Self levelling over UFH mats - how to get it flat?

[cirlam]

Hi,

I'm tiling my 12m^2 conservatory - Concrete base, Self levelled, 20mm Jackoboards, Prowarm mat, self levelling compound, then 600mm square porcelain tiles.
So far I have self levelled the base, and stuck the jackoboards down - all really nice and flat so far.

Now I need to fit the UFH mat, and self level over the top - how do you ensure you get a good finish (flat/level) over a relatively large area?

Everywhere I've researched just shows people trowelling the SLC over the mats. When I've tried to use self levelling compound this way before (just trowelling it freehand), I have had really poor results - recently I've been resorting to setting out wooden battens (levelled on the heads of screws ~25cm apart) to form bays, and pulling a straight edge across it.
This gives me great results, but is time consuming and I don't really want to put loads of screws into my insulation boards If I can avoid it.

 

[JMC tiling]

screws are the best way I find.

 

[cirlam]

Thanks - do you screw straight into the insulation boards then?

Was considering using strips of a 6mm jackoboard between the UFH runs to create rails that I can pull a straight edge across. Although maybe a bit overkill..

 

[Dave]

Thanks - do you screw straight into the insulation boards then?

Was considering using strips of a 6mm jackoboard between the UFH runs to create rails that I can pull a straight edge across. Although maybe a bit overkill..

Nothing is overkill if it works. 👍👍

 

[cirlam]

Thanks - I ended up using strips of electrical conduit covers (about 5mm high) to form bays. Worked a treat, and easy to pull the plastic conduit up out of the self leveller when dry