No primer

[Unused Account 1]

talking to a rep ,he said no need to prime ply or plaster,the flexi addy already got built in polymers and addittives ,what you think

 

[White Room]

I tend to check the manufacturers instructions, If you use Sovereign Porcelflex is must be primed, my mates floor has been down for years and he didn't prime but it's been live for years.

 

[Joseph Kover]

talking to a rep ,he said no need to prime ply or plaster,the flexi addy already got built in polymers and addittives ,what you think

Better to be safe than sorry

 

[Flintstone]

always prime!

 

[Spud]

Who does he work for , I want to call his boss

 

[Aston]

When you read closed statements like this it makes you shake your head in disbelief.

Primers have 2 main functions
1. Control suction
2. Aid adhesion
They can improve flexabilty and help with regards to waterproofing but essentially they mainly do 2 things.

So, if they have more polymers to 'aid adhesion', increase flexibility and improve the waterproofing ability, then that doesn't mean the suction has necessarily been controlled...it could be very high suction, which will require maybe 1, 2 or even 3 coats of appropriately diluted primer, built up over a period of time so that each coat can be perform its role.

It's a ridiculously naive statement but a rep will only tell you what he/she has been told by the company they work for, (unless the rep has had some actual experience?)

 

[Joseph Kover]

I also mix in the Adhesive as well on every job

 

[LM]

talking to a rep ,he said no need to prime ply or plaster,the flexi addy already got built in polymers and addittives ,what you think

If cement based adhesive comes into contact with Gypsum based substrates ettringite crystals can form which will lead to debonding of the tiles, as well as the other factors mentioned above i.e. to control suction the proper advice is to always prime with an SBR/Acrylic based primer!
That rep is gonna cause a lot of hassle for his company with advice like that!

 

[Andy Allen]

You haven't said what rep...
Tile rep, adhesive rep, tool rep, ect

 

[White Room]

If cement based adhesive comes into contact with Gypsum based substrates ettringite crystals can form which will lead to debonding of the tiles, as well as the other factors mentioned above i.e. to control suction the proper advice is to always prime with an SBR/Acrylic based primer!
That rep is gonna cause a lot of hassle for his company with advice like that!

Then we come back an age old question, how does gypsum plaster finish survive on sand/cement undercoats.

 

[hmtiling]

Then we come back an age old question, how does gypsum plaster finish survive on sand/cement undercoats.

Pva sorts that one

 

[Old Mod]

Then we come back an age old question, how does gypsum plaster finish survive on sand/cement undercoats.

Now I've read about that quite recently, and I can't for the life of me remember where or what it said! Haha
Not a lot of help I know. But I'm trying to jog my memory.
But I seem to remember it works one way round, but not the other.

 

[hmtiling]

Now I've read about that quite recently, and I can't for the life of me remember where or what it said! Haha
Not a lot of help I know. But I'm trying to jog my memory.
But I seem to remember it works one way round, but not the other.

I think I remember hearing that the amount of gypsum in a skim coat isn't enough to cause a reaction.
I could also have made this up

 

[LM]

Then we come back an age old question, how does gypsum plaster finish survive on sand/cement undercoats.

I'm going by a site meeting I had several years ago where I was being asked to use Evo Stik OPF by the builder, who was suppling all materials. I wanted primer for the walls which he wasn't supplying, henceforth a debate started about it. The Evo rep said it wasn't needed, but I wasn't happy so I got a BAL/Ardex rep involved because I wanted to use their products. The site had 150 houses to be tiled and I wasn't for cutting corners. There was a site meeting with BAL, the building company and myself and the BAL rep went into it in detail explaining the chemistry of it to the point that the builder gave up and decided to pay more and run with them.
I've been on a few sites where cementitious adhesive has been used with no primer onto gypsum and there has been failures. When the tiles were removed the layers of dust (ettringite crystals) could be seen and they are what caused the separation.
For me on all my sites we prime, always!

 

[White Room]

I'm going by a site meeting I had several years ago where I was being asked to use Evo Stik OPF by the builder, who was suppling all materials. I wanted primer for the walls which he wasn't supplying, henceforth a debate started about it. The Evo rep said it wasn't needed, but I wasn't happy so I got a BAL/Ardex rep involved because I wanted to use their products. The site had 150 houses to be tiled and I wasn't for cutting corners. There was a site meeting with BAL, the building company and myself and the BAL rep went into it in detail explaining the chemistry of it to the point that the builder gave up and decided to pay more and run with them.
I've been on a few sites where cementitious adhesive has been used with no primer onto gypsum and there has been failures. When the tiles were removed the layers of dust (ettringite crystals) could be seen and they are what caused the separation.
For me on all my sites we prime, always!

I've seen jobs where cement based adhesive has been applied to gypsum plaster and there's never been a problem.

 

[LM]

I've seen jobs where cement based adhesive has been applied to gypsum plaster and there's never been a problem.

So have I in the past and I can't explain it, but I'm no chemist and I'm not taking the risk for the sake of priming a wall

 

[White Room]

Me neither

 

[Aston]

Just use your common sense and experience and if you don't have either of them, go with this old saying, "if in doubt prime"

 

[SJPurdy]

Then we come back an age old question, how does gypsum plaster finish survive on sand/cement undercoats.

As I understand it the ettringite is formed during the hydration phase of the portland cement. If the sand cement is already set then skimming over it with plaster should be ok because it is only the plaster that is setting.
But if the wet Portland cement mix is applied over a set plaster surface then the ions required for the formation of the ettringite can be taken from the plaster surface while the cement is hydrated and so the crystal ettringite layer can form where the two meet; giving a weaker bond.