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Charles218 08-18-2012 02:09 PM

Seal, Stain, or Leave it Alone?
Our brick chimney was just repaired about two weeks ago, the brick facings were loose and falling off. I understand that this is caused by moisture getting trapped in the brick. The brick that was replaced, about 12 courses, was painted and we now need to paint or stain the new brick to match the old. The contractor has told us that we can either stain the brick, or seal it and then paint it. I'm confused about the best way to proceed. Do I stain it and be done, or seal it and then paint? Either way, which stain or paint should I use?


tony.g 08-18-2012 04:22 PM

Quite possibly the reason your chimney bricks were spalling was that they were painted in the first place. Paint or any sealer can trap moisture within the brick and when the moisture turns to ice in winter, it expands and shales the brick face off.
Being very exposed, and subject to water ingress from above, painted chimneys are particularly prone to this problem. Best advice is not to paint; if you have to for cosmetic reasons, you may have to be prepared for further trouble in the future.

Charles218 08-18-2012 04:29 PM


Thanks for your response!

Unfortunately, the house was painted when we purchased it fifteen years ago, the brick have been spalling little by little since we moved in. The new bricks that were just installed are a totally different color then everything else so we do need to match the colors. With that in mind, which is the less of two evils, paint or stain?


tony.g 08-18-2012 04:59 PM

Whatever you use (paint or stain) should be breathable (aka microporous).
This allows moisture vapour to escape rather than remain trapped in.The vast majority of paints/stains are not and most people who slap this on to their brickwork are not aware of the potential problems.

Have a read of this;

Its a UK firm so you won't have their stuff but it explains the principle well. If you tell a retailer that you need a breathable product, they will know what you mean. Whether it will match your existing colour exactly......?

Charles218 08-18-2012 08:33 PM

The article that you referred to is quite informative, thanks. It mentions "Sd" values, is that universal? Will I find it, or something similar, here in the US? In the end, I just want to make sure that I use a product, be it stain or paint, that will give the best protection possible.


tony.g 08-19-2012 10:58 AM

The 'Sd' of a paint is just a measure of its vapour permeability when compared with an equivalent thickness of air. For example,the old traditional limewash has an Sd value of 0.02, which means it will transmit the same amount of vapour that a 0.02m (ie 2cm) thickness of air will.
If a paint has an Sd value of, say, 0.4, it will only transmit as much vapour as 0.4m (40cm) of air, so that would be far less permeable.
Obviously these are metric measures and might not be applicable in the US, though there will be an equivalent system of quantifying the vapour permeability of a paint.
It's probably a case of explaining to a retailer that you need a permeable paint and asking how manufactures define this so you can compare products.(You need a proper paint retailer - don't waste time asking at any of the big DIY stores!).

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