No this is not a plea for help, in fact I have to cut maybe 3 more pieces and I’m DONE cutting it for now. Rather, it’s another alternative way to do it. Someone once suggested a large putty knife (or small wallboard knife, whichever way you want to think of it), which I tried. It made smoother cuts than trying to use a utility knife, which simply does not score deep enough for the 2" thick stuff., but it was still a bit messy and the bottom of the cut got a little ragged as the foam compressed. Today I found the trick (almost but not quite too late). SHARPEN the putty knife: http://www.finehomebuilding.com/how-to/video/cutting-rigid-insulation.aspx
I just picked up the last two sheets I should need, and since I can’t fit an 8’ piece of anything in my car, i cut them in half in the HD parking lot. Before I left I took my big putty knife and fired up my belt sander and put a sharp edge on the side of it - MUCH better. SLices right through, hadrly any tearing. It would be even better if I had a proper sharpening stone to make the edge truly knife sharp, but already it is far superior to using it before doing this. Give it a try.
My search also turned up a specialty tool which is basically a large knife with a saw handle that is curved somewhat like a pirate’s cutlass. The video for it on the product page makes it look liek it works extremely well for all sorts of insualtion - both the typical fiberglas batt and the extruded stuff, but there was no price given. I’m no Norm Abrams to need every specific specialty tool - the putty knife and a few minutes filing a sharp edge on it is no doubt a fraction of the price of this special tool.
I was ready to say I use a hot wire cutter and just aquired a “hot knife” I’m itching to try, but have no need YET.
But in the parking lot of HD, Nope, those wouldn’t work very well without electricity.
All I got out of the link was a chevy truck commercial.
There are small little utility knives that have a blade that is about 4-5 inches long. Designed so that you can break off a piece of blade as the tip gets dull, with a new sharp one and the blade Extended all the way out they should slice right through the rigid foam easily. That is how I cut the foam prior to getting the hot wire cutter.
Odd, link still works fine for me, it goes to the Fine Homebuilding web site with a video at the top showing the use of a sharpened putty knife. There are ads on the sides like here but none of them are for Chevy trucks. Better check for spyware and browser redirects.
I tried the link again. The last time when the chevy truck ad ended, apparently the “tape” stalled and went no further. This time it moved on to the Fine home building segment on cutting rigid foam insulation with the sharpened putty knife, and other segments.
Rand - Thanks for the tip and link. I will give it a try as it looks very simple and effective. I first tried a kitchen knife but the thickness of the blade caused problems. I then used the hot wire cutter from Woodland Scenicswhich I didn’t like too mich as the wire didn’t stay tight causing a less than straight cut. I then tried a foam hot knife which I picked on E-Bay for $14 plus $10 shipping (yes the shipping was almost the cost of the knife). It has worked great and makes cuts up to about 5 inches in depth which is handy when cutting diagonal angles and curves on two inch foam.
I’ve been using the 1/2" and 1" (wide) breakaway utility knives you can get 5 for $1 at the dollar store. You get nice clean cuts and very little debris. You extend them about half-way for 1" foam, all the way out for 2". I also use a couple of filleting knives with 1/2" wide blades for general carving of foam and keep a sharpening stone handy. The real trick is that the blade always has to be razor sharp, you can’t cut much with a dull blade and foam will dull a blade pretty quickly.
That one I tried on my previous layout with exactly those results. Way too messy. With a sharp thin knife or the putty knife I only get a few slivers, often large enough to pick up with my fingers, although I just runt he shop vac after cutting. Of course ont he previous layout I was cutting holes for the Tortoises with a Dremel and a router bit - needless to say, Dremel in one hand, shop vac hose in the other to prevent a pink snow from settling over everything.
I strongly urge you not to use a hot knife. The gas from the burning foam is very hazardous to your health. Styrofoam cuts easily with a serrated knife, hacksaw, floral knife, cookie cutter, or X-actoо knife. It also can be carved in to very life like rocks. An example shown below. The mountains are cut with an extremely sharp fillet knive.
It also does not self-ignite, and is classified non-flammable and non-hazardous.
There was a web site where they did videos of trying to set this stuff on fire by things like droppign a soldering iron on it, and even using a match and candle to directly ignite it. It doesn;t burn. There’s a whole myth out there that this stuff is dangerous, and if you drop a hot tool on it you’ll set it on fire and burn down potentially your entire house. The MSDS and actual testing say otherwise.
Proper ventilation shoudl be used for ANY sort of cutting process regardlessof the material - even particles of material that are not actually poisonous can harm your lungs if breathed in.
Despite the huge weakening of regulatory bodies in the past 20 years, leading to all sorts of dangerous products, I think this insulation was tested when it was invented to avoid just that. Filling walls of homes with very flammable products that produce toxic gases would tick off even the most disinterested consumer/voter. I could be wrong, though.
