giving different opinions on tile backer boards for timber sub-floor

[JKami84]

i have a timber subfloor - 18mm floorboards on joists. 

I'm having electric UFH in some of the area.

 

I'd like some insulating properties to make the UFH heating more efficient. 

 

1 tiler said he would only use 6mm hardiebacker cement board.

 

another tiler said he would use 10mm Delta board (which is cement coated but foam centre). he didnt just say this for insulating, he said he prefers it as it 'absorbs' some movement. 

1st tiler said only full cement board is rigid enough. he also said if i want insulating, will still need a cement board first - but this is not an option for the floor height.

 

2 views on the same puzzle.... 

 

its confused the hell out of me. 

[torre]

Not a tiler but we have successfully used the 10mm cement faced foam boards screwed to the floorboards with plenty of the large backer board washers, then a flexible tile adhesive and flexible grout. This was recommended to us on the basis there'll be a bit of movement with any timber floor, so better to allow for it - my concern with the cement boards is they may be more stable across the board itself, but that means any movement is focused more at the joints between boards.

 

If you're having electric UFH and it'll only be on for short periods then I agree the insulation is a plus.

[Nickfromwales]

On 09/02/2026 at 16:10, JKami84 said:

i have a timber subfloor - 18mm floorboards on joists. 

I'm having electric UFH in some of the area.

 

I'd like some insulating properties to make the UFH heating more efficient. 

 

1 tiler said he would only use 6mm hardiebacker cement board.

 

another tiler said he would use 10mm Delta board (which is cement coated but foam centre). he didnt just say this for insulating, he said he prefers it as it 'absorbs' some movement. 

1st tiler said only full cement board is rigid enough. he also said if i want insulating, will still need a cement board first - but this is not an option for the floor height.

 

2 views on the same puzzle.... 

 

its confused the hell out of me. 

You just need 6mm or 10mm tile insulation (not cement backer) boards, set down into flexible tile adhesive over the original chipboard flooring (cleaned and primed with 50/50 water/PVA immediately before laying) and then put the UTH wire on to the insulation board and off to go. Done loads of these over the years, on concrete or timber, ground and 1st (and 2nd) floors, and no issues.

 

You can tell when they lack experience, when they only quote directly what the manufacturer or rep recommends.

[dave2878]

forget the pva . never use it , its not fit for tiling , jacko board or  other insulation board glued ans screwed . ufh fitted . staple though the netting to make sure it doesnt float , then self level ontop . then tiling after priming the self level. suitable primer sbr ect, definitely not pva  

[Nickfromwales]

1 minute ago, dave2878 said:

forget the pva

For tiling on to yes. For fixing and priming the substrates and underlayment, then its perfectly good! Been doing this for 30 plus years.

 

Above those layers you use a tile primer such as Ultra, if it's needed. No need whatsoever to screw these boards down, does nothing but waste screws, time and money.

[Nickfromwales]

 

 

 

 

 

 

[dave2878]

cool got ye , i would just use normal primer anyway  as i dont carry pva in van  and i screw it but thats just preference, i either staple or rapid set ufh down as i have had them float before   i never tile straight on  in case i damage them . 

nice work 

[Nickfromwales]

16 minutes ago, dave2878 said:

cool got ye , i would just use normal primer anyway  as i dont carry pva in van  and i screw it but thats just preference, i either staple or rapid set ufh down as i have had them float before   i never tile straight on  in case i damage them . 

nice work 

Been bitten once, so now I leave the multimeter hooked up whilst laying, if I'm not self levelling. I use mitre bond and activator to pin the UTH mats / wires down, as once the bastards float you're screwed!

 

I use the grout float to skim the wires / mats so there's no metal trowel going against them, and always fit a second, redundant probe for the thermostat in case the original one carks it  

 

Thanks. Got the knees and back to show for it though!  

[JKami84]

You guys have been helpful. 

It seems like the 10mm foam filled boards like marmox or delta board ARE sufficient for my bouncy timber floor ... Just as much as a cement board would be... And will provide some insulation. 

 

I also hear the benefit of foam filled for allowing flex of floor rather than cement board - so UFH or not , may still be a better choice. 

 

The area of the floor being UF heated (living space) is much less creaky or bouncy than the kitchen part .. so I also overthought thinking I'd use cement board in one part and foam one in the other part . Lol. I'm going nuts 

[dave2878]

can you not lift a few of the floor boards and add in some dwangs to brace the floor and make it more rigid , 

[dave2878]

21 hours ago, Nickfromwales said:

Been bitten once, so now I leave the multimeter hooked up whilst laying, if I'm not self levelling. I use mitre bond and activator to pin the UTH mats / wires down, as once the bastards float you're screwed!

 

I use the grout float to skim the wires / mats so there's no metal trowel going against them, and always fit a second, redundant probe for the thermostat in case the original one carks it  

 

Thanks. Got the knees and back to show for it though!  

good idea on the mitre mate will have to try this . i fee; your pain with the knees and back 25 years of this has taken its toll 

[Nickfromwales]

4 hours ago, JKami84 said:

You guys have been helpful. 

It seems like the 10mm foam filled boards like marmox or delta board ARE sufficient for my bouncy timber floor ... Just as much as a cement board would be... And will provide some insulation. 

 

I also hear the benefit of foam filled for allowing flex of floor rather than cement board - so UFH or not , may still be a better choice. 

 

The area of the floor being UF heated (living space) is much less creaky or bouncy than the kitchen part .. so I also overthought thinking I'd use cement board in one part and foam one in the other part . Lol. I'm going nuts 

The subfloor needs to be robust, so no loose screws / nails, and no excess movement. Nothing will survive a moving deck.

 

If the deck is nailed down, then I’d punch a 5.0 x 60mm screw in where every nail is, right alongside it, and get the preparation done properly.

 

Is the bounce because they’re original, smaller joists, or because the deck isn’t fixed down properly? 

[JKami84]

There are a few creaks. I'll get them screwed down. 

Maybe one area of bounce. I don't think it needs screw for every board - which are nailed. But definitely a big bag of screws is a good idea. 

They need pilot holes I imagine. I put a few in and I think I made them worse as the board tried to lift