Clay bricks

[ajk1]

For normal 4" wide clay bricks used a sface brick on exterior building walls, is the composition of the brick relatively constant throughout, or is the portion closest to the face of the brick more dense and impermeable than the portion near the centre of the brick, given that the face of the brick is perhaps more highly heated when it is fired then the interior of the brick. Specifically, is the permeability relatively constant throughout, or is the portion near the surface significantly more impermeable?

 

[dik]

Cryptoflorescence can occur when soluble salts from within the brick are carried by moisture to the underside of the fireskin and accumulate and form crystals that can have an expansive effect and can cause the 'face' to spall.

a2mfk: It is common for sealers to be applied several decades after original construction. You are correct that they can make problems worse and the proper sealer has to be selected. One of the main problems with early sealers was the discolouration of the surface.

A big problem with early renovation work was the treatment of soiled and discoloured brick. It was common practice to lightly sandblast the surface. With older bricks, this removed the fireskin and left the softer brick body exposed which hastened deterioration. Hope9010: there are numerous examples of this early restoration in Toronto.

Dik

 

[ajk1]

Hi dik;

Yes you are absolutley right about many examples in Toronto of damage done to brick by inappropriate restoration methods. I am very much aware of the damage done in early restoration in Toronto, where agressive cleaning methods including sandblasting destroyed the brick. I have worked on heritage restoration of such structures. In one case of a building constructed in 1890, we designed a rebuild of the exterior walls with brick salvaged from the interior walls (the interior was gutted to make it part of a new condo tower, but the exterior walls were decalred heritage by the City). However in my current case under discussion there was no cleaning of the walls ever done (they were built in 1966).

Thanks for the description of cryptoflorescence. Is this a recognized engineering term? If so, can you refer me to any publication that defines or describes this, so that I can have a source in case I ever use the term?

As for sealers on brick, in 1997 I discussed this with the masonry expert (Paul Maurenbrecher, since retired) at the National Research Council of Canada and he was against using sealers on either new or old brick. Perhaps some engineers may suggest a breathable sealer, but I would be skeptical, since there are no recognized standards defining "breathable".

Thanks again for your help. Much appreciated. (by the way, ajk1 and Hope9010 are both me.)

 

[ajk1]

dik...one other question: how do I tell if the spalling is due to cryptoflorescence?

Also, is there any test for determining if the brick is subject o cryptoflorescence?

 

[Ingenuity]

"Thanks for the description of cryptoflorescence. Is this a recognized engineering term? If so, can you refer me to any publication that defines or describes this, so that I can have a source in case I ever use the term?"

"Crypto" is basically hidden efflorescence, as generally described in this document pertaining to concrete. Hope it helps, somewhat. [ignore][/ignore]

http://www.ccanz.org.nz/images/document/IB44.pdf

 

[ajk1]

Ingenuity - thanks for this reference. It is very useful.

I don't believe that there are any signs of efflorescence on the exterior of the brick in any walls of the building. Would you expect to also see some exterior efflorescence, if there were a cryptoefflorescence problem?

 

[a2mfk]

Efflorescence is common in my experience in Florida along cracks in CMU, concrete, and even tile grout. All it means is dissolved salts in the material have been brought to the surface by moisture from within the material. I do not know of it being a cause of anything like spalling, it is merely an aesthetic issue, though I suppose it may be indicative of moisture movements and contaminants within the material.

ajk- Surface sealers with brick and CMU- I have never heard them highly recommended by anyone other than surface sealant companies. It would seem they are too prone to failure, would have to be reapplied often, and in brick in a freeze/thaw climate may actually cause more problems.

 

[dik]

There are good sealers and they do work. A problem with historic brick is that some brick surfaces are close to grade and they get wetted... these are subject to freeze-thaw deterioration and there are numerous examples of this in Toronto. Most sealers require re-application after a few years, and the better ones do not discolour.

Dik

 

[ajk1]

Some have asked if I can post a picture of the spalled brick, and I finally have one. Please see the attached picture. Note that the ceiling inside is at the same elevation as the head of the punched windows.Please let me know if you have any other comments.