Expanding foam sealant

Gaps & Cracks is the can I’d keep on a plumbing truck, and I’ve used it. Great Stuff’s sheet calls it a ready-to-use, minimal-expansion polyurethane foam that fills, seals and insulates gaps up to 1 inch.

The sheet lists where it goes, and pipe penetrations are on the list, along with rim joists, sill plates, outdoor fixtures and attics. It adheres to wood, metal, masonry, glass and most plastics.

It’s tack-free in 10 to 15 minutes and trims in an hour, cures rigid, and can be painted, stained and sanded. Great Stuff says one 12-ounce can equals up to 22 tubes of caulk.

Its code paperwork is the reason it’s my top pick. ICC-ES ESR-1961 lists Gaps & Cracks among the Great Stuff foams evaluated for filling the annular space where pipes and conduits pass through wood fireblocking.

This listing is the Smart Dispenser version. Great Stuff says the dispenser threads onto the can, stays on, and can be reused for up to 30 days, with no drip because the foam stops when you stop.

Where it lost points: a 10- to 15-minute tack-free time scored 8 against Loctite’s 6 to 8, and it cures rigid, which scored 7.

Great Stuff warns that its foams aren’t for filling closed cavities or voids, such as between walls and under tub surrounds, and that cured foam shouldn’t be exposed above 240°F.

Great Stuff gives its tack-free and trim times at 70°F, give or take 5, and says cure depends on temperature, humidity and bead size. It also says the skin of cured foam can discolor in natural light, so paint or coat any foam that shows.

My call: that tub-surround warning is the one plumbers break most. Foam the pipe hole in the plate, not the cavity behind the tub.

Loctite’s Tite Foam is the foam I’d use outside, and I’ve used it. Loctite’s technical data sheet calls it a closed-cell polyurethane foam that expands to fill, seal and insulate gaps and cracks inside or out up to 1 inch.

Loctite names plumbing jobs directly: sealing around wiring and plumbing penetrations, gas line penetrations, outside water faucets, rim joists and crawlspace drafts. It bonds to wood, metal, stone, brick and PVC.

It’s the fastest here: tack-free in 6 to 8 minutes, cuttable in 45 to 55 and cured in about 24 hours at 73°F and 50% humidity. A 12-ounce can runs about 134 feet of ⅜-inch bead, per Loctite.

The cured foam is a flexible solid with more than 25% movement capability and a service range of −40 to 176°F. Loctite says it resists UV better than standard foam, but still recommends painting or coating exposed foam.

Where it lost points: Loctite says it isn’t a fire stopping material and shouldn’t be used where fire stopping is required, which scored 7 on code evaluation, and it expects one-time use, which scored 7.

Read its limits before it goes near pipes. Loctite says not to use it against chimneys, heater vents, steam pipes or surfaces above 187°F, and that it doesn’t bond to polyethylene, PTFE (Teflon), siliconized and some plastic and rubber surfaces.

My reading: PEX is a polyethylene, so foam won’t grip PEX itself. It can still fill the hole around it, but don’t count on it to hold the pipe.

Loctite gives an 18-month shelf life for an unopened can and prints a best-by date on the bottom. The foam is bright white, which shows against dark siding, so plan to paint it.

My call: store the can warm. Loctite wants the can above 41°F for at least 12 hours before cold-weather use.

Pestblock is the foam I’d use where a pest is following a pipe into the house, and I’ve used it. Great Stuff’s overview says it’s made to block insects and pests by sealing the gaps, cracks and holes where they get in, and it contains no pesticides.

Great Stuff lists PVC pipe penetrations, electrical cable lines, water faucet penetrations, attic hatch frames, rim joists and sill plates as where to use it. It names spiders, ants, bees and cockroaches among the pests it blocks.

Like Gaps & Cracks, it fills gaps up to 1 inch, forms an airtight, water-resistant barrier, and is for interior and exterior use. Great Stuff’s sheet says tack-free in 5 to 15 minutes. It’s pale gray, not cream.

It carries the same paperwork: UL Classified, CCMC 13074-L and ICC-ES ESR-1961, which lists Pestblock among the foams evaluated for pipe holes through wood fireblocking.

Where it lost points: a 5- to 15-minute tack-free range scored 8, it cures rigid, which scored 7, and Great Stuff doesn’t give a yield for it, which scored 7.

One listing slip: the Amazon text says tack-free in 20 minutes in one bullet and 10 to 15 minutes in another. I use Great Stuff’s sheet, which says 5 to 15.

The same Smart Dispenser applies: thread it on, leave it attached, and use the can again for up to 30 days, per Great Stuff.

The listing adds that it adheres to wood, metal, masonry, glass and most plastics, and cures rigid for trimming in an hour, then can be trimmed, sanded, stained and painted. Great Stuff says the skin can discolor in natural light, so coat foam that shows outside.

My call: foam alone won’t stop a determined mouse at a big hole. Pack the gap with copper mesh or steel wool first, then foam over it.