When it is too cold to pour concrete in Maine: what to do

Published 24 September 2026

Knowing when it is too cold to pour concrete in Maine comes down to one number: 40°F. Once the air falls to that mark, the American Concrete Institute calls it cold weather, and concrete can still be placed, but only as a protected pour.

In Portland the air crosses that line for a large part of the year, so as a concrete contractor in Portland, ME we pour most driveways, patios and walks in the warmer months and plan anything outside them as a cold-weather job.

Cold weather for concrete starts at 40°F, not at freezing. The American Concrete Institute's guide, ACI 306R-16, uses the term whenever the air has fallen to, or is expected to fall below, 40°F during the protection period, the days after placement. An older definition, more than 3 days in a row averaging below 40°F, still appears in ACI 306.1 and in CIP 27 from the National Ready Mixed Concrete Association (NRMCA).

The newer wording matters because one cold night can do the damage. ACI 306R-16 calls for protecting concrete from freezing until it reaches a compressive strength of at least 500 psi, and NRMCA puts that at about two days for most concrete kept at 50°F. If fresh concrete freezes before then, NRMCA warns, its potential strength can drop by more than 50% and it will not be durable.

Portland's low reaches 32°F or colder on 144.1 days in an average year, according to NOAA's 1991-2020 normals for the Portland International Jetport, while the high stays at or below freezing on only 40.7 days. January's normal mean temperature is 24.0°F, with a normal high of 32.4°F and a normal low of 15.6°F.

The median last spring freeze at the Jetport is April 26 and the median first fall freeze is October 15, a median freeze-free season of 170 days; in 2025 those freezes came on April 21 and October 10. Those are 32°F dates, and the ACI line sits higher, at 40°F, so a pour can be a cold-weather job on a night that never reaches freezing. By month, the low reaches 32°F or colder on this many days in an average year:

• October: 6.3 days
• November: 18.3 days
• December: 26.7 days
• January: 29.3 days
• February: 26.1 days
• March: 24.5 days
• April: 11.9 days
• May: 0.7 days

A cold-weather pour needs warm concrete, a thawed base and cover that holds the heat until the concrete can survive a freeze. NRMCA's recommended minimum concrete temperatures at placement, based on ACI 306, are 55°F for sections under 12 inches thick, 50°F from 12 to 36 inches and 45°F from 36 to 72 inches. Driveways, walks and patios are far thinner than 12 inches, so they fall in the 55°F group.

NRMCA says to remove snow, ice and frost before placing and to make sure the forms, the subgrade and any steel set in the concrete are above freezing; the subgrade may need to be insulated or heated first. Once the concrete is placed, NRMCA lists insulated blankets and tarps, or straw covered with plastic sheets, as common protection, with enclosures and insulated forms when conditions call for more. Fossil-fueled heaters inside an enclosure should be vented, for safety and to prevent carbonation.

Cold also slows everything down: a 20°F drop in concrete temperature roughly doubles setting time. Accelerating admixtures speed up setting, but NRMCA is clear that they do not prevent freezing, so they never replace heat and cover. Near freezing, a curing compound or impervious paper or plastic takes the place of water curing, and the Portland Cement Association (PCA) advises curing for at least 7 days, longer when temperatures are near 40°F.

Interior slabs and below-grade work go ahead most readily in the cold, because they can be closed in or covered; open flatwork is the hardest to protect.

Footings and frost walls sit below grade, where the forms can be insulated and the pour covered, but the frozen-ground rule applies in full: no footing goes on soil that still holds frost. If an addition or a garage has to start in the shoulder season, our page on concrete footings and frost walls explains how we plan that work.

Exterior flatwork poured late in the year faces two more limits. NRMCA says concrete that will freeze and thaw, even only during construction, should be air-entrained and kept from freeze-thaw cycles until it reaches at least 3,500 psi, so all our outdoor concrete is air-entrained. And PCA says concrete that may not dry out before its first freeze should get no deicing chemicals during its first winter, which we explain in keeping deicers off new concrete in its first Maine winter.

Plan exterior flatwork for the freeze-free months, away from their edges, and treat anything outside them as a protected pour. The median dates give a window from late April to mid-October, but with the cold-weather line at 40°F, days near either end can still need cover, and in spring a base that is still frozen has to wait.

Tell us your timing when you ask for a quote. We put it in writing, watch the forecast for the days after the pour as well as the day itself, and bring cover to any job near the 40°F line. For a pour that has to happen in the cold, the quote also spells out:

• Concrete temperature at delivery, matched to the thickness of the pour
• Base condition: free of snow, ice and frost, and above freezing
• Protection: blankets, tarps, an enclosure or insulated forms, and for how long
• Curing: a curing compound or sheeting in place of water
• A backup date if the forecast turns, rather than a pour into a freeze