I’m not so sure if the interviewee said that. It sounds like the OP doesn’t fully understand the process, if he thinks the purple stuff is just a cleaning solvent. The purple primer is involved in a reaction with the PVC to chemically fuse the two pieces. I can see the OP suggesting it is a cleaning solvent, the interviewee arguing that the primer is part of the reaction, and misunderstanding ensuing.
Clearly, the interviewee isn’t an expert in this stuff if they think you apply primer to one side and adhesive to the other. That ain’t right either.
It sounds like you are both partially right and partly wrong. This candidate is correct about it being a 2-part system and you’re wrong about the primer being a cleaner… but you’re right that you apply both products to both the pipe and the fitting, and the candidate wrong if they really only put primer on the pipe and glue on the fitting.
I guess it depends just what the question asked whether you’d deduct points… if you were asking what they’ve done, well, that is what the person did so he’d be right insisting that’s what it was and the way they did it. If you’re asking more along the lines of “tell me how to do this process correctly” then it sounds like they don’t know the correct process.
I have never seen such a torrent of pedantic answers in my life, and I’ve been on the SDMB for 17 years…
Yes, Napier may have mis-characterized the primer as “cleaner,” but that’s completely irrelevant to the question he asked, which is: was the process described by his interviewee possible?
The answer is: no, unless this is some new system that nobody on the SDMB knows about, which is pretty damn unlikely.
OK, “cleaner” and “primer” aren’t exactly the same thing, but they can be combined and are sometimes sold as the combination:
I don’t think the primer is chemically bonding anything. Plasticizing the PVC a little and letting molecular chains diffuse across the joint a little bit wouldn’t be creating any bonds, it would just be more like heat welding in this sense.
It’s not important to determine whether I know how pipe welding works. We already hired me. That cow wandered lonely out of the barn, lo, 37 years ago. What I thought happened was that the solvent and cement cause the PVC to go somewhat into solution especially in the neighborhood of the joint, and then the solvent diffuses away from the joint causing it to freeze (very nearly the way the heat diffuses away from a joint in thermal welding), and eventually evaporates away. I didn’t appreciate that the cleaner or primer or combination does much more than remove dirt that might have interfered, though I have always noticed how soft the PVC surface gets after this first step, and would never have tried a test assembly on something recently treated with the first step for this reason.
But we really only need to know how much the candidate knows about how pipe welding works. And it was their example, after all, not mine. When the question is, “What is something technical you’ve done and feel experienced and knowledgeable about?”, they shouldn’t get their own example wrong.
It does sound as though the candidate misunderstands how making cemented PVC pipe joints work, and therefore flubbed their own technical experience example.
If by some chance any of us do learn that somebody makes a two component epoxy system for PVC pipe, and for some brilliant reason decided the two components should be clear and purple, let us make a pact that we will reconvene, and will feel silly indeed together. And, if this candidate does not get the job and it came down to this one detail. I will contact them and sheepishly apologize.
Not important for the question of the interviewee, but solvent cement does actually create chemical bonds between the two pieces. The solvent unlinks some of the polymer chains in each piece and they join to chains in the other piece, or to the PVC resin in the cement.
There is a lot of bad information and different approaches to this stuff out there. You can find many how-to videos and sites that say to let the primer dry before applying the cement, which is pointless - the chains are unlinked only while the piece is still wet. I’ve heard people argue that you should put cement on only the outside piece, because any on the inside piece will be pushed into the tube and create turbulent flow. There are arguments that primer is not only unnecessary, but might make things worse. It isn’t surprising to me that an interviewee is convinced of the rightness of something that seems pretty wrong to the rest of us.
No, the law quoted says that primer has to be purple. If you made a two part system like an epoxy where the two parts react with each other, neither part would be a primer in the sense the law is referring to. It would be important to avoid making either part of an epoxy(like) system purple because combining one agent from the solvent welding system with one component of the epoxy(like) system should not be expected to work at all, or, worse, could make the plumbing appear stuck together and then explode on the application of pressure.
The problem is not with the Uniform Plumbing Code, but how 1000’s of localities inspectors read them.
Contractors are always concerned with their schedules and to be honest typically want to avoid inconveniencing inspectors by making them bring UV lights or even spend the time using UV to check the joints.
It gets complex too as International Fuel Gas Code requires “contrasting color” so people often just use the purple here too.
While both 705.14.2 in the 2006 IPC, and Section P3003.14.2 in the 2006 IRC allow for exceptions there is a cost. Also if you download the “instructions” for these products you will see they actually require the installer to have a UV flashlight to provide the inspector.
The problem is that the installer doesn’t decide what the inspector wants but the installer pays the price if they think they do.