Guys and gals

I have just come back from my sister inlaws and they are in the process of having some work done. Job comprises a new kitchen with wet UFH in new screed. Tiles are 1000x500 porcelain.

What is the quickest time the floor will be able to be tiled? Is it possible to force dry the screed without fracturing it?

They are off on hols 14th April and expect the kitchen to be in when they get back on the 23rd! The screed isnt being laid until this week

I ha a look at the architects gumf and there was no spec for the floor except for it meet BSCP202 which im assuming is BS5385. I have told them to ask for a full spec and time scale and advised to have a decoupler.

Any idea what the screed is..?

Doh! I knew id forget something obvious! Is sand/cement judging by the 6 bulk bags on the drive

Now if i recall correct for sand/cement screed and wet UFH, the commission time for ufh is 21 days after laying.. this is to allow the screed to cure... if it was an Anhydrite screed then it is 7 days.. so really there is no fast track here..

And once the wet UFH is fired up and allowed to slowly heat the substrate then it has to be on for 7 days.. all the info can be found in BS EN 1264 part 4...

Hope that helps..

Thanks Dave, she is gonna do her nut! Its been bugging me ever since they said they were have wet UFH and that the job would be complete in 6 weeks. As it stands now that 6 weeks was up on 1st April

screed depth should be 65mm and thats 65 days 1mm a day , heated floors are are little quicker as Dave said above

What about if they use a decoupler? That would allieviate the drying time but would the heating still need to be commissioned first?

The 21 days is for the screed to cure before commissioning scott... that is the set time stated in BS5385:4

I just checked and i was right... my memory isn't so bad after all....

The un-coupler will help if the screed isn't dry ,as it will act as a vapour equalisation and allow the floor to dry.. but cracking the heating on after 21 days and heating the screed up can force dry it..

I have PM'd Ajax just to get him to clarify it for me then ill show them the thread

Doest the heat have to be turned down at a slow rate as well? I thought it was 5 degrees up to temp and then 5 degrees down?

does anyone have a copy of Part4?

So 21 days before commissioning the heating then turn it on to ambient temp? prob 20 degrees ish? Then 5 degrees per day up to max temp, 55 degrees? 28 days to max temp then potentially a cool down time too.

Originally Posted by Scott

What about if they use a decoupler? That would allieviate the drying time but would the heating still need to be commissioned first?

Yes Scott heating must be commissioned prior to laying decoupler

Sand cement screed shpuld be cured by covering with polythene for 7 days following installation. Any underfloor heating should be left un heated for 21 days following this period. That makes 28 days.....The BS says leave for a MINIMUM of three weeks to dry. This will not be sufficient time for a sand cement screed. Typically for 65mm you would be able to tile after about 6 weeks without an uncoupler and as soon as the heating commissioning cycle is completed for heated screeds. As the screed is unlikely to have been cured properly this means that comissioning is absolutely essential as the screed will not have acheived its ultimate strength and may well crack at this point in time. If you use an uncoupler then you would not need to repair these cracks. If no membrane is used then you would be wise to repair the cracks before tiling. If no curing was carried out then it would be best to use Uncoupling in my opinion.

Scott you could consider using a different screed bed mortar than sand and cement there are fast track systems available all the major tile adhesive manufacturers make them I am not sure which products you would need but i think Ardex make A35 mix which can receive floor tiles within 24 hrs, I am sure mapei make one too you would need to check with their technical dept check about the ufh commisioning but these screeds are used extensively in the commercial tiling game with great sucess

Thanks for the input guys, im not doing this job btw its a job for my sister inlaw. I just want to make sure its not rushed and goes wrong.

Gary the sand/cement is already on site

there is not really a fast track system as far as I am aware. Ok there are fast drying screeds but the rules in UFH remain the same. commission after 28 days (incl 7 days curing)

What would happen if the matting went down before the ufh was commissioned? Wouldnt the matt cope with the movement? As you say if the screed cracks then a mat over the top would remove the need to repair the cracks. So if it cracked under the mat would it affect the finished floor?

I spoke to schulter yesterday and they dont advise the use of thier mat on wet screed without the floor being commissioned first.

can't the kitchen be fitted before the floor is laid scott? that would save a lot of time. but i'm guessing they're wanting the floor laid to the walls not up to the feet of the units?

Thats whats going to happen i think, although could be tricky getting some of the cuts around the kitchen as these are 1000x500. I have told them to put the ditra down so the tolerance for that can also be included in the final unit height.

Update on this is the screed went down last week and they want to tile this week, without a matt of any sort. Apparently they have done it before and its been fine.

They said theres an 80/20 chance of success/failure, i wouldnt lay a floor knowing there is a 20% chance of failure. Bananas if you ask me. I have advised against it but sugested at the very least ditra and an S2 on the top to make sure the adhesive has a decent amount of polymer for porcelain on UFH.