1st Anhydrite screed ? - Tile Advice

[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.

 

[Lee@emctiles]

Love it........love the advice that can be gleamed from this forum.

#education #education #education

 

[Ajax123]

Love it........love the advice that can be gleamed from this forum.

#education #education #education

i just want to help people avoid the issues

 

[Aspect Tiling]

Been to see the job this morning. Not much to add really from my original post. Not ready to tile until start of July so any drying concerns are reduced now. In terms of adhesive, Anhyfix seems to be the best bet (would prefer a slower set but sure I'll manage). As I mentioned before the floor was laid in 2 separate rooms with a wall removed later. Despite their best efforts to get both rooms level there is now a 3mm height difference from where the wall has been removed. Thinking of feathering this out with adhesive or using Anhylevel which I think may be the best bet.

Again I mentioned to the customer that the floor will need sanding (low laitance) before priming but he has supposedly been told by a Lafarge chap that visited the site recently that a good clean/vac and it's good to go. He also supplied the customer with a gallon of primer, the make of which I'm yet to confirm. This is the only area that now concerns me but I've got a fair bit of time to get it sorted.

Once again thanks for your help.

Pete

 

[Ajax123]

Been to see the job this morning. Not much to add really from my original post. Not ready to tile until start of July so any drying concerns are reduced now. In terms of adhesive, Anhyfix seems to be the best bet (would prefer a slower set but sure I'll manage). As I mentioned before the floor was laid in 2 separate rooms with a wall removed later. Despite their best efforts to get both rooms level there is now a 3mm height difference from where the wall has been removed. Thinking of feathering this out with adhesive or using Anhylevel which I think may be the best bet.

Again I mentioned to the customer that the floor will need sanding (low laitance) before priming but he has supposedly been told by a Lafarge chap that visited the site recently that a good clean/vac and it's good to go. He also supplied the customer with a gallon of primer, the make of which I'm yet to confirm. This is the only area that now concerns me but I've got a fair bit of time to get it sorted.

Once again thanks for your help.

Pete

you are the floor layer, not the "lafarge chap" whichever that may be and not the client. The lafarge Chap is possibly an expert in the supply of liquid screed (or possibly not). He is most definitely not going to be an expert in tiling and sub floor preparation. Now then... If the floor fails and you have not prepared it in the manner recommended not only by your adhesive supplier, but by your entire trade association, and the tiling fails for what ever reason, be it prep, moisture, adhesive failure or whatever, do you really think the "Lafarge chap" will stand side by side with you to defend the failure. If you get the adhesive rep on site and he says "did you sand the screed" do you think he is going to stand by your side when you tell him no. I would be unable to offer you a defence were you to go ahead without preparing the screed in the correct manner. If it fails it will end up costing you and your reputation and you won't see the Lafarge chap for dust...

The "Lafarge chap is wrong, plain and simple. ALL SCREEDS AND CONCRETEs SHOULD BE MECHANICALLY ABRADED PRIOR TO THE APPLICATION OF BONDED FLOOR COVERINGS INCLUDING, TILES, VINYLS, WOOD FLOORS, RESINS AND LEVELLING COMPOUNDS. This requirement is set out in the tiling associations guide to tiling to anhydrite screeds

If you go ahead and ignore the sensible advice given by your own trade body and your adhesive supplier then, whilst I mean no offence, you deserve all the pain it creates for you... Sorry but there it is.

 

[beanz]

If there is a failure, and the rep comes out, remember to say "YES, of course I sanded it...."