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On a previous thread regarding concete, there was a question about using pieces of brick to support rebar in a concrete slab. I stated that I had been told to not use it, but I don’t have any definitive answer as to why it is not recommended, I assumed it was because some old brick lacks strength and will crumble easily, but it could be for other reasons. I purused my entire library on working with cement and found the following (my entire library consisting of the two books that I quote from below…)
A 1988 Portland Cement Association publication “Building with Concrete, Brick, and Stone” states:
“In laying out the reinforcement, support the rebar on wire stilts (bar supports) made specifically for the purpose, or on pieces of broken concrete or rocks. Never use clay brick for this purpose.”
A U.S. Department of the Army booklet “Concrete Masonry, and Brickwork”, 1975, states that supporting rebar “can be done by means of built-in concrete blocks, metalic supports, spacer bars, wires or other devices… The use of rocks, wood blocks, or other unapproved objects to support the reinforcing steel is prohibited.” No specific mention of brick bits, but my guess is that it would be in the “unapproved objects” catagory. A couple of paragraphs later in a reference specifically for footings, the manual states: “Concrete bars or clean sound stones may be used in footings to support the steel…”
Thus I guess stones can be used – which means that it can only be done in the Northeast as we don’t have stones out here in the Northwest, only rocks. (No brooks out here either, only creeks – although we do have a Brookstone, which is where I bought my Swiss Army watch…)
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One thing to consider is that the wire rebar "chairs" are very inexpensive. The ones I used recently on a project were somewhere around $.50 a piece and held 2 rods about 8" apart.
*Casey- I tied rebar for many years when I was young and beleive me we put a multitude of things under it. When I was pouring the footing for my own house and used pieces of clay tiles from the roof, the inspector failed my inspection citing that the clay and concrete will not bond together and that the lime in the concrete will accelerate the disintegration of the clay thereby allowing moisture in and rusting the rebar causing early failure. I bought it just so I could pass inspection. Recently I drove over many of the freeway bridges that I know have a multitude of things holding up the rebar in the bottom of the footing and they were still standing, and that's been 30 years.Jim
*Gentlemen. I checked with an academic as well as a hands -on engineer about the warning against usi gn clay brick to support reinforcing. He suspected it might be because of moisture causing a volume change in the clay brick.I quoted Jim Orban's building inspector's reasons for not allowing it. My friend said that could also be. But he really had no answer. His final comment was that he thought he had read that clay brick fragents were being used as aggregate, so the prohibition made no sense. If I learn anything more definite I'll keep you posted. GeneL