paint not taking on parts of wall

[t45]

Hi there,
I had my walls skimmed and I have painted them.

Everything seems fine apart from some areas that seem not to take the paint. There is one area where there are what seems to be circular oil marks – nothing has been put on the wall apart from what was used for skimming and now paint – yet the paint doesn’t seem to cover these circle marks and not idea why they have appeared – any ideas? Is this plaster or paint related?

Using Dulux light and space range – white

I shall try to upload photo...many thanks

 

[footprints]

Sounds like PVA it's like painting teflon!
Sand lightly and apply a coat of Zinsser Bin 123 as a primer. Heard it said that oil based primer works too but I would use the 123 myself.

 

[opps]

circular oil marks

Do you mean fish eyes? They are areas where the paint effectively pulls itself away from the surface, creating paint free craters. If yes, they are normally the result of silicone contamination.

They can also occur when applying water based paints over oil based paints that are still releasing their solvents.

PVA seldom causes fisheyes but it may be the case that was a high point in the old plaster and the new plaster is extremely thin at that point, in which case, as footprints said, the PVA might be affecting the ability of the new paint to adhere properly. I would second his recommendation to use either Zinsser BIN or Zinsser Bull's Eye 123. I can also confirm that oil based undercoat works but you have to wait longer for OB UC to dry. Expect any coated area to dry more slowly. do not panic if it looks wet for longer.

 

[misterhelpful]

If the areas are relatively large, it could be over-polishing of the plaster, i.e., the surface is too smooth/shiny to accept the paint properly. If you allow the first mist coat time to dry thorughly, without trying to continuously get it to cover, it will often be fine when you use your two full coats of finish emulsion.
Us decorators can usually spot an over-polished patch before we start and can use a very fine sand paper to give a 'key' for the mist coat (Plaster isn't really a sandable surface but, with experience, you can do it without causing damage.)

As mentioned, a high grip primer/thinned oil-based undercoat can be used to make life 'easier'.

 

[opps]

Us decorators can usually spot an over-polished patch before we start and can use a very fine sand paper to give a 'key' for the mist coat (Plaster isn't really a sandable surface but, with experience, you can do it without causing damage.)

Good point, I hadn't thought of that.

I routinely sand brand new plaster using my 150mm rotex and dust extractor with 80 grit paper. I don't need to apply a mist (read: "search") coat as the change in plaster colour shows me any low spots that need a refill. I then apply two wet on wet coats diluted by 10% water. The advantage is that the wall has a more even coverage that (normally) only requires one more full fat coat.

It works for me but every man to his own.

Oh, and if I like the client, I sand down the penultimate coat with 220 grit so that the overall finish feels smoother (yeah, I am sad). I even sand new lining paper after the first coat of paint..

 

[t45]

many thanks - this is very interesting - here is a picture -

 

[t45]

please see image above. I misted the wall and then applied 2 coats of dulux light and space white emulsion....I also did the same in another room and have another mark where the paint doesn't take very well.....

 

[t45]

another picture but different wall

 

[misterhelpful]

Good point, I hadn't thought of that.

I routinely sand brand new plaster using my 150mm rotex and dust extractor with 80 grit paper. I don't need to apply a mist (read: "search") coat as the change in plaster colour shows me any low spots that need a refill. I then apply two wet on wet coats diluted by 10% water. The advantage is that the wall has a more even coverage that (normally) only requires one more full fat coat.

It works for me but every man to his own.

Oh, and if I like the client, I sand down the penultimate coat with 220 grit so that the overall finish feels smoother (yeah, I am sad). I even sand new lining paper after the first coat of paint..

Nowt sad about that...we all try to achieve the best results possible.

I remember finishing my apprenticeship 25 years ago and feeling pleased with the results I was getting but 10 years later I was laughing about those results. Another 10 years later, I was looking back and laughing again. These days I don't do much of the hands-on work but when I do, I strive for perfection,rarely achieving it. (It's tricky when you have to use decorating products you are not used to because you decided to move to a different country and basically have to learn about them all from scratch!)

We're all always learning.


Back to the OP:

The spots do look more like some kind of contamination, whether it be PVA, grease, oil... who knows? One of the high grip, stain blocking, primers would be the best route to see if they cover better before applying more paint. I would recommend the Bullseye, because spot priming with a water based product makes blending in easier. Just be careful if you go with BIN, and use a brush, because it dries very quickly and can leave brush marks in the middle of you wall - a foam mini roller would be my preferred method for this product.

 

[opps]

I strive for perfection,rarely achieving it.

Likewise, however, by definition, perfection is unobtainable.

I almost feel honour-bound to apologise to clients at the end of a job, then I remind myself that I provided the best job that I could within the price constraints

 

[t45]

Many thanks - this is really useful – ive no idea what the marks are or how they have appeared. The Walls were freshly skimmed and i misted them myself – i will try some high grip, stain blocking primers – BULLSYEYE sound good but which would b best in this situation BIN or BULLSYEY

 

[t45]

would you recommend light sand after applying the BIN or BULLSEYE

 

[opps]

I haven't used Bullseye 123, I have only used BIN.

BIN can be recoated in 45 mins, 123 in an hour.

The downside to BIN is that you will need to wash rollers and brushes in household ammonia whereas you will only need water for the 123.

There is no need to sand either.

 

[t45]

Many thanks for all of your advice e- can I just ask, is there a less expensive stain blocker/primer as Bin and Bullseye are quite expensive and the surface area of the wall is not that big. Does either Bin or Bull come in small pots?

 

[opps]

Many thanks for all of your advice e- can I just ask, is there a less expensive stain blocker/primer as Bin and Bullseye are quite expensive and the surface area of the wall is not that big. Does either Bin or Bull come in small pots?

You can use bog standard oil based undercoat. You will need to wait until the next day before overcoating it with emulsion.

From memory the smallest tin of BIN is 500ml. You would also need to buy a bottle of household ammonia to clean the brush after.