Egger Protect - Self Levelling Compound etc

[DanielShepherd]

I'm having underfloor heating fitted from Nu-Heat and as part of the install i'm getting all the rooms prepped in a 60's bungalow with a 2011 extension. Great fun for me the extension is on a decline and goes out by about 14mm.

 

I'm having the lo-pro system from Nu Heat which is 14mm pipes in a castelated panel cover by self levelling compound at 24mm thick and then tiles on top. If I don't sort the decline in the floor out when we pump the self leveller over the pipes we'll end up with 38mm at some points unfortunately.

 

So I bought some Mapei Renovation Screed in and planned originally to do the entire extension (as it's actually out of wack nearly 50mm from the hall way in total, but that's a different story) I decided against this increase of weight (and mass of work) and treat the room separately with just the 12-14mm of so out to cope with. The flooring in there is Egger Protect chipboard - their P5 product laminated on top and bottom with a waterproof membrane (like melamine?) 

I was using some XPS sheets to make up 10mm as I already had them so free, less weight on the floor, more insulation and less SLC to use. I did worry they'd just crack going over it - but I primed the floor and poured half a bag over the XPS and the floor just as a tester.

The next day I was surprised, the centre of the pour was rock solid on the XPS sheets and it was at the minimum depth of about 3mm, also solid on the Egger Protect. No problem I thought. Nu Heat had sent me Primer G as they had no Eco Prim T Plus in stock, but I checked and it said Primer G was only for porous surfaces, i'd already coated the Egger Protect boards with this so I e-mailed technical support at Mapei to see if I could apply Eco Prim T over the top and all my problems started...

They told me...

"Waterproof chipboard such as Egger Protect are not suitable to receive any type of primer, these types of chipboard need to be over boarded with either exterior grade plywood or a cement based backer board."

Ah - damn. The problem here is I don't want to raise this floor level up too much as the underfloor heating pipes need to continue through from the hall way. I also didn't want to ideally spend more money, more time and add more weight to the floor either.

At this point my flooring was going to be Egger Protect -> Mapei Renovation Screed -> Nu-Heat Casterlated panels and pipework -> Nu-Heat Lo Pro Quickset SLC (made by Mapei) -> Tile Adhesive -> Anti Fracture Matting -> Tile Adhesive and finally large format porcelain tiles!

Of course the last thing I want is the very bottom of this the renovation screed on the bottom to delaminate from the Egger Protect board and cause faliure - having said that, there's so much weight on top, and so many flexible things - flexible renovation screed, flexible panels and pipes, flexible quickset, flexible adhesive, a flexible mat, more flexible adhesive and a flexible grout that i'm not sure i'd see any issue on the top anyway.

I tried to come up with all kinds of solutions. Egger say you can tile directly onto Egger Protect and list some tile adhesive they recommend - I asked Mapei about instead of using Plywood or Cement backer board, could I use 1mm-2mm of a cement based tile adhesive and pour the renovation screed onto that. Yes they initially said before changing to

"We would not recommend the proposed system suggested as whilst the Ultraplan Renovation screed 3240 is suitable for use over tile adhesive residues, we would not recommend the use of Mapei Ultraplan Renovation screed 3240 over a complete bed of adhesive as the compressive strength of the product could cause excess stress resulting in the tile adhesive being pulled away from the chipboard surface."

I'm not sure how 3mm-6mm of SLC would cause the tile adhesive to be pulled away from the chipboard surface when they recommend laying 10mm of porcelain tile? But I suppose with everything else on top too?

Has anyone got any other suggestions. I asked if I could use 3.6mm plywood as it's not going to be structural and it's basically just acting as a bonding board. I also thought a layer of plywood might actually just cause more undulations, more movement etc unless perfectly flat - I'd have to screw it into the chipboards and joists I guess - as any laying with tile adhesive will surely cause the same problem as above...having it ripped away due to the compressive strength. 

They told me that only 5.5mm marine grade plywood would be suitable and that cement based backer board is even thicker. 

I'm at a bit of a loss. It's either 3.6mm plywood anyway, don't bother at all and let the SLC over the underfloor heating just go thicker in some areas and deal with the slower response time there, the tile adhesive method, or even sand the laminate layer off the top (LOTS of work), prime that and apply the renovation screen to what is essentially just chipboard now. I can't help but think Mapei are being massively over cautious which is understandable as they don't want to say "yes you can do this" unless it's in their carefully constructed technical guide as it would come back to bite them.

[MikeSharp01]

The difference in thickness will slow the response in the thicker areas but only on the up and down slopes. Once you are running at a constant temp there won't be any noticeable effect and how often do you watch the response on your radiators. 

[DanielShepherd]

3 minutes ago, MikeSharp01 said:

The difference in thickness will slow the response in the thicker areas but only on the up and down slopes. Once you are running at a constant temp there won't be any noticeable effect and how often do you watch the response on your radiators. 

 

In your opinion not worth the hassle and money of trying to deal with the bonding to subfloor issue? Just make sure the castellated panels can stick down to the Egger Protect I guess!

[MikeSharp01]

 

10 hours ago, DanielShepherd said:

In your opinion not worth the hassle and money of trying to deal with the bonding to subfloor issue? Just make sure the castellated panels can stick down to the Egger Protect I guess!

I supposed they could be glued down - plenty of glues will stick to Egger or screwed down, you will then make up the level with the self leveling above the pipes makes more sense, not sure of the additional weight. You need to check that floor will take it either way you are either putting it above or below the pipe system so might as well put it above. Also watch out for what happens to things if you do level up by the amount you are playing with EG socket heights and etc.