Spray paint over old paint

[Johnny Allround]

Hi Burts, I’m not saying you have done anything wrong. The pin hole phenomenon has baffled many a good tradesman I have worked with. However I personally would have mixed a very much thinner mist coat and added some pva bond to it, about a 1:6 ratio. This in my experience has always worked for me. Mist coats are there to seal the new plaster and to pick out any imperfections that need attending to before further coats, hence were your at with the pin holes. If it’s really bad a thin skim might be the answer if not it’s the trusty filling knife. Q)1 spraying will still show all the faults in your ceiling. Q)2 spraying over a roller coat will produce its own characteristic finish without trace of the previous coat. It’s interesting to note that a lot of tradesmen still like to brush line off sprayed surfaces. Must be an oldies trait like me. Hope this helps.

 

[burts]

Hi Burts, I’m not saying you have done anything wrong. The pin hole phenomenon has baffled many a good tradesman I have worked with. However I personally would have mixed a very much thinner mist coat and added some pva bond to it, about a 1:6 ratio. This in my experience has always worked for me. Mist coats are there to seal the new plaster and to pick out any imperfections that need attending to before further coats, hence were your at with the pin holes. If it’s really bad a thin skim might be the answer if not it’s the trusty filling knife. Q)1 spraying will still show all the faults in your ceiling. Q)2 spraying over a roller coat will produce its own characteristic finish without trace of the previous coat. It’s interesting to note that a lot of tradesmen still like to brush line off sprayed surfaces. Must be an oldies trait like me. Hope this helps.

There were no imperfections after the mist coat at all.
The plasterer is also the best plasterer I know and being a plumber, I know a lot.

So you would use 1 part paint 6 parts water?

I’m pretty sure PVA is a big no no these days and very much old fashioned with old paint.

 

[Johnny Allround]

1:6 for the mist coat and always pva bond in with it. It’s always worked for me so don’t see me changing something that works. Sorry thought there were pin holes in the ceiling. Is decorating something you also do, just wondered why you were interested in a spray option. I looked into it for new build jobs.

 

[lostinthelight]

I think if pva improved paint then manufacturers would include it in the products ...who knows , perhaps they do but I would leave it at that

 

[burts]

1:6 for the mist coat and always pva bond in with it. It’s always worked for me so don’t see me changing something that works. Sorry thought there were pin holes in the ceiling. Is decorating something you also do, just wondered why you were interested in a spray option. I looked into it for new build jobs.

Yes pin holes and tiny craters after a top coat had dried. Nothing to do with the mist coat on my opinion.
No one has been able to give me an answer.

It is indeed a baffling one.

Was interested in a spray gun because I will forever do my own painting and the smooth finish is immense.

I’m going to buy a dry wall sander today and just start again

 

[burts]

I think if pva improved paint then manufacturers would include it in the products ...who knows , perhaps they do but I would leave it at that

I’ve neber heard anything good about PVA. People say it a lot also before tiring to help adhesion. It does the opposite

 

[opps]

Yes pin holes and tiny craters after a top coat had dried.

Could they have been air bubbles left by the roller?

 

[opps]

1:6 for the mist coat and always pva bond in with it.

I follow the manufacturers advice with regards to thinning. I cannot see any positive to using PVA (a substance which re-emulsifies when wet).

On the occasions when I have unknowingly painted over PVA it has been akin to painting over glass.

 

[Johnny Allround]

Each to there own! It’s funny really been using this method since 1981 never once had an issue.

I follow the manufacturers advice with regards to thinning. I cannot see any positive to using PVA (a substance which re-emulsifies when wet).

On the occasions when I have unknowingly painted over PVA it has been akin to painting over glass.

 

[opps]

https://diy.evo-stik.co.uk/product/general-purpose-pva

Scroll down to the question about using it as a primer for paint and the answer is a resounding no.

I don't know why your Everbuild PVA recommends it's use.

I have no idea who wrote the article in your screenshot. Perhaps it was a plasterer. Actually I doubt it was a plasterer (and I seriously doubt it was a decorator), they recommend hiring heaters to dry plaster but omit to mention the importance of opening the windows to increase airflow. In my experience air flow is even more important than heat.

AFAIK PVA will invalidate most paint manufacturers warranties. I am happy to believe that it has never caused you any problems but I frequently see people recommending PVA as a primer for tiling as well. They claim that they have never had any problems. When you tell them that causes the formation of ettringite crystals they just repeat that they have never had any problems.

I can only imagine that the amount of PVA that you add is so low as to not be a problem. The fact that it isn't doing harm doesn't mean that it is doing anything positive though.

The following link demonstrates what happens if someone uses 1 part PVA to 5 parts water. The roller ends up pulling the previous coats of paint off.

https://groups.google.com/forum/#!topic/uk.d-i-y/GLD8mcnm_Hg

 

[burts]

Could they have been air bubbles left by the roller?

I honestly couldn’t say. My mate come round and said he’d never seen it. It can only have been the paint, I never thinned and it required thinning..... dust maybe ..... or drying to quick creating some kind bubble.
I’ve now skimmed over with easifill ....... even 120 grit on a power sander wasn’t helping. Whatever it was, was a real tough layer.