Painting new plaster.

We've come across this once before, I think the same thing anyway...
We stripped it and primed it with Zinsser 123 which I think wasn't ideal but given that this was a tiny area it sufficed and I did make the client very aware of the fact that I was guessing.

I did try and find out what was going on with this wall although I didn't get very far and the client was jumping up and down wanting her wall done yesterday and saying she'd just pay for us to get on and do anything we needed to do. I didn't have time I would normally have liked to research this whole thing and like you I got conflicting info.
The plaster we had did seem very highly polished and over trowelled seems most plausible. I've never heard of the term mapping and I looked all over today to find it...maybe it's a local term dunno.
My eventual conclusion, after speaking to a lot of different people was that this was a problem with the plaster not with the paint. We were told various things - dirty water in the plaster; old plaster; over troweled plaster; too much PVA in the plaster....I think over trowelled sounds as I said most plausible but let's hope a plasterer comes in here and sheds more light as I'm just guessing.

I have now taken to priming any very shiny plaster with a shellac based primer or an alkyd where appropriate as penetration is better.

Since this is a new house and the areas you are talking about are large can you refer back to the builders or is that just a silly joke?

I think your painter friend was wrong. If the first coat doesn't stick the next coats won't make it stick any better and nothing you do after will make it "eventually come right". Also over time, with additional coats of paint, the internal stress of multiple coats may exceed the adhesion of the sealer to the plaster and peeling will result.

Mid sheen paint will draw attention to any surface imperfections - matt would be better as it doesn't catch the light.

I have an awful feeling that stripping the walls is going to be your best option.
Cait

 

how would you strip the walls back?

 

If it was plastered in November, and was painted at Christmas, it cant have been dry.

The other important bit here is, what "type" of emulsion was used to coat the plaster up with...

 

The thing with new plaster is that you are supposed to put trade paint on, or paint for new plaster within the first six months, your not supposed to use paint that has vinyl in it, and I would think mid sheen would have been the wrong type of paint to use.
I cant think of any other reason, others might have more suggestions.

 

What does it say on the front of the bucket, i.e. what kind of crown emulsion?

 

Some misconceptions here:

a month is plenty of time for a wall to dry out even assuming it's been floated and skimmed. Plasterboard skimmed dries within 3-4 days.

The most likely reasons are:
1) Plaster over polished
2) No mist coat - if you stick undiluted paint straight onto plaster it will come off

If paint doesn't stick, no point in overpainting - it will never come right - only choices are:
1) Strip back to plaster, sand (which will key the surface) and remist then repaint
2) PVA and reskim

Either way I don't envy you.

Tangoman

 

unlucky - You say...I do think the plaster finish itself is at fault as 3 of the rooms are perfect.

If it's the plaster, then how are 3 rooms perfect?

 

Was this a self new build or a builder managed? If latter, demand he sort if out.
If former ask the plaster
if he used PVA
did he use any dirty water on job

If he answered yes to any of the questions you can ask him to do it again, or go to his federation if he belongs to any. But first you can try british gypsum and ask them why?

 

it is so smooth it is like glass

That's the problem then! If the plaster is like this then you need to sand it prior to painting in order to provide a key - you can do other things but this is the easiest and cheapest route.

Sorry I know this does not help now, but may help others.

Tangoman

 

how do you strip the walls back??

 

In our case we stripped the walls with a scraper. Our client had already primed the walls with a thinned down supermatt before we got to the surface (she'd been planning to do the work herself originally) and yet the whole lot came off in great sheets, no adhesion at all.

Cait

 

PVA???

Did somebody else say PVA?
How many posts are there on this forum about NOT using PVA in this way?

You can use a power sander - hire one for this, it needs to be really powerful.

The fact that you have so many coats on means that you will have to strip it all back otherwise there is no way you will be able to get it even.
It's not impossible - I've done it a few times, but it's a horrible job and makes a right mess - expect a dusty house for a few weeks.

Hence much easier if you can scrape it off - try using a sharp wood chisel carefully to start it off, and then see if you can switch to a paper scraper with which you can use more power and less care. Try steaming it and letting it cool down again before stripping.
Sand as last resort.

Tangoman

 

If there really is poor adhesion another way to start the paint removal off is to get some broad masking tape and press it hard onto the wall and rip it off...hopefully that willl rip the paint off and give you a nice long edge to start scraping. I've used a filling knife for scraping paint back before because it's a thinner blade sometimes you can get under the paint easier...just be careful,it's also sharper and can dig into the wall more readily.

LOL Tangoman didn't you know that PVA could sort everything in the world out...all decorating problems you ever knew of plus it will cure world poverty, child cruelty, stick PVA on drug traffickers and it will make them stop...you have no idea...I'm popping it on my husbands baldy heed tonight because a guy in a hardware store heard once from his mate who's cousin's a painter that it makes your hair grow back.
Cait