The Old Tradesman

The tips library

Glue joints

A glue joint isn't glued. Primer and cement soften both pieces and they weld into one, and that only happens when the fit, the primer and the hold are right.

Tip 1

Dry fit first: it should bind a third to two-thirds of the way in

The number

Before any primer, push the pipe in dry. It should start to bind between 1/3 and 2/3 of the way into the socket.

Dry fit depthA pipe pushed dry into a fitting socket, cut away. It should start to bind between 1/3 and 2/3 of the socket depth. If it drops to the bottom dry, Spears adds a coat of cement on PVC; the Wavin CPVC sheet says do not install it.DRY FIT, SOCKET CUT AWAY1/32/3mouthbottomPIPEStarts to bind 1/3 to 2/3 ofthe way in. That bind is whatpresses the weld together.Drops to the bottom dry?PVC (Spears): extra coat on the pipe.CPVC (Wavin sheet): do not install.

Why. Solvent welding softens both surfaces and presses them together. That bind is the pressing. No bind, nothing pressing.

The tell. Pipe drops to the bottom of the socket with no drag. On PVC, Spears accepts that if you add a coat of cement to the pipe. On CPVC, Wavin's sheet says don't install it. The sheet with the part wins.

Spears also says don't try to join wet surfaces. Water in the line gets dried out first.

When to stop. Spears says don't force a dry fit and don't use parts that don't mate right. Wrong schedule or the wrong fitting gets swapped, not jammed in.

Sources

Tip 2

Bevel the end so it doesn't scrape the cement off

The number

Cut it square, take the burrs off inside and out, and bevel the outside edge. Spears says 10 to 15 degrees. Weld-On says about 10 to 22. Spears says follow the cement maker, so the can's sheet wins.

Why. A square edge works like a squeegee. Weld-On says it scrapes the cement off right where you need it and can push the extra into the waterway.

The tell. Cut an old joint apart: a ridge of cement at the bottom of the socket and bare streaks on the socket wall.

When to stop. Spears wants a fine-tooth saw (16 to 18 teeth per inch) for a square cut. If you can't get the end square where it sits, cut it where you can, and add a coupling.

Sources

Tip 3

Prime until the plastic goes soft, and test it with a scrape

The number

Scrub primer into the socket, then onto the pipe a little past the depth it goes in, until the surface turns soft and semi-fluid. That's 5 to 15 seconds, longer on big pipe or in the cold. Second coat on both. Then scrape it: a few thousandths should come off easy.

Primer scrape testA PVC pipe end with the primed band, where the printing is erased. A blade scrapes the primed surface and a few thousandths curl off easily. Scrub 5 to 15 seconds, longer on big pipe or in the cold, and give both parts a second coat.THE SCRAPE TESTPRINT 1/2 PVCprint erasedprimed a little pastthe insertion depthA few thousandthsshould come off easyScrub until soft and semi-fluid:5 to 15 seconds, longer on bigpipe or in the cold.Second coat on both.Scrape pulls nothing? Prime again.

Why. Primer softens the surface so the cement can fuse the two parts instead of sitting on top. Spears says the most frequent cause of joint failures is not enough penetration and softening.

The tell. The scrape pulls nothing off, or the printing on the pipe is still sharp. Weld-On says work it until the maker's markings are erased.

CPVC is the exception on how much: Wavin's CPVC sheet says primer goes on sparingly and must not puddle in the fitting.

When to stop. Skip primer only when the can says no primer for that job and your local code allows it. Oatey's no-primer line covers non-pressure drain lines only, and Wavin's CPVC sheet wants a can labeled One-Step. On a job that gets inspected, the inspector decides, not the can.

Sources

Tip 4

Heavy on the pipe, light in the socket

The trick

Cement goes on right away, while the primer is still wet: a liberal coat on the pipe, a light to medium coat in the socket. Dry fit went all the way to the bottom? Spears adds one more coat on the pipe.

Why. Pushing the pipe in drives socket cement toward the bottom. Weld-On says too much there puddles and can soften and weaken the pipe and fitting walls.

The tell. A ridge of cement inside the pipe, or a soft, blistered wall when you cut one apart.

When to stop. Too little leaves gaps for pinhole leaks, Weld-On says. A joint that leaks on the test is not patched: Wavin says cut it out and throw it away.

Sources

Tip 5

Quarter turn, hold it, and look for the bead all the way around

The number

Push it home with one quarter turn, no more. Hold it about 30 seconds on PVC (Wavin's CPVC sheet says 15). A full bead of cement should show around the whole joint.

Quarter turn and holdA pipe pushed into a fitting socket with one quarter turn, held about 30 seconds for PVC (15 seconds on the CPVC sheet). A full bead of cement shows all the way around. A gap in the bead means pull it apart right away and redo it.ASSEMBLE, HOLD, READ THE BEAD1/4 turn going in,then no more turningFull beadall aroundHold about 30 s(PVC). CPVC sheet:15 s.Gap in the bead: pull it apart now and redo it.

Why. The softened surfaces push the pipe back out until the cement grabs, so you hold it. The quarter turn spreads the cement evenly around the joint.

The tell. A gap in the bead, or a pipe that crept back out of the socket. Spears says no bead or a gap in it means not enough cement: pull it apart right away and do it again.

Weld-On says hold longer when it's cold or the pipe is big. On CPVC, Wavin's sheet wants primer, cement and assembly done inside 60 seconds, one fitting at a time.

When to stop. Once it's home, no more turning, and Spears says don't move it for at least 2 minutes. Found the gap after it set? Cut it out and make a new joint.

Sources

Tip 6

Cure time runs on the thermometer, not the clock

The number

Spears, 1/2 to 1-1/4 inch PVC, before a test up to 180 psi: 1 hour at 60 to 100 F, 2 hours at 40 to 60 F, 6 hours at 20 to 40 F, 8 hours at 10 to 20 F. Wavin's CPVC table: 1 hour above 60 F for 1/2 to 1 inch, twice that for 1-1/4 to 2 inch.

Why. The solvent has to work its way out of the joint before it's strong. Cold slows that down, and Spears says humidity over 50 percent stretches it too.

The tell. Weeping at fresh joints on the first test, or a pipe backing out of its socket.

Higher test pressure takes much longer. Spears's own table runs about six times longer for 181 to 315 psi, and Wavin says double its times before testing up to 400 psi.

When to stop. Below 10 F, Spears says extreme caution. Its best results are between 40 and 110 F. And Wavin's clock starts after the last joint is made, not the first.

Sources

Tip 7

Black to white: transition cement, drains only, where code allows

The number

ASTM D3138 transition cement is for ABS to PVC in non-pressure work only, 25 psi or less, like an ABS building drain to a PVC sewer. It is not an all-purpose cement. California's plumbing code bans solvent welding PVC or ABS to a different material except where its Section 705.9.4 allows.

Why. Each plastic has its own cement. ASTM wrote D3138 for that one drain tie-in, not as an all-purpose can, and says to use the specific cement made for each material everywhere else.

The tell. Black glued to white with plain all-purpose cement.

When to stop. A building drain to sewer tie-in usually needs a permit and an inspection. Where code won't allow the glue joint, it's a listed mechanical transition coupling.

Sources

Tip 8

Let CPVC hot lines move: 4 inches per 100 feet

The number

Wavin's sheet says its CPVC grows 4 inches per 100 feet with a 100 F rise. Smooth straps that let it slide, never anchored tight, never run dead into a joist. Wavin's example: a 60 foot run of 1/2 inch needs a 30 inch loop for that swing.

Why. Wavin says expansion doesn't change with pipe size and only matters on hot lines. Pinned down, that growth loads the glue joints and bows the pipe.

The tell. Bowed hot lines, ticking when the heater runs, or a run that ends tight against framing.

Wavin's support spacing for horizontal runs: every 3 feet at 1 inch and under, every 4 feet above that. Holes through studs 1/4 inch bigger than the tube.

When to stop. A tee cracked from being pinned gets cut out and rebuilt with room to move. Strapping it down harder is what broke it.

Sources

The Old Tradesman is a cartoon character. Every tip on this page stands on the sources listed under it. He is the voice. They are the authority. The drawings are diagrams, not photographs.

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