Just a quick one, when sticking a decoupler to a low laitence anhydrite screed would you use a gypsum based adhesive? (creative impressions addy being used to stick the tiles)

It is a spot on way to do it... how big an area is it.?

Not big (8 m2) but it is a shower room, and if memory serves me, the gypsum based addys aren't recommended in wet areas? Is that right or am I getting my wires crossed!!!! (The wet room bit has just occurred to me after writing the first post)

No they are not and neither is Anhydrite screeds.. So ye waterproof it..

Is there a specific product suggested for this or will a standard tanking solution suffice?

You can use a tanking paste ye as well...

Is the floor heated.?

Originally Posted by Dave

You can use a tanking paste ye as well...

Is the floor heated.?

Yeah, wet!

Check suitability of tanking paste on heated areas before hand.. but Ajax did say a while back that tanking pastes etc can be used..

Many thanks as always Dave.

might be worth a call to Sab at creative impressions. They do a range of water resistant grouts now as well. specially for this type of scenario. I found out today. Although Daves tanking suggestion is equally valid and sensible.

Quite few comps trying to accommodate these screeds now Al..

Originally Posted by Ajax123

might be worth a call to Sab at creative impressions. They do a range of water resistant grouts now as well. specially for this type of scenario. I found out today. Although Daves tanking suggestion is equally valid and sensible.

Thanks Alan,I've got to give them a bell about the order of addy so will ask the question then.

Do report back with your findings Bri.. all the more info on this matter the better

nicobond are about to launch their gypfix as well. they will operate through distributors so it will be easier to pick up a few bags here and there which is good news.

Originally Posted by Ajax123

nicobond are about to launch their gypfix as well. they will operate through distributors so it will be easier to pick up a few bags here and there which is good news.

Hopefully this could be the answer to my immediate problem.

we are about to tile 2 floors, this friday/saturday, both anhydrite, both wet areas, both wet ufh, been reading up on spec adhesives to use as we have never tiled over this screed before but is it worth me using the proper addy as the floor was just pumped in on friday 5th August?? i know all about the drying times etc, we have voiced our concerns to the boss & told him we are not being held responsible when the floor lifts but he is adamant its to get tiled this week!!!!!!!!

I'm just about to start the floor that I started this thread about and it was laid on 22nd April, the UFH is currently being comissioned and the screed is still showing signs of moisture, (not much though) and just out of interest I stuck an offcut of tile to it with flexy cement based adhesive and it didn't take much to prise it off the next day. There is no way on earth that your floor will be ready in 10 days!!!!!!!

Bri i know that m8, the screed was 70mm thick thats why i asked if it was worth using a gypsum based addy or just stick it with a rapidset flex as its gonna lift anyhow. the guy we work for can be a nightmare at times, he wants the house sold then worry about things after hes got the pennies in the bank.

Just out of interest i was reading the weber book & it states in it that you can use a cement based addy on a sealed anhydrite screed. This would be ok for us if it was 63 days down the line!!!!

A lot of builders hope that gravity keeps the tiles on some floors,lol.
They run a mile too when it goes belly up.

Cement based can be used and to be fair I didn't put any primer down I just did it as a bit of an experiment to see what happened, gypsum is the way forward and you can get away with slightly more moisture content in the screed, not as much as your screed will have in it though!

Robson. If you use cement it WILL fail. If you use gypsum it MIGHT fail. If you use cement it will delaminate along with the tile thus leaving the tiles un useable. I have never seen a failure with a gypsum day yet but my understanding is that the failure due to moisture is at the tile addy interface. This means that the tiles would come away clean and be reusable. Not sure if this is true or not. This job could be the way to find out though cos sure as eggs is eggs if you tile it next week it won't be dry. The underfloor heating should also be commissioned. This one seems doomed. The trouble for you is that as a professional you are accepting a contract and carrying out an installation that you know to be incorrect. A disclaimer may not cover you and you could end up liable for the inevitable repairs. My personal advice ........ as a self confessed anhydrite expert....... Walk away from it or do it properly. At 70mm which itself is far too deep you will be looking at two months.

Bri......I may well use that as a means of showing people what happens when they do it wrong........when I call on site tak a couple of tiles and some addy and stick them down. See which one fails......hmmmmm. Some of he ills might want to do the same. E.g when you are asked to tile the screed do a quick to tile sample patch. One with gypsum one with cement. Not sure how practical this suggestion is so I shall now stop waffling and get back to my cuppa

I'm going to step by step photo this job Alan and I'll also do a proper sample of cement based with a primer. If I can I'll video it so that the different amounts of pressure required to prise the tiles off the floor can be seen.

Originally Posted by Bri

I'm going to step by step photo this job Alan and I'll also do a proper sample of cement based with a primer. If I can I'll video it so that the different amounts of pressure required to prise the tiles off the floor can be seen.

Will look forward to the pics bri. We know cement and primer stick ok if all is perfect but will still be interesting to see.

Ajax, we work with this guy direct even though he has subbied out the rest of the works to another company, owner of this company we are friendly with also, the both of them know we should be waiting roughly 70 days for this to dry out & they also know that we are not goin to be held responsible for what happens with these floors, this could be the ultimate test to find out what happens when the floor fails.

if you knew this guy you would know what hes like, more money than a horse could ???? he will be on the sunday times rich list replacing his dad when the old man goes ( very high up may i add )

we are not keen on this he knows our concerns, we have been here before with him on a few occasions & he is a man of his word so i will let you know what the outcome of this will be, never know miracles could happen!!!

Why have weber got it in their "Tile Fixing Solutions" book that u can go over a sealed Anhydrite screed with almost all of the cement based addys?? I know you & Dave have tried a few different addys for this screed. Cheers folks.

They do say in there book to seal with weber PR360

If all is perfect I.e. The screed is dry and properly cleaned and vacuumed and primed with typically two coats of primer there is no reason to expect a problem. The issue is that the system is jot robust to "poor" workmanship.... Using the phrase in the least offensive way I can ..... whilst I know of hundreds of tiled floors using cement which are fine I have also seen lots of failures as well. I have yet to see a failure with gypsum on gypsum. It seems a more robust system to me. It is more the norm in Europe ... Especially France where something like three million plus square meters will be laid and tiled this year

Originally Posted by ROBSON MCGREGOR

Why have weber got it in their "Tile Fixing Solutions" book that u can go over a sealed Anhydrite screed with almost all of the cement based addys?? I know you & Dave have tried a few different addys for this screed. Cheers folks.

Only if the floor is dry though !

I take it this screed is going to be the way forward in terms it will probably replace a cement based screed?
This has been a nightmare for us so far & its just goin to keep getting worse, i would love to wipe my hands of it but my partner has worked for this guy for 14/15 years so its not as easy as just walking away.

The only good thing will be that we can walk away from this with our reputation still intact as we are dealing with him direct.
How hard is it to get the old adhesive up from an Anhydrite screed? Gypsum & Cement based addys? Worst case scenario we go back for the repair in 2/3 months time, by that time it will be dry.

Originally Posted by ROBSON MCGREGOR

I take it this screed is going to be the way forward in terms it will probably replace a cement based screed?
This has been a nightmare for us so far & its just goin to keep getting worse, i would love to wipe my hands of it but my partner has worked for this guy for 14/15 years so its not as easy as just walking away.

The only good thing will be that we can walk away from this with our reputation still intact as we are dealing with him direct.
How hard is it to get the old adhesive up from an Anhydrite screed? Gypsum & Cement based addys? Worst case scenario we go back for the repair in 2/3 months time, by that time it will be dry.

I guess its the way forward until something else comes along. I hear a few major house builders will be using it as standard from January.
I also wonder how we will get on when a few years down the line and you turn up at a house to tile the floor and you don't know for sure if its Anhydrite/Gyvlon or normal screed ? What about when there are 2 differing screeds ie original sand and cement from an old house and teh extension they have just had built is Gyvlon ?? gotta be 2 adhesives ?

I have had 4 Gyvlon screed floors offered to me in the last 2 months, One I turned down due to the client being very uncooperative when I voiced my concerns, he wanted it done right but did not want to wait or be inconvenienced at all.