Help: punctured water tank

[Jerry Woodward]

I did a real bonehead maneuver. I was drilling a pilot hole (5/32) for a screw through some glass/core under the settee and went to far, puncturing the water tank on the other side. I have since cut away a square access port and have access to the hole. It is near the bottom of the tank. It is a 47 gal polyethylene tank. I am trying to decide how best to repair it, knowing that not much sticks to polyethylene. But it is just a small hole and it seems that there should be something I can fill it with.

1. fill with an epoxy or adhesive. I have 5200 and I bought some JB Weld Plastic Bonder 2-part urethane adhesive. Does 5200 stick to polyethylene?

2. Use some sort of hot knife and fill with a blob of molten plastic

3. drill, tap and screw a nylon machine screw into the threaded hole with some sort of thread sealant.

Any other ideas?


Thanks

[billknny]

Polyurethane will not stick.

You can weld polyethylene. Try a youtube search. You'll find lots.

[clockwork orange]

Yes you can weld polyethelene and for a hole that size it may be the best solution. You can buy a cheap welder and supplies at Harbor Freight, should be adequate for something like this.

Steve.

[john61ct]

West Systems has repair kits, based on their G/flex. Surface prep is everything.

Small enough hole, mechanical plug (cork rubber?) tapered from the inside?

https://www.practical-sailor.com/iss...s_12522-1.html

Welding works, but only if you match the material. Danger is, structural weakening, especially low down.

[john61ct]

3M Scotch-Weld DP8005

TAP Poly-Weld*

Loctite All-Plastic Super Glue

**not** JB Weld

[thinwater]

I interviewed the engineering departments of the two largest manufacturers for an article. They both suggested installing a small bulkhead fitting. That is the advice they give installers when they do that--you are NOT the first one, it is apparent quite common.


That said, I've put self-tapping screws in tanks like that and they held for ages. No need for sealant, it won't help. I once had a large PE chemical tank delivered, and the freight company had stapled the BOL to the tank! If it ever leaks, put a gasket on both sides.


Although welding and adhesives can be made to work, they are not the best answer for a clean, round hole.

[thinwater]

https://www.practical-sailor.com/iss...s_12522-1.html


A short primer on PE tank repair.

[Jerry Woodward]

Thanks for the suggestions guys. Drew, your article in practical sailor is very timely, but welding seems pretty extreme for a small hole. Your idea of a self tapping screw is similar to what I was thinking, drilling and tapping, but a self tapping screw sounds like it would work. Do you think I need a "self tapping" screw or would a regular machine screw work? I would assume just get the size where the threads extend just beyond the diameter of the hole, stainless of course.



John, those adhesives you recommend, do you have any experience with them, or are those just manufacturers claims?

[a64pilot]

I like your idea of a nylon screw, plastic on plastic is I think the way to go, no corrosion ever, and no thermal expansion issues either, and your only enlarge I guess the hole a tiny bit so you don’t lose anything if it doesn’t work, but I’d bet money it will work, and last.
There just isn’t much pressure is why I think it will work, and work well.

Just don’t tap the threads completely, make it an interference fit. If you overtap maybe a wrap or two of Teflon tape.

My worst bonehead move with a drill was helping a friend install a car stereo in an old air cooled VW. He was drilling a hole in the dash, and suddenly gasoline started pouring from the hole.
We had both forgotten that a Bug’s gas tank was just in front of the firewall, thankfully he stopped drilling with the old 110V sparky drill just before the gas appeared, or I don’t think I would be here.

[Jerry Woodward]

Yes, the nylon bolt sounds good, but the threads would be straight and the nylon bolt would be straight and they probably wouldn't form a tight seal. I like your idea of wrapping with teflon tape, this would probably seal it. On the other hand, a tapered metal screw would cut new threads and the taper should create a tight seal. Yes, corrosion is a concern, but it is fresh water. I can always check and replace if necessary after a season.

[Pete7]

Originally Posted by Jerry Woodward

Thanks for the suggestions guys. Drew, your article in practical sailor is very timely, but welding seems pretty extreme for a small hole.

Its welding but not with a gas axe, that will probably make a horrendous mess.

We used to repair gouges in skies with the plastic rings beer cans come tied together with. Using a cigarette lighter melt a small strip of beer can plastic and drip into the gouge. Allow to cool and file flat. Done properly it would last the season easily.

Also used the idea to repair a cracked plastic trailer mud guard, with additional heat from a soldiering iron. Ended up with a long spilt welded together with a series of little rings along the crack similar to a continuous weld before it is ground down.

Btw, I have a steady hand but am no a welder, tried it once, made right bloody mess.

[clockwork orange]

I just remembered that about a week after I bought the truck im driving now it developed a fuel tank leak. It was caused by something getting between the tank and one of the straps that hold it up. I repaired it with an epoxy kit that I bought at an auto parts store sold for fixing plastic tanks. That was about 3 years ago and so far so good and I had forgotten about it. I have also rebuilt a Yakima rocket box (Roof rack box) which I got for free because someone forgot it was on their suv and drove into the garage causing extensive damage. I used epoxy and glass with proper prep and again, worked fine, probably abs plastic though which glues well. For your problem though I think I would probably do as others have suggested and use a ss sheetmetal screw. I would use a pan head with some butyl tape or similar under the head for good measure. Actually I saw recently on a plastic tank site where they suggested silicone for installing fittings so maybe a dab of that under the head.

[Terra Nova]

Originally Posted by clockwork orange

...use a ss sheetmetal screw. I would use a pan head with some butyl tape or similar under the head...

This. A #10 should do the job.

[thinwater]

Nothing that complicated. No sealant or tape. No tapping. No plastic screw. Just a tight fit. It's probably that simple.

If it leaks someday, I'd replace it with a through bolt with gaskets on both sides. That can't leak if done properly.

BTW, sealant or tape is NEVER recommended for PE tanks. Ask the manufacturers. Just clean threads. You only use sealant if the threads have worn... which happens.


If you must use sealant, I'd try a drop of Sika 291 (not 3M products--not as good on PE) under the head only.

[a64pilot]

Originally Posted by Jerry Woodward

Yes, the nylon bolt sounds good, but the threads would be straight and the nylon bolt would be straight and they probably wouldn't form a tight seal. I like your idea of wrapping with teflon tape, this would probably seal it. On the other hand, a tapered metal screw would cut new threads and the taper should create a tight seal. Yes, corrosion is a concern, but it is fresh water. I can always check and replace if necessary after a season.

Well the Stainless crowd has a following, but if you only lightly tap the threads it will be an interference fit for a plastic screw, similar as to npt in function, don’t fully run the tap through.
I don’t like sheet metal screws for something like this because the threads are so coarse, but I bet it would work.
It won’t take much to seal, there is no significant pressure.