I fixed an old problem of a low hanging black/grey valve cracking the tank when it bottomed out.

The tank however was re-assaulted on my last outing by a hidden fire ring.

The tanks are ABS plastic and cannot (as a previous owner and a well meaning garage attendant attempted in prior repairs)
be repaired with either JB weld, PRC 7 epoxies or fiberglass. Neither adhere.

I used similar technologies, and although it might be a 'half ass' repair, it so far has been durable and strong. It was 20x cheaper and easier than replacing the tank.

3m and devcon both make two part epoxies rated for ABS and CPVC and PVC. The 3m is pricier than all get out, and needs a fancy injector gun. It is made for professional types.

DEVCON makes a plastic two part and I bought 4 tubes at a local sears hardware for less than one 3m. It comes in a black paired syringe and is called "Plastic weld". It comes out clear/white and is white when mixed.

The 3m is black.

Here is how I used it.

Feel free to chime in with comments, criticisms, and of course, ribald remarks.

sand any glossy surface with large grit sandpaper. Degrease. If you can widen a crack with flex pressure, retain that technique for later. It will helpg get the epoxy past the crack. Make sure your tank is clean and dry. I poured 5 gallon buckets of chlorine bleach/water to disinfect and chase any nasty bits out. leave tank open and in the sun to dry.

I used a clear plastic cleaner like you use for plastic pipe joining.

Dab it in and let dry.

Cut a width of fiberglass cross weave to bridge the crack several inches on either side.

Mix up a bigger batch of epoxy than you need. Use a body putty applicator *wide flexible spatula* and quickly mix the epoxy (most have a working time of LESS than 4 minutes. Don't waste time.

Put a generous amount down the repair site and flex and push to get the epoxy into the crack. Repeat application which leaves a generous layer of epoxy.

Place the dry glass over repair and used latex gloved hand to tap the mat into the epoxy, saturating it with epoxy. Smooth the mat down and try and leave a bit of epoxy on top.

Make up a second batch and apply it over the repair and feather it onto the adjoining area.

It will be ready in about 45 minutes.

Let it cure for a day before you stress it.

Good luck. My repair has lasted a year.

I wish I had an ABS black tank.

My ABS process is similar, but instead of relying on the adhesive properties of epoxy, I rely on the solvent characteristics of ABS cement to effect a weld. I have repaired canoes and kayaks this way and they later broke other places while the repair held.

I use ABS cement and ABS filings from a horseshoe rasp or a power Surform. I mix up the two into a slurry, use ABS cement to soften the tank area to be repaired and slop the slurry on. If the area is big, I lay a plastic bag on the bench, lay down a little slurry, then some fiberglass window screen, then more slurry. I cover the whole thing with clear plastic, and use a roller to assure full saturation and even distribution. Then I sand and coat the area to be repaired with ABS cement and, after removing one layer of the plastic, apply the patch and duct tape it in place to dry. After it sets up, the other layer of plastic can be removed,and more slurry can be applied or more cement or sanding and cosmetic touches.

That is an interesting technique, Bill.

That was actually plan "B".

I had found a source for ABS sheeting and was going to either use it for the bridge, or rasp it into shavings.

I would say "great minds..." but I won't give myself the pat on the back..lol.

Not to butt in but thanks. I just got back from a weekend in Indiana andd Michigan and found a leak near the outlet for black water tank , will try to repair this wekend. Its great when this group start to read each others minds and helps out. Now if you could all focus on a new job for me it would be nice.

quote:

Originally posted by SLOOP JOHN B:
Now if you could all focus on a new job for me it would be nice.

A job like this, or, are you looking to change your vocation employment "Money Making" job?

Bill NY; The big bank said why not buy the little bank then the bigger bank said why not buy the big bank then the really big big bank said lets buy the bigger bank. The real estate market is softer in Chicago now and 28 appraisers were told Bye Bye. I have been doing vol. work and just finished a deck ,a patio, and a fence. Now on to installing some solar roof vents . Got to do something to fill in the time til the market comes back.

If, like me, you try to fix the tank about ten or twelve times and it still leaks, check this thread with a link to a really good source.
http://barthmobile.com/eve/forums/a/tpc/f/3631087061/m/...711039061#6711039061

Well, to post an update on this repair.

It held well, all the way up to the point where I bottomed out on a driveway, which fractured it and caused it to weep drops here and there. Not good though, but it made it through the camping.

I clearly needed to rethink this, and try and weld the plastice first.

Got it home and pried off all the epoxy, and ground down the cracks into a 'v'. Found that some of what I laid the repair over was stubborn epoxy and more fiberglass, so that came off too.

This time I used a plastic welding kit and ABS rods to fill the crack. The Harbor Freight welder gave up the ghost an hour into it, and I switched over to a large soldering iron.

After the weld was done, I filled the tank with water and noted any weeping.

Drained the tank (took the sewage out prior to repair in a 5 gallon bucket to be dumped in my septic tank, flushed it with bleach and water..I must love my family)

Fixed and rewelded the couple of pinholes, filled it again and found no leaks. Reinforced repair by laying the repair with fibreglass window netting and layering it with more Plastic Weld epoxy.

It held on a subsequent trip nicely..wish me luck.

That will be the LAST repair attempt.

quote:

Originally posted by Windsor Dalrymple:
The Harbor Freight welder gave up the ghost an hour into it.

Yeah, same thing happened to me. Twice. I used a dimmer for a heat control on a soldering iron (well, really an old Dupont explosive rivet heater).

Some plastic welders, like the one sold by Urethane Supply, are little more than controllable soldering irons. I finally bit the bullet and bought a Seelye plastic welder.

Why not replace the tanks (see: http://www.plastic-mart.com/class.php?cat=34). You can look around the bottom area and design a larger capacity, shorter tank and they will make it. Their 45 gallon only costs $170. That would seem to me to be a permanenet fix for a lot less effort.
Tom

Because I am a cheap SOB with not a lot of excess cash laying around.That, and when I fixed it we were due to leave on a trip in a week, and I could not guarantee a replacement would appear in that little time.

My time + a $30 welder and +30 of materials is easier and cheaper than dropping the whole tank.

BUT

It is a gamble for sure.

If I now have to replace it, I will be a bit more behind...

I used a product called marine-tex to repair my tank and it has held for about 3 1/2 years. It's a two part mix and can be found in most marine stores, Home Depot and Lowes.

I have used this material for repairs on my boats and it will adhere to just about anything. You can work it into the cracks and shape it. I used a putty knife to apply it and if you wet the tips of your fingers you can shape it without it sticking to your hands.

I carry a spare kit in our Barth for the little mistakes one makes while RVing.

Costs about $10. to $20. depending on the size of the repair.

ED

It's a good idea to stop-drill any cracks, BTW.

Fortunately my tanks and fittings are pretty well up and out of the way - an the stubby wheelbase on my coach makes bottoming out less of a problem.

Stop drilling is better than not stop-drilling. However, drilling plastic introduces stresses of its own, which may bite you later. I have had better success using a hot rod to make stop holes. The heat allows any stresses to relieve themselves as the plastic cools. As long as the rod is not too hot. It needs to be just hot enough to make the hole. If you do stop drill, be sure to resharpen your drill to about a 60 degree angle, or buy one for plastic to minimize the stress risers you create.

Yeah, Marine Tex is wonderful stuff. I have done some incredibly bootleg stuff with it under field conditions that ended up lasting quite a while. Same for JB Weld, Devcon Plastic Weld and Shoe Goo. A while back, curiosity required that I test Marine Tex against the structural adhesive used to hold airliners together. It was equal, as far as my practical testing went. As with Ed, I always have some.

Many tanks are made of Polyethylene, which can be a difficult situation, owing to its waxiness. V-cutting and roughing up the surface will help adhesion considerably. I have used a number of adhesives, from a hot glue to Shoe Goo to Marine Tex. They all held, to varying degrees. In my playtime, I was able to induce a leak on a scrap PE tank with everything except actual plastic welding with the proper rod, which always works. The previously-mentioned method for ABS is almost bulletproof.

3M DP 8005 is supposed to mend PE. I haven't used it yet, but I would expect it to be good, coming from 3M. The tool is overpriced, but you can cobble one up with two dowels, a little metal and a caulking gun. You don't need the nozzle, either, just mix what squeezes out and apply. I carry some with me now, just in case.

3M 4693H is also claimed to stick to PE. It has the advantage of coming in a single, squeezable tube, so you don't need a twin-tube squeezer/applicator.

BTW, to help with identifying, HDPE, LDPE and PP float in water.

To test for LDPE or HDPE, mix 3 parts rubbing alcohol to 2 parts water.........LDPE will float but HDPE will sink.

If you have a piece to test, HDPE can take boiling water, but LDPE cannot.

I use this technique to help identify welding rod, too, although rod is often color-coded to a degree. Burning a sliver can also help identify a plastic.

I am another Marine-Tex adherent. It's a substance which, I have found, adheres to almost everything. I plugged a crack in the water jacket of an old Chrysler Crown marine engine that was still holding water when I sold it 3 years later, & I've made innumerable boat repairs with it. I once had a FWD GMC motor home with a drain valve mounted right below the center of the rear bumper, a spot guaranteed to trip on anything higher than a tar strip on the pavement. By the time I sold that coach, there must have been a pound of Marine-Tex from repeated repairs to the drain valve, but it always held up until the next time I smacked it on something.

With a roll of paper towels, a roll of duct tape, a can of WD-40, & a Marine-Tex repair kit, you're equipped to fix almost anything.