Removing limewash, sanding brick faces, acid, blast or other means?

[WimWam]

I have a 1910 London house covered side and back with limewash, then masonry paint on top, it was like this when we bought it and have been trying to figure out how to remove it ever since. The masonry paint is fairly loose and peeling in most areas (common for paint over limewash).

Chemical Paint strippers or steam (Doff) will lift the masonry paint without much problem. The question is how to remove the limewash from the bricks. These are London yellow stocks. Acid has been tried with little success but from memory I'm not sure which acid it was.

I've tried sanding the face on a test area (it's a outside cupboard or lean-to that will probably end up internal via an extension in the future). This was done with a speed controlled 7" polisher with a 30 & 60 grit ribbed silicon carbide disc. Inevitably, this takes some of the brick surface with it, leaving the surface looking quite 'open', notably small air pockets in the bricks become visible. I've seen this brick 'look' on many buildings around london which presumably have had a similar treatment either via blasting or sanding. While I've seen it done elsewhere I'm still unsure this is the right approach.

I've read about the TORC wet blasting system as being a possible solution, however when sanding the bricks with a disc, it was apparent that the limewash is harder than the yellow bricks themselves. This makes me think that any kind of blasting would be inappropriate as once it had gone through the limewash in one spot, it would eat into the bricks quicker than it would take off neighbouring limewash?

I've uploaded a photo of the limewashed bricks, and the sample area.

 

[wessex101]

Old powdery limewash should come off with warm soapy water a stiff bristle brush (not wire brush) and a large helping of elbow grease (it is bloody hard work). As you have found to your cost any aggressive mechanical stripping or strong chemical agents will probably just ruin the bricks.

There are specialist firms out their that clean historic buildings but I suspect they will be prohibitively expensive.

 

[WimWam]

With soap and water? Are you sure thay wasn't whitewash, rather than limewash? As I mentioned, the limewash appears to be harder than the bricks.

Professional quotes are around £6k but they basically involve wet grit blasting...

 

[wessex101]

Like I said when it is old and powdery, not as easily as whitewash granted, it takes several attempts and you always seem to keep the slight colour tint in the bricks. The paint in photo 3 does not look like limewash.

 

[WimWam]

Well i'll try that later with warm water, soap and bristles and see what happens.

I'm not sure which photo is photo three (i'm on a mobile) but the white brick closeup shows masonry paint on the right still present, on the left side it's just the limewash.

The photo showing bare bricks on the lower half - the top half has a complete layer of masonry paint present, but underneath that it's limewash.

 

[stuart45]

A well made and applied limewash that is well carbonated is hard to remove, but white vinegar helps to break it down.

 

[Tigercubrider]

Worth asking about soda blasting. It's very gentle yet effective

 

[WimWam]

Right, well... for the record, I tried warm soapy water + stiff brush and didn't really get anywhere. The domestic brick cleaner, annoyingly unspecified concentration of "1-10% Hydrochloric" did kind of get somewhere but fairly ludicrous effort.

Probably the most exciting movies on YouTube

Soapy water

Also brick cleaner (<10% Hydrochloric acid)

 

[wessex101]

The opposite of watching paint dry! Fascinating.

Actually that was quite interesting. If the limewash is that tough it is going to cost a fortune to try and strip it, I think I might be inclined to just apply a new coat of limewash over the top to freshen it up.

 

[StephenStephen]

I've had some success removing lime from brick using 'spirit of salts' which is 32% hydrochloric acid (from a local hardware shop) - you can tell it's working because of the fizzing, though don't breath in the fumes! I'm not sure I'd attempt an area that big though.

 

[WimWam]

The only unexplored options are wet grit blasting, particularly the TORC system, and perhaps some
kind of acid gel or poultice (doesn't appear to exist).

But anyway, is sanding the face of the bricks really that bad?

 

[stuart45]

But anyway, is sanding the face of the bricks really that bad?

Yes, it does irrepairable damge to them as you can see in the photo.
Try using some white vinegar.
Limewash often had various things added such as glue and size which can make removal harder.

 

[WimWam]

Vinegar is incredibly weak compared to hydrochloric brick washes of various strengths. I tried <10% and 18-20% which still took too much effort and knackered the lime mortar at the same time.

Currently exploring acid gels.

 

[Zaceverett]

Did you ever manage to strip the limewash? I have exactly the same problem.

 

[WimWam]

Well, i had one chap turn up while i was out, he used hydrochloric with a Torc machine and got a decent result, HOWEVER they left the wall absolutely reeking of acid - obviously not neutralised at all, and those fumes can easily flow in through airing bricks and corrode metals and fittings. It was also a very expensive quote. The other caveat to that result is that the ‘limewash’ was a bit different in different areas - seemed much tougher higher up the wall. A different chap again with a Torc system could not achieve the same result - with or without acid. Even acid at 36% (you shouldn’t go over 20% for walls). Despite its relatively gentle abrasive nature the Torc had to be ramped up to max to make any headway into the other areas of limewash, which would then rapidly damage the brick with pitting. So we stopped the sample there. There was a suspicion that this limewash may have had something else added, possibly even white cement maybe (guessing). The coating has probably been on there since at least 1959 (at least, the wall has been white that long, perhaps overcoated since then).

Hydrochloric and much elbow grease (or Torc) seems to be the way to do this. It is possible to hire a similar system to the Torc bit you’ll need to do some training and also be able to hire a massive compressor (the kind that attaches to a tow bar, often seen for roadworks etc). I considered that route so i could take it slowly and cautiously in my own time, however the compressor requirement made it unmanageable for me - no tow bar for a start.

How did it end up? I sacked it off, cleaned it ul, repointed entire wall in NHL3.5 and then painted it in white Keim Soldalit mineral paint. It wasn’t what i really wanted but i think what I wanted and what was possible were just not possible.