Self levelling screed and PVA

[caluson]

I'm in the process of a new build in the Western Isles and in need of some advice.
I've installed wet UFH and it's been screeded badly and neeeds to be filled in and lowered in places. I can lower to a degree with a hired polisher, but should i fill in with the self levelling screed before or after firing up the UFH system?
I've also had a couple of quotes for tiling over the screed and one person seemed a bit blase saying he could put extra adhesive below the tiles in the shallow areas to even it out. The other chap arrived with a five foot spirit level and got all technical with levels etc and said that the whole of the floor needes to be painted/coated in PVA before tiling.
Is there a set proceedure that needs to be followed for my situation or should i just listen to what the tiler says and be done with it?

Many thanks, Calum

[whitebeam]

Hi and welcome..

DON'T USE PVA.

[grumpygrouter]

As per Whitebeam... DON'T USE PVA!!!

As for the floor flatness, BS states it should be within about +/-3mm over a 2m distance under a straight edge. Depending how far out it is, it may be possible to fill the low bits with with extra adhesive bit ideally the floor should be as flat as you can get it first. You don't state what type of screed you have. Is is a sand/cement screed or a gypsum based one. Gypsum based either needs priming correctly and/ or a gypsum adhesive not a normal cement based one.

[caluson]

Many thanks for your replies, and it's a sand cement screed that's been layed.