screed instead of latex - TilersForums.com

[bluesky]

went to deliver tiles of a job i`m starting on monday to discover that the builders have decided to lay screed over the top of electric cables 30mm thick .this was instead of laying 20 mm insulation board then cable then latex to build up to the correct height . they have told my customer that it will all be dry in time for monday as they have added pva to the mix! normally i would allow minimum of 3 weeks for this screed to dry but also i am concerned about the heating up times and costs .normally latex will only cover the cables my 2-3 mm.if i am correct with regards to screed not being dry could i get round this by using ditra.?
many thanks for any input.

 

[Spud]

tyco have got an electric ufh cable that can be screeded over with sand and cement but that 30mm screed wont be ready for tiling on monday and i am not sure why they put pva through it, with wet system ufh its normally a 60mm fibre screed that is used so i would be a bit wary of future problems unless they can show you some technical data to back up their preparation method

 

[Alan.P]

I wouldn't so much be concerned with the laying of the tiles, 30mm of screed to heat up before getting to the tile might be asking too much, I await to be corrected, Bal green screed could be used, site circumstances permitting.

 

[White Room]

I'd be concerned about the cable being able to heat the floor with 30mm screed on top

 

[DHTiling]

The screed is to thin imho...If it was a leveller with finer sands so that it binds better but normal type screeds with coarse sands will more than likely crack at that depth..50/60mm is usually the minimum...and no modifier in the screed...

 

[RockCeramics]

seems to me that the builder is trying to cut corners and costings down.
& the qoute of the week is.
"we have added pva to the mix! "
why does every builder feel the need to add pva?

 

[Ajax123]

is the screed straight onto the concrete subfloor or is there insulation underneath it?

 

[bluesky]

screed is straight on to concrete base no extra insulation- looks like another postponed job!

 

[Ajax123]

One assumes that the conrete slab was not mechanically prepared - it would be very un usual to see this done to say the least. BS8204 treats this as an unbonded screed although the industry terms it partially bonded. This means that the minimum depth should have been 50mm. 30mm is simply too thin for sand cement and there is a real risk that the screed will crack when subjected to heating. Additionally if the concrete underneath is new this can take an age to dry properly (100mm concrete takes in excess of 12 months to dry) so the residual moisture in the concrete will want to rise through the screed. Additionally PVA degrades when in the presence of alkalis (cement is alkaline) so over a period of time the screed will potentially begin to fail although this is relatively low risk and not something you as the tiler need really worry too much about.
The best idea would have been to use an anhydrite screed at this depth if they had to screed it but I cannot think why they did not go with the original plan except to cut costs cos insulation would have been more expensive than the screed at this depth. The other problem of course is that the efficiency of the underfloor heating will be seriously impaired cos they will now be trying to heat up the entire slab and not just the screed. This one is a deffinite candidate for an uncoupling mat in my opinion.
Why can't people just build things properly!!:incazzato:

 

[bluesky]

am i correct then with drying time of 21 days for the 30mm screed then use ditra mat with spf ?