PVC and Plastic Pipe When the Temperature Drops

Why this matters

A PVC joint made in a 30 F garage looks exactly like one made in July. It goes together, it holds when you push on it, and it is not a joint yet. Cold changes three things at once: the pipe gets brittle enough to crack when it is dropped or cut carelessly, the solvent cement works slower and can turn to jelly in the can, and the wait before the line can take pressure stretches from hours toward days. A tech who treats a January joint like a July joint gets a line that passes the eyeball test and lets go at the first pressure test, or worse, a week later behind a finished wall.

What cold does to the pipe itself

PVC loses impact resistance as it cools. Rigid PVC is a tough material at room temperature and a notch-sensitive one near freezing. The same stick that bounces off the truck bed in summer can split lengthwise when it hits frozen ground in winter.

The damage hides at the ends. A hairline crack at a pipe end is easy to miss under frost or dirt, and a fitting slid over it seals for a while. In cold weather, inspect every end you are about to join: wipe it, look at it in good light, and flex it gently. If a stick was dropped or struck on an end, cut a couple of inches off that end before you use it, and look again at the new end.

Cutting is where cold pipe cracks most. A ratchet-style shear cutter puts a wedge into the wall, which is exactly the load a cold pipe handles worst, and it can split the pipe or leave a crack running back from the cut. In the cold, use a fine-tooth saw or a wheel-type tubing cutter, then deburr and bevel the end.

Bending and springing are off the table. Forcing a cold run into alignment, or springing a pipe sideways to get it into a hub, stores stress in a material that is now less able to carry it. Cut to length, use the fittings the run needs, and support it so nothing is pulling on a joint.

Length still changes with temperature. PVC moves about 3.0 x 10^-5 inch per inch per degree F, which works out to roughly 0.36 inch per 100 feet per 10 F change. That figure assumes unrestrained pipe at ordinary service temperatures. A run installed tight in a cold space will grow when the space warms, so leave room at the ends and at offsets for it to move.

What cold does to solvent cement

Solvent cement is not glue. The primer and the solvents in the cement soften the surface of the pipe and the socket, the two softened surfaces fuse when you push them together, and the joint becomes a joint as the solvent leaves. Every part of that depends on temperature.

• Softening is slower. Cold PVC takes longer to soften, so primer matters more in winter, not less. Where the code, the cement maker or ASTM D2855 (when the spec calls it up) call for primer, it goes on until the surface is visibly softened, which takes more passes when the pipe is cold.
• Evaporation is slower. The solvent has to leave before the joint has strength. In the cold it leaves slowly, so set time (when you can handle the joint) and cure time (when it can take pressure) both stretch.
• The can thickens. Cement left in a cold truck overnight gets thick and slow to flow. Thick-but-flowing cement that warms back to normal is usable. Cement that has gone to a jelly, will not flow off the dauber, or strings like cooked cheese has started to cure or lost solvent, and it goes in the trash. Do not thin it with primer or cleaner unless the maker's instructions allow it; most do not.
• Moisture on the pipe blocks the bond. Pipe carried from a cold truck into a warm, humid basement sweats, and frost on pipe stored outside looks like dust. Either one keeps the primer and cement from reaching the plastic. Dry the surfaces with a clean rag right before primer.

The hazards follow the solvent. Primer and cement vapors are flammable and an inhalation hazard. In a closed crawlspace or a small mechanical room, ventilate before you open the cans and keep ventilation running until the vapor clears. Where ventilation cannot keep the space clear, the respirator the product SDS calls for is used only by a tech in a written program under 29 CFR 1910.134 (which 29 CFR 1926.103 applies to construction work); a tech outside that program does not do the work in that space until it can be ventilated. Keep space heaters, torches and anything that sparks out of the vapor zone, which settles low because the vapor is heavier than air. Never warm a joint with a torch or heat gun: heated PVC gives off hydrogen chloride, and the solvent around the joint can ignite.

The wait before the pressure test

Every solvent cement can carries a table of set and cure times. The usual layout has rows for pipe size, columns for temperature bands (commonly something like 60 to 100 F, 40 to 60 F, and below 40 F), and often separate tables for low and higher test pressures. The coldest column is several times longer than the warmest one, and the larger the pipe, the longer the wait. Read the table on the can you are actually using; the numbers differ between cement types and makers.

The temperature that sets the column is the temperature of the joint, not the forecast high. A joint made in an unheated crawlspace at 35 F lives in the 35 F column even if the afternoon outside reaches 50 F. If the space stays cold overnight, the clock runs at the cold rate the whole time.

Do not test plastic pipe with air. Pipe and fitting makers warn against testing PVC and CPVC with compressed air or gas. A brittle failure under stored air throws fragments, and cold makes brittle failure more likely. Test with water where the code and the AHJ allow it. In an unheated space below freezing, a water test can freeze in the pipe, so either test when the space is above freezing or drain and blow out the test water right after the test with the line depressurized. Some jurisdictions require a specific test for drain, waste and vent work; ask the inspector what they accept in winter.

Other plastics, briefly

• ABS keeps more impact resistance in the cold than PVC and uses its own cement. Where an ABS line meets a PVC line, the joint needs a listed transition cement or a mechanical coupling, and that question is covered in ABS, PVC and the Mixed Drain Joint.
• CPVC is at least as notch-sensitive as PVC in the cold and needs the same care with cutting and handling. It uses CPVC cement, sometimes one-step without primer where the listing allows.
• PEX stays flexible in the cold, which is why it is a winter favorite. Expansion-style fittings are the exception: in the cold the tubing and ring shrink back onto the fitting more slowly, so the maker's cold-weather instructions often call for fewer expansions per turn or more time before the joint is full. Read them for the system you carry.

Worked example: a well line in a cold garage

A plumbing tech is replacing a cracked section of 1 inch Schedule 40 PVC pressure line where a well line runs through an unheated garage. The garage air reads 34 F at 8 am. The cement and primer rode in the truck box overnight, and the truck sat at 18 F.

The cement first. At the truck, the tech opens the cement and finds it thick but still pouring off the dauber in a sheet. That is cold, not ruined. The closed cans go into the warm house for twenty minutes, set away from any flame or pilot light, while the tech turns off the well pump at its breaker, isolates the line, relieves the pressure at a faucet downstream, and cuts out the damage.

The pipe. The new stick rode on the rack. The tech checks both ends, finds them clean, and cuts the two lengths with a wheel cutter rather than the shear cutter in the bag. The existing pipe ends get the same inspection: one shows a short hairline crack running back from the old fitting, so the tech cuts 2 inches further back and looks again. The new end is clean.

The joints. The pipe surfaces are dry, since the garage and the pipe are both cold, but the tech wipes them anyway. Primer goes on in three passes on each surface until the surface is visibly softened. Cement goes on both surfaces, the pipe goes in with a quarter turn, and the tech holds each joint for longer than usual, because a cold joint can push back out of the socket before the softened surfaces grab. The overhead garage door stays open a foot and the door to the house stays closed, so the vapor goes out and not into the kitchen.

The clock. The joint will sit at about 34 F, which puts it in the coldest column of the can's table. Say the table on this can, for 1 inch pipe at the line's working pressure, reads 6 hours in the 60 to 100 F column and 48 hours in the coldest column. The coldest column is 8 times the warm one (48 divided by 6). The joint was finished at 10 am, so at the cold rate it is not ready to pressurize until 10 am two days later.

The call that changes it. Forty-eight hours without well water is not acceptable to the homeowner. There are two honest options, and one dishonest one.

1. Warm the space and move columns. The tech closes the garage, keeps it ventilated for the time the can's instructions give for vapor to clear, and then places an electric space heater well away from the joints and the cement cans, with the cans already back in the truck. If the garage air and the pipe come up into the 40 to 60 F band and stay there, the joint moves to that column. Say that column reads 12 hours. Then the wait is 12 hours from when the joint reached that band, not from 10 am. If the garage only reaches 45 F at 1 pm, the clock starts at 1 pm and the line can take pressure at 1 am. Counting the three cold hours from 10 am to 1 pm as part of the warm wait would be wrong.
2. Do the repair with a mechanical coupling. A listed compression or push-fit repair coupling rated for the pressure and the pipe needs no cure. On a line that must be back today, that is often the better call in January.
3. The dishonest option is to pressurize at noon because the joint "looks set". Set is not cure. A joint brought to pressure early can hold at static pressure and fail later at a pressure spike when the well pump starts.

Both joints sit in series on the only supply line, so neither can be left to cure while the other carries water. The tech takes option 2: the fresh cemented joints are cut out and the new section goes back in with listed repair couplings at both ends. The ticket notes the garage temperature, the cement table column that ruled out the cemented joints, and the couplings used. Had the line been able to stay down, option 1 would have been the call, with the clock start and earliest test time on the ticket.

The restore. When the line goes back in service, the tech stands to the side of the couplings, not over them, opens the valve slowly to let the line fill, turns the pump breaker back on, and watches the couplings with the pump cycling through at least one start and stop. A weep, a bead of water at a coupling or any movement of the pipe in it is a stop: close the valve, relieve the pressure at a faucet, and reset or replace that coupling.

Where the call forks

• Bigger pipe. Cure times climb with diameter. A 3 inch or 4 inch joint in the coldest column can wait days. On large-diameter work in winter, plan the cemented joints for a day the space can be held warm.
• Below the can's lowest column. Some cement tables stop at a temperature, and some cans state a minimum application temperature. Below it, the can is not telling you the joint will ever cure properly. Warm the space or use a mechanical joint.

References

• ASTM D2855, Standard Practice for Making Solvent-Cemented Joints with PVC Pipe and Fittings, where the AHJ or the installation spec calls it up
• Solvent cement and primer manufacturers' set and cure time tables and SDS for the products you carry
• 29 CFR 1910.134, Respiratory Protection, for any respirator use in an unventilated space (applied to construction by 29 CFR 1926.103)
• See related: ABS, PVC and the Mixed Drain Joint
• See related: How to Solvent-Weld PVC in Cold Weather; The PVC Joint That Let Go in January