Building concrete forms with screws

The v.1 instructions for the various ovens call for nailing together the forms used to build a slab base and the hearth pieces. Newer instructions have shifted to using screws. Should be a one-to-one exchange, right? Three-inch wood screws instead of three-inch nails?

Not so fast. Which screws you purchase is an important decision.

The wood screws you’ll find in the “wire goods” aisle at the big box hardware store look like they should do the job. They’re chrome-plated, they look hefty, and they even have a nice deep Phillips head.

The problem is, they are not meant for being applied using a drill, at least not without pilot holes. They’re serviceable for a few things, but building a concrete form is not one of them. Also, they’re expensive. Johnny Homeowner (that’s me!!) pays through the nose for that pack of 25 wood screws.

What you want are construction screws. These are sold by the pound, just like nails, and the box costs just a couple bucks more than the plastic package in the wire goods section. They are zinc-plated, they’re not meant for structural applications (framing a wall or other load bearing structure), and they will corrode after a while.

For a concrete form, they’re excellent. They have a coarse thread like a drywall screw, only much stronger. (Don’t use drywall screws, by the way; they can shear off before you’re done.) They have a smooth upper shank so that they’ll pull into your second piece of wood without trying to bring the first piece along. The “Type 17” point is a kind of pilot drill that helps you get the screw started easily. They have a Torx star head that won’t strip out, and the box in the photo includes a Torx T-25 bit for your driver.

You’ll find they are a pleasure to use compared to the wire goods version.

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