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Question DetailsAsked on 12/14/2016

Can I use roof tar or silicone roof sealant at temperatures below 0?

I need to install a stove pipe for a customer and I need a roof sealant that will adhere to asphalt shingles in temperatures below 0. Does anyone have a recommendation? Thanks in advance for your help.

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2 Answers


I know of only one adhesive (2-component) workable at those temps without preheating - and it costs around $300 per tube and has very short shelf life - used by the military and NASA for emergency repairs in arctic or space conditions. Plus, you really want to heat the surfaces to which it is being applied anyway to above freezing to thaw out any frost and dry out the surface so it will stick properly.

Your solution - long extension cord and a hot air gun on low or more likely medium setting (not over about 150 degrees max), heating about a 1 foot area around the location being sealed for usually 3-5 minutes, to about 110-130 degrees shingle UNDERSIDE temp. Pay attention to instructions on the asphaltic adhesive about application temps - usually down to about 20-40 degrees min but try to at least stay above 40, and pay attention to flammability of the sealant fumes. (Some people swear by Geocell 4500 roof bonding sealant - personally I do not like the way it works - too much like silicone, but many do like it). You do not want to heat the adhesive as it is applied because it will run and can catch fire - preheat the surfaces it is being applied to bring the general area up to proper temp or above, and keep the caulk tube warm (indoors until needed, then when carrying outside and until actually ready to apply keep under jacket (see, tell your wife beer bellies do have a legitimate use), in plastic bag if opened or already loaded in caulk gun). Oh - and hint - laying it on the defroster in your truck to get it nice and toasty warm works TERRIFIC - except the sealant expanding and oozing out of the tube down behind the dash not so good, though it does give the truck a permanent "workman" odor. Heating that way by placing in a few wraps of aluminum foil or in a large disposable aluminum tray does work though, getting it to around 100-120 degrees typically in a half hour or so of exposure on full defroster heat and fan.

My favorite brand - ATCO (American Tar Company - company now called Field ATCO) A300 Asphaltic Roof Sealant in tubes (both sizes) or cans - or ATCO Fibered Asphaltic Roof Coating in quart and larger cans. (Fibered if it is in a location exposed to weather - that is a roof patching compound workable to about freezing and made for permanent exposure and wet application). My experience - karnak #229 rubberized roof sealant also fairly good, DAP NOT good workability at cold temps, and silicones useless at cold temps (and pretty much in general on roofs, in my opinion). Problem with silicones and latex sealants is they not only have to be applied at temps above 40-50, but have to be kept there till cured - for days. Asphaltic sealants only have to be kept warm for workabilitiy and adhesion, but can freeze immediately after application is completed. They will not fully cure till they see some duration of warm weather, but will still be waterproof even if not cured.

One recommendation if applying in cold weather though - if avoidable (like not patching an actual leak point in a rusty flashing, for instance), do NOT apply to areas expected to be exposed to water before spring is over, because runoff running over uncured sealant can bleed a black trail of discoloration over the roof below that point - not very noticeable on dark shingles, but really noticeable on light colored ones. So if you have to "caulk" flashing, do it in concealed under the edge of the flashing, not right at the edge. That is the right way to do it anyway, so it is not exposed to sunlight, because the ultraviolet in the sunlight weathers and cracks it, shortening its life.

Actually, since you are talking stove pipe isntallation - while I like a bead of asphaltic sealant under the outer edge of the concealed part of the flashing to prevent lateral water migration on top of the flashing that lies under shingles (though a rolled seam edge on both sides can do that too, which I prefer when putting on new flashing and boots) to prevent it getting in under the shingles, a normal boot-type roof jack does not need ANY sealant. Youtube video link below shows how a roof jack fits up under a couple of rows of shingles uphill of the roof penetration (have to pull and replace some nails or staples to slip it in under the shingles, and careful not to tear the water membrane) and it overlies the next couple of rows downslope. No sealant necessary (though a lot of installers, as shown in the video, put a protector "berm" bead to prevent lateral water movement toward the penetration point), water just runs off the uphill shingles and off the raised portion of the boot and jack itself down onto the base flashing pan and then off that onto the top of the shingles beside and downslope of the lower half of the jack, which is lying on toip of the shingles at that point. This tuck-under and overlay combination colledts any water getting ini at the uphill side of the jack and aroundthe jack and redirects it back on top of the shingles to run off - same philosophy, but with one piece, as step flashing along a chimney or wall.

Where the pipe/duct penetrates the roofing and waterproof membrane I prefer to put a secondary seal in locales prone to ice damming or severe storm blowunder - a piece of ice and water shield with duct hole cut in it and pressed down around and left domed up around the ducting like a boot, and adhered to the water barrier membrane/tarpaper if not a hot exhaust duct; or a low-profile sheet metal bootless roof jack with legal duct clearance for the type of ducting, again sealed around its perimeter flashing with an overlayer of ice and water shield around and domed up on it so any water coming in under the shingles cannot flow down through the roof penetration. Takes an extra 5 minutes or so to do but that secondary protection of the penetration hole makes a big different - both in the event of water entering from below the boot, and also if leakage runs down the water barrier from further up the roof. For ducts/pipes that do not require an airgap around them, there are also prefabricated low flexible rubber boots you press down around the duct or pipe and seal and nail/screw down to the sheathing to provide a watertight seal around it at the water barrier - look very similar to exterior vent boots but lower profile and not designed to be exposed to weathering, but more flexible and easy to put on before the jack goes in.

Answered 3 years ago by LCD



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