Patches flashing through new plaster after mist coat.

[Sharpey]

Hello all.

I had some ceilings skimmed a couple of months back and today began painting them.

I have used matt white paint thinned with water by around 20-30% and given it three coats in quick succession.

The majority of the ceiling looks fine, however there a few spots that the paint doesn't seem to be covering well. It is really noticeable at an angle.

I'd like to know if this is a problem before I do the finish coats because the last thing I want to do is do the finish coats only for the same spots to flash through.

I've taken a couple of pictures to help show what I mean...

Untitled

• Sharpey
• 6 Apr 2013
• 1

Untitled

• Sharpey
• 6 Apr 2013
• 1

Untitled

• Sharpey
• 6 Apr 2013
• 1

I would really appreciate some advice on this. I am guessing it has something to do with the plastering but I wouldn't know whether it is a big problem or not.

Thanks for reading and for any advice

 

[Pigeon85]

Just how quick was quick succession?

Did you notice any shiny patches of plaster before you started? That is my first thought when seeing these pics. Shiny plaster stops the paint from absorbing, give it a scratch to see if it comes off easy

 

[Sharpey]

Thanks for the reply.

It was one after the other, no stops in between but I wasn't painting really fast or anything, just normally.

These patches did look different to the rest of the ceiling yes, I was concerned about them before I started.

When you give them a scratch, do you mean with sand paper? Will that not mess up the finish?

 

[Pigeon85]

Just use a finger nail, now would be the best time to sort it out if it does come away from the plaster.
It means it has not adhered to it properly.
Painting them as quick as you did could well have meant you pulled off the paint that was previously applied

 

[Sharpey]

Yeah I think it was the quick coats that were taking off the old paint. Having read up on it, it looks like these spots is where the plater has been over polished.

I have sanded off the paint and given the plaster a light sand to provide a key. I've gone over this with a few more coats and it seems to be taking much better now. Of course there is a ridge where the paint layers have built up around it which is really annoying on a new skim but hey ho.

There are a few small bits that I must have missed with the sanding and the same problem remains. I think I have a tiny bit of Zinsser BIN left, would it be OK to just touch these up with that and apply the finish coats over?

 

[Pigeon85]

You could try filling and sanding the ridges, by all means use the zinsser. Any filler you use give a mist coat before painting.

 

[Sharpey]

Nice one Pigeon85, appreciate all the help

 

[Pigeon85]

No problem hope it all goes well

 

[joe-90]

What you should have done is coat the patches with an oil undercoat.

 

[Sharpey]

What you should have done is coat the patches with an oil undercoat.

Thanks. I have Zinsser BIN, which is shellac based, could I use that instead (in the future if this crops up again).


Looking at it this morning it looks a lot better.

 

[Pigeon85]

Oil undercoat would be better, it takes less to cover it than the bin.
I was just going on what you said you had instead of going out to spend more money. I should have mentioned it really.

 

[Sharpey]

No worries. I just wanted to know if the BIN is adequate as Joe mentioned the oil based undercoat. I will just use the BIN as it's what I have.

 

[Robbie uk]

As Joe says, the good old oil based undercoat will be suffice over these marks, then finish with the emulsion. They may be patches of PVA on the surface of the plaster, these are hard to cover with emulsion and can flake off easily later on if not treated.

 

[Sharpey]

Thanks.

I still have a ceiling left to do, the on in the OP has turned out really nice (I sanded the patch and applied Zinsser BIN to the specks I missed).

I always see oil based undercoats recommended on here for various reasons. Are you referring to gloss undercoats? If so, won't that leave a shiny surface that needs to be keyed?

 

[Bosswhite]

Thanks.

I still have a ceiling left to do, the on in the OP has turned out really nice (I sanded the patch and applied Zinsser BIN to the specks I missed).

I always see oil based undercoats recommended on here for various reasons. Are you referring to gloss undercoats? If so, won't that leave a shiny surface that needs to be keyed?

No just a standard white oil based Matt undercoat.

Its the age old technique of covering up stains before painting with Emulsion,used by older Trade Painters and Decorators, cheap and works better than most modern products.