Anhydrite screed

[paulpa]

hi, what is meantby friable, in relation to anhydrite. mention is made on removing prior topriming/fixing .
I have sanded my screed so far, but i have a browny/darker colour that looksshiney, is this the latency as it seems imposible to remove.
Lafarge said it was not and a 60 grit sand is all that is required. Is thiscorrect?
many thanks.

[Dave]

I take it is the gyvlon LL screed. ?

Friable is just the weaker milky residue that can be left on the surface , after sanding the screed should not be shiny.

60 grit floor sanding is spot on. The floor should be sanded and hoovered.

How long has the pour been down and is there UFH in it. ?

[andy allen]

the latency is the loose material the settles on top of the screed, this needs to be removed by sanding the floor, then vacum the floor and apply two coats of primier.

[paulpa]

Thanks.
Yes i did have a milky loose dust at early stages. Now i just have a discolouration in places. Some areas white as when laid, others a dark and even a 40 grit industrial sander can't move this. I guess just keep sanding all floor with 60/40 grit, hoover, wipe over with damp cloth to totally remove dust?, then use a sealer \(bal APD) applied 1st coat 1:! then second at 90 degrees un diluted?
Screed been down with under floor heating running for 2 months at 75mm thickness.

[paulpa]

With Under floor heating i have read several schools of thought about turning it on after tiling.
1) leave off hrs. before and turn on at low setting 48 hrs after tiling.
2) Leave off for 2 weeks
3) leave on at low heat while tiling.

Now what is the ideal scenario?

Most talk about the "room heat" after turning back on, but is it not the water temp going through the pipes that should be the consideration. I.E i can have the room stat at 17% but the initial water heat may be 60%. Likewise i could have room stat at 21 degrees but have the water temp set at 20 degrees.

[paulpa]

And can i not edit my post?
% is meant to be Degrees and in 1) leave off 48 hrs.

[Ajax123]

darker patches can indicate it is not quite dry. Get someone to do a moisture test before you tile to confirm. The Low Laitance screeds do not generrally form a laitance as they contain additives which prevent it from forming. This means that they do not need to be sanded to remove it. However as the scree will be contaminated with construction dust and debris it will need to be lightly sanded using something like a 60 grit paper to remove this contamination and then vaccuum it thoroughly before priming. Consider also using a gypsum based adhesive in preference to a cement as these are fully compatible.

[paulpa]

Hi, Should it not be dry 2 mths after laying with the under floor heating on force drying for atleast 6-7 weeks?
I don't know anyone with a moisture detector.
I have already chosen BAL adhesive.

[Ajax123]

Hi, Should it not be dry 2 mths after laying with the under floor heating on force drying for atleast 6-7 weeks?
I don't know anyone with a moisture detector.
I have already chosen BAL adhesive.

depends on depth. Typically at 50mm you can expect a natural drying time of 2 months. with the application of heating this will be reduced but it depends largely upon site variables, temperatures and ventilation.

a simple test to give you an indication of whether it is dry is the polythene bag test. place a sheet of polythene on the screed about 1m square and weight it down with a couple of house bricks. LEave it in place for a couple of days and then check to see if there is any condensation or discolouration of the screed. If there is it is nt dry. If there is not it is probably dry but a proper test should be done at that point. A hair hygrometer costs about 80quid so not an expensive peice of kit compared to the cost of your tiles failing. These come pre calibrated with simple instructions.


When you say frce drying......what sort of temperatures are you running the water through the system at?

You have cosen Bal and it looks like you have been given the right advice on the use of the primer so I will that alone. If however you have not yet bought it and you find the screed is slightly damp still it is a realistic possibility to look at the Gypsum alternatives. Up to you though.

[paulpa]

Thanks,
When you say "hair hygrometer costs about 80quid "
Could you point me to one as i,m happy to pay that for one.
Water has been running at 50 degrees.
I have taped some bags to the floor with heating on ( or should it be off) to test this way as i imagine with it on i will get condensation regardless?
When we talk about force drying, how much does this speed up the process?
Originally for 1st 3 weeks i had a large dehumidifier in the house too.

[paulpa]

IMG_8688.jpg

here is a picture of the colour difference. one patch the colour it was laid the other patch dark. No matter how much you sand the dark it is extremely hard to remove. No idea wh it is like this?

[Ajax123]

IMG_8688.jpg

here is a picture of the colour difference. one patch the colour it was laid the other patch dark. No matter how much you sand the dark it is extremely hard to remove. No idea wh it is like this?

ok that helps a lot. The screed is Low Laitnce Gyvlon Screed. All you are aiming to do by sanding it is to remove any construction debris. There is not a friable laitance on the screed so this does not need to be removed. Indeed the surface should be very hard and dense which from your descrption it is. Looking at the colour if i had to hazard a guess I would say it is still slightly damp but this is not possible to determine properly from a photograph so a moisture test is the right thing to do. If you do a web search for the F Ball and Co website and then search the site for Digital Hygrometer this will show you the kit you need. You can buy these from lots of other sources so a search might be worthwhile to find the best price. Once you have finished with it put it on E-bay or the like or even give it to your tiler ....... the polythene bag test can be done on a hot screed so that is not a problem. When you place the hygrometer on the floor you need to leave it in place for 48 hours then read it. if it is above 80% the screed is not dry enough to tile using the Bal system. If it reads 80% or below leave it for a further 24 hours and re read it. If it remains below 80% you can assume the screed is dry. If it has moved dramatically then the screed is probably nearly dry and I would leave it a further 7 days and repeat the test. Dont leave the hygrometer in the same place for more than 72hours. the flooriung companies will say it needs to be below 75% RH. This is because there is a tolerance of 5% built into the test. As it will be a brand new calibrated hygrometer the reading you are after is 80%. Anything below this you should be safe. If the readings are above 80% post on here and I can advise further.

The temperature for the heating is spot on. If you have a further 5 degrees C to put it up .... you could bump it up to 55 if you wanted to. I am very surprised if it is not dry as that temperature on a 50mm screed well ventilated or dehumidified I would expect to be dry within probably about 3 or 4 weeks tops. Do you know what is underneath the screed or have there been activities such as plastering which might have added moisture to the atmosphere thus impeding the drying. Force drying would normally speed the drying considerably unless the screed is excessively deep.

there are a few options available to you in terms of speeding up the tiling process such as using an uncoupling membrane or using the gypsum based adhesives. if this is of interest let me know and i will put some more detail on here.

[paulpa]

Thanks. I will look to find a supplier. Does the UFH need to be off for the test?

[paulpa]

Looking closer, i,m not sure the dark areas are moisture/damp because the area where all pipes leave manifold is dark too yet a cupboard that has no UFH is actually the whitest in colour of the entire floor area.
Maybe just some chemical reaction but i will attempt to find a meter to test.

[Ajax123]

ok that would make sense. the top gets harder as you heat it as you "bake" on the surface effectively. The darker patches could simplyy be silt distribution from the sand that was used in the mix.

Thinking about it if you have had the underloor heating running at 50 for three weeks I would be very surprised to see it damp but a test is stil needed to confirm. yes the heating will need to be switched off for that test. Dont just turn it off from 50 degrees though. Reduce it gradually by 5 degrees per day down to about 25 then switch it off.

[timeless john]

50 degrees paints pictures of Dudley Moore on the beach in the film 10.

[paulpa]

Ok got the F. Ball Digital Hygrometer

Now to see what we get. 80% here we come!!! ( i hope)
I think the dark areas are a mixture of dust / dirt from air particles that settled while all the other work has been going on.
Yes the floor is like a rock.

Can't wait to get the floors tiled, can get a kitchen fitted then!!

p.s Anyone want a cheap Hygrometer lol

[paulpa]

Are there any other companies like Creative Impressions that do a gypsum flexible adhesive?
GBTA looks ideal and can be l;aid at 85%!!!

Anyone want some BAL single part flex at a discount AHHHHHHHHH
And some APD oh and some wide joint grout
What confuses me is we tile on walls that are plastered walls with BAL ( cement based) which is gypsum and have no issues, so why do we have issues with Anhydrite. ( is that a dumb question)

BTW one room tested shows 81% moving on to another now.
Apparently 4 hour test as i have DPM between screed and subfloor

[paulpa]

With GBTA adhesive, would i require a gypsum based grout or could i use the cement based BAL ( better with water spills i believe?

[Sir Ramic]

Are there any other companies like Creative Impressions that do a gypsum flexible adhesive?
GBTA looks ideal and can be l;aid at 85%!!!

Anyone want some BAL single part flex at a discount AHHHHHHHHH
And some APD oh and some wide joint grout
What confuses me is we tile on walls that are plastered walls with BAL ( cement based) which is gypsum and have no issues, so why do we have issues with Anhydrite. ( is that a dumb question)

BTW one room tested shows 81% moving on to another now.
Apparently 4 hour test as i have DPM between screed and subfloor

Yes Gypfix from N&C

[Ajax123]

forbo flooring also do one called Alphycol 725. Not sure if Weber gt theirs up and running yet and Ultra are talking about one as well but that is probaby a little while away yet.

Paulap a 4 hour test is not long enough for the unit to acheive equilibrium but if it reaches 81 after 4 hours it is not going to go back down so you are right to be thinking gypsum.

You can still use the cement based grout if you want to as this sticks to the sides of the tile rather than to the screed underneath. If the screed is still wet you may get some efflorescence at the joints but this is easily dealt with generally. Creative impressions do a range of hgypsum based grouts as well though if that would be your preference.

[Ajax123]

the wals thing is down to the direction of moisture and the much reduced level of moisture borne sulphates coming into contact with the cement in the adhesive. A small amount of primer will generally deal with this. That sad there are still many problems with cement based adhesives on gypsum walls.

[garythetiler]

which manufacturer is the most competitive on price for the gypsum adhesive

[paulpa]

725 Alphycol (dust reduced)
Cement-based tile adhesive for direct fixing of floor tiles on anhydrite based screeds. Suitable for underfloor heating systems.
Cement based?

OK need help, i,d rather get a compatible adhesive and sleep at night so which one?

"Paulap a 4 hour test is not long enough for the unit to acheive equilibrium"

According to instructions being in situ over night with unit switched off is enough time followed by a 4 hour test

Can;t actually find prices on the 725 adhesive

[paulpa]

Another interesting point is: Walls are rendered with sand/cement yet plastered with Gypsum.
I have never come across the plaster separating from the render??

Am i worrying about something that happens to a small % of jobs most likely having not prepared the site in the 1st instance.
What do the Europeans use, they use more anhydrite than the UK and in general more tiles too.

[paulpa]

WOW and i thought BAL were expensive. No competition i guess.

[paulpa]

Worth posting i thought. Found on my travels
http://www.gyvlon.co.uk/2011-11-November.pdf

[Ajax123]

I wrote that

[Ajax123]

Another interesting point is: Walls are rendered with sand/cement yet plastered with Gypsum.
I have never come across the plaster separating from the render??

Am i worrying about something that happens to a small % of jobs most likely having not prepared the site in the 1st instance.
What do the Europeans use, they use more anhydrite than the UK and in general more tiles too.

There are far more gypsum addys available in europe..... Weber, pci, forbo, uzin, kreutz, mapei, benfer to name just a few.

[Ajax123]

The two most common in the uk are creative impressions gbta and nicobond gypfix