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Bayman 09-02-2008 12:26 AM

How to cut styrofoam insulation
I'm going to do the siding on my house as due to the boom in our province there aren't any available carpenters in my small town......

I will be applying styrofoam insulation on the outside, but there are a couple of questions I have on this:

1. What is the best way to cut the insulation
2. What blade should I use
3. Should the blade be reversed


Termite 09-02-2008 12:34 AM

Use a utility knife. Score and snap it like sheetrock. Nail it up with cap nails.

Just checking...
You're overlaying foam over some sort of structural sheathing such as plywood, right? Foam shouldn't be applied directly to the studs without some sort of structural substrate.

Bayman 09-02-2008 11:36 AM

I am using styrofoam over stucco siding......first I am using furring strips at 16" on center and then installing styrofoam between the furring strips......the siding will be nailed to the furring strips.....

Is it critcal that the furring strips be nailed/screwed to the 2x4 behind the stucco/1x6 boarding(note: this is a 1950's home and has full 1" lumber), or would just nailing the furring strips to the 1" lumber be sufficient...

Termite 09-02-2008 04:15 PM

I wouldn't say it is critical to hit every stud, but you should make every effort to hit the studs where you can.

Bayman 09-02-2008 05:27 PM

I am using the Zircom stud finder and it's very difficult to find any studs with it.....I have it set to deep's probably due to the stucco(concrete)......

Wildie 09-02-2008 07:56 PM


Originally Posted by Bayman (Post 154348)
I am using the Zircom stud finder and it's very difficult to find any studs with it.....I have it set to deep's probably due to the stucco(concrete)......

A metal screen is used behind the stucco, and this will kill any signal from inside.
I would recommend ripping the stucco off.
Stryrofoam usually comes in even multiple widths. eg. 24"
Perhaps its available in 16" widths, but I personally have never encountered this..
Once I insulated a house with tongue and groove siding. I placed the strips wide enough to allow 24" sheets to be installed between. Then nailed aluminum siding to the furring strips.
About cutting! I found that an electric carving knife works well. Only thing is that it won't be much good for carving meat, when you are finished.

Bayman 09-02-2008 09:10 PM

I have the styrofoam sheets they are 4x8

I was in Walmart today, had I known about the electric carving knife I would have bought one.......darn will have to travel the 2 hr ride again.....we live a long ways from the city.....

Maintenance 6 09-03-2008 09:36 AM

What I've done is to rip the styrofoam on a table saw. If you are using 1x2 furring lath on 16" centers, cut your styrofoam panels to 14-1/2". Install a lath on a stud, then install a panel. Repeat the process. It goes quicker than trying to cut panels in between after the lath is up, plus you can get it tighter. A little silicone caulk will hold the panel in place until you get the next lath in place.

Bayman 09-03-2008 03:03 PM

Maintenance 6, with regards to cutting on a tablesaw, do you recommend any particular blade and does the blade need to be put on backwards.....

shumakerscott 09-04-2008 12:18 AM

You want the thinest blade for less mess. From my experience turning the blade is for cutting metal. If you have a dust collector, the type with the blow up bag, I would use it. I was considering using my bandsaw because it has a very thin kerf. They also sell hot wire cutters. If you could find the correct type of wire then make one yourself. It would be mess free because it melts the styrofoam.

Maintenance 6 09-04-2008 07:45 AM

You don't have to be concerned about finish. I use whatever blade happens to be in the saw. It doesn't make a difference. The stuff cuts like butter anyway. Kerf width won't be a concern either. You're going to end up with a narrow strip of off-fall anyway that you use to fill in around windows, voids, etc. You'll certainly make dust though, so a smaller kerf would mean a little less dirt.

Bayman 09-04-2008 10:14 PM

Thanks for all your input guys, it is much appreciated......

wizodd 09-15-2008 07:25 PM


Originally Posted by Wildie (Post 154407)
Perhaps its available in 16" widths, but I personally have never encountered this..

4'x8' sheets of pre-scribed foam are available with scores every 16" and the middle section is scribed at the middle (so you can get 48", 24". 16" and 8" strips.)

Hot wire is the best, and least messy, other than that, slow feed speed, small teeth, and narrow kerf. Definitely use dust-collector & dust mask!

Bayman 09-15-2008 11:58 PM

Guys, I tried out the various methods suggested here and found that the best for me was to score the styrofoam with a utility knife and snap was the fastest as well...

Bayman 09-16-2008 12:05 AM

Oh, I have another question with regards to nailing the furring strips to the stated earlier I am attaching the furring strips over a stuccoed house.....

I have a Bostich framing nailer and a small compressor that goes to around when I tried to attached the fulling strips(1 3/4 x 1 1/2) with the Nailer the nails went through the strip but not through the stucco and into the 2 x4, instead they bent up......

Any suggestions how I can solve this problem.......

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