Crack in black tank? Is it ABS or Polyethylene?

[Cheapfix]

I'm trying to fix a crack in my black tank. I thought all black tanks that are black in color, and affixed to ABS pipes, are are made of ABS. Apparently some genius decided to make black polyethylene tanks when polyethylene can be almost any color. There is a clue that the tank might be polyethylene: Even though it's glued to ABS pipe, ABS cement wasn't used. It's a yellow glue that's all over the pipes, tank, and fittings. It doesn't appear to weld the fittings like you'd see on ABS. But I'd say that doesn't mean much considering how speed seems to be the main factor in how RV's get built. They used the same glue for ABS pipe to ABS fitting connections. One yellow glue for all waste plumbing.

This is a 2006 Keystone Everest if that's any help. Any ideas on what type of plastic holding tank I'm dealing with (or how I find out)? Thanks!

[LMHS]

You want to make "ABS GOO" to repair/glue ABS with. ABS Goo is easily made by dissolving ABS shavings in MEK. MEK is nasty stuff. Use with plenty of ventilation. I installed ABS tanks because I know how to repair ABS thanks to owning a vintage Apache popup which had walls made from ABS. I bought my MEK from Home Depot (paint section) and I got my ABS by shaving ABS tent stakes (gave me yellow ABS Goo) bought at WalMart and shaving ABS from ABS plumbing pipe (gave me black ABS Goo) bought at Home Depot. I simply put the shavings in a short mason jar, add MEK and seal the metal lid tightly. Let stand overnight and stir the next morning. Might need to add more MEK or shavings. If it dries out, add more MEK. If too thin, add more shavings or leave the lid off so the MEK evaporates. Apply with a putty knife.

[BrianinMichigan]

You can buy sheets of ABS from Amazon. A few years ago I had to repair a crack in my black tank where the drop point is on the tank. I did multiple layers of the plastic and glue. Still holding up.

[NamMedevac_70]

If your home remedies fail then visit a boat or RV repair shop.

[time2roll]

Plasti-Mend is premix ready to go.

If this is a thin weak spot or a flex point the Plasi-Mend website has some sheet ABS for sale. I used some of the thin sheet on a corner and it is holding 10+ years. Can be cut to size with a utility knife and formed around a bend with a heat gun. Get it cleaned & fitted, load both with the goo and prop it into place for an hour+. Touch up and fill any gaps around the edges next day. A bit of an art to apply, and you need to move fast but works beautifully.

Some have reported success with adding some ABS plastic chips to a can of solvent.

[opnspaces]

I honestly think Plasti-Mend is just ABS filings dissolved in Acetone. But it's just easier than concocting your own homegrown blend. I assume you could take some ABS pipe and a grinder and make a big pile of shavings. Melt these shavings into some Acetone until you have the consistency of ABS glue.

I have read (maybe it was on the Plasti-Mend website) of people using it and fiberglass screening to repair large tank holes. So it or an acetone ABS gel concoction should work for you as well.

Two bits of unsolicited advice:
1) Layer the repair over a few days. If you slop the glue on too think the ABS on the tank will get soft. It's not the end of the world if it does. You just have to let it sit for a day or so to evaporate the Acetone and harden up.

2) I asked the Plasti-Mend people if I could substitute aluminum window screening over the fiberglass screening as I figured it would be stronger. I don't remember their exact answer. But they basically said they do not recommend the aluminum screening and to only use fiberglass window screening.

[Cheapfix]

time2roll wrote:
Polyethylene surface will feel soft compared to ABS is a hard plastic.
I recommend Plasti-Mend for ABS. Polyethylene probably needs to be welded.

Thank you for confirming that. I noticed how hard it was compared to my fresh water tank which I know is polyethylene. When I knocked on it, it sounded like the ABS pipes. The fresh tank didn't. So it really Sounds like it's ABS. I'll still test the filings, but I think I can proceed with some of the prep for the mend. Will let you guys know.

As for Plasti-mend, how does it work for firming up large areas? The crack is only a few inches. But it was right along the corner of the tank heating pad that was glued on. I want to firm up the whole area, which is about 10" x 18", just in case it made the whole area brittle. I was going to use a concoction of ABS filings desolved in ABS cement with fiberglass screening for added strength. But if Plasti-mend is better, maybe I should use that.

[opnspaces]

My black tank had that same (I assume) yellow glue on it when it cracked. I used Plasti-Mend on it and it has held up fine.

As suggested take a few shavings off your existing tank and see if it dissolve in either Acetone or in ABS glue. There should be plenty of excess tank material you can shave off without danger of making a leak from the flanges where it is bolted up.

[time2roll]

Polyethylene surface will feel soft compared to ABS is a hard plastic.
I recommend Plasti-Mend for ABS. Polyethylene probably needs to be welded.

[Cheapfix]

It turns out there is/was a yellow ABS cement. I found it listed on random small store websites, but not on Amazon. It's the same as the black, but yellow so you can better see the weld. It only works on ABS. I can't find anything yellow that binds polyethylene to ABS. So I'm thinking the tank is most likely ABS. When I drill the holes at the ends of the crack, I'll collect some shavings and see if they desolve in ABS cement. If they do, the tank is ABS for sure.