Flooring and Carpeting/chicago brick sealing mishap
G. Gabe wrote at 2012-07-19 01:27:58
Hello and I am very sorry to hear what's happening to your bricks. I
specialize in importing and the installation of antique chicago brick.
In my years of dealing with this type of brick I have to say that I always
discourage my customers in sealing the brick. Clay bricks are best left
alone and just installed in the manner that best suits you. Efflorescence
is the only condition that you should be concerned about. And even
then this condition is very easely controlled. My advised to you
do not seal Chicago brick.
Joolaroo wrote at 2013-09-24 12:30:40
I've just been reading about this elsewhere. The problem looks like a bad case of efflorescence. That white salt is calcium carbonate. It is created when moisture moves up through the bricks and evaporates. The water carries calcium hydroxide to the surface, which turns to calcium carbonate when meeting carbon dioxide in the air.
It can occur anywhere, any time wet bricks are drying off, though its said to be worse in the first few weeks / months they are first exposed to water and wet/dry cycles, but I suppose some bricks may go on doing it for years.
When it occurs on unsealed bricks, it may be swept off. However, there is a tendency for sealers to trap the white salt beneath them. It cannot pass through to the surface and be removed, and so there's not a lot in the shortterm that can be done about the unsightly white staining, except to strip the sealer to get access to the white salt for removal, then reseal. Efflorescence can reoccur though.
Apparently leaving the bricks for weeks/months to do most of their efflorescing before sealing, is one approach to avoiding it. The other is to use a breathable sealer which will not trap efflorescence if it does occur, so it can be swept away.
Given the fact that you are able to sweep some of it away, it seems at least some of it is able to get through the sealer and be removed. You could wait and see what happens over time, removing as much with a broom as you can that comes through. If there are enough patches that simply will not budge, you may want to get the contractor back to strip it. This would be the time to have a good talk about the type of sealer that is to be reapplied, and timing of reapplication to try to avoid the problem in the future.
There's so many paving sealers out there its terribly confusing, but from what I've read it seems there are two main types - surface sealers and impregnating sealers (and water and solvent based versions of each, as well as matte, semi-gloss and full-gloss finishes, with or without colour enhancing effects). From what I further understand, if you wish to avoid efflorescence you either go for a surface sealer which is breathable as mentioned above (allowing release of the salts), or you go for an impregnating sealer which, because it forms a barrier inside the paver, doesn't allow the white salt to reach the surface where it may be seen. I've checked the prices on these 'better' sealers are pricey.
To be honest, I'm just about tearing my hair out with all there is to learn and consider, the costs of doing it right, and preparing myself for all that can go wrong.