When Chris Ellis of Brewster, Mass., was looking for the right tool to cut rigid-foam insulation, he tried a utility knife, a kitchen knife, and a saw. None of those options worked especially well. So Chris created something that works beautifully. As Chuck Miller demonstrates in this video tip, a 2-in. putty knife with a sharpened blade cuts through the foam like butter.
In this FHB Podcast segment, the crew offers expert advice on insulating an old home and finding the right contractor to do the job.
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After watching this vid a little while ago I used the sharpened putty knife to do my basement in November going through a few dozen 2" sheets of extruded foam and the approach works very well. I'd cut on the concrete floor using a thin piece of plywood as the straight edge. I was surprised to find such a clear "grain" in the foam; it can be sliced up very easily length-wise but across the foam it's always trickier.
Anyway, the sharper the knife the better. I used a cheap harbor freight cutoff wheel tool to grind down one edge into a pretty sharp blade. Also, to avoid ripping the top when cutting across, score a thin trench first, then deeper on each pass.
I cut several sheets with a circular saw before this and the sharp putty knife is cleaner (no dust), quieter, and much faster, not to mention more accurate, too. I cannot imagine a better way to do it, thanks!