Hoping for some advice on the underfloor heating project I was doing. Basically when covering the heating mat in a levelling compound, I completely underestimated the amount of compound needed, and only managed to cover about 80-90%% of the floor. To make things worse I poured from the middle out, which has caused the edges to have either no or very little compound. The bulk of the mat is covered and fixed in place by compound, however I'm worried about the edges, and exposed heater elements.

I guess at this stage I'm wondering what my options are, and any advice would be greatly appreciated. I'm guessing they're somewhere in the region of:

  • Fill the spaces with an extra levelling compound
  • Tile as normal but using more tile adhesive over exposed area's
  • Start a new

I've uploaded some photos for amusement/reference: https://i.stack.imgur.com/ex61l.jpg

  • Why are you shying away from doing another pour? That seems to me like the obvious solution.
    – isherwood
    Nov 27, 2017 at 17:51
  • I was under the impression a second pour wouldn't bond with the one which is there, and I'd just end up creating a similar uneven surface. I could be wrong, going to look into it now =)
    – Martin
    Nov 27, 2017 at 17:55
  • We can't really address that without knowing what product you're using, but I doubt that's the case.
    – isherwood
    Nov 27, 2017 at 18:03
  • You may need to prime the first layer to encourage bonding since some time has passed.
    – isherwood
    Nov 27, 2017 at 18:05
  • I used: screwfix.com/p/cementone-floor-levelling-compound-20kg/3820h not sure if that is any help. And thanks for your help @isherwood I'll look into getting it primed, re-poured, and levelled out. =)
    – Martin
    Nov 27, 2017 at 18:11

1 Answer 1


Judging by this language in the instruction sheet...

  1. Allow to set (approx. 4 hours).

  2. Finish by levelling off with a further layer of SBR modified Bostik Cempolatex One Pack.

I'd conclude that you may apply a second layer of the product without priming. Whether it's appropriate to modify the compound with Bostik Cementone SBR is unclear, but that seems to apply to thicker applications.

  • 1
    Just a quick follow up to this. I applied a second layer of the compound, without priming, around the edges and feathered it out with a float. Its levelled quite nicely and ready for tiling. Thanks for your help =) If there appears to be any negative effects, once its up and running I'll give an update for anyone else in similar situation, but so far so good =)
    – Martin
    Nov 30, 2017 at 22:32

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