Crack repair in Thetford toilet

In an earlier thread I sought advice on how to repair a crack in the plastic surface beneath the Thetford toilet seat. A number of wise TM'ers pointed me in, what I believe, was the right direction. I wanted to share some detail about the repair outcome.

In the first photo you'll notice the crack in the cover beside the penny. The plastic material is thin and not very effectively reinforced (IMHO) so it is susceptible to breakage. So, don't let your seat (with its hard plastic pads) slam down unnecessarily on the cover & sit gently --especially if you're a +200 lb'er -- like me.

I took the cover to Philip's Plastics, a plastic fabrication & machining specialty shop, located at 3801 E Roeser Rd., Unit 18, Phoenix, AZ. 85040 (Ph 602 470-1808). It's a very high tech shop with computer guided milling machines, plastic cutting & welding, etc.. The work was performed by Matt Brewer, the General Manager. I share this in case anyone decides to ship a part of some kind for repair. Apparently, this shop gets stuff shipped to them all the time. They were a first class operation & I toured their facililty.

He tested the material and said that he did not believe that it was polyethylene. He believed it to be an ABS-based plastic. I know this contradicts what some were told by the thetford factory.

Anyway, the 2nd photo shows the reinforcement that he fabricated for the underside of the cover. This fits perfectly over the cracked area and I guess he used a bonding agent that reacts well with ABS-type material. I'm sorry that I didn't get the name of the bonding agent but he seemed pleased with the resulting bond. He also machined a mirror piece to reinforce the opposite (unbroken) section of the cover.

Then he cut a deep grove in the crack (from the top side of the cover -- where you saw the penny) which extended beyond the ends of the crack. He didn't cut through the entire depth of the crack -- but I'd guess that he went through more than half of the material's thickness.

Next he cut a strip of plastic off the backside of the cover -- where it abutts the trailer wall. You can see the photo of the back edge where he removed about a 10 inch strip.
He did this because he did not have an identical plastic match & he wanted to use the exact same material as a welding rod.

I watched him work a gas torch and simultaneously heat both the channel that he carved with his dremel and the plastic strip (now a welding rod) -- to an ideal temperature and consistency to promote welding of the plastics.

I probably would have ruined a dozen or more covers but he made it look easy. I'm sure that it took considerable skill.

Anyway, the weld produced a raised surface which he carefully ground down. I may go further and polish the surface with something or other -- but it really is unnecessary. The last photo is the final result.

I thank all of you for your input on this project. I will install softer bumpers on the underside of toilet seat as soon as I find some. I went to ACE hardware and was told that the bumpers that were recommended are no longer available (they checked on-line too).

Oh, I was charged $40 for repair and considered it a bargain.

Eric