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Re: hollow red clay block

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I just went through this exercise reviewing a building built in 3 stages: i) over 100 years old built of multi-wythe brick, ii) less than 100 years, probably 60-80 years old in clay tile units, iii) last about 50 years old, built of concrete block. The whole structure has not been maintained and is suffering from varying degrees of deterioration. Part i is probably in the best condition despite cracks, Part ii is in the worst condition from the point of view of the wall units spalling, part iii has actually suffered the most damage due to cracking due to poor workmanship, failure of portions of the roof and mis-use and lack of maintenance. I contacted the Canadian Masonry Design Centre, a local consulting engineer expert in masonry and researched two books: one by Christine Beall and the other by Dr R Drysdale et al. There is not a lot out there in Can or USA on clay units and reportedly manufacture of them has dwindled to about one plant in Can and about three in US. They are still being used a lot in Europe (my own eye-witness account) so you can try there. The problems with them is that they are very subject to capillary action so that they are very susceptible to freeze-thaw action, which I can verify as my building had one wall with a canopy over it for an unloading dock- that wall was in much better condition that the other walls with no overhang. Concrete block on the other hand is much more porous so it absorbs water but also dries out much more easily and is stronger. The clay units apparently are stronger in compression but are much weaker in tension and are brittle. This probably explains why they have lost favour even in milder climates here in North America. I hope this helps, as you stated there is not a lot out there, and some of this is anecdotal.

Jim Wilson wrote:
I'm searching for info on old hollow red clay block in an existing building. I can't find anything useful through Google or at NCMA or BIA. Does anyone have any leads on this stuff? All I want to do is to have something relatively conclusive to tell an owner and an architect that we can't add any load to an existing block wall. Jim Wilson, PE
Stroudsburg, PA

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