This is what is occurring: Rain gets in behind the fired front through the mortar joints. The expansion of freezing water breaches the top surface of the brick, leaving the inner surface exposed. The interior of these bricks were not fired and are beginning to crumble. With the surfaces opened up to water, and they will act like big sponges. They will eventually crumble completely.
How can these bricks be repaired?
Here's a photo of Gen Obata's porch in TGH that he just emailed for illustration.
3 comments:
Posting for Dave Lewis:
That glazed (white) brick can't really be repaired. It has to be replaced. Of course it's most proper to replace each & every damaged brick in it's entirety. However, if called upon to do it on a more restrictive budget, I might try to get creative and cut a few corners, errr, bricks. I'd cut the replacements in ½ or to 1/3, and after chiseling out part of the old, damaged brick, insert the glazed portion of the brick I'd just cut. The trick is to replace bricks that aren't necessarily still attached to the structural brick behind them, and not have the white glazed veneer of brick all come tumbling down. Thus, the idea of leaving part of each damaged ashlar as support, and minimizing the vibrations associated with chiseling them out.
Now, let's talk about WHY the glazing is damaged...
IMHO, it was caused by a bad choice of mortar mix. I think there was not enough lime in the mix, or they used a mix with a masonry cement that was too hard (type 'S' instead of type 'N'). The mortar MUST be softer than the brick & glazing so the freeze/thaw cycles allow the mortar to give, rather than crushing th e brick or glazing.
Now there is another possibility...
The brick behind the glazing might have been wet when the repointing was done, or thejob delayed too long, thus trapping water in the brick. The result, when frozen, is obvious. This process is as old as the Ozark Mountains, which used to be tall like the rockies. It's something that must be continually taken in to account, and kept up with, or our buildings will be, just as certainly, eroded, and washed to the sea.
Just to comment on the other wonderful examples of brick in the images, they are all "wire cut" bricks; sheets of clay cut into their "brick size" ashlars by a process of forcing a screen of wires thru, like cutting cheese with a wire-type cheese cutter. In their creative zeal, someone thought to mix iron stone (ore) in with the clay. After firing, being used for building, and being exposed to the elements, the iron did what you'd expect - it rusted, rendering the patina that we see today.
The other example, with the white grains in the 'skid marks', is another creative notion with good results. The wire cutting process caught a few of the flecks of minerals and drug them across the surface. I can't, for the life of me think of the name of the mineral, but it's used for the mineral coating on roof shingles, and it's mined right here in Missouri.
Oh, we could go on about the spectacular culture of brick here in St. Louis, but maybe we can save that for another day.
As an owner of a Tower Grove home with similarly crumbling white brick and a restrictive budget, I'm wondering if there's anything else that can be done. The idea of cutting away a portion of each brick makes me nervous, especially when so many of them are crumbling. I'm not a fan of painting brick, but is there something that can be done to cover them - reglazing perhaps? Anything? Are you aware of anyone else in the neighborhood taking the approach Mr. Lewis suggests, or trying anything else? We love our house, but the peeling white bricks are becoming an eyesore!
The person who provided that photo of his crumbling white brick is considering having a mosaic scene placed over it. I can't imagine what kind of sealant could be used.
I did find this page on Google: http://www.google.com/search?hl=en&q=repairing+glazed+bricks&btnG=Google+Search
Also, if you're not on the TGS yahoo group, you're welcome to join:
http://groups.yahoo.com/group/TGSouth/ It's for TGS/H residents only.
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