Painting grey concrete blocks, inside and outside

[curiousorange]

In an extension I have some cavity wall made of grey concrete blocks. I would like to paint both the indoors side and the outdoors side white.

What would be the best way to do it please?

What should I do to prepare the surfaces? Do I need any undercoats or pre-treatment please? Am I right to think it should be masonary paint for the exterior and emulsion for the interior?

Thanks

 

[PrenticeBoyofDerry]

Use masonry paint for both inside and out.
the walls need to be clean and dust free, this can be done by power spraying them down.
The walls will need to be primed first assuring all the pores are filled, prior to painting.

 

[curiousorange]

Thanks, what do I prime the walls with please?

I've also noticed, when looking though similar questions here, that some people suggest painting the interior with emulsion, some people suggest masonary paint. What is best please?

Its in a heated room, not a garage. I suspect that whatever its painted with now, in the future its likely to have emulsion painted over it, if that makes any difference.

 

[JohnD]

use a water-based masonry paint. The instructions on the tub will tell you to thin the first coat with water and mix well, this helps it soak into the dry and absorbent surface of the blocks. If they are very hungry and suck the moisture out of your brush, it does not hurt to apply two mist coats, thinning the first with a bit of extra water. You will know when you have killed the suction as the following coats will not sink in so fast, and you can then use a roller for subsequent coats if the surface is not too uneven.

Masonry paint, when dry, is stronger and more dirt-resistant, and can be washed clean with water or even a hose. Rough unplastered walls tend to hold dirt and dust, which is why I agree masonry paint is more suitable. You can also brush or hoover it clean. Emulsion paint is more easily scuffed and marked on a rough surface but is fine on smooth plastered walls as there are not usually high points and knobbles to get knocked or scratched.

Whatever you do, DON'T PUT PVA ON WALLS THAT YOU INTEND TO PAINT

 

[joe-90]

If they are very hungry and suck the moisture out of your brush,

Thirsty John, thirsty.