Looking for advice on slate floor on anhydrite screed.

[Playwrightpete]

Please could someone tell me if I am doing this in the correct manner.
The screed was laid mid may 2016, I have just removed the laitance layer with a STR 701 floor preparation machine and now have a lovely white floor.
I plan to seal the screed with primer G, with a single coat of 1 to 1 and use but anhyfix adhesive to fix the slate tiles. But manufacturer of primer G recommends two coats. So you could use a cementitious adhesive to fix tiles , without a slip mat.
Is it best to commission the under floor heating before laying the tiles ? and also what is the best tile sealer LTP MPG or MP90 ?
Any advice would be appreciated. Thank you.

 

[One Day]

My method - Don't trust the fact that it was May - take readings with a hygrometer box/es.
Vac the floor properly, and seal using BAL SBR at 4:1 - this simply reduces water absorbtion from the adhesive and the last of the dust.
Fix using Anhyfix as usual.
(for extra safety I'd always recommend Ditra)
If you plan on using a cement based adhesive - I would definitely use Ditra.

Sealer - I use Universeal products - I can't comment on LTP sorry!

And it's 100% essential to commission the ufh - especially if you aren't using Ditra.

 

[peteablard]

If I was using a cement based adhesive I'd use the primer the adhesive manufacturer recommends. I've used Weber on anhydrite before and primed with PR360. Mixed 4:1 it takes about 6 coats before it won't take any more. If using anhyfix I'd prime with Tilemaster prume plus. As stated above the heating must be commissioned and moisture readings must be taken. If you use a gypsum based adhesive you'll be able to tile with a slightly hight moisture reading, 85% rh V 75% rh with cement based

 

[Lithofin BOB]

Sealers, Both good products , mp90 is fila

Other professional products are avalible!!

 

[Ajax123]

Please could someone tell me if I am doing this in the correct manner.
The screed was laid mid may 2016, I have just removed the laitance layer with a STR 701 floor preparation machine and now have a lovely white floor.
I plan to seal the screed with primer G, with a single coat of 1 to 1 and use but anhyfix adhesive to fix the slate tiles. But manufacturer of primer G recommends two coats. So you could use a cementitious adhesive to fix tiles , without a slip mat.
Is it best to commission the under floor heating before laying the tiles ? and also what is the best tile sealer LTP MPG or MP90 ?
Any advice would be appreciated. Thank you.

no no no and again no

don't use cement based adhesive to stick directly. As it is natural stone you should uncouple as a requirement of the british standard. Your use of anhyfix is fine but you would be better to use their primer as well in my opinion... tilemaster . If you do decide to use a cement based adhesive then I would avoid Primer G like the plague on anhydrite. Use a water dispersible epoxy primer instead.

My advice would be

prime with tilemaster acrylic primer. then stick down uncoupling mat with anhyfix, then tile using whatever cement based adhesive you like.

 

[widler]

I'd just go the whole hog and use tilemaster primer, tilemaster matting stuck with anylfix and tile with rapid or standard s1 setaflex

 

[hmtiling]

no no no and again no

don't use cement based adhesive to stick directly. As it is natural stone you should uncouple as a requirement of the british standard. Your use of anhyfix is fine but you would be better to use their primer as well in my opinion... tilemaster . If you do decide to use a cement based adhesive then I would avoid Primer G like the plague on anhydrite. Use a water dispersible epoxy primer instead.

My advice would be

prime with tilemaster acrylic primer. then stick down uncoupling mat with anhyfix, then tile using whatever cement based adhesive you like.

I don't think you're right on the British Standards Alan. I've had a good look through and found nothing to say it's a requirement for heated screed with stone. Also, I've had discussions with Schluter and Dural, who couldn't confirm that is the case either.
Stand to be corrected though.

 

[hmtiling]

I don't think you're right on the British Standards Alan. I've had a good look through and found nothing to say it's a requirement for heated screed with stone. Also, I've had discussions with Schluter and Dural, who couldn't confirm that is the case either.
Stand to be corrected though.

That being said I'd agree it's best practice

 

[peteablard]

I think it is British Standard, I'm sure someone copy and pasted it on here once. I also may have dreamt it so stand to be corrected too!!

 

[One Day]

It's a recommendation by the British stone federation. It may be in the latest bs5385, but it's not in my copy (2009)

 

[hmtiling]

It's a recommendation by the British stone federation. It may be in the latest bs5385, but it's not in my copy (2009)

I know the stone federation do. But pretty sure it's not BS

 

[Bill]

So all this talk of recommendations actually means diddly squat?

 

[peteablard]

So all this talk of recommendations actually means diddly squat?

So you wouldn't recommend decoupling then?

 

[Bill]

So you wouldn't recommend decoupling then?

I am just wondering what happened to all the lovely stone floors I have laid without decoupling? Don't recall having any problems. I know there is nothing wrong with using one but sometimes there is no need so long as you use the correct adhesives.

 

[hmtiling]

I would STRONGLY recommend using one with a heated gypsum screed as in my experience they crack more often than they don't. With regard to screeds in general then it comes down to how well they been put down and unless I've done something myself I can't vouch for that and will use a decoupler when heated and stone.

 

[Ajax123]

I know the stone federation do. But pretty sure it's not BS

Hmmm!! I know I read it and it was actually one of the schluter guys that pointed me in the right place for the clause. However you appear to be absolutely correct. I cannot now find it in my copy either. that is really really frustrating... maybe I dreamed it.

Still I would always recommend decoupling natural stone from heated screed. The reason is simply due to the different coefficients of linear thermal expansion which can place stress on the natural fissures in stone leading to fracturing. This I see most often on marble and travertine but it still holds true for other stone.

 

[Spare Tool]

I'm just doing a bathroom in a house with wet heated trav floors through most of the ground floor, no uncoupling and there's more cracks than Blackpool promenade in July

 

[SJPurdy]

There are some weak stones available that crumble/split when subjected to the stresses created by thermal cycling, using an uncoupling layer under these may reduce the probability of them failing. If I was still tiling then I would pass on the advise that an uncoupling membrane is recommended by the stone fed for fixing (all) stone tiles over a heated floor. Personally if tiling onto a concrete floor then I can't see that it is necessary with slate as I've fixed hundreds of m2 in the past and have not had any fails however as it is an anhydrite screed then I would recommend using one as described above (stuck down with an anhydrite compatible adhesive onto the sanded, vacuumed floor with primer as recommended by the adhesive manufacturer; and then a cement based adhesive over the top to fix the slate) because then there can be no contact between the cement and anhydrite screed (so the membrane will have two purposes).
I have seen slate fixed over ditra crack but that was because no movement joints used where they were needed! I have also seen porcelain tiles crack when fixed directly over anhydrite (primer barrier then cement based addy) this because the water temp being passed through the screed was not correctly regulated and far too hot (not even raised slowly in temp after fixing the tiles). So make sure movement joints are used if needed, check the water temp regulated correctly and raise it's temp slowly up to the user temp when the floor fixing is finished and adhesive cured (I can't remember how long to leave it and how many degrees per day are recommended).

 

[Time's Ran Out]

I am just wondering what happened to all the lovely stone floors I have laid without decoupling? Don't recall having any problems. I know there is nothing wrong with using one but sometimes there is no need so long as you use the correct adhesives.

With or without UFH!

 

[hmtiling]

There are some weak stones available that crumble/split when subjected to the stresses created by thermal cycling, using an uncoupling layer under these may reduce the probability of them failing. If I was still tiling then I would pass on the advise that an uncoupling membrane is recommended by the stone fed for fixing (all) stone tiles over a heated floor. Personally if tiling onto a concrete floor then I can't see that it is necessary with slate as I've fixed hundreds of m2 in the past and have not had any fails however as it is an anhydrite screed then I would recommend using one as described above (stuck down with an anhydrite compatible adhesive onto the sanded, vacuumed floor with primer as recommended by the adhesive manufacturer; and then a cement based adhesive over the top to fix the slate) because then there can be no contact between the cement and anhydrite screed (so the membrane will have two purposes).
I have seen slate fixed over ditra crack but that was because no movement joints used where they were needed! I have also seen porcelain tiles crack when fixed directly over anhydrite (primer barrier then cement based addy) this because the water temp being passed through the screed was not correctly regulated and far too hot (not even raised slowly in temp after fixing the tiles). So make sure movement joints are used if needed, check the water temp regulated correctly and raise it's temp slowly up to the user temp when the floor fixing is finished and adhesive cured (I can't remember how long to leave it and how many degrees per day are recommended).

10 days then 5degrees a day I believe

 

[Bill]

With or without UFH!

both

 

[One Day]

I'm just doing a bathroom in a house with wet heated trav floors through most of the ground floor, no uncoupling and there's more cracks than Blackpool promenade in July

One of Tom's then???

 

[Spare Tool]

One of Tom's then???

Well it certainly wasn't me, its a reet bloody mess

 

[Bill]

C'mon guys, how do you think the Roman baths fellows laid stone, in the incredibly hot steam houses?

It is all about using the correct gear for the purpose.... no decoupling mats 2000 years ago.

 

[hmtiling]

C'mon guys, how do you think the Roman baths fellows laid stone, in the incredibly hot steam houses?

It is all about using the correct gear for the purpose.... no decoupling mats 2000 years ago.

I thought they did decouple with sand

 

[Spare Tool]

It is all about using the correct gear for the purpose.... no decoupling mats 2000 years ago.

And no 12mill travertine or Polypipe either

 

[One Day]

C'mon guys, how do you think the Roman baths fellows laid stone, in the incredibly hot steam houses?

It is all about using the correct gear for the purpose.... no decoupling mats 2000 years ago.

No direct bonding to poor quality substrates either. I know there's no need for uncoupling a lot of the time, but an uncommissioned heated floor of dubious quality, combined with thin, weak stone... That's getting uncoupled. And if a customer will pay for it (and generally they will if i spec' it) then why the heck not?!

 

[Old Mod]

I thought they did decouple with sand

In fact they did, it's explained in one of Schluter's Ditra video's.
The sand was used beneath the floors to decouple it from the building, that way the building would settle, and the floor would stay in tact.

 

[hmtiling]

In fact they did, it's explained in one of Schluter's Ditra video's.
The sand was used beneath the floors to decouple it from the building, that way the building would settle, and the floor would stay in tact.

Was beginning to think i'd made that up

 

[Bill]

combined with thin, weak stone...

This is the cause of most of the problems.... customers scrimping or think they are getting a bargain stone.

Most stone floors used to be 2omm minimum. Some of the trav I have fitted recently is like tracing paper.