What happens when the ambient air temperature drops by an interval of 18°F (10°C)?
Smart guys know that the pot life and cure time of epoxies doubles for temperature drops of this interval. This means that if the data sheet says the gel time is 25 minutes at 73°F, you will have to wait about 100 minutes at 37°F (2 intervals of 18°F drop) to observe the first thickening. Of course, the reverse is that for every interval of 18°F rise in ambient temperature, the gel times (and cure times) of epoxies are halved. Finally, keep in mind that most ambient cure epoxies start to go into hibernation between 35-40°F; that is, the epoxy won't cure at or below this temperature range.
Since not all of you are blessed to work in a warm climate year-round, what can you do to get epoxy to perform when it’s cold?
The first step when cold weather strikes is a little advance planning. The night before the project, bring your epoxy containers into your office (or home base
ment) where the heat stays on. When transporting, leave the containers in the cab (if this can be done safely) rather than in the unheated pickup bed. Another option is to deliver the epoxy the day before to the job site and bring a portable electric baseboard heater to warm a small room or closet. For larger jobs, one of our customers tows a work trailer with baseboard heaters and a generator to maintain his epoxy at a toasty 85°F and he leaves the epoxy trailer at the site. The other benefit of extra warm components is that mixing Parts A and B is easier and faster when the A an B component viscosity is reduced by warm storage conditions. Finally, you can tent almost any substrate (see image above) and add supplemental heat in larger areas using propane, diesel or electric heat sources.
SEE THE LIGHT
Infrared heat lamps are useful to keep small quantities warm and a 40 or 60-watt standard light bulb can be hung inside your epoxy injection pump to keep the reservoirs warm (keep the bulb away from internal wiring and hoses). If your epoxy is in 5-gallon pails, you can get an external heater which clamps around the bucket regulated to 160°F maximum from Grainger or McMaster Carr (specify the heater band model for poly containers and don’t forget to vent the bucket).
For cold weather crack injection using taped ports, it may be difficult to precisely locate the crack under the injection nozzle and this problem is magnified when the resin viscosity is higher due to the cold. An alternative is to install our small ribber tips on the cracks located with toothpicks and then spread the surface seal. Pull the toothpick to inject into the sealed-in tip. The seal can also be cured a bit faster using an industrial electric hot air gun at its low setting (if you see smoke, it’s too hot).
MIXING TIP, WARNING--BE VERY CAREFUL
For many two-component epoxies, you can study the product data sheet or call the manufacturer for advice regarding cold weather (and cold substrate) applications. Since ambient temperature curing epoxies give off heat (exotherm) during the curing process, you can use this property to your advantage by mixing the epoxy in bulk early (prior to use) and allowing it to sit in the container for an extended period as it warms itself. Take great care and know your specific epoxy properties including the approximate gel time at the mixing temperature so you don't create a dangerous condition of the cross-linking reaction generating too much heat and/or smoke or potentially even fire by allowing the mixed bulk epoxy to stay in the bulk too long. It's best to use a metal bucket for this rather than plastic. If your epoxy does generate excessive heat, carefully add dirt or sand to the hot mix to help dilute and cool it. DO NOT add water.
WATCH OUT FOR
Frozen water in concrete cracks is a known frustration. Also, you will have longer waiting times for the surface seal cure and for injection resin cure so don’t inject too soon and don’t strip the seal too soon.
For coatings, remember to look for less than 85% humidity and air temperature 4°F or more above the dew-point. Dew point consideration is many times more important in cold weather due to the high probability that it is close to the actual air temperature. Invisible dew trapped under impermeable epoxy is a problem potentially leading to early delamination, especially if the substrate is not permeable.
Generally, you need not worry if the temperature drops overnight after the epoxy has been placed (hopefully under significantly warmer conditions). Why? Because the epoxy will probably go dormant below 35-40°F, but will begin to cure again once the temperature rises.
Electric hot air guns and/or electric blankets designed for concrete can be used to provide temporary warmth to a cold substrate. Take care to avoid heating the surface or any standard epoxy to over 200°F.
If you are performing work with a concrete or steel substrate subject to large temperature swings due to very cold nights and warm and/or direct sun exposures, be sure to carefully plan the use of rigid (load-bearing) epoxies in consideration of substrate expansion/contraction movements. For epoxy injection, that means placing the seal during the hottest period of the substrate rather than the coldest to avoid the cracking of the seal caused by the thermal cycle expansion and contraction of the concrete.
If you are performing coating work with epoxies (especially floor coatings), avoid the combination of poor circulation of air and the use of torpedo (gas or diesel fired) heaters in enclosed spaces. This combination can be lethal due to the build up of carbon monoxide but can also lead to uncured coatings that exhibit severe blushing due to the absorption of excessive carbon dioxide from the internal combustion exhaust.
For more cold weather tips and discussion of your project specifics, please call us at 800-757-6773 or 650-261-3790.