Solvent welding is a process where a chemical is applied to two plastic surfaces with an identical or similar molecular structure which causes the molecules on both surfaces to break apart. When the two surfaces are pressed together and as the solvent evaporates, the molecules of the two surfaces reform and bond together. This results in the two surfaces being molecularly bonded to each other. This is very different from gluing materials together, where the glue itself bonds to each surface so you are left with three layers: the first material, the glue and the second material.
|Solvent welding is typically used for some plastics e.g. PVC and ABS. The process does not work for plastics such as polypropylene and polyethylene as their molecular structure means that they are not affected by solvents.|
There are several steps required in the solvent welding process:
1. The pipe should be cut square, all swarf removed and the edge chamfered (filed) to an angle of between 22.5 and 45 degrees. This prevents the sharp cut edges from acting like a knife blade and pushing all the cement in front of it
2. With a dry cloth or paper towel, wipe the socket and pipe to remove any dirt. If the pipe is an old one, use some emery cloth to roughen the surface and remove any deposits
3. With a clean paper cloth, wipe some pipe cleaning fluid around the socket and the pipe. DO NOT TRY TO DRY FIT THE PIPE IN THE SOCKET AFTER DOING THIS AS THEY WILL STICK TOGETHER!
4. Measure the depth of the socket and mark the pipe with a fine permanent marker pen
5. Paint cement into the socket and set aside (it is important to do the socket first as you can’t easily put down the pipe once it is painted). Next paint cement onto the pipe up to the depth of the socket
6. Push the socket on to the pipe until you feel it hit the stop inside, checking that it has gone in up to the mark you made on the pipe
7. Keeping the socket vertical if possible, so excess cement does not run down the inside of it to the other side, wipe away any drips and excess cement from around the joint.
Solvent welding of PVC and ABS pipe is a permanent process and cannot be undone.
1. Wear nylon gloves to prevent the cleaner and cement damaging your skin.
2. Do not wear vinyl gloves as these will melt with the cleaner and cement.
3. Work in a well ventilated area to dilute the fumes.
4. Measure twice, cut and cement once.
5. Take extra care to mark ABS properly before pushing together. The joint sets VERY quickly.
6. PVC can be turned a little to line it up once fully in the socket, but ABS cannot.
7. Do not twist the pipe as you push it into the fitting as this may result in leaks.