Masonry Paint on Different Surfaces - Prep?

[Damian30]

Hi,

I apologise in advance for the daft question...

I am just about to paint the inside of my garage with smooth masonry paint. There are 3 surfaces in the garage - plaster, breeze block and aircrete blocks.

I just wondered whether I can put a full coat straight on to these surfaces or whether I would be best prepping them in some way first (e.g. watered down first coat, etc).

Any advice much appreciated.

Many thanks,

Damian

 

[misterhelpful]

Providing the surfaces are dry, and unlikely to get wet by penetrating water, then it is ok to use diluted (10% water) masonry paint as a first coat. You could also use diluted pva (such as unibond) as an alternative, which as you stated that some of the surface is plaster, would be my reccommendation. It is unwise to use neat paint directly onto bare walls as firstly, it will be much harder work, but more importantly, it may dry as a film on the surface which will lead to flaking and peeling in the future.

 

[Damian30]

Hi,

Thanks - I have some B&Q PVA in the garage. What would be the dilution ratio and would you prep all the walls?

Many thanks,

Damian

 

[misterhelpful]

For this type of job the ratio is usually 5 parts water to 1 part PVA but double check the container as some brands may vary.

Providing the surfaces are clean (no dirt or mould) and sound, no real prep is required as the PVA will seal dusty surfaces. If mould is present, clean with a fungicidal wash or mild bleach solution, rinse thoroughly, and allow to dry fully before beginning work.

Be prepared to apply a few coats of paint, as most blocks tend to have many little holes in them which can take a few coats to completely cover.

 

[Damian30]

Hi,

Thanks again for the advice.

I have been reading a few other posts which suggested that using PVA to seal plaster was a bit of a no-no and a watered down emulsion would be better. I'm guessing that this advice is probably in relation to new plaster where there is a risk of sealing in the moisture.

I'll probably make a start at the weekend, in the meantime if you have any further reassurance then that would be appreciated!

Many thanks,

Damian

 

[misterhelpful]

PVA is suitable for sealing plaster providing it is dry and the PVA correctly diluted so that it is absorbed into the surface. While it's true that it can leave a film when applied too thickly, in 20 years as a decorator, I've had no trouble.

My suggestion is based on the fact you are using masonry paint on plaster rather than a standard emulsion, which would be more suitable for that particular surface.

As I said before, watered down paint will do the job as well so the choice is yours.

 

[Damian30]

Hi,

Thanks for the time taken to explain your thinking.

Understood now - will still go with the PVA. I guess brushing it on is the best approach.

Thanks again,

Damian