Installing parquet over overfit type UFH boards

[sb1202]

Looking for advice from anyone who has installed a "wunda" rapid response type UFH system. Currently installing one in a reno property but getting so much conflicting advice from manufacturers and floor installers about fixing the finished surface, which will be 15mm engineered parquet.

Wunda, who are the market leader, say that engineered wood (and ceramic tile) can be bonded direct to the xps tiles. However, from googling, speaking to suppliers etc, the Wunda overfit boards and pipes are identical to all every other suppliers. The boards are all exactly the same spec which is essentially 20mm overfit, EPS400 (400KPA compression strength) boards with a 200 micron foiling on top. 

 

Whilst the boards are all the same, no one seems to be in agreement when it comes to installing the finished floor. Some say there needs to be a min 5mm SLC screed over the boards, some say min 10mm, some say min 12mm. Flooring installers say min 15-30mm?

After numerous searches on installing SLC screed over the boards, I found loads of posts where people have experienced the SLC cracking - despite following instructions. With that said, it's made me a touch uneasy about this system and looking for anyone's experience. 

(I have since found a few influencers who installed parquet direct to the overfit and so far, they don't have any problems. (See pic))

[JohnMo]

We have similar floor buildup in our summer house, not parquet but is and laminate flooring, the performance is pathetic even at 40 degs. In the end I decommissioned it.  You need the pipes in close contact with something that fully envelopes the pipe so you have zero air gaps. So a screed or self levelling compound will improve things. Your thickness needs to thick enough to stop cracking from small movements. So will depend on make and exact product you use. I would looked to a self levelling but flexible compound.

[Nickfromwales]

I thought it was the 400 micron for tiling etc directly on to? 
 

I’d want that spec anyways, if using this system, as it’ll be a much more efficient emitter / diffuser of heat.

 

As above, get at least 3-5mm of SLC down, but who cares if it cracks? In actuality, it’ll be hidden under the flooring and the glued joints (and the fact it’s all glued down robustly) will keep it controlled. Shouldn’t affect the parquet at all imho.

 

Have you checked that the parquet is suitable for 27° or above? You’ll need to run this at quite high temp to be effective at heating the room. 
 

The SLC would help a lot here, so don’t omit it!!  If you can do 5-8mm or 10mm then do so. Consider mesh matting as a binder, if you’re really panicking about cracking / degradation of the SLC.

[sb1202]

2 hours ago, JohnMo said:

We have similar floor buildup in our summer house, not parquet but is and laminate flooring, the performance is pathetic even at 40 degs. In the end I decommissioned it.  You need the pipes in close contact with something that fully envelopes the pipe so you have zero air gaps. So a screed or self levelling compound will improve things. Your thickness needs to thick enough to stop cracking from small movements. So will depend on make and exact product you use. I would looked to a self levelling but flexible compound.

I've tested this with some spare boards and the SLC doesn't fill the gaps as well as direct bonding the parquet to the boards. 

The parquet is fixed with an MS adhesive which is sticky, has a viscosity similar to honey and has self levelling properties. When the parquet blocks are laid onto the adhesive and slid into place, the adhesive spreads and is forced into any gaps. It makes a solid seal. 

With the SLC, it's less viscous and certainly flows faster but it flows along edges before settling and leaves small pockets under the foil. A spiked roller didn't make any difference or compress it into the pipes.   

 

[sb1202]

2 hours ago, Nickfromwales said:

I thought it was the 400 micron for tiling etc directly on to? 
 

I’d want that spec anyways, if using this system, as it’ll be a much more efficient emitter / diffuser of heat.

 

As above, get at least 3-5mm of SLC down, but who cares if it cracks? In actuality, it’ll be hidden under the flooring and the glued joints (and the fact it’s all glued down robustly) will keep it controlled. Shouldn’t affect the parquet at all imho.

 

Have you checked that the parquet is suitable for 27° or above? You’ll need to run this at quite high temp to be effective at heating the room. 
 

The SLC would help a lot here, so don’t omit it!!  If you can do 5-8mm or 10mm then do so. Consider mesh matting as a binder, if you’re really panicking about cracking / degradation of the SLC.

200micron is the thickest foil available. I haven't seen 400mircon anywhere?  Tile can be direct bonded on thinner foil boards, it's the kpa rating that matters for tile. These are 400kpa rated for tile, which is overkill for engineered wood.

 

Cracking may not an issue with slc over concrete, but these are xps boards which have a lot more movement. There are a lot of horror stories with Wunda floors, particularly with slc and glued down floors.  Common issues are chunks of slc lifting, hollow spots and slc turning to dust along cracks. Most problems are with lvt, but people have had the same problems with tile and engineered floors.

 

Over 27°?  Curious you say this as I install a lot of this parquet. I've never seen any engineered wood that's rated over for 27°. I haven't heard or seen any complaints about the wunda system needing to run at high temps.