Better to be on the safe side.
Forty-eight years ago, as a plumbing apprentice, we used ABS schedule 40 piping and fittings for DWV work. At that time, only cast iron pipe and fittings were permitted for use below grade. Transition from cast iron was made using a caulk ferrule inserted into a cast iron hub, packed with oakum and poured molten lead.
As I learned the hard way, if you attempt to caulk the lead too soon, the caulking tool will go straight through the heated ABS ferrule. I also came to learn that you had to wait for the molten lead to cool somewhat before pouring the joint. Rocking gently back and forth in the lead ladle until the molten lead started to curdle slightly as it sloshed while rocking. Those who wanted to cheat cut corners by simply stuffing the raw pipe into the cast iron hub.
However, this was easily spotted by sharp-eyed plumbing inspectors who often required the transition joint be redone properly.
Then came no-hub cast iron and fittings, and eventually, since change doesn’t happen overnight, away went our lead pots, burners and on rare occasions we would melt a pig of lead by torch into a lead ladle, heat the ladle with torch until the lead was molten and rocking revealed it was ready to pour. More often than not, this was for a replacement closet flange lead joint.
A new introduction
It wasn’t until 1977 that our local supply house began stocking PVC schedule 40 pipe and fittings, and we made the transition from ABS. It was taboo to mix ABS with PVC using solvent cementing. We encountered more than a few failed transition joints where PVC solvent cement did not properly bond PVC/ABS. You could knock them apart with a hammer and that was also true for PVC joints assembled without using primer.
My bosses in 1977 didn’t want to use primer, but changed their minds when callbacks for failed joints grabbed their attention. At that time, all-purpose solvent cement looked promising, but our local plumbing inspectors wouldn’t allow its use.
Transition from ABS to PVC had to be made with either a no-hub or rubber fernco coupling. We dealt with multiple AHJs (Authority Having Jurisdiction) who each had their own code modifications. In one township, no fernco couplings could be used, whereas in a neighboring township, no no-hub couplings were allowed! You could also use male/female transition fittings.
The first thing we had to do, after driving to a job site with ABS strapped to our roof racks, was work out the deformity from being exposed to sunlight. We would position the ABS pipes to let the sun’s rays bend it back straight again and then move it inside away from direct sunlight. Leave ABS in direct sunlight long enough and grab it barehanded would teach you a painful lesson about solar heat gain!
Every now and again, we would encounter a weekend warrior’s mix and match conglomeration of PVC and ABS with a variety of solvent cements, caulking, epoxy and various tapes in an effort to seal up weeping joints. Today, of course, they can slap on some Flex Seal and call it a day. In reality, professionals are only supposed to have one transition between PVC and ABS on each site.
A range of colors
Solvent cements that are specifically formulated to solvent cement PVC to ABS are labeled as Green Transition Cement, and the color allows inspectors to visually confirm you utilized the proper cement. Oatey ABS to PVC Green Transition Cement, Weld-On ABS to PVC Transition Cement in Green, and others are available through wholesalers or at the local big box DIY stores because they cater to weekend warriors. On the PVC side, assuming you are using a PVC coupling, you use primer and cement formulated for PVC.
For many years we used clear PVC primer and it didn’t matter if some of the primer ran down the pipe or over the fitting. It was easy to determine if primer had been used because it etches away the lettering on the PVC pipe. On the other hand, a joint joined using cement only was obvious and easy to detect because the lettering ran into the joint with no alteration.
Then came the primer from hell. Purple, if you ask me, should be limited to fake dinosaurs! Inspectors fell in love with purple primer because they could see it from across the room. Extra care had to be exercised to keep your craftsmanship from looking like a kindergartener’s abstract watercolor attempt at art. God forbid you spill a can of purple primer or dribble onto a floor or splatter a wall.
ABS is lighter in weight than PVC but both need to be adequately supported every 4 feet. Bear in mind the added weight for water or sewage when considering proper support — such as when the drain is clogged. Maximum operating temperature limitations differ too. ABS upper temperature limit without being pressurized is 180° F whereas PVC is 140°. Both list 100° maximum operating temperature if under pressure: www.engineeringtoolbox.com/plastic-pipes-operating-pressure-d_1621.html.
My 2012 IPC code book 707.1 “Prohibited Joints” specifically cites: Solvent-cement joints between different types of plastic pipe. If the job you’re on will be inspected, it’s best to ask for permission because forgiveness may not be in the cards! Worst-case scenario is the plumbing inspector decides to change his mind, and suddenly you’re in a conflict. Don’t think that can’t happen either.
When we were building our new home in 1993, I used clear primer on all of our PVC joints, and this was for four bathrooms, kitchen and three laundry tubs. We had just finished another new home the previous week along with two commercial applications in a mall — all using clear primer with PVC and no issues when inspected.
The plumbing inspector decided to drop by my home’s construction and loudly shouted who’s the plumber on this job! I thought he was clowning around — surely he knew this was my own home, right? This particular plumbing inspector had a well-earned reputation as a bully-with-a-badge, but we had never butted heads in prior inspections.
I was up in the rafters, having just completed the last PVC joint in the vent piping. He demanded I come down and then wanted to know what kind of primer I was using. I had, as we always did, both the primer and cement cans taped together, which helped avoid accidentally spilling primer and/or cement. The label on the primer confirmed it was fully compliant with codes and the correct primer for PVC.
He looked me in the eye and demanded I rip out 100% of the PVC and start over with purple primer. “I don’t know what’s wrong with you idiots. Can’t any of you read the plumbing code book?”
Well, yes, I can and had, and the code book (BOCA at the time) specifically stated clear primer could be used if approved by the AHJ. Clearly it had been, because that’s all we had used for years right up to the week before my unscheduled surprise inspection. That’s why you should check with the AHJ before using Green Transition cement on your ABS to PVC changeover. Did I rip out the hundreds of feet of PVC I had already installed? I asked the PI if he knew whose home this was and he said he didn’t care.
“Is this the hill you want to die on?” I asked.
As it turned out, it was, but it didn’t turn out the way he thought it would. He was almost fired (kept a job with the township by one vote) and was demoted to a job at the sewage treatment plant. He eventually worked his way back to being one of their plumbing inspectors and conducted himself properly on our inspections until he retired.
This article is also available at: https://www.pmmag.com/articles/103055-dave-yates-abs-or-pvc