New Cemfloor Liquid Screed - TilersForums.com

[Dumbo]

I phoned the BAL technical guys and they've said that yes they have tested cemfloor screed. They recommend cleaning the surface of the screed to remove all dust and building residue and then applying one of their cement based adhesives directly to the surface. He said there is no need for sanding if the surface of the screed is in good condition.

Best option . Go straight the top and hear it straight from the horses mouth .

 

[Timmy Mcguire]

Ya exactly JCR. They said because its a cement based screed there is no need to sand it as the adhesives are also cement based; I guess its the same as for Sand:Cement screeds; just make sure the surface is in good nick and well cleaned.

 

[Ajax123]

I phoned the BAL technical guys and they've said that yes they have tested cemfloor screed. They recommend cleaning the surface of the screed to remove all dust and building residue and then applying one of their cement based adhesives directly to the surface. He said there is no need for sanding if the surface of the screed is in good condition.

And how do they recommend cleaning the surface? The usually accepted term is "lightly abrade"

 

[Ajax123]

I return to my previous comment. It is not BAL that will pick up the tab if it goes wrong...

 

[Dumbo]

And how do they recommend cleaning the surface? The usually accepted term is "lightly abrade"

If you're deliberately ambiguous if give you plenty of options to say what the tiler did wrong if it fails .

 

[Ajax123]

Cemfloor is an additive driven liquid screed tested by CSTB by manufacturer Cemexa

The CSTB certificate reference is
Document Technique d’Application
Référence Avis Technique 13/13-1214*V1
Cemfloor
Cemfloor Macro
Cemfloor Métal

Here is the link if you want it....

13/13-1214*V1 - Document Technique d'Application - http://evaluation.cstb.fr/avis-technique/detail/13-13-1214-v1/
you can use Google translate if you have a whole to spare.

The relevant section is 4.54

It says
L’applicateur doit procéder à l’élimination de la pellicule de surface.
Le ponçage s’effectue à l’aide d’un appareil monobrosse équipé d’un
disque abrasif (grain 16) ou d’une brosse nylon dure ou métallique.
Cette opération est suivie d’un dépoussiérage efficace

This translates as follows
The applicator must remove the surface film.
Sanding is carried out using a single-piece machine equipped with a
abrasive disc (grain 16) or a hard or metallic nylon brush.
This is followed by effective dust removal

Up to you of course....

 

[Ajax123]

If you're deliberately ambiguous if give you plenty of options to say what the tiler did wrong if it fails .

Yup. Best advice is sand the screed. If you do that you can't really go wrong and no one can argue.

 

[Timmy Mcguire]

Hi Ajax thanks for your advice. If I could get your opinion on another thing that the screeder said about floor; he said to treat it like a sand:cement screed or a cement based quick drying flowing screed that comes in bags. Is there a reason why these don't need to be sanded?

 

[Ajax123]

The need for sanding us much misunderstood. It does a number of things and us particularly important where liquid screeds are concerned as these gave a tendency to firm eigher a naturally occurring surface skin in the case of self curing screeds or an artificial skin in the form of a curing agent in the case of usually cement based screeds. Sanding removes these layers. Liquid screeds also have a tendency to form a much more closed surface than hand applied screeds so sanding helps open the screed to allow your primer to penetrate into the surface. Equally importantly is the need for the screed to be "clean and free from dust, dirt and contaminants likely to affect adhesion" which us what the floor covering standards all say. Active building sites can be dirty places with mortar, plaster, mud, filler, and plenty of other surface contaminants getting on the screed. Regardless of screed type it is best practice to lightly and are all screeds and concrete prior to applying bonded floor coverings. I would not differentiate between bagged, fast drying hand applied or liquid screeds or indeed powerfloat concrete. My advice is sand the screed. Just because you don't does not make it right. If you were to paint a gloss paint on your wooden doors at home you would sand them first. If not you would see the paint peel off soon after. It's the same principal. If it didn't peel off it would be down to blind luck. I would rather advise based on sound sensible practice than trust to luck.
Trouble is when I argue this point It can come across as sour grapes as i work for an anhydride company. I have worked with most ttypes of screeds in my time jnckuding liquid cement based screeds and self comlacting concretes as well as hand applied screeds. My advice has never changed.

 

[Glynn]

If you have any doubt stick to your tried and trusted method, sand and prime. arguing over preparation is a pointless task. It must be done. We do masses of testing with our adhesives and competitors adhesives and I have not found any results that were better not primed. we have adhesives that will go direct to a sand/cement screed un-primed but sanding and priming will give you a stronger bond and more sleep at night. This is our industry and we are the ones who pick up the tab when things go wrong not the screed company. Which industry do you trust most?