Any advice-priming

[kaharrison9]

Hi All
Has anybody any thoughts on the bathroom i'm about to start.
The walls were skimmed 5 days ago over plasterboard.
It appears totally dry and this morning i have primed using Mapei g which i was hoping to tile onto two hours later.
4 hours on the primer on the plaster has a very high shine and if i nick with my finger nail i can then roll of the primer like a skin.
Any ideas if something is wrong,have i not allowed the plaster to dry long enough?i used a heavy roller may i have put on to heavy a coat,i am been impatient and should let the primer to dry?
Any pointers as a very concerned before starting.
Thanks all
Kev

[jay]

hi what type of primer (acrilic or pva) name might help

[kaharrison9]

Hi mate
Mapei primer g (acrylic)
At the moment reckon it could off the wall in large areas.
Also applied it neat which maybe i should have diluted.
Cheers
Kev

[oldgit]

Hi mate
Mapei primer g (acrylic)
At the moment reckon it could off the wall in large areas.
Also applied it neat which maybe i should have diluted.
Cheers
Kev

10 to 1 would have been fine or none at with most mapei wall adhesives.

[jay]

not up with that brand normally yes you do dilute just wait someone who has used this product will drop you a line sorry

[kaharrison9]

Cheers old git
Any ideas on what next should it harden off,will the tiles key to the primer without pulling the primer off the wall or even attempt to peel it off and try it diluted?
Very worried before i start.
Cheers
Kev

[oldgit]

not really sure if it has to come off,but if its peelable its not doing anything good at all.

[Dave]

Mapei primer G is a synthetic primer.....If the plaster surface was over troweled then you need to use a stiff bristled brush to roughen the surface before priming if using cement based adhesives...If the surface was too smooth then the primer will not impregnate fully and form a skin as you found out...

Watering it down to 2:1 can help help but more than 1 coat might be needed if you water it down...

Always read the instructions....

[kaharrison9]

Cheers Dave
I think you have described it exactly.
It has not impregnated at all and i have basically rolled half of the primer off by my hand!! The rest i'm going to use a sander tomorrow.
Do think it's a combination of polished plaster and me not having a ratio of water.
On the bottle theres very little info as there's 10 differant languages and not much room for info in the paragraph.
Kev

[Dave]

Hi kev...

You will find this >>> Primer G better info for you....

[kaharrison9]

Cheers for that.
Back at it tomorrow thought i was getting a head start working today!!
Kev

[Dave]

No probs kev.....sometimes when using these synthetic primers neat on gypsum it is better to either sand the surface for a better key/absorption...or water down and apply 2 coats...

I find acylic primers better for gypsum substrates...

[kaharrison9]

Thanks again Dave
Up to now always have used acrylic and no probs so kicking myself for trying differant.
I've removed just about all the primer from the walls where the tiles go from floor to ceiling but there are large lengths of areas where it is to be tiled just a third up with this been only 3 tiles up would you think it would be okay to tile directly onto the primer without any future probs.
Also do you think the customer will have a problem painting on top of the primer where areas are not to be tiled?
Sorry for so many questions but in a proper pickle
Cheers
Kev

[Dave]

If it peels then remove it and it is difficult to paint over as it is on the surface....so needs removing as well...

No need to apologise kev..how will you know if you do not ask..?


enjoy...

[kaharrison9]

Cheers for your time.
Going to be a right slog tomorrow but at least it'll put us back on track.
In time to come may laugh about it.
Picture the scene i was only chatting with the plasterer/plumber who tiles as well all the time with PVA why best not to use PVA!!
Kev

[Dave]

The good thing is kev.....you only make a mistake once when you have to correct like this......

It's called experiance...

[whitebeam]

So true

[Swanseajack]

Hi All
Has anybody any thoughts on the bathroom i'm about to start.
The walls were skimmed 5 days ago over plasterboard.
It appears totally dry and this morning i have primed using Mapei g which i was hoping to tile onto two hours later.
4 hours on the primer on the plaster has a very high shine and if i nick with my finger nail i can then roll of the primer like a skin.
Any ideas if something is wrong,have i not allowed the plaster to dry long enough?i used a heavy roller may i have put on to heavy a coat,i am been impatient and should let the primer to dry?
Any pointers as a very concerned before starting.
Thanks all
Kev

Am I reading this right?

Correct me if I am wrong, but I was taught not to tile over new plaster for 28 days. The reason being that the plaster may appear to be dry, but it has not cured. You should have tiled directly to the plasterboard.

I will allways wait a minimum of 3 weeks for tiling, depending on house occupation/seasons etc.

[kngjason]

i use SBR not PVA. SBR replaces conventional PVA’s due to its excellent durability, reduced shrinkage and its increased flexibility. The SBR Bonding Agent allows internal and external renders to flex. Unlike PVA it will not re-emulsify in damp conditions.

Ardex, BAL and Nicobond are the three suppliers I use most. Their products are similar in many respects, sometimes one will make products the other don't, and I also find some of there products more useful in different applications. All three of them have one thing in common, they all specifiy that under no circumstances may PVA be used before using any of their adhesives. If you do all guarantees are void.

basicly!!
When you treat a surface with PVA it partly soaks in and parlty sits on the surface of the substrate much in the same way as wallpaper paste.

If PVA gets wet it becomes slightly live again, it doesn't completely return to it's liquid state but it becomes sticky.

When you spread tile adhesive onto the wall, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip.

Most tile adhesive works by crystalising when it sets (some are slightly different such as epoxy based ones) but generally they all work the same way. Once the adhesive starts to set crystals from and expand into any imperfections in the substrate surface (at a microscopic level) to create a grip. PVA stops this process by creating a barrier between the substrate and the tile adhesive. Basically a moist layer of PVA is then holding the enitre weight of the tiles, grout and adhesive and stopping a great deal fo the mechanical grip occuring.

[kngjason]

Oh it also stops a chemical reaction occuring between the cement based adhesive and a plaster substrate, known as "Ettringite failure".

[Dave]

Try this jason....pretty much what you said..

http://www.tilersforums.co.uk/tile-a...s-primers.html

[Swanseajack]

Read my post above guys, he shouldn't be tiling after plastering the walls 5 days ago.

Come back to the primer issue when the walls have dried out/cured.

[Dave]

I have read it... what do you want us to add to it...thought you said it all in your post..?

[kngjason]

Try this jason....pretty much what you said..

http://www.tilersforums.co.uk/tile-a...s-primers.html

that would of been easier lol

[kaharrison9]

Swansejack
Ideally would have been plasterboard but i mentioned earlier that 3 of the 4 walls would be half painted/tiled-the reason for the skim.
Explained to the customer that i thought the plaster should be left longer but he was adament for us to go after 5 days and he would accept any consequences after.His explained his situation was a wife and three teenage daughters and one bathroom practically out of use and and no way would they wait any longer.Also the plasterer/plumber was itching to step in to tile had i delayed longer.
As you was taught 4 weeks why have gone against your teachings and tiled in 3?
Yesterday was long day,4 hours sanding then used an acrylic primer which bonded without a problem then started.
If i was to use a synthetic primer again as Dave earlier mentioned would definatly do 2 coats with a water ratio,sand the skim and also brush it on lightly though sticking with the acrylic for the time been
Kev