Used PVA As Primer, Forgot To Dilute... Mud Cracking

[kingofspoons]

First post, so hello, and sorry, I'm another person who only signed up because I need help with something.

I had a couple of rooms plastered about 5 weeks ago. The plasterer applied GTEC Smartmix Xtra - Joint Cement. The rooms, previously, had wallpaper over plasterboard.

Few days ago, after giving the plaster a light sanding, I used Durabond PVA as a primer but did not realise the product required dilution for this purpose (recommended ratio is 4 parts water to 1 part PVA). The next day I applied the first coat of Dulux Supermatt water based emulsion (applied neat). I didn't think there was anything out of the ordinary when the paint dried to a cracked mud effect finish as it was the first coat. Now that I've applied a second coat, only to be left with the same effect, I'm... concerned.

It was suggested I lightly sand a test area before applying a slightly diluted coat of the emulsion to it - to see whether this solves the mud-cracking issue. Is this a reasonable course of action? I'd like to hear from someone, in the know, as to whether this needs to be tackled in a different way in order to avoid future/more complicated problems.

Thanks in advance.

 

[JohnD]

you should never use PVA under paint. The correct primer for painted plaster is diluted matt emulsion.

someone will be along with a suggestion, I'm sure.

 

[Nige F]

Zinsser BIN , laden brush , applied evenly will Seal the wall Topical and true

 

[opps]

SuperMatt can be problematic when painted over any non porous surface.

Years ago I painted it over oil based eggshell on a wall to hide the bright red colour- it cracked, more coats and it cracked/crazed I rang Dulux and they told me I shouldn't have used it over non porous surfaces, i suggested that they mention that on the tin...

As suggest BIN will help.

Normal trade matt might be ok.

Alternatively use a steam stripper to try to remove the pva, the steam will soften it but you run the risk of blowing the plaster

 

[kingofspoons]

So, I've already the mistake of applying neat PVA and a couple of coats of the Supermatt emulsion. Going forward, is there anything wrong with just trying the 'light sanding before applying diluted coat' method?

 

[opps]

I can't see how sanding will help. You can't feather out emulsion and adhesion isn't your problem.

The problem is the supermatt paint over a non porous surface. thiining it might make it even worse.

 

[opps]

Nige Fs suggestion is the best- the BIN is alcohol based and will reduce the risk of the pva being reactivated by the water in the emulsion. BIN can be tinted and would suffice as a low sheen and very durable finish.

It will smell but the smell disappears very quickly and will be touch dry faster than emulsion

 

[misterhelpful]

Zinsser BIN , laden brush , applied evenly will Seal the wall Topical and true

Nice one Nige, that flew right over my head!!

 

[opps]

BTW don't use meths to clean your brushes after using the BIN (as per the instructions on the tin)- household ammonia is far better and cheaper (but stinky).

It is alkaline based so it will break down the BIN on the brush rather than just diluting it.

Pour the ammonia into a cut up milk/coke bottle, put the brush in, agitate it a bit and go and have a cuppa. Then remove the brush and rinse it in water. All of the BIN will wash away and not leave any residue in the sink. The stuff in the bottle can be left outside over night- the ammonia will evaporate and you will be left, in time, with clear water and white dust at the bottom.

I normally apply BIN with rad rollers but to date the only ones that I have found that don't swell and balloon are the wooster branded ones. You might get away with a crappy (non foam) rad roller but expect to ditch it after.

Do not be tempted to over roll- it dries too quickly to allow you to do that.

With regard to the SuperMatt- only ever use it on ceilings- there is so little acrylic in it that you cannot wipe away finger marks- period. sure it is good at covering new plaster but completely impractical for anything other than ceilings. I just stick with the standard Dulux Trade Matt- 2.5 coats over new plaster is normally sufficient.

V important- if you do decide to keep the BIN as the finish coat- never clean the walls with ammonia based products- EVER

Good luck

 

[jondecs]

When I come across 'mud cracking' I find a THINNED SOLVENT BASED UNDERCOAT solves the problem of waterbased paints reacting the pva/ too thick emulsion / cracking on caulking/etc. let it dry. Then two coats of any type emulsion.

Good luck

 

[jondecs]

Zinsser BIN , laden brush , applied evenly will Seal the wall Topical and true

Nice one Nige, that flew right over my head!!

 

[TheDec]

Well I am going to add my twopence worth here, any oil based paint would be well capable here of sealing the surface, yet the fact remains that it is going to be applied to a paint of which will in my opinion always remain unstable.

In this case as opps as said the paint system has not and never will be able to form a bond with the underlying substrate, this makes it unstable within itself and also subject to movement. This is bound to cause the paint to both crack and craze when it feels the need to do so.

I know that not all may agree yet I believe that the lasting cure would be to remove seal and start again. I feel flack pointing in my direction.

Dec

 

[misterhelpful]

I feel flack pointing in my direction.

Not from me.

That is certainly the best way to prevent any future problems but I fully understand the dilemma of removal, and the fear of making it look worse, as opposed to trying to get away with some sort of cover up solution.

Rather you than me kingofspoons, so good luck, whichever method you choose!!

 

[jondecs]

Well I am going to add my twopence worth here, any oil based paint would be well capable here of sealing the surface, yet the fact remains that it is going to be applied to a paint of which will in my opinion always remain unstable.

In this case as opps as said the paint system has not and never will be able to form a bond with the underlying substrate, this makes it unstable within itself and also subject to movement. This is bound to cause the paint to both crack and craze when it feels the need to do so.

I know that not all may agree yet I believe that the lasting cure would be to remove seal and start again. I feel flack pointing in my direction.

Dec

Don't worry I agree too
Thats why I would'nt invest in expensive primers.

 

[TheDec]

Jon,

It really is the only way I think, anyway I have just taken off my tin hat so
perhaps the flack ain't coming my way.

Dec