There are quite a few threads regarding this type of screed and there seems to be a mixed response on the correct adhesive to be using. I had a read of a bag of Mapei proflex today and although it is cement based, it says providing the substrate is sanded, hoovered and primed with eco prim, it is a suitable addy. I was under the impression that a gypsum based was the preferred adhesive to be using. Am I getting my screeds and addys mixed up or is there more than one correct way to be going about this? Thanks as always, Bri.

Cement based adhesives are fine Bri.. if the prep is done correctly, but gypsum based adhesives do not react with gypsum screed.. so that is the advantage.. if their is no reaction risk then that is the best adhesive to use but cement based can be used no probs ... it is all down to the prepping and correct priming..

Thanks for confirming Dave. This subject seems to have alot of grey areas!

It does ye but if a Gyvlon training day is within your travelling distance then please do attend.. well worth it IMO..

I went to a training day presented by Alan (Ajax) last year, which was vvvery helpful, although i've still to come across a anhydrate floor yet. As Dave says above you can use cemant based addy as long as the prep in done right, but tbh there are more and more gypsum addy's on the market now, i'd use one of them, saves all the hassle/doubt etc.

Which brands do gypsum based? I remember someone saying they had to get some from France?!!!! Maybe I'm going mad!

Pretty sure Webber do one...

Originally Posted by Stewart

Pretty sure Webber do one...

Thats the one I remember Stewart. Seems a bit extreme to have to import it!

Alan (Ajax) will be along to gives us some outlets. maybe!

creative impressions do one,

Originally Posted by Stewart

Pretty sure Webber do one...

They did import some from weber france but at present they are making their own in the uk and as soon as it is ready they wil announce it.. so for now it is GBA from creative impressions and another i can't remember the name.. but Ajax knows it.. and there is Kerakol ideal 40 but beware on that one as i tried it and it failed and the back up from tech was appalling., but i have heard it is fine without the use of a membrane.

Just been informed by Lee from Twitter, that Weber don't do their weber.col anhydrite anymore.

I beleive Kerrakoll do a cement based that can be used without priming. Not sure how that works.
I'd be interested in a one day Anhydrite course, where do I sign up?

BAL do a 1 day one with lafarge givlon.Dave Rowleys the guy from BAL.Theyre nationwide but as of this year i think its around £30 now due to people signing up then not turning up.You get some BAL buckets and some variset i believe

Originally Posted by Stewart

Just been informed by Lee from Twitter, that Weber don't do their weber.col anhydrite anymore.

They do.. just not in the UK.. but like i said they are working on a uk version.

Originally Posted by advancetiling

BAL do a 1 day one with lafarge givlon.Dave Rowleys the guy from BAL.Theyre nationwide but as of this year i think its around £30 now due to people signing up then not turning up.You get some BAL buckets and some variset i believe

One way of selling products..

The ones we arrange are FREE!!

Gotta agree with that Dave.No sympathy with the prices they charge

I will see if we can get a training day sorted further south than the last one..

Bal have not come back to me yet with any further anhydrite training days. Not sure why but may be the uptake due to the charge. Worth while days though IMO.

I am happy to present another day for TF whenever you guys say so.

Now to the addys

the risk of cement is primarily chemical reaction between the cement and the gypsum. The way to avoid this is

1. Use a suitable sulphate barrier
i. Epoxy Primer is best at this
ii. Good quality acrylic usually in 2 coats
a. Most of the primers we have tested require dilution especially if over low laitance as the surface
is so much harder and denser than the old fashioned stuff
b. Problem here is that most manufacturers don't recommend dilution. Problem with that is the surface will not allow the primer to penetrate the screed surface which leads to a weak bond between it and the screed.
iii. SBR is ok but can soften with water and heat so be careful

2. Eliminate one of the required ingredients for the reaction to occur
i. Bear in mind Screed will always contain some moisture so you will never eliminate all of this so beware particularly of over wet screeds with cement adhesives.......put cement of wet anhydrite and it WILL fail.

ii. Bear in mind the use of uncoupling which divorce the tile face and its own section of adhesive from the screed but are often stuck down with cement addy so won't stay fixed for long

iii. Brings us to the primary recomendation i.e. get rid of the cement altogether and use a gypsum based addy or at least one which will not react

Gypsum Products available
a. Easily Available
i. Creative Impressions GBTA

b. Soon to be launched or relaunched

i. Niocobond (not sure of name but think will be Unique - Launch approx July)
ii. Weber (now making in the UK due to cost but no launch date yet)
iii. Forbo Flooring (Available bu at present will be imported) - Alphycol 725

Non Gypsum Products available

i. Kerakoll - H40 ideal
ii. Benfer - Benfer Gyps
iii. Tubbed dispersion adhesives (Yes I know you don't like these but they do stick tiles to Gypsum
screeds)

Hope this is helpful - I will happily accept updates that I am not aware of but this is to the best of my knowledge so far

Originally Posted by Dave

I will see if we can get a training day sorted further south than the last one..

Lol...... What about further north?

Originally Posted by Stewart

Lol...... What about further north?

Further north... Al.. you got a passport..

Actually Dave I have not but then I get nosebleeds any further north than Newcastle. I did have a day booked in for BAL in Glasgow back in March but it got cancelled due to lack of numbers.

I'd pay £30 for a days training. I'll have to ask at Boydens in Sutton. I'm sure they were opening a BAL training there.

I just found an email I got from BAL for one of their courses, seems I've missed the anhydrite ones.

You're right they do charge £30, but you get..

25kg BAL Quickset Render

20 kg BAL Fibrebase

20kg BAL Rapidbase

20 Ltr BAL Mixing Bucket

If you turn up.

If TF can do one within the M25 I'd be happy to come along.

I'd even travel for one of these days.

I would also be quite happy to travel, but if it's hundreds of miles it takes a bit more effort to fit it into the schedule, so more difficult to attend.

quoteiii. SBR is ok but can soften with water and heat so be careful

I've used load on exterior and never had any problems, also used on external screeds aswell.

Originally Posted by whitebeam

SBR is ok but can soften with water

Can it? How about all those swimming pools that have in screeds and renders?

Panic not - SBR has good resistance to water but can become more elastic when you warm it up too much - this would really only be of concern in heated screeds which are abused.