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We are laying a concrete floor inside a room in an old stone building. Do we need to leave an expansion gap around the edge? The room is open at the front so we are not insulating or anything.

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Concrete has about the same expansion rate due to temperature as steel [this is why reinforced concrete does not break apart from thermal stress]. A stone walls are likely have another coefficient of thermal expansion (and perhaps some other constraints).

It is sound practice to isolate slabs from existing structures absent a compelling reason to tie them together. A compelling reason would be structural necessity. Apathy is at the other end of the scale. Other reasons, may fall in between but generally toward the non-compelling end.

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I do not think you need an expansion joint around the edge. The concrete should shrink slightly as it cures, and create it's own expansion gap naturally. However, I am not familiar with your loacale and the environmental conditions and building codes. I would suggest speaking to a professional if you're unsure. A simple phone call to your local building department may answer your question better for your area.

  • If you don't know, giving this sort of answer is worse than saying nothing. Different cements have different shrinking characteristics; some cements are engineered to shrink in one direction but not another, like roadways. – wallyk Nov 13 '14 at 21:03

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