Patch or replace gray tank?

[FlyJake]

Hey everyone,

I have a 1984 Tiffin Allegro that I got a yr ago and finally got around to working on the gray water tank. There seems to be at least 3 areas with cracks that could be patchable (watched a great YouTube video) for like $30 in materials. A new tank is about $280 and install would be another $200ish.

The question is do I try and patch it or just replace?

Thanks for your thoughts!
-Jake

[Grog]

If the tank is made of polypropylene or polyethylene, there is no glue for these 2 materials. A manufacturer did come out with an attempt at one but with brand new plastic it was a 50/50 shot at working. Let alone on 37 year old plastic.
You can try using some polyurethane caulking as a temporary solution. It should hold up for a few years before you have to redo the caulking.

[Winemaker2]

Originally Posted by Grog

If the tank is made of polypropylene or polyethylene, there is no glue for these 2 materials. A manufacturer did come out with an attempt at one but with brand new plastic it was a 50/50 shot at working. Let alone on 37 year old plastic.

You can try using some polyurethane caulking as a temporary solution. It should hold up for a few years before you have to redo the caulking.

3M 5200 is a PU adhesive / sealant that is intended for permanent use. I can attest that removing it, short of using a torch, is next to impossible.
You might experiment on a good area of the tank, solvent clean, rough it up with sandpaper or wire brush in a drill and apply a bead. See how well it sticks after a week or so cure then decide whether to try the fix vs replace.

I know little about plastic welding but wonder whether that is an option with those materials. Harbor Freight has units that are reasonable $ for a DIY fix.
Whats to lose? With either of the above?

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[TheVintageRV]

Plastic welding is an option. There is a company in MN called GasTankRenu that welds the plastic fuel tanks in cars and trucks with good success.

[FlyJake]

Thanks for the thoughts everyone!

Any suggestions on how to patch the cracks?

ABS cement?
JB weld?
Flex tape?

[biker art]

Originally Posted by FlyJake

Thanks for the thoughts everyone!

Any suggestions on how to patch the cracks?

ABS cement?
JB weld?
Flex tape?

I have repaired holding tanks by using fiberglass cloth imbedded into the plastic after heating the tank plastic to soften it up enough. Then I used the fiberglass resin and added more cloth until I had a good repair. Using a propane torch on small areas allowed me to get the cloth to bond to the tank before using the resin. It was a cheap but good repair for a do it yourself project. You could try it and if it doesn't work you're only out about $20.

[Winemaker2]

Originally Posted by biker art

I have repaired holding tanks by using fiberglass cloth imbedded into the plastic after heating the tank plastic to soften it up enough. Then I used the fiberglass resin and added more cloth until I had a good repair. Using a propane torch on small areas allowed me to get the cloth to bond to the tank before using the resin. It was a cheap but good repair for a do it yourself project. You could try it and if it doesn't work you're only out about $20.

Now thats a creative approach!
Would never think of it but will try to file it away for future.

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[HarryStone]

https://www.youtube.com/watch?v=7IMAtlPSORs

[rogerstg]

Originally Posted by FlyJake

The question is do I try and patch it or just replace?

I'd try to patch it first.


It used to be that polyethylene required flame treating for the special glue to stick, but now there is Infinity Bond MMA 500 that does not seem to need any pre treatment. I only have experience with the old method for repairing canoes, so you might want to investigate the new glue further.

Infinity Bond MMA 500

[Argosy]

Eternabond. I patched a tank 15 years ago and it's never been a problem.

[D Gardiner]

Originally Posted by FlyJake

Hey everyone,

I have a 1984 Tiffin Allegro that I got a yr ago and finally got around to working on the gray water tank. There seems to be at least 3 areas with cracks that could be patchable (watched a great YouTube video) for like $30 in materials. A new tank is about $280 and install would be another $200ish.

The question is do I try and patch it or just replace?

Thanks for your thoughts!
-Jake

If you can get a new tank for only $280 I would jump on it.

On our RV that was not an option. We went with the plastic welding method. We did order the proper LDPE welding rods and stainless steel reinforcement mesh. Can’t find the Amazon link right now. Also went with the hot-air welder.
The trick is to grind the plastic down to clean material, drill the crack ends (as you did). Recommend filling the crack first, and grind smooth, as necessary.
Next using the hot-air welder to embed the mesh. Then cover the mesh with more LDPE rods. The last trick is to melt the plastic until it becomes transparent and fads the LDPE filler rod. This takes a lot of patience and some practice so as not too burn the old HDPE tank plastic.
Also,
In our case the gray and black tanks were wedged in casing extra stress on the outlets for the dump valves. With some trimming of the tank outlet length, and some slack on the two tanks, we achieved a stress free fit. The last thing we did was to add an extrasupport strap to distribute the water load.