Gurus This is a great website – I wish I’d found it sooner I’m dizzy going round the www looking for information As per title I’m looking for real-world BTDT advice on engineered oak laid on anhydrite/UFH I'm about halfway through my renovation with a small local builder. So far three rooms screeded with Supaflo - gypsum screed. One of these has UFH. Alarm bells started ringing when this was switched on - the screed cracked in the line of a tight leash of pipes heading to the next phase The screed company advice was to repair this with ? an epoxy resin Anyway all looks well with the repair. This room will eventually be laid with riven slate The floor has been down three months so I hope no issues with dryness here However next up is our main kitchen/living area ~ 11m x 6m My wife is fed up with all the mess and I want to get the floor down asap I've found what looks a good deal on engineered oak 220 x 21/6mm in 2200 lengths at £36.50/m2 It's T&G all round and micro-bevelled The supplier recommends Elastilon Strong as a relatively easy diy option Their website says to use a poly moisture barrier but I've read elsewhere not to use DPM over gypsum Questions.... Can someone explain the DPM issue? Is the oak flooring + Elastilon a good idea anyway or should I stick with fully glued? The Elastilon will cost £7.50/m2 so there's not a huge premium over primer/ glue etc + my time for free How will I know when the subfloor is dry enough? The screed company quote 70 days for 55mm and won't commit to a definite answer if the UFH is used to "force dry" Can I hire a Tramex type meter or get someone in to measure the moisture? Is there any other way to be sure? I well realise that supply and fit is the best option But this is stretching my budget as is and I definitely can't afford an expensive mistake I'd be very grateful for your advice
thats a long first post ! For start off, you say the screed cracked and epoxy was applied? to the whole area or was it applied to the cracks? As for the rest of your questions, i want to double check something first before i reply.
Sorry for the length - tried to cover all the background from the start. The crack was in one long - 5m - jagged line I don't know if it was a structural problem or the builder was just being extra careful I just mentioned it because I wondered how much experience the builder/plumber had with UFH rather than I was worried about the crack itself It was maybe 1mm wide but only 2-300mm from the "outside" edge where there will be sliding/folding doors I was not there when it was fixed but it looks as though it was widened and filled -there's a little spill over along the crack but the rest of the slab was left as was.
If over = instead of I had no input in this, didn't know there might be a choice - I assumed because gypsum screed flows easily round UFH pipes
When the under floor heating was switched on was it on low or did they have it on high as that can cause the cracks, that happened on a job I was on last week. Carpets going down so not sure what they did to fix it if anything.
This is water under the bridge really The water was at approx 45C - as low as the stat on the circuit would go The screed company say start at ambient and increase 5deg/day That would be possible only by changing the stat (or maybe the boiler temp could be turned that far down - will check tomorrow) But I think the real problem was the tight pipe layout in that narrow strip They are still short blind loops at the moment but will be the feed/returns for the next section so the local temp. will drop anyway But as I said originally, I'm not so bothered by that I just want to make sure we get the next bit right
Hi, on reading your post i think i miss read it last night. The area where the wood flooring is being installed does not have underfloor heating? can you just confirm that bit please? Anyway, as for reading the moister of the subfloor you need to do so with a hygrometer and you need to see reading below 75%. They say not to install a dpm as it will trap moister and can send the subfloor weak and sends it back to a wet mix as such. Personally i dont agree with this as the floor is now solid. Applying a surface dpm wont increase the moister in the base so how can it send it back wet? personally i would guess in the cases where there has been issues its been due to failed dpm under the subfloor or a pipe leaking. This would then increase the moister and yes it will then send it back to a wet screed. Problem is that this kind of subfloor is relatively new and rare so no real fault finding as such has been done. People just simply point a finger at what they can blame issues on rather than proven it.
Yes the bit yet to be laid will have UFH + oak flooring The older bit that cracked is still waiting for riven slate The problem for me will be getting the moisture level accurately measured in the new bit so I can get on with the floor asap And I would still like to know if this oak + Elastilon Strong +/- dpm is a good idea Elastilon website says Elastilon is 3mm PE foam with v. low water absorption So I can't see the difference ( nor the need for) between that and another layer of thin sheet poly dpm Is there a different scenario if moisture migrating downwards from fully glued option into bare gypsum slab and glue does not work?
It's a safer option to float the engineered wood. If your going to stick you really need to grind the surface of the screed, prime and then glue. I wouldn't fancy sticking it if the screed before had cracked. I would leave the screed to dry out properly, test a few areas with a hygrometer to make sure it is dry and float the wood over a ufh approved underlay. You should check with the wood manufacturer their product is ok to install floating over ufh if you haven't already.
you can purchase a flooring Hygrometer for around £130. You may be best buying one and selling it on when finished with it. The reason why you put a sheet of plastic down is to act as a moister barrier. Not as a dpm. As the floor is floating you can get a build up of moister as the temp goes up and down in the room and floor. When the product is bonded it acts as insulation and you dont get the same effect as when there is a air gap between the concrete and the flooring. The elastilon underlay wont absorb moister but it wont protect the flooring either as it doesn't have over lapping plastics between the runs. You need to check with the subfloor manufacturer if they are o.k with a plastic sheet over the subfloor as some dont like it. This will make a difference to how you install the flooring. Also with the flooring being floated you will insulate the heating system. Make sure you check out the tog rating of underlay and flooring etc other wise you wont get any heat transfer through. Also note that you have chosen a wide plank. Be careful with wide planked products over underfloor heating. Ideally you should be looking for a narrow strip and you would be best gluing. There is the worry that the floor has cracked but i would guess this is down to too much heat to fast. Note that you will damage the wood flooring also if the floor is run too hot or warmed up to fast etc. Ideally underfloor heating should be used as a second heat source to take the chill off the floor. Dont suppose this is the case ?
Thanks Matt Re. hygrometer - can you suggest reliable makes? I think I now get the moisture barrier concept - I've asked screed company about this Elastilon website "Thermal conductivity: 0,038 W/mK (at 0°C)" Is this 0.38 tog? The flooring company say the engineered oak has never been scientifically tested but that they have sold lots without problems I would be inclined to accept that - I don't suppose their version differs greatly from the norm re heat transfer I guess they would also know by now if they had problems with wide boards cupping etc. The cracked floor was a different room. The floor in question has not been poured yet. But I hope I have now learned enough to properly condition both the floor slab and the flooring We will also have a 7KW woodburner.
fball Hygrometer as above mate. The wood manufactorier wont tell you if they have issues with there product over underfloor heating. End of the day the product is not faulty and being a natural product cant be faulty. The wood is simply reacting to the environment it is in. We go out and masses of complaints on wood floors over under floor heating where the temp has been too high or teh product is to wide. The blame is not with the manufacturer but the installer or the person that controls the heat of the subfloor.
