Self levelling compound advice

longwalks1

I’m renovating our kitchen and there’s a low spot in the middle of the concrete floor.  Kitchen is 7m x 3.5m and it dips to about 30mm below level for 2m in the middle of the room. It isn’t an obvious ’dip’, only really detectable with a 6ft level.  I need to level it to fit underfloor heating.  I was going to use Mapei Ultraplan self levelling compound, but max pour is 25mm, would I get away with a single 30mm pour, or do 2 pours? And if I do 2, would I need to prime the 1st pour once it’s dry?

any advice greatly appreciated 

FreeBear

With a 30mm dip, I'd build up the low point with some screed first, and then hit the whole area with SLC. If you try to fill the full depth with SLC in one go, there is a good chance the stuff will crack. Even if done in two layers, cracks may well appear.

And no, no need to apply primer between pours as long as the first layer is still damp.

grumbler

I see Mapei "Ultraplan Renovation Screed 3240" - Fibre reinforced self-levelling compound designed for the renovation/refurbishment of existing floor substrates. ... Can be used from 3-40mm

andyhop

Weber floor flex will go 50mm in one go. You’ll need a few hands to mix , pour and flat

If you do multiple, follow manufactures guidelines and prime between 

Bradden

grumbler said:

I see Mapei "Ultraplan Renovation Screed 3240" - Fibre reinforced self-levelling compound designed for the renovation/refurbishment of existing floor substrates. ... Can be used from 3-40mm

This product is very good from my experience.

longwalks1

Thanks everyone, also, would I need to bring the dip in the centre of the room up to current level/high point, and then do the whole floor another 5mm or 10mm, so the UFH boards (I’m thinking Wunda UFH components, the 20mm insulated board system) have a complete level floor to be stuck to?  Or could I get away with just bringing the dip up to level?

would the join from new SLC and existing concrete floor be too prominent/obvious to fix UFH boards to? (They are similar to kingspan/celotex in design)