Can I join ABS to PVC?

It's possible to join ABS to PVC, but it's only supposed to be done with a mechanical coupling, not glued. If you just came here for the answer, you can stop reading... but I think you want the whole story. Here goes.

Today, there are two commonly used plastics for drain, waste, and vent pipes inside of homes; ABS (black) and PVC (white, mostly). This is almost all that's ever used in new residential construction here in Minnesota, and I suspect for the rest of the country as well. For most systems, a plumber will use one material or the other, not but both. This makes all of the connections simple; the plumber uses a solvent cement (aka glue) made just for that material, things stick together, and everyone is happy...

Until then the "handy" homeowner comes along and messes it up.

For the most part, ABS and PVC are not supposed to be glued together. We'll turn to the 2015 Minnesota State Plumbing Code for some background on this topic.

If we turn to chapter 7 of the MN state plumbing code, we can find a bunch of info on drains. Section 705.1.2 ABS Solvent Cement Joints (for ABS) says the following, among other stuff:

So that says you can glue ABS using something that meets ASTM D 2235. That's the standard for solvent cement for ABS.

Section 705.7.2 Solvent Cement Joints (for PVC) says the following, among other stuff:

So how can these two materials be connected together? We need to turn to section 705.11.3 Plastic Pipe to Other Materials:

That means that if ABS and PVC are connected together, some type of adapter or fitting needs to be used. That's it, that's all that's allowed. The image below shows one such adapter on the right side. This has a stainless steel band going through the middle for rigidity. The coupling on the left lacks a metal band in the middle and also lacks UPC approval.

If you stop by any home improvement store, you'll be able to find a green cement that will connect ABS to PVC, and it might even have an IAPMO approval stamp on it (UPC), so what could the problem be? I mean, it's approved, right?

The problem is in the standard. If you look up the technical specifications for the product, you'll find that it meets ASTM Standard D 3138. You'll find the following information on the ASTM website https://www.astm.org/DATABASE.CART/HISTORICAL/D3138-04.htm. I added the bold.

That spells it out pretty clearly, yes? ABS to PVC cement is only meant to connect an ABS system to a PVC system. An example of this would be an ABS drain system inside of a home connecting to a PVC drain system just outside the building, or vice-versa. That's the only place that this cement is supposed to be used.

Just for fun, I did a little experimenting at home to show how some of these different types of cement hold up. I started by cementing a bunch of materials together with a bunch of different types of cement. I waited 24 hours, then cut each one roughly in half, down the middle.

Next, I cut each section in half lengthwise and put the coupling in a vice to get the materials to separate.

I got most of the connections to separate, but not all of them.

The easiest section to separate was the PVC to PVC without purple primer. Next was the ABS to PVC without purple primer. The ABS to PVC connections with purple primer were as strong as the PVC to PVC connections with purple primer, if not stronger. It actually seemed to pull the surface of the ABS right off of the pipe. The only connection that refused to come apart was the ABS to ABS; the plastic would probably rip apart before that connection would fail.

Again, an ABS to PVC glued connection isn't technically correct, but this connection is highly unlikely to fail. I think failure is close to impossible; if I hadn't used a vice, there's no way I could have separated the two. There's no need to lose sleep over connections like this.