Anhydrite screed question

[Matthew77]

The surface layer is a friable layer that must be removed.
All the contaminates that are in the screed float to the surface.
I'm not exactly clued up from the real technical side of these screeds, our resident expert Ajax is the technical guy for explaining it.
I have never tiled to an calcium screed without the laitance being removed & I never will.
AnhyFix is the adhesive to use, it's sticks like the proverbial.

Thanks at least by the sounds of it I have chosen the right adhesive!

I don't plan on tiling onto it without the laitance being removed either as everything I've read about these screeds the emphasis seems to be on removing the laitance and making sure the screed is dry. Its a shame theres not a bit more info around regarding the importance of the removal time of the laitance as it is hard as hell now!!! I've tried floor scrapers, a saw blade in a floor scraper, wire brush attached to an angle grinder and nothing seems to want to touch it!

 

[Stef]

The link that Radim put up is a floor grinder, it's got replaceable pads on it.
If that doesn't remove the surface laitance then nothing will.

 

[judge]

Here you go mate http://www.brandontoolhire.co.uk/en/surface-preparation/534-floor-preparation-system.html

 

[Matthew77]

The link that Radim put up is a floor grinder, it's got replaceable pads on it.
If that doesn't remove the surface laitance then nothing will.

So just to clarify, in my picture the light parts on the floor are laitance free and the darker parts are the laitance that need removing? I'm only asking this as i went over the top of the darker bits (with a new sander belt on) and let it spin over the same place for a few minutes and all it seemed to do was make it darker in colour!!

 

[Matthew77]

Here you go mate http://www.brandontoolhire.co.uk/en/surface-preparation/534-floor-preparation-system.html

Thank you.

 

[Coop5]

I feel like a dumba$$ as ive literally just posted the same question!

I had a gyvlon screed layed over my ufh, and now I realise that it needs sanding and priming before tiling. . Doh !! I was just told it takes a day per mm to dry out.

Anyhow, my system has not been on yet so may not be as tough as yours. But I now need to get sanding asap!!

On inspecting the surface, I can see a few black bits which look like rubber! I assume this is the type of thing we need to remove !?

 

[Stef]

The laitance on top of the screeds probably only 1mm.
I remember the 1st one I done, I done the exact same thing, you will end up going into the actual screed.
It's only the top friable layer that needs to come off.

 

[Matthew77]

The laitance on top of the screeds probably only 1mm.
I remember the 1st one I done, I done the exact same thing, you will end up going into the actual screed.
It's only the top friable layer that needs to come off.

So the top pink layer which I thought was the laitance which is about 1mm thick doesn't need to be removed it's just the friable layer on top of the pink stuff that needs to come off!?

None of the top layer is friable it's all really well stuck down! This is the part that confusing me the most so I've kind of decided to remove all the pink stuff just to be safe?

I've been using a diamond disk grinder this morning and have managed to remove a lot of the pink layer down to the whiter coloured screed. After lunch I will carry on and finish removing the rest.

Thanks for everyone's input on this it's been really helpful, next time I have a anhydride screed to tile I will be better prepared due to the information here and hopefully help others too. Especially the part about removing the laitance shortly after the screed has been poured!

 

[Coop5]

Hi mate,

I have the exact same issue with my new extension.

Its been down now for nearly six weeks and I've only just realised about the laitance needing to come off.

I have been on the phone to the company who make my screed, they state that the surface (which is currently very smooth) needs to be sanded down so that it appears to have the same texture as a matchbox strip!

I have ordered a str710 for this job, which comes with copper disks and varying other corses.

what sander did you end up going for ?

Cheers

 

[Coop5]

Hi mate,

I have the exact same issue with my new extension.

Its been down now for nearly six weeks and I've only just realised about the laitance needing to come off.

I have been on the phone to the company who make my screed, they state that the surface (which is currently very smooth) needs to be sanded down so that it appears to have the same texture as a matchbox strip!

I have ordered a str710 for this job, which comes with copper disks and varying other corses.

what sander did you end up going for ?

Cheers

 

[Matthew77]

Hi mate,

I have the exact same issue with my new extension.

Its been down now for nearly six weeks and I've only just realised about the laitance needing to come off.

I have been on the phone to the company who make my screed, they state that the surface (which is currently very smooth) needs to be sanded down so that it appears to have the same texture as a matchbox strip!

I have ordered a str710 for this job, which comes with copper disks and varying other corses.

what sander did you end up going for ?

Cheers

I ended up using a diamond concrete sander blade on a angle grinder. Purely because I live out in the sticks a bit and after doing a internet search last night none of my local tool hire company's stock anything for floor sanding so I'd of needed to wait another day and drive 4+ hours to collect and return something like what you mention.

If you can hire one of the previously mentioned and recommended machines. It's a bit of a nightmare trying various methods for yourself and I wouldn't recommend the way I did it if you have access to a proper machine.

I was recommended to go for a 80 grit by both of the tile adhesive company's if that helps at all?

 

[Ajax123]

What I fail to understand is that these screeds have been around for years and the number of issues in the old days generally revolved around poor prep and laitance removal. Any of the major adhesive suppliers, Mapei, Saint gobain, Ardex, bal, etc etc, all of the major screed manufacturers, cemex, hope, aggregate industries etc etc have free downloadable literature on preparation, both the UK binder manufacturers, ourselves as Gypsol and the other one who make the screed used in the op post offer specific advice online, or in person, the tiling association, the contract flooring association and any number of private consultants can tell you laitance must be removed prior to tiling..... there are countless threads and posts on this and other forums.... It's hardly a flipping secret is it??? Why don't builders and for that matter tilers, know.... Perhaps they choose not to...I don't know...Ok some may never have come across anhydrite before but really.... If you use something you've never used before it doesn't take much research to find the info on the net... Using the excuse that the screeder never said really doesn't wash for me....

 

[Ajax123]

Broken Link Removed

 

[Stef]

It's thanks to you Alan that i know as much about these screeds as I do.
If you want to keep ahead of the game then you have to do your research.

 

[Matthew77]

Thanks for your input Alan.

I was fully aware that the floor screed needed sanding before tiling as like you said all that information is available through the places you stated. I was passed on information from the Screeding company regarding floor tiling by the builder, I also spoke to 2 adhesive technical departments as previously mentioned in another post. They both stressed the importance of removing the laitance.

What was quite confusing for me is being told that removal of laitance should be done within the first couple of weeks as that wasn't stated in either of the two spec sheets for the adhesive company's I use neither was it mentioned in the info from the screed company passed on by the builder or the technical departments of the adhesive company's. This info may be available from other adhesive company's or on the internet but from a tile fixers point of view I'm only going to be reading the spec sheets for the adhesive I'm using and the screed that has been laid. For example one of the adhesive company's stated that no primer should be used with their product but the other specified primer. Tile fixing info isn't always universal and can be very specific to that company's product.

Sometimes we we just need a bit of confirmation that what we are doing is correct when using a new product that is unfamiliar to us.

Thanks again for everyones input much appreciated