painting a concrete retaining wall

[gsouth]

We are nearing completion of some fairly major works around the house and one of the last jobs is to decide what to do with a poured concrete retaining wall... that was here when we purchased the house.

It's one of those walls where they used formwork on either side and then poured concrete into it.
The surface of the wall is pretty good but there are a few air pockets (small) in the concrete.

We have decided to paint it, and I have some of the paint left over from the render job - it's a paint specifically made to go over render and granosite - it's really thick - it's called Taubmans Armawall Satin

My questions are:
1 - should I fill the airpockets? And if yes, what with?
2 - should I have a sealer/waterproof layer - the wall doesnt' retain much and there's no water penetration that we can find anywhere along the wall (it's been around for at least 15 years)
3 - What do I use to clean and prep the surface?

Cheers
Geoff

[Master Splinter]

Whatever you paint it with, you may end up having the problem of the paint bubbling as water builds up behind the paint. If you haven't backfilled it yet, make sure that the back of it is well drained and covered in a few coats of bitumen or other waterproofing stuff.

Concrete can be etched with citric acid prior to painting to give the paint some grip; you can get this from your paint shop. If the concrete has a really smooth 'off form' finish, hitting it with a belt sander with a 40 grit paper just to take the gloss off could also be a good idea.

Little holes could be filled with something like the acrylic render from bunnies.

In fact I'd be half tempted to bag the whole wall just to give it a bit of texture, otherwise any irregularities in the wall stand out like the proverbial.

[Bleedin Thumb]

Sorry MS I dont think citric acid will do much for etching concrete. Hydrochloric will do the job. Also find it hard to imagine using a belt sander on concrete.

Gsouth, read the instructions on the paint tin re: prep and suitability of the paint.

filling the hole can be tricky because you dont want the filler to have a different texture or absorbion properties to the rest of the wall. I would be tempted to use a sand/cement mix about 3:1.

MS's suggestion of perhaps bagging the wall first is very good if you can see the form board joints etc. Mind you if you were to bag it then you can use oxide in the mix so you wouldn't have to paint or plugging up holes.

[Master Splinter]

Ye of little faith in modern abrasives! I've happily belt sanded ceramic tiles, porcelain tiles and concrete. Yea, I wouldnt want to do huge areas with it, but thats mostly because waving a belt sander up and down a wall is hell on the arms after a while.