New Cemfloor Liquid Screed

[Timmy Mcguire]

Hi There,

Just wondering if anybody has had any experience tiling onto cemfloor liquid screed. The screeder is telling me that its a new cement based screed and that it doesn't need to be sanded or primed before putting the tile down? The surface is smooth and rock solid but I've always sanded and primed all liquid screeds before I put tiles down? Any advice would be greatly appreciated.

 

[Ajax123]

Nightmare.... the screed, as with every other screed should be sanded to remove and surface contamination. There may not appear to be a laitance in the same way as you see with anhydride but there will be aling with other construction contamination. Sanding is a simple requiremen of the contract flooring association guidelines and the tiling association guide. I've had loads of people say it does not need sanding but if you look at the CSTM certificate it clearly says requires surface abrasion prior to bonding floor coverings. I had one guy tell me the CSTM doesnt apply the UK.... hang on says I... why not... because we use different during agents here.... stick it in writing along with the warranty for the floor coverings says I... no response...

 

[Timmy Mcguire]

Thanks for your reply Ajax. Ive been going back and forth with the screeder who installed the floor and he is adamant that no surface sanding is required it just needs to be cleaned to remove any building dirt and dust. I am cautious to tile onto the screed without further guarantees (i.e. he'll take all responsibility). Has anyone tiled onto cemfloor without sanding it first? Has anyone had/heard of any problems with this screed?

 

[Ajax123]

Is he going to guarantee the tiles if you don't sand it...

 

[Timmy Mcguire]

No not yet but that's what I'm asking him to do before I lay the tiles on the un-sanded screed. He says BAL and Mapei have carried out trials with their adhesives and they have approved using their adhesives on cemfloor without sanding it?

 

[Tile Shop]

Then if he doesn't guarantee it, get it in writing from both BAL and Mapei that they've tested it and which of their adhesives they recommend along will an installation procedure.

If they can't produce that for you, i'd be looking for a tried and tested alternative screed.

 

[Timmy Mcguire]

Ive asked for a copy of the test results from BAL and Mapei along with an installation procedure and hes to get back to me with those. The floor is in perfect condition with no cracks and is perfectly smooth the surface is rock solid with no dust and it is even difficult to scratch with a nail. I'm just wary of tiling to it without sanding as Ive always been told that this is a must with all liquid screeds!!!

 

[Dumbo]

Just phone bal technical . Take him out of the loop .

 

[Italy]

Thanks for your reply Ajax. Ive been going back and forth with the screeder who installed the floor and he is adamant that no surface sanding is required it just needs to be cleaned to remove any building dirt and dust. I am cautious to tile onto the screed without further guarantees (i.e. he'll take all responsibility). Has anyone tiled onto cemfloor without sanding it first? Has anyone had/heard of any problems with this screed?

Here in Italy, all liquid screeds,
they are based on cement, not anhydride.
care must be taken if there are stains
of light color in the screed.
those stains should be scratched.
are water residues.
I scrape only those points, very evident when
you put the primer.
in any case, always the primer before laying.

 

[Timmy Mcguire]

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.

 

[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?

 

[Timmy Mcguire]

Glynn, I agree 100% with your comment; but if the screeder is saying that he isnt going to sand the screed then why should it be the tiler that has to foot the bill for doing the screeders work? Have tilemaster carried out any tests on cemfloor screed yet?

 

[Ajax123]

Glynn, I agree 100% with your comment; but if the screeder is saying that he isnt going to sand the screed then why should it be the tiler that has to foot the bill for doing the screeders work? Have tilemaster carried out any tests on cemfloor screed yet?

The tiler should not foot the bill for preparing the screed. It should be priced for as part of the floor so that the client picks up the bill. Tat way it gets doe to the tilers satisfaction so there is no argument about whether its sanded enough or not. I have always felt that the sanding should be part of the preparation and as such is best carried out by the tiler. that is also the opinion of the Contract Flooring Association. That said the cost of sanding 100m2 is maybe £150 to £200. The cost for replacing the tiles if they fail for whatever reason will be significantly more and you can bet your life that neither the screeder, the screed supplier, nor the adhesive company will stump up any cash for that.

Its really very simple. Take the screeders word that it needs no sanding and take the risk and hope it works. It might well do but there's no real guarantee and there will be an argument as too who is responsible if it does go wrong... and it'll cost you. Sand the screed in the way you normally do and in the way you appear comfortable with so that you have the peace of mind that you have done it correctly and avoid the risk. As I said in my previosu post .... up to you. Not up to the screeder, BAL technical, the screed supplier or anyone else... its up to you.

 

[Glynn]

Ajax 123 is right and BS 5385 basicly states "make sure the substrate is fit for tiling". That is the fixers responsibility to make sure it is fit to tile. If you have to do the extra prep work then you should charge for it or explain and let the client organise it themselves. We have not done any testing with the Cemfloor Screed but would automaticly treat it has any other sand/cement screed. Sand, prime, fix.

 

[Lee@emctiles]

Well they say everyday is a school day.

Saw someone post on LinkedIn about CEMFLOOR

"Cemfloor pumped in, curing agent sprayed over, ready to accept tiles in as little as 2 weeks with no sanding or special primers."

Should have known to check here shouldnt i!

So it does need surface removal?

 

[Ajax123]

Well they say everyday is a school day.

Saw someone post on LinkedIn about CEMFLOOR

"Cemfloor pumped in, curing agent sprayed over, ready to accept tiles in as little as 2 weeks with no sanding or special primers."

Should have known to check here shouldnt i!

So it does need surface removal?

Yup. It has a during agents on which will prevent primer penetration and subsequent adhesion. Quite a few people have fallen for the "it doesn' t need sanding" spin but simple fact is that the cemex cstm certificate mention earlier in the thread is pretty categorical. It should be abraded...