Tiling to Anhydrite screeds... A method statement from PCI.

[Dave]

Here are some guidelines that PCI have allowed me to type up for all you PCI users who need a method statement for tiling to anhydrite screeds...

Tiling to Anhydrite screeds by PCI.

Anhydrite screeds are now becoming more and more apparent in the market place,and as direct result of this PCI construction systems are being asked to specify products for this type of finish.

The following is issued as a guidline :

It is important that the screed has been laid as per the latest manufacturer's data sheet,paying particular attention to:

1. Underfloor heating
2. Residual moisture conten
3. Flor finishes-surface preperation.

1.
Anhydrite screeds are suited for underfloor heating since they are laid much thinner than traditional screeds, and therefore eliminate air pockets and voids around heating pipes etc....

In heated calcium sulphate floors,movement joints should be carried through both the screed and the tile bed dividing the tiling into area's no greater then 40m2, or in accordance with the sceed manufacturers instructions....
The area bounded by the movement joints should be square to rectangular with the width to length ratio not exceeding 5 to 8 mtrs.....

2.
Residual moisture content of 0.5% or less must be obtained before the application of primer G, drying times of the screed is normally approximatley 1mm per day uoto 40mm and 0.5mm per day thereafter at 20c,65-70 relative humidity.
To reach this figure of 0.5% witht he use of underfloor heating, it should be borne in mind that this will increase the humidity of the site.

It is therefore essential that good ventilation be maintained during this period of drying.

3.
If underfloor heating is being used- turn off 48 hrs prior to the following applications..and commissioning of the heating.

Ensure that the surface of the screed is free of any dirt,dust,oil,grease or any other contamination likely to prevent a good bonding surface.
The finished surface should be abraded/sanded then cleaned with a vacuum cleaner if laitence is present.

Apply primer G, diluted 1:1 with water to the whole area, ensuring a continous coat of the primer without the formation of puddles.

When dry a second coat must be applied NEAT as above.

Primer G is coloured blue to facilitate this application.
When the primer is dry then tiling can be carried out with the appropiate PCI adhesive to suit .

If underfloor heating is integrated in the system th en this must be left off for a further 48 hrs after completion of the grouting and then gradually increase the heat over the next 7 days.
This will reduce the possibility of any thermal shock being appied to the over all system..

[penkhull]

I've heard a new way of doing this. If you use an uncoupling system you can complete the floor with out removing the finer particles on the surface and without priming. The whole point of an uncoupling membrane is that it doesn't stick to the floor.

It was confirmed that this would work by Lafarge although they would still prefer you to prime the floor they admitted there was no need.

[whitebeam]

Do you mean just lay the uncoupling direct onto the floor without any adhesive

[penkhull]

No you need to stick it down to hold it in place but then it doesn't matter if it comes away, it doesn't really matter what you stick it down with.

[whitebeam]

If it comes away it will be cracking all over the place, don't sound good to me IMO

[Phil Hobson]

I've heard a new way of doing this. If you use an uncoupling system you can complete the floor with out removing the finer particles on the surface and without priming. The whole point of an uncoupling membrane is that it doesn't stick to the floor.

It was confirmed that this would work by Lafarge although they would still prefer you to prime the floor they admitted there was no need.

Sorry I must be thinking of a different decoupling membrane, I use Ditra or Dural CI. Both of which Need the fleece to be securely fixed to the substrate. Otherwise you might as well lay cling film, and save a lot of money

[Dave]

No you need to stick it down to hold it in place but then it doesn't matter if it comes away, it doesn't really matter what you stick it down with.

In theory you still use the required adhesive for the job... but if it does uncouple then the membrane will cope.. as there is no deflection then it just sits on the surface...

You can actually get another brand of uncoupling membrane that doesn't stick down, it just lays loose and locks together at the edges so it doesn't move as you tile..

So to answer your theory above.. then guy from lafarge is correct in a sort of way.

But my post is what a PCI user need to do, to use PCI adhesives.. uncouplers is another thread.

[Ajax123]

I've heard a new way of doing this. If you use an uncoupling system you can complete the floor with out removing the finer particles on the surface and without priming. The whole point of an uncoupling membrane is that it doesn't stick to the floor.

It was confirmed that this would work by Lafarge although they would still prefer you to prime the floor they admitted there was no need.

Who at Lafarge confirmed this Penkhull

[Ajax123]

In theory you still use the required adhesive for the job... but if it does uncouple then the membrane will cope.. as there is no deflection then it just sits on the surface...

You can actually get another brand of uncoupling membrane that doesn't stick down, it just lays loose and locks together at the edges so it doesn't move as you tile..

So to answer your theory above.. then Alan from lafarge is correct.

But my post is what a PCI user need to do, to use PCI adhesives.. uncouplers is another thread.

Not guilty (I don't think) although I agree that the uncoupling membrane should at least be nominally adhered to prevent rucking and horizontal movement.

Back to the thread though. I am not familiar with primer G although I know it is an acrylic. The first coat being diluted is good practice as this encourages the primer to penetrate into the surface. However you need to be a little carefull in the application as you are "adding" water to the screed which will need time to dry out - I owuld think 24 hours.

I still prefer to see Epoxy Primers with cement based adhesives. whilst water dispersed the way epoxy cures it uses a good proportion of the water in the curing process. Epoxys are also much better at preventing the migration of sulphates so are much more robust against the dreaded ettringite reaction. Of course Gyspum adhesive is even better still at preventing this reaction. I think PCI do a gypsum adhesive in Germany - they certainly do a gypsum leveller.

Other than that PCI seem to have it pretty correct.

[peckers]

Not guilty (I don't think) although I agree that the uncoupling membrane should at least be nominally adhered to prevent rucking and horizontal movement.

Back to the thread though. I am not familiar with primer G although I know it is an acrylic. The first coat being diluted is good practice as this encourages the primer to penetrate into the surface. However you need to be a little carefull in the application as you are "adding" water to the screed which will need time to dry out - I owuld think 24 hours.

I still prefer to see Epoxy Primers with cement based adhesives. whilst water dispersed the way epoxy cures it uses a good proportion of the water in the curing process. Epoxys are also much better at preventing the migration of sulphates so are much more robust against the dreaded ettringite reaction. Of course Gyspum adhesive is even better still at preventing this reaction. I think PCI do a gypsum adhesive in Germany - they certainly do a gypsum leveller.

Other than that PCI seem to have it pretty correct.

What make of epoxy sealers would you recommend for anhydrated floors and cement based adhesives?

[Dave]

Not guilty (I don't think) although I agree that the uncoupling membrane should at least be nominally adhered to prevent rucking and horizontal movement.

Back to the thread though. I am not familiar with primer G although I know it is an acrylic. The first coat being diluted is good practice as this encourages the primer to penetrate into the surface. However you need to be a little carefull in the application as you are "adding" water to the screed which will need time to dry out - I owuld think 24 hours.

I still prefer to see Epoxy Primers with cement based adhesives. whilst water dispersed the way epoxy cures it uses a good proportion of the water in the curing process. Epoxys are also much better at preventing the migration of sulphates so are much more robust against the dreaded ettringite reaction. Of course Gyspum adhesive is even better still at preventing this reaction. I think PCI do a gypsum adhesive in Germany - they certainly do a gypsum leveller.

Other than that PCI seem to have it pretty correct.

That is just the same as using adhesive Alan.. it will get wet.... but as mentioned above.. it does say to leave to dry..between coats.

[penkhull]

Who ever the technical guy is who covers Derby. If you think about it it makes sense if you stick the uncoupling membrane down with a rapid SPF it will defo hold in place whilst you tile it and then if it uncouples after you have tiled it the membrane is doing its job.

I do think if you're going to do it by a more conventional method then an epoxy primer is better once you've removed the smaller particles that come to the surface, at least then you know you've got it covered, with an acyrlic type primer you have to keep soaking it in until its saturated.

[Ajax123]

What make of epoxy sealers would you recommend for anhydrated floors and cement based adhesives?

Tremco CS Epoxy (2 coats neat) or Laybond Screedmaster Epoxy (dilute 1:1 with clean water - 1 coat usually sufficient but 2 to be certain) are the ones I usually point people towards. They also serve to make the surface much harder and more stable.