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Re: Fire Damaged Slab on Grade

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Jonathan Smith wrote:


What recommendations do you have for collecting information for a condition
survey of a residential single family dwelling garage slab-on-grade
(presumably a turned down slab at perimeter) that has been subjected to a
fire? I plan to visit the site this weekend. I realize that the extent of
potential damage is a function of the fire duration and burn temperature and
possibly the type of aggregate.

I've had exactly this come up before. I resorted to simple visual examination. My rationale was as follows:

1) The effects of the fire should be visible on the surface since that is the only part directly exposed to the heat.

2) Extreme dessication, material "change of state" or thermal effects ought to be determinable by visual examination, physically abrading the surface, etc.

3) If there is indication of damage in one location from visual examination, one may conclude that it is probably in evidence elsewhere even if it is not readily apparent.

4) In most instances, repair of the slab will be somewhat costly compared to simple replacement, since such repair will likely include crack injection and resurfacing with an appropriate product. Even a cementitious product is rather costly to install compared to the cost of a new slab. Also, since all such repairs must be disclosed, this will in effect devalue the structure as a whole.

I admit the foregoing is on the "conservative" side. We have to call 'em as we see 'em, and unfortunately in our area here, once you start talking about petrographic analysis, etc., the potential client isn't going to want to go there because in their estimation the expense is not worth the effort.

Also, bear in mind that our low costs ("you get what you pay for") for construction here on the Texas Gulf Coast have a bearing on how limited an investigation can be. It doesn't take much for the developer to say "never mind, we'll just rip 'er out and replace 'er."

Bill Polhemus, P.E.
Polhemus Engineering Company

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