1st Anhydrite screed ?

[Aspect Tiling]

Hi all,

Not yet seen this job which is as good as mine but I'll put all the info I have from a brief conversation with the customer and update when I've seen in person.

75m2 anhydrite screed layed by Lafarge approx 4 weeks ago.
1 room (originally layed through 2 rooms with a wall since removed from what I gather).
55mm deep.
Wet underfloor heating (currently being commissioned/turned on).
600x600 polished porcelain to be fixed.

Customer is aware of anhydrite issues if not done properly after receiving support from Lafarge. However when I mentioned about removing laitance he said that an additive had been added to slow the curing which resulted in no laitance. Can anyone confirm or heard of this before.

Lafarge have supplied the customer with a list of recommended gypsum based adhesives (not sure which yet) but does anyone have any personal recommendations? (CTD preferably)

Also I know a decoupling mat would be a good idea but does anyone see it as essential for this installation?

Thanks

Pete

 

[Stef]

Ajax (Alan) is your man for this.
If he sees this then he will prob give you the advice but as far as I know all gypsum based screeds have a laitance on the surface that needs removed.
As for adhesive I've only used TileMaster AnhyFix & it's a fantastic product..

 

[Dougs Third Go]

some anyhdrite screeds are low laitance, but as Stef says, Ajax is your man.

 

[Ian]

Even if there appears to be no laitence, you will still need to give the screed a sand to open the surface to give the primer/adhesive something to key to.

 

[Lee@emctiles]

This should give you the info your require Pete

Anhyfix Technical Guide

 

[Ajax123]

Low Laitance does not mean no Laitance. Lafarge screed a data sheet (screed a is their product) recommends that it should be sanded regardless. The low Laitance additives can also impede drying so be a bit careful with moisture testing. No requirement for uncoupling with porcs although it won't hurt if you can get the money for it. 4weeks is not long enough for 55mm to dry out. If they are only just commissioning the UFH you've got another 3weeks to wait anyway.

 

[Aspect Tiling]

Thanks for the replies. I'll go through the data sheet with the customer to ensure they understand the process. I won't be ready for the job till around mid June so hopefully that solves the drying issue.

Regarding the sanding, I presume hiring something is the way forward given the size of the room?


Pete

 

[Ajax123]

Thanks for the replies. I'll go through the data sheet with the customer to ensure they understand the process. I won't be ready for the job till around mid June so hopefully that solves the drying issue.

Regarding the sanding, I presume hiring something is the way forward given the size of the room?


Pete

you could hire in a floor sander or I guess you could get someone in to do the prep itself prior to tiling if the job will stand the cost. If you want some contacts for that let me know.

mid June will certainly help but to force dry the screed they need to get the temperature up. If they are running it on a "low temperature" it will not help drying appreciably...

 

[High Peak Tiling]

Low Laitance does not mean no Laitance. Lafarge screed a data sheet (screed a is their product) recommends that it should be sanded regardless. The low Laitance additives can also impede drying so be a bit careful with moisture testing. No requirement for uncoupling with porcs although it won't hurt if you can get the money for it. 4weeks is not long enough for 55mm to dry out. If they are only just commissioning the UFH you've got another 3weeks to wait anyway.

Sorry to be slighty off topic with your thread Aspect.

Alan, why in this instance is the uncoupling membrane not a requirement?

 

[Ajax123]

It would be a requirement with natural stone tiles on heated screeds. The tiling standards make no such recommendations for much harder tiles like porcelaine opr ceramic.