Last Autumn there was a mention in a thread about 1950's brickwork being porous. About that time I had to drill a couple of holes in the gable wall - it faces SW - and the debris was like a crumbly paste rather than dust for about 15 - 20mm in. The bricks are heavily patterned - a vertical herringbone groove - which I think are Rustic(?) from c. 1950.
Is it worth treating the wall and, if so, what sort of gunk to put on it?
AIUI, there's 2 families of waterproofing treatments - there's the non- breathable silicon-based ones (Thompsons WaterSeal being the best known
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- and there's the much more expensive but water-vapour-permeable silane/siloxane based ones (which are less well known, but Liquid Plastics K501 is an example
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you've already found out, there's also a division between water- based and solvent-based versions of silicone treatment. AIUI solvent- based are the older generation products (I believe silane/siloxane treatments were also solvent based at one time, but have already been discontinued).
I've treated a large Victorian building built from very soft red bricks with K501, because the brickfaces were spalling from frost damage. This was 2 years ago - and the last 2 winters have shown the spalling has been completely halted.
With my building it was wise to bear the considerable extra cost of a breathable treatment, as it's unlikely that all points of water (rain) penetration could be sealed - and the solution relies on controlling the level of moisture in the brickfaces (by permitting it to pass out again as water vapour) down to the point that spalling is stopped.
I can't tell you what will be right for your building, or even if it is necessary, but bear in mind these treatments are non-reversible - so do you homework before plunging in.
Can you post a close-up pic of the damage, and another showing the extent of the problem?
More or less all above ground wall bricks are porous. What you propose is a classic mistake. Read SPAB's guidance on such things if you're still tempted.
I've read the SPAB advice (and been on a couple of of their very good training courses) - but I disagree with their purist standpoint on masonry treatments.
They would have you cut out and replace every spalled brick. In my case that would have been several thousand bricks. A cure is no cure - if it bankrupts the customer.
I asked a lot of different people, got a lot of different answers - but the best advice I got was "it depends", and that for my situation silane/siloxane was the solution *most likely* to make a sane compromise.
So far - results have borne this out.
If you live in a scheduled ancient monument you'll probably have to do it the hard way, similarly if the problem is small (or your wallet very large) it's probably no hardship to go for the rolls-royce solution. For the rest of us, there's compromise.
its simply based on properly understanding whats known on the subject
Saying the ideal is to replace a spalled brick, but that replacing 100 isnt practical is just stating the obvious. I dont think claiming spab wants you to replace 1000s of bricks on a terraced house is very credible. Its also got nothing to do with the question in hand.
Thanks for this info - wondered about the relative merits of solvent/non.
No spalling of bricks at all; some shallow, inadequate, repointing coming off on the gable triangle but the rest is OK.
Apart from the minor bit mentioned above, there's none to see. It's only the obvious slight dampness to 20mm or so that worried me. It also must remove a lot of heat from the wall in cold weather when there's a goodly wind.
>>> although the solvent-based one looks a bit nasty!
I'd rather avoid coating the wall. I prefer something that soaks in and that can easily be renewed by simply spraying on another dollop (I've never like paint on exterior wood and use other treatments where possible).
Well, there's no spalling and post-war ex-council house isn't historic!
SPAB says that one cause is frost on damp bricks; I can't stop frost or rain, so doing nothing might eventually lead to spalling. A poromeric coating would shift the equilibrium by excluding water and allowing vapour to pass through. With heating inside and heat from the sun outside this should work.
>>>>> although the solvent-based one looks a bit nasty!
But isn't the K501 a silane/siloxane product? AIUI this is not a coating, but a series of silicone-like particles that can move about within the brickwork. They simply occupy space that would otherwise contain water.
Dear Peter Brick is supposed to be porous. If it is not causing any problem do not treat it. If, however, it is accumulating water to the extent that you are getting frost damage or loosing heat badly then I see no reason why you cannot treat the brick. All treatment ideally should be reversible in accordance with good SPAB practice and the idea of putting on a layer of silicone is not a good one. If , however, you can infuse the silane based products mentioned but others in this thread it is naturally removed over a period of decades and as far as we know can do no harm. BRE did work with silanes some 30 plus years ago on statues that were degrading (I think limestone but cant remember) I know the firm Safeguard, having bought from them for 35 years or more and they are reputable and have their own research PhD a chap called Eric ? with whom I have spoken in the past and you could do far worse than them
Thats right. I have rendered walls and some north facing bits were spalling, but not others. I traced it to rain bouncing off the window drip boards and making the wall above slightly damp. Those areas ALONE have been treated and repainted, and the damage has stopped.
You need to get the problem udnerstood before looking at solutions. And in your case there is no problem. Pretty much all bricks are porous and get wet and freeze, this doesnt cause spalling. Spalling only happens if the bricks are so saturated with water that the only way for the freezing water to expand is by pushing the brick face off.
No problem, nothing to solve. This is well demonstrated by the fact that the brickwok has been coping just fine for 50 years.
Siloxane coatings, if repeated, clog the evaporations paths, then damage can result.
SPAB is criticised here by those that havent read what they say & taken the time to understand it. However they do know their stuff on this topic. It turns out the way old houses handle dampness is a fair bit different to what people thought a couple of decades ago, and to some degree some of the same principles apply to more modern builds too.
D'you know, I was thinking about that yesterday (might have been due to the Liquid Plastics treatment being several hundred quid): if the bricks themselves aren't spalling then there can't be that much water in them and, as you say, if they've been OK for 60 years...
So, thanks Tabby, Chris and TNP fo 'confirmation' and thanks to others for the v. useful information and links.
I'll see what happens this Winter then, if I do anything at all, a treatment will last 10 years+ and probably won't be necessary at all.
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