how to remove paint from brickwork?

[Fred]

Hi,

Following advice from this group, I am now staring to paint the inside of my single skin brick garage with bitumen paint to waterproof it. But... one wall is already covered in paint. I checked with the manufacturer of the bitumen paint and they advised removing the existing paint first. I had hoped I might be able to paint over it ;(

I don't know whether this is masonry paint or emulsion or what because it was there when we moved in.

I have tried a flap disc in an angle grinder and it does remove most of the paint but judging from the dust, it is also removing some of the brick too. I know some people are quick to warn about the dangers of angle grinders; are flap discs any safer? I presume the danger is from discs shattering and high speed fragments flying towards the operator?

I haven't used a wire brush for the same reason; I thought it would scratch the bricks.

I tried a paint stripper, all I had at home was "yellow" nitromors. It certainly took the top layer of paint off but the bricks are still white rather than red, and I have now run out.

So what do you suggest I buy and try next?

A quick google suggested paint stripper but also sand blasting and pressure washing. The problem would be that I have only emptied half the garage and moved the rest into the middle, so to pressure wash I would need to empty it completely. There was a suggestion that pressure washing would damage the mortar though and this is not good mortar to begin with. It is quite sandy and I have tried to repoint where it has crumbled already.

I see you can get sand blaster attachments for pressure washers. Are they any good? But aren't we back to where we began that any abrasive will scratch the brick?

TIA

[Jim K]

but if it's inside your garage AND you are going to slap bitumen paint all over it - why does it matter if it's scratched/abraded? for the bitumen paint plus whatever else, you *need* a good key (as, presumably, the manufacturer you spoke to was intimating)?

Jim K

[stuart noble]

You probably can, but no manufacturer is going to tell you that. Suck it and see on a small area

[Fred]

Hi. I have had since another email from a different manufacturer of bitumen paint; this manufacturer has said you can over paint, so now I don't know who to believe! I think your suggestion of trying a small area is the only way to see.

In reply to Jim, since the wall will be covered I suppose it won't matter about scratching the bricks with an abrasive.It's just it makes a lot of mess and the garage is not empty. if it were empty, then that would be a different matter.

Perhaps I'll try to skim the top layers of with a quick sand and over paint what's left. What's best to us: a flap disc, a wire brush, I wonder whether a sander would be adequate?

Thanks again.

[Spamlet]

Can't see why you can't over paint: it's only a garage after all. On the other hand, as it is a garage, if you did want to get the paint off, it is one place where you could slap on caustic soda or caustic soda based strippers, and hose down. Getting paint off masonry is never easy - but easier outdoors than in! (People who put gloss paint straight on to plaster are swine!)

S

[The Medway Handyman]

They are spot cleaning tools. Doing an entire wall would take ages & fill the garage with damp sand :-)

[stuart noble]

If the paint is masonry, or anything water based, caustic won't touch it, but might well soak into the brickwork and create a new headache.

If the surface is clean and reasonably sound, I'd be inclined to leave well alone. Maybe a quick going over with a wire brush to remove loose stuff, but abrasion probably isn't going to significantly improve the chances of the bitumen bonding to it. The danger is always that it will pull the old paint off, but that is usually obvious during the application

[Jim K]

dustsheets?

for just this purpose I've used one of these in an angle grinder

in 230mm grinder? but I've used em fine in a 4" angle grinder)

- let it have a go all over

- any obviously loose stuff will fly off no bother with little pressure from you

- if bits stay put leave em on and paint over

- steady away.....

Jim K

[Phil L]

I can't understand why you are concerned about scratching the bricks when you intend to slop bitumen all over them.

[Jim K]

echo

[Fred]

I was going to remove all flaky patches anyway.

I think this is what the one manufacturer was afraid of.

Thanks.

[Fred]

I might have tried on the external side of the wall but not the inside. I just wondered what they were like generally?

[Tabby]

The only downside of not stripping it first is that the underlying paint might peel off one day. Since its not going to come off easily I'd almost certainly overpaint.

NT

[Fred]

How strange. They sell this 75mm one for 4" grinders:

they sell the one you quoted, which is also 75mm, but state it must be used in a big grinder. The wires in yours seem much more substantial, do they think a small grinder would not have the power to spin it? A big grinder will be heavy though.

Re. yours and Phil's question about why I was worried about grinding, I did a google and found a number of postings on web sites and forums advising against scratching bricks because it damaged the glaze. I read these out of context: these were posts about removing paint from external walls where the final appearance would have been important. I suppose I was also unsure whether this was a purely cosmetic issue. You are quite right that these walls will be covered and so I can proceed this way.

I haven't got a wire cup (yet) but I do have a flap disc. I had another go at it this evening and am making progress.

Thanks again.

[Spamlet]

Er no: we covered all this quite recently in a long thread on paint stripping, and the main problem with caustic is how to keep it in contact with the paint for long enough. 'High tech' strippers have thickeners and form a protective skin to keep the caustic in contact with the paint for periods up to a week. Then paint and stripper can often be peeled off in one sheet leaving clean masonry beneath.

There may be some caustic sensitive materials in modern walls for all I know, but with traditional materials, acids are the problem: not alkalis. Sodium hydroxide simply turns into sodium carbonate and washes out, on exposure to air.

If the paint is water based and still stuck, the OP does not have a damp problem in his garage after all.

S

[Spamlet]

> yet they sell the one you quoted, which is also 75mm, but state it

In my experience, a wire cup will just cover your wall with grey metal deposits that will look horrible and then go rusty. The 'brush' should match the material to be brushed as much as poss - steel for steel, brass for brass etc. Your flapwheel is probably nearer the mark, but really, as others have said, you are just making unnecessary work for yourself. Personally I wouldn't even bother with the bitumen. Limewash will be brighter, and can be topped up as often as you like.

S

[stuart noble]

So the blurb says but, in practice, there is no way to keep caustic on a vertical surface, whatever thickener is used. If it dissolves the first layer of paint, it then slides downwards. The real point here is that caustic only works on oil based paints, so there is no point using it on the typical masonry paint or emulsion.

But both are penetrative and hygroscopic. Not something I'd want in my bricks

[Fred]

I wasn't making work for myself, I was hoping to over paint, it was the manufacturer that wanted to make more work for me! ;)

I did remove some more with the flap disc last night, until that wore out. I did find that it wasn't making as much dust, so perhaps I was learning to hold it better or apply the right amount of pressure the more I used it? It seems I could have saved myself the work but as it's 3/4 done, I may as well finish the last bit. Thanks.

[Fred]

I don't know what the paint is but I guess it is either masonry or emulsion, so I think both are waster based aren't they? I don't think I ever had a big damp problem: the dpm is at ground level so a couple of bricks on the first course have peeling paint from where those bricks must have got wet in the past. Perhaps it's not just the sanding where I am making work for myself; perhaps I shouldn't be painting too! I am hoping to line the walls next with celotex and the advice here was to coat the walls with the bitumen first. If it turns out to have been unnecessary at least I haven't wasted too much money, I guess the paint is only about £30 to do the whole garage. Thanks.

[Dave Liquorice]

Seems a bit odd to have a damp proof coating on the coldside of the insulation. With the celotex aren't you going to end up with a void with damp proof on both sides thus capturing any damp...

Warm air holds more moisture than cold and the inside of the garage will, generally, be warmer than outside and this warm relatively moist air will make it's way into the void(*) and if not actually condense raise the RH in there.

(*) Unless you foil tape all the joins etc as one would normally do with celotex etc.