Charlie: Is there any advantage in adding the so-called fiber to the concrete mix of a house slab?
Gordon
Tom: Fiber mesh concrete is used all the time. Would I add it to a slab? If you’re designing it with steel like you’re supposed to, and it’s not designed for the fiber mesh, and you’re using the five-sack or five-and-a-half-sack mix that’s required by the engineer, no. Extra is not better. You’re doing exactly what you need to do. Where the fiber mesh comes in, usually, is sidewalks, flat work, like roads or driveways, where you’re driving. That really works well with that type of concrete because it does tighten the surface up, but as far as a slab, no.
Charlie: All right. Then he says he’s planning to use five-eighths inch thick CDX plywood for the roof decking. Is that good enough or should he go three- quarters?
Tom: Three-quarters is way too heavy. The only time you would use three-quarters … and if you use three-quarters you’d have to redesign your structure to handle it. That means your rafters are going to be designed with a heavy roof load. You would do that if you had a true tile roof, but if you’re using any regular style roof or some of the lightweight lookalikes, like metal, or tile that might have a coating on there, then no. Even half-inch would be fine on sixteen inch centered rafters. If you want to use five-eighths, it’s a little stronger. I actually have that on my house, but don’t go three-quarters, ever.
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