Q.: I am a structural engineer in New York. We generally restrict pour size to 60 feet by 60 feet. The contractor is asking for written documentation, such as from ACI, CRSI or a similar agency, to support this limitation. Do you know any reference to this pour size?

A.: We have searched a bit on this and can't come up with any reason for limiting the size of a pour other than the limit on what the contractor has the ability to accomplish. But today, with laser screeds, and so forth, some contractors are placing as much as 100,000 square feet of concrete each day (as a single continuous pour) with the blessings of engineers and specifiers.

We don’t know of any reason for placing 60x60-foot sections. There is nothing in ACI with that kind of language, though sanitary facilities have a spec calling for concrete to have complete joints every 30 feet (with water stops), but that may be a poor guideline too.

You certainly do want to limit the size of the panels (between control joints), based on thickness of the slab and other factors. Panels should generally be much smaller than 60x60 feet.

One rationale for checkerboard pouring in the past was that some shrinkage would occur in the first slabs before the adjoining pad was placed, therefore control joints wouldn't be as wide, but the amount of shrinkage over the short time between pours wouldn't amount to anything worthwhile.

If you are not laser screeding, then wet screeding or setting screed pipes would be the way it is done. We have seen truss screeds used to span 50-foot wide sections, but that is pushing things near their limit—unless flatness isn't an issue.