Painting non-paint grade aggregate blocks

[f0rmula]

I have a garage built from 3.5N lightweight Fibolight blocks. They’re medium density aggregate, rather than aerated concrete (AAC), but they’re “non-paint grade” blocks. How much of a disaster will it be if I attempt to paint the interior? (Exterior is already clad in timber)

http://www.mkmbs.co.uk/prodb019603-440mm-x-215mm-x-140mm-fibolite-block-35n

It’s just the inside of a garage, so it doesn’t have to look phenomenally pretty, but I obviously don’t want it to look like a complete disaster. Do they suck up paint (what with all the cavities)? Also, if I do attempt this, what paint would I want to use? Do I need a masonary paint, or would emulsion do?

Thanks for any replies.

 

[misterhelpful]

Non paint grade usually just means that the blocks are not really suitable aesthetically as a finished surface for painting - dense blocks are usually classed as a paintable finished surface. That said, it doesn't necessarily mean you can't paint the lightweight ones (unless manufacturer's instructions suggest differently), but they will be harder to paint and not look so good as smooth ones.

If you have a spare block lying around it may be worthwhile testing some paint on it before you start on the actual wall. I would use smooth masonry paint on them and apply a first mist coat watered down by around 20% followed by another 1-2 full strength top coats.

Be prepared for an aching arm, especially if you are not used to painting, as working the paint into all the little holes to get an acceptable finish is hard work.

 

[f0rmula]

Excellent. Thanks for the reply. I think I'll give it a go.

Would this cheap paint be "smooth" a smooth finish, as you've suggested:
http://www.screwfix.com/p/no-nonsense-trade-masonry-paint-brilliant-white-10ltr/13039

... or would I need to get something that actualy says "smooth" on it, like:
http://www.wickes.co.uk/Wickes-Smoo...uR6yODPLWO0tzf3FytvR_pV8UAftXqjkS2xoCIpnw_wcB

I wasn't really planning to spend too much as it's only a garage, but if the first option isn't suitable I can get the second (or something someone else can suggest).

It's a 42m^2 of walls, and with the coverage (10m^2/l) probably going to be a bit lower due to getting the paint in the little holes. How much do you think I'll need for the number of coats you suggest? 2? Any guess you make is probably going to be better than mine.

Cheers

 

[misterhelpful]

Well, the 'cheap' screwfix paint does actually say smooth on the tin as well.
As for how good it is, I couldn't tell you. I would rather use a quality masonry paint as it has better coverage, i.e., it will be more likely to cover in less coats but not necessarily cover a greater area.

As the first coat will be watered down a little, I would suggest that two tubs of that would be plenty - I would expect to get a mist coat and one topcoat out of a single tub. You may even get away with just one tub if you are happy with the finish after one full coat.

 

[ic1927]

Done a few factory internals with this type of block and what we did was mix artex up to a consistency as you would use for a heavy pattern like broken leather, and roll it over the walls prior to applying emulsion. It helps kill the suction and it fills up the smaller holes and works out a lot cheaper than emulsion. A 25 kilo bag goes for around £12 at the merchant I use, that will mix about two and a half 10 litre buckets.

 

[misterhelpful]

Done a few factory internals with this type of block and what we did was mix artex up to a consistency as you would use for a heavy pattern like broken leather, and roll it over the walls prior to applying emulsion. It helps kill the suction and it fills up the smaller holes and works out a lot cheaper than emulsion. A 25 kilo bag goes for around £12 at the merchant I use, that will mix about two and a half 10 litre buckets.

Interesting tip. I suppose as the type of block the OP has are generally suitable for rendered finishes then the Artex would be fine.