Anhydrate screed prep spec check

[Spud]

spoke to Ardex help desk........... we de scabbed it with a brute, primed it well, and fixed ditra after 3 days......

How long did the sanding take you and which machine did you use ?

 

[m3fitter]

How long did the sanding take you and which machine did you use ?

the USA don't adhere the ditra to any substrate, thus totally creating a total floating floor, ignoring all substrates..

 

[Ajax123]

Alan I have found if there is any moisture in the anhydride that sand paper discs clog and grip the floor causing the rotary machine to overheat, when taking the laitence off of anhydrite floors carborundum stones work far more effectively on a rotary machine and as they have a smaller surface area on damp areas they don't strain the motor or gear box of the machine unnesscesarily
dust is a big issue and we went over to dustless grinding and bagged dust collection I really think saying a 150 m floor can be done in an afternoon with a rotary machine is un realistic but if you have done it then I must be doing something wrong and would appreciate some tips
we have tried several types of machine and spent a fair amount of money tooling up for anhydrite prep work and all floors are different I suppose depending on the product and installers

The so called "low Laitance" screeds most certainly take longer as the surface is much more consolidated. If it's a proper non low Laitance material the Laitance almost falls off on its own making prep much easier. I agree if it's done too soon the disks can clog up and I know a few guys who have had more success with the carborundum stones. Another dustless option would be enclosed shot blasting with which I have also had some success especially if the screed is contaminated with lignite or similar.

I also find that people sometimes work too hard to open the surface taking off more than they need from the surface. This is another potential issue of the low Laitance screeds as it can be difficult to know when the Laitance layer is actually off. This is another advantage of the non low Laitance stuff as it is pretty obvious when you've got the Laitance off. Laitance should be microns deep, may be up to half a mm... I sometimes get told that a "Laitance" is 10mm deep. This would not be Laitance but a defective screed usually caused by over watering... This can be much more difficult to sand properly.

 

[Ajax123]

spoke to Ardex help desk........... we de scabbed it with a brute, primed it well, and fixed ditra after 3 days......

I can say without a shadow of a doubt that if you have stuck ditra down after three days of the screed being installed using an Ardex system there is absolutely no way on earth that it would still be stuck down after 3months...

 

[Spud]

the USA don't adhere the ditra to any substrate, thus totally creating a total floating floor, ignoring all substrates..

Think we got some wires crossed here ?

 

[Stef]

I can say without a shadow of a doubt that if you have stuck ditra down after three days of the screed being installed using an Ardex system there is absolutely no way on earth that it would still be stuck down after 3months...

I tiled an anhydrite screed after 7 days, builder was desperate to get clients in & that floored lasted 2 or 3 months.
Think the floor had given up after a couple of weeks but wasn't ripped up till then.
When I say ripped up what I mean is the tiles were picked up from where they were laid.

 

[Ajax123]

I tiled an anhydrite screed after 7 days, builder was desperate to get clients in & that floored lasted 2 or 3 months.
Think the floor had given up after a couple of weeks but wasn't ripped up till then.
When I say ripped up what I mean is the tiles were picked up from where they were laid.

not surprised. Would still be wet.

 

[Stef]

not surprised. Would still be wet.

It was just before this job that I started really finding out about gypsum screeds Alan & this is when I was bombarding you with a hundred & one questions.. [emoji1][emoji1]

 

[Ian]

I tiled an anhydrite screed after 7 days, builder was desperate to get clients in & that floored lasted 2 or 3 months.
Think the floor had given up after a couple of weeks but wasn't ripped up till then.
When I say ripped up what I mean is the tiles were picked up from where they were laid.

Out of interest Stef, what adhesive did you use on this floor that failed?

 

[Stef]

Out of interest Stef, what adhesive did you use on this floor that failed?

I'm certain that it was Weber rapid SPF with one coat of PR360.
We had stuck two off cuts down, one primed the other no primer & they both peeled off the floor in a couple of days.
We gave the floor a quick once over with a bit of sandpaper.
Everyone knew it was going to fail but they just wanted the floor down to get the client in then deal with it at a later date.

 

[Ian]

I'm certain that it was Weber rapid SPF with one coat of PR360.
We had stuck two off cuts down, one primed the other no primer & they both peeled off the floor in a couple of days.
We gave the floor a quick once over with a bit of sandpaper.
Everyone knew it was going to fail but they just wanted the floor down to get the client in then deal with it at a later date.

What made me ask is, BAL make green screed, that can apparently be used within hours of a cement based screed being laid (personally never used it), I wonder what would happen if the likes of anhyfix was used on a calcium screed after a few days? I assume tilemaster have tested their product rigorously, I wonder if a wet screed was in the testing???

 

[Stef]

What made me ask is, BAL make green screed, that can apparently be used within hours of a cement based screed being laid (personally never used it), I wonder what would happen if the likes of anhyfix was used on a calcium screed after a few days? I assume tilemaster have tested their product rigorously, I wonder if a wet screed was in the testing???

Interesting Bri, you can modify Weber with AD250 to go over a green screed & as long as the moisture can escape from the screed then it does make you wonder.
I wouldn't risk it though, test the screed if it's dry enough go for it with a gypsum addy.
Get rid of laitance in the 1st ten days & bingo.
I suppose Alan could answer the question of a green screed?
I know TileMaster state on AnhyFix that it must be 85% RH or below but I wait till it hits 75% RH or below.

 

[Ian]

I'd like to see what happened, maybe I'll get a chance one day to stick a tile to a fresh screed! Not really likely in the real world though.

 

[Ajax123]

What made me ask is, BAL make green screed, that can apparently be used within hours of a cement based screed being laid (personally never used it), I wonder what would happen if the likes of anhyfix was used on a calcium screed after a few days? I assume tilemaster have tested their product rigorously, I wonder if a wet screed was in the testing???

It would depend on what sort of tile it was. If it were porcelain it would almost certainly fail as the adhesive would remain quite wet and would not achieve it's strength. If it were stone it would probably stick. I have seen other gypsum adhesives abused in thus way without too many issues in all honesty but it would be bad practice to advise laying the tiles before the screed was dry enough.

 

[m3fitter]

I can say without a shadow of a doubt that if you have stuck ditra down after three days of the screed being installed using an Ardex system there is absolutely no way on earth that it would still be stuck down after 3months...

well, without trying to be awkward Ajax, I called the client to arrange a photo session after I saw your post, I have checked this floor thoroughly, its solid, and fine no cracking or anything suspicious , its been 14 months now... I have enough experience of substrates to know what will adhere and what won't, we always test an area to see adhesion, porosity prior to...