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Community and Q&A

Saw/equipment to trim foam flush with framing?

frasca | Posted in Green Building Techniques on

I’ve almost talked myself into trying open cell foam in my 2×4 wall cavities and have read this piece: https://www.greenbuildingadvisor.com/article/installing-closed-cell-spray-foam-between-studs-is-a-waste as well as the sister piece in Fine Homebuilding.

I was wondering what gear people have had success with when trimming the foam clush with the face of the studs. I’ve seen videos on YouTube of people using sawzalls with 2′ long flexible ‘butcher knife’ blades, and could rig up something like that, but was wondering if the community had any better ideas.

Many thanks!

Max

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  1. GBA Editor
    Martin Holladay | | #1

    Max,
    Here is information from an article I wrote for the September 2007 issue of Energy Design Update:

    Trimming Spray Foam
    Trimming excess spray foam insulation takes time and wastes foam, so skilled spray foam contractors do their best to avoid overfilling stud bays. More trimming is usually required for open-cell (½ -pound-per-cubic-foot) foams like Icynene than denser closed-cell (2-pound-per-cubic foot) foams like Corbond. There are two reasons why 2-pound foams are rarely trimmed: since they have a higher R-value per inch than softer foams, fewer inches of foam are required; and since dense foam is difficult to trim, installers have a strong incentive not to overfill stud cavities.

    Like A Sawzall
    When ½ -pound foam needs to be trimmed, contractors can use a Sawzall-like tool with a reciprocating blade. One such tool is the air-powered polyurethane saw
    (#PUSAW36) manufactured by Demand Foam Cutting Systems (see Figure 9). The polyurethane saw uses an Ingersoll Rand sander motor; it has a 23-inch blade
    and a blade travel of 1 ¼ inch. The $285 tool requires an air compressor that can deliver 7 cfm at 90 psi.

    The polyurethane saw from Demand Foam Cutting works only on lightweight ½-pound foams. “Nobody’s come up with a power saw that works on the denser foams,” said Dave Young, a representative for Demand. “There are foam rasps you can use, but using a rasp is messy.”

    Neal Ganser is the president of Corbond, a manufacturer of 2-pound foam. Ganser agrees with Young that dense foam is difficult to cut. “Sawing is really not an option,” said Ganser. “As you saw it, the foam tries to re-expand and fill back in.”

    Installers of dense 2-pound foam try very hard not to fill stud cavities completely. “A good sprayer installing closed-cell 2-pound foam shouldn’t have a lot of cleanup,”
    says Ganser. “We particularly discourage sprayers from buying equipment for trimming back 2-pound foam.”

    Steel Curry Combs
    Ganser realizes, of course, that even the most careful installer occasionally needs to trim sprayed foam; for trimming small amounts of foam, hand tools are adequate.

    “The most popular hand trimming device is a curry comb,” said Ganser. Designed for grooming horses, curry combs come in two basic varieties: rubber and steel. Foam installers are looking for the steel curry combs, also known as spiral curry combs.
    A steel curry comb consists of an assembly of concentric toothed steel rings attached to a handle (see Figure 10).

    Ranging in price from $5 to $9, they can be bought in tack stores, ranch stores, or wherever equine products are sold. Decker Manufacturing produces two plain steel
    models and one stainless-steel version (model SS15). When rubbed against cured foam, a steel curry comb abrades the surface (see Figure 11). “One of the good
    things about a curry comb is it leaves slightly larger pieces than other tools, making cleanup easier,” said Ganser.

    Shearing Knives
    Small foam protuberances can be cut with long-bladed shearing knives that are usually used for pruning Christmas trees (see Figure 12). Shearing knives are sold by companies that supply arborists and tree farmers. The best shearing knife on the market is the German-made Brush King knife with a serrated 16-inch blade (about $54); one source of Brush King knives is Oesco in Conway, Massachusetts.

    Powered Foam Planes
    When a spray-foam job requires a contractor to trim a great deal of 2-pound foam, hand tools are not an option. The fastest way to abrade protruding foam is with a powered foam plane. Foam planes are equipped with spinning brushes or blades.
    Two manufacturers of foam planes are All Phase Fabrication and Calman Industries.

    QuickPlane
    All Phase Fabrication manufactures the air-powered QuickPlane, an aluminum-bodied foam plane that comes in two sizes (see Figure 13). The 16-inch model costs $1,937, while the 24-inch model costs $2,125. All Phase recommends using their hardened steel blade for trimming 2-pound foam and their “special purpose brush” for trimming ½-pound foam.

    Operating the QuickPlane requires a robust compressor able to deliver 23 cfm at 90 psi. According to All Phase, using the QuickPlane results in a “high volume of dust particles.”

    Plane Easy
    Calman Industries makes an air-powered foam plane called the Plane Easy (see Figure 14). Like the QuickPlane, the Plane Easy is manufactured in two sizes. The 16-inch model costs $1,200 equipped with a wire brush or $1,635 equipped with carbide
    steel blades; the 24-inch model costs $1,250 equipped with a wire brush or $1,870 equipped with carbide steel blades. The manufacturer recommends using a compressor that can deliver 23 cfm at 125 psi.

    According to Calman representative Kimberly Holt, most residential foam contractors should use the wire brush. “The blades are more aggressive — they can take out an electrical box, so for residential work the brush is better,” said Holt. “On a big commercial project, like a cold storage room, the blades work faster.” Calman Industries recommends their nylon brush for trimming softer ½ -pound foam.

  2. frasca | | #2

    Wonderful. Thanks for sending that Martin!

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