'to screed or not to screed' over electric underfloor heating?

Discussion in 'Builders' Talk' started by toekneer4, May 4, 2004.

  1. toekneer4

    toekneer4 Member

    gotta tile over some electric underfloor heating, the type thats loose wire rather than woven into a mat.
    The owner has put the heating flex down and taped it in position ready for tiling over with slate tiles.
    Ive never tiled over this stuff before, and after reading the text that goes with it it says either screed first, then adhesive/tile, alternatively you can set the flex straight into the adhesive..
    looking at the job it would seem easier to me to screed it all first(self leveling with flexi adative)then adhesive/tile off that.
    Im thinking it would keep the heating flex in place and also protect it from my grooved float when applying the adhesive...
    but like i said not any experience in this...
    so any advise would be great....Thanks
  2. dj.

    dj. New Member

    can't find loads of info but what i did find should answer your question. flex must be screeded 30 to 50mm, the mat can be used with adhesive. this info is from one company only so i don't know if different firms recommend different applications, anyway click on this for the info i got hold of http://klimaunderfloorheating.co.uk/klima-underfloor-heating-cable.html

    hope this was of some use..dj.
  3. diysaster

    diysaster New Member

    I'm by no means an expert, but I did this same job about 3 weeks ago in my bathroom.

    I decided it was going to be a lot less hassle to do it in one go - ie. a thick layer of adhesive to cover the cable and lay the tiles onto.

    I took the advice of Topps Tiles, who told me that a normal adhesive with flexi additive wouldn't be good enough for my wooden floor with underfloor heating, and I needed to use the ludicrously expensive BAL flexible 2-part adhesive (which I think was about 60 quid a bag, including the liquid). This just about did 2 square metres at approx 5mm thick. I also thought it best to use a large plastic (rather than metal) adhesive spreader to minimise the chance of damaging the cable.

    I've never tiled a floor before, but I think I ended up doing a pretty good job, despite having to work bluddy fast (the adhesive is only useable for around 40-50 minutes once you've mixed it up). I didn't have time to clean up as I was going, but the goo left on the tiles cleaned up very easily after it had dried.

    And don't forget the grout needs to be flexible too or the heating will cause it to crack. Both the adhesive and grout were only available behind the counter at Topps (probably because of the price!)
  4. Nooby

    Nooby New Member

    Hi. I used the same heating wire in my bathroom last year. Laid it down in the 'S' pattern, taped it in place and then I just spread the flexible tile adhesive (designed for use on wood) over it using a plastic spreader. 10 months on, no cracks and a lovely warm floor. One thing tho', my floor was very small, just over 1m2. Good luck.
  5. toekneer4

    toekneer4 Member

    this is the problem... im doing about 20-sq-m of flooring..
    which is why im thinking it might be easier to poor a load of self leveling compond over it first giving me a nice flat surface to work off and maybe making it quicker overall.. as i can spread the adhesive with a bit more abanden!!
    dont know if thats the right word!!
    the thought of spreading the adhesive over the wires and being carefull etc over such a large area is filling me with dread..
    Im thinking day one- mix a load of self leveling compound with flexible additive..poor it over, use a roller to spread it out quickly over the floor..1 - 2 hours later go home..come back next day start the tiling as normal quickly spreading adhesive and laying!!!
    what you all think??? waste of time ???
    should i just crack on with setting the flex in the adhesive??? decisions decisions.....
    i suppose im hoping someone will comne along and say thats how i did it and it was dead fast and easy....
    but then nothings ever easy!!!
  6. dj.

    dj. New Member

    i think you've got the right idea tk, but ive not used the stuff did you check out the link i left you before?
    seems like it would take loads of adhesive and time to do it the other way!! dj.
  7. toekneer4

    toekneer4 Member

    yeah i did check the link dj ...thanks
    Ive since found out what the heating cable manufacturer is and gone to their web site http://www.floorheatingsystems.co.uk/home.htm
    its pretty informative with instruction downloads etc
    and as i thought it does suggest in large areas to screed first to save on time and the amount of adhesive used...Thanks again..
  8. diysaster

    diysaster New Member

    Yikes, that's a big floor to tile. I'd have to say that for that size, screeding would be the way to go.
  9. bilco

    bilco New Member

    I think you have three choices;

    1..stick tiles directly using a solid bed of adhesive

    2..apply min 60mm screed then tile

    3..fix 25 deep battens at 400 ctrs arround heating, fill void with a dry/weak sand cement screed, fix ply deck and tile
  10. dj.

    dj. New Member

    bilko:- manufacturer recommends a screed over flex then tile with adhesive. if it is done a different way the manufacturer will not give you a warranty/guarantee on their product.
    as for battons, then infill, then ply, then tile with adhesive, sounds like a load of unnecessary work to me.
    have you checked the above links? dj.

    TK:- checked out your link, i think you know the score, have fun coz it's a big un. dj.
  11. bilco

    bilco New Member

    Hi DJ

    I read; "after reading the text that goes with it it says <u>either</u> screed first, then adhesive/tile, alternatively you can set the flex straight into the adhesive.."

    Sand and cement screeds over heating needs to be a minimum thickness...if that's not possible, you are left with the other two alternatives
  12. dj.

    dj. New Member

    ello bilko, yes i see the either or on the link, but it does say quote "if possible cover the cable with a thin layer of latex based levelling screed". this, under this manufacturer, is an either or situation. but judging the size of the room wouldn't it be better to cover the flex before tiles are put down therefore protecting the cable from damage. also one of the manufacturers,i think, tells you not to walk on the cable.
    i just want to give the best info that i know.
    ta for your reply dj.

    ps the thickness was only 3-4mm step 6 check it out http://www.floorheatingsystems.co.uk/PDF/Cablekit.pdf
  13. toekneer4

    toekneer4 Member

    yeah thats right dj.....
    but of course went into topps tiles on saturday and they dont do latex self level screed or anything that can be mixed to do the job...typical init...was going to do it on monday..
    so now ive gotta source out somewhere that does the stuff..
  14. dj.

    dj. New Member

    tk can't help much with suppliers, but, go to this link again

    scroll right down to the bottom and there are a few more links you could try, remember it's pdf so you cant click directly on the link, well i couldn't, let me know how you get on cheers dj
  15. woodsmith

    woodsmith New Member

    Any decent builders merchant will sell self levelling compound. One tip, get a meter and test the electrical resistance of the wire, then test it again once you have put the screed down and again just before you lay the tiles. The readings should all be the same, if you have damaged the wire whilst laying the screed better to know before you lay the tiles.

Share This Page