Plastic Experts ? (cracked polypropylene toilet cover)

I noticed a 1.5 inch crack in the polypropylene rim of our thetford toilet. The crack exists at the point where one of the toilet seat "feet" contacts the rim (see photo). The polypropylene is thinly constructed and lacks support at the point of the crack. The area can be deflected with minimal force.

I'd sure hope that my 200 lbs & 6 ft 1 inch frame -- is not an excessive load. My wife has made it clear that I'd better not blame her -- since she weighs 1/3 less.

So, all blame aside -- I'm considering repair options. I once stopped a crack in the frame of my Jeep CJ5 by drilling small holes at each end of a crack. Do you think this might be helpful with polypropylene ? I also have to pull the toilet to replace a slide valve seal -- so I was thinking that I'd try to reinforce the area with some kind of polypropylene strip and plastic adhesive.

I could shop around for a used rim but that could be a pain in the "a$$", and I don't want to "waste" my time with a repair that's likely to fail.

Any plastic experts around ?

[ShrimpBurrito]

I had the same exact thing happen to me. Crack looked identical. A new part from Thetford is going to cost you a sizable dime...IIRC, about $200. My first attempt at repair was to glue a galvanized strip of metal over the crack from the inside. However, this was before I knew about polyethylene's resistance to anything adhesive, and the JB Weld I used quickly failed. On top of that, the galvanized strip rusted quickly.

I consulted with a Thetford engineer about polyethylene adhesives earlier this year for a different issue, and he said the only thing they have found to remotely work is a 3M product. The name of it escapes me at the moment, but I posted it here a few months ago. He said it wasn't an end-all-be-all, so he made the suggestion with reservation. I went online and priced it at about $80 for the smallest tube I could find. With the high price and uncertainly of its effectiveness, I decided against using it.

Instead, I bought a pair of toilet seat bumpers like these:


...and screwed them to the underside of the seat a few inches on either side of the crack. I used the long ones, not the circular ones, but they come together. I first installed them with the supplied screws, but they quickly rusted and made a mess. So I switched them out with stainless screws. Since they are thicker than the existing bumper that made the crack, the load is distributed among them instead. That relieves the stress on the crack, but also cuts the load on any individual bumper in half, which should help in making more cracks.

So far, it has worked like champ. No complaints, and it is an extremely cheap and easy fix. If you are concerned about more cracks, you can install another pair back closer to the hinge, but just be sure that all of them are bearing weight after put them on.

Note that these bumpers are sort of a soft rubber, and are flat on the bottom. You don't want the ones made from molded plastic, as they will not squish under weight, and they also have protruding screw housings that are not flush with the bottom of the bumper. The ones you don't want look like this:



Dave

[Wavery]

Originally Posted by ShrimpBurrito

However, this was before I knew about polyethylene's resistance to anything adhesive, and the JB Weld I used quickly failed. On top of that, the galvanized strip rusted quickly.

I consulted with a Thetford engineer about polyethylene adhesives earlier this year for a different issue, and he said the only thing they have found to remotely work is a 3M product. The name of it escapes me at the moment, but I posted it here a few months ago. He said it wasn't an end-all-be-all, so he made the suggestion with reservation. I went online and priced it at about $80 for the smallest tube I could find. With the high price and uncertainly of its effectiveness, I decided against using it.



Dave

That's a good fix Dave and you were smart not to buy that 3M adhesive. It has a "Converter" that's supposed to change the molecular composition of the polyethylene to something that their adhesive will adhere to......... I tried it (on my kayak). It works (on the surface) as long as you don't put pressure on it. Once you would sit on that seat, it would crack the "Converted" surface.

The proper way to repair polyethylene plastic is to "Weld"it with a plastic welder and polyethylene welding rod. I've done that also and it works great.

I took my kayak to a body shop near my house. They have a professional plastic welder and they weld polyethylene bumpers and body parts all the time. They charged me $20 for the weld (the guy just happened to be welding a bumper at the time).

Gentlemen, you've given me the expert guidance I'd hoped for. I will incorporate both of your ideas -- I'll have the rim welded to "like new condition" & I'll head over to my favorite ACE Hardware for several packages of soft bumpers.

Thank you again for your sharing your knowledge & experience. I love this forum !

You are in better shape than I am. I have a crack about 8 inches long running diagonally from upper left to lower right as you face it from the doorway.

I always sit on the top when shaving because standing up I can not see my face in the mirror.

Sorry to hear that -- but I'm sure a plastics welder can do the repair. You just need a failed, slide-EZ valve (like mine) to motivate you to pull the toilet. Today I called a welder on the other side of town, and he said they'd do the repair for anywhere from $20 - $40. I'm going to suggest the $40 and ask for a few, reinforcement welds around the cover's perimeter to be sure that it doesn't happen again in other places. Maybe they can add some material to strengthen it from the underside (?). I think the soft bumpers will also be a big help. Sure wish I could have blamed my wife.

I've had to repair plastics many times. Cracks, as said, drill at both ends of crack, then repair. Then what I've done to fix is to make a mixture of MEK (Home Depot or similar) with ABS. ABS is black but can be painted. Essentially take about a 1/4 cup of MEK and mix in pieces of ABS. I literally took an ABS pipe and started grinding it with a bastard (yes, that's the name of the tool) to get ABS dust. Mix it in until it gets to the consistency of pancake batter and it's good to go.

I mix and store in glass - an old pickle or jelly jar is perfect. I've used that batch with many different projects, not just the original.

The mixture dries fast, is strong, sandable, paintable, and it bonds and effectively becomes part of the part you are repairing.

Also, here is a method used for Apache trailers but can be applied anywhere. http://www.apachepopups.net/OldSite/pdf%20files/abs.pdf

Finally, I also understand Harbor Freight might have a plastic welding kit but I have not seen it.

The usual warnings apply - only work in very well ventilated areas. Work with on test materials before going to the real rodeo. A little dab'll do ya.

[Wavery]

Originally Posted by TM_Matt

I've had to repair plastics many times. Cracks, as said, drill at both ends of crack, then repair. Then what I've done to fix is to make a mixture of MEK (Home Depot or similar) with ABS. ABS is black but can be painted. Essentially take about a 1/4 cup of MEK and mix in pieces of ABS. I literally took an ABS pipe and started grinding it with a bastard (yes, that's the name of the tool) to get ABS dust. Mix it in until it gets to the consistency of pancake batter and it's good to go.

I mix and store in glass - an old pickle or jelly jar is perfect. I've used that batch with many different projects, not just the original.

The mixture dries fast, is strong, sandable, paintable, and it bonds and effectively becomes part of the part you are repairing.

Also, here is a method used for Apache trailers but can be applied anywhere. http://www.apachepopups.net/OldSite/pdf%20files/abs.pdf

Finally, I also understand Harbor Freight might have a plastic welding kit but I have not seen it.

The usual warnings apply - only work in very well ventilated areas. Work with on test materials before going to the real rodeo. A little dab'll do ya.

This method works quite well on ABS plastic. It will not work on polyethylene. Polyethylene does not weld chemically like ABS Plastic.

Polyethylene is like wax. Think of trying to glue a candle stick together.

BTW...........I'm not sure that the toilet seat is polyethylene. To be honest.....I don't know what it is. Someone else said that it is polyethylene and I guess that I just took his word for it.

[mcgyver210]

Have you checked with Thetford on if they would warranty this issue. The Electra Magic has a 3 year warranty so depending on when you purchased you may still be under warranty or close enough that Thetford might help you out.

The trailer is an '07 but it was maunufactured in 8/06. I think I'm well past the warranty period. When I spoke to the plastics welder -- he said that he would take his best guess at regarding the type of plastic (poly this or poly that) and do a small "test" weld on the back. Apparently, the exact composition is not all that obvious even to an experienced plastics person. Anyway, the test would help determine what needs to be used to make the repair.

Hey, thanks for the ABS repair information. I'm sure the thetford is not ABS but I'll hang onto the method. It sounds very useful.