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Discuss Porcelain on ufh sand n cement screed in the Tiling on Underfloor Heating area at TilersForums. USA and UK Tiling Forum

J

Jas0n

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Hi,

I’m struggling on finding enough info about porcelain tiles being laid straight on screed with ufh.

The underfloor heating has currently been running for about 6-8 weeks at no more than 20 degrees. A few cracks have appeared over that time.
I was hoping to now uni bond the floor and lay the porcelain tiles straight on the floor.

I have seen a few people on the forum mentioning matting floors first, but I’m wondering if I really need to if the floor has had time to move and crack and also dry out for quite a while.

I would really appreciate someone’s advice who has been in this position

Thanks

Jason
 
OP
F

Flintstone

How Big and severe are the cracks? What’s the room? how long has the screed been down? How did you turn on the underfloor heating?
 
OP
J

Jas0n

The cracks are just hairline cracks and probably about 8 of them. It’s a 30m2 room and the screed has been down since the middle of September. The ufh has been running on and off for 6-8 weeks. When it was first turned on the heating engineer had it turned right up for a few hours through the boiler settings without a thermostat and it was baking. Since the stat has been put in, which was a day after the heating engineer done his part, the temp has been set at 18.5 constantly and at occasional times pushed up to 21 degrees
 

Ajax123

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Jason. You need to increase the temperature of the heating up to maximum for a minimum of 4 days then switch it off for 48 to 72 hours. You should technicaly moisture test but the heating has been on for a while so i would think its dry by now. That will complete the commssioning process. As the screed has cracked I would recommnd the use of uncoupling so,ply to prevent this cracks fro reflecting through the tiles at a later date. It is not something I normally suggest with porcelain unless the screed is unsound. Essentially as it has cracked it's unsound. You could repair the cracks but it' nearly as cheap to put a mat down and that gives you belt and braces.

At this point we usually hear the cry "is it really necessary...its so expensive" . My answer...its cheaper to do it properly now and only do it once than repair it later if it fails.

Unibond PVA is not the correct stuff to use. Use a proper acrylic or SBR primer and a cement based powdered tile https://www.tilersforums.com/forums/tile-adhesive/...
 
OP
J

Jas0n

Thankyou Ajax123 and localtiler. I will go and buy DITRA Matting to put on the floor first. I was hoping that wouldn’t be the case, but I really don’t want to take a chance and make repairs in a few years. Especially it being in my own home it will break my heart.
 
OP
W

WetSaw

Doesn't have to be Ditra ( even though I'm a Schluter ****..) there are a lot of mats available for a less money.
 
OP
U

Unused Account 1

Done 2 70 metre floors on new builds for an i surance company as they never used ditra matting ,ufh,
 

Ajax123

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Done 2 70 metre floors on new builds for an i surance company as they never used ditra matting ,ufh,

As i said. It is not a requirement for porcs but if the screed is unsound it is foolhardy not to use uncoupling. That is what it's designed for. If such a job went to court after a failure whoever decided uncoupling was not needed would lose. Still at least you got some more work out of it eh
 

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