Underfloor heating - to screed or not to screed?

[dazlp]

Hi, Looking at putting electric UFH down in the kitchen onto an uninsulated concrete floor. Plan to use 6mm insulation boards under the mat, but my question is do I need to lay a screed down over the mat before then laying the tiles + adhesive? Most of the UFH manufacturers offer the choice of both (you need to screed first OR you just apply a full bed of adhesive over the mat (carefully) and lay tiles on top.

We want to keep floor level as low as poss so the obvious solution is to go without the screed. Any one got any advice on pros/cons/experience?

Cheers

 

[Dumbo]

A friend of mine once cornered an ufh rep at a show and challenged him about the fact that they say it doesn't need screening telling them that wasn't the way to do it. The response was "I know we just do it to get the diy market " . I think that says it all really .

 

[Flintstone]

100% you need to cover with self leveller to do the job right. It won't add any extra build up hight as long as you don't pour too much

 

[One Day]

Definitely needs covering. Spend extra time taping, gluing or stapling your mat /cables and you can use a thin covering. The only way to get a perfect finish by fixing direct to the mat is with blobs or spot fixing. And that leads to failure.

 

[dazlp]

Thanks to all for the guidance....looks like it's a weekend laying the compound then!

Cheers again

 

[Kia tiling]

Definately latex. Make sure your joint where the cable meets the tail is going to be submersed. Be careful with tape cos you can leave air pockets. The best way i find is spray glue and scrimtape it all down. The scrim allows the latex to fully encase the cable ensuring no failure. The de-coupling combination system like ditraheat, Variopro, DCM-pro are excellent, the future probably. Especially when they bring out a mat with insulation properties!

 

[Dumbo]

UFH cables need to be fully encapsulated in some form of cementitious material to dissipate the heat away from the element otherwise it is liable to burn itself out. The runny consistency and high flow properties of SLC make it much easier to fully surround the cable. You don't gain anything by using adhesive only as you still need to get the same result... and KG for KG it is usually more cost effective to use levelling compound because each KG goes further and as an added advantage it makes the tiling go much easier as the floor is flat as a pancake. On top of this, if you ever need to replace a tile, you've got much more chance of being able to do that if it isn't fixed direct to the elements.

Floors are as flat as a pancake if the person using the slc knows what they're doing .

 

[Dumbo]

That is very true, to be fair even in the hands of an idiot it should be flat. The pro will get it flat AND level.

No it could be smooth

 

[Dumbo]

To be honest the term self levelling compound goes against trade description .
It doesn't self level or even self flat itself at best it will self smooth but to be honest most of the time if you don't know what you are doing you you will still get trowel and guage marks .

 

[Spacey]

Self leveling properties of compounds don't kick in until depth from 5mm up
Still need to know what your doing with it tho

 

[Dumbo]

Self leveling properties of compounds don't kick in until depth from 5mm up
Still need to know what your doing with it tho

That was the best advice I got . Don't go under 5 mm

 

[One Day]

Pound for performance, I reckon Tilemaster Rapidlevel 30 is the best.
I know Balls and others do some which flow brilliantly but they're pricey.

 

[Flintstone]

Rapid level 30 is pricey too, where i shop!

 

[Spacey]

I often use Superflow 30 It's not bad

 

[Dumbo]

You're probably all going to laugh at this but I use palace thick bed leveller for dry areas and ultra level it 2 for wet rooms and karndean type flooring . Wish I could get more of the karndean jobs it's easy money compared to proper tiling .