Black tank cracked

[Chaz]

Just a quick question:
  A buddies black PLASTIC tank is cracked at the top - probably from being sucked out he says as they were living in it while building a house - and he is taking it to Talladega this next week. It's not a real bad crack and he is replacing it when he gets back but can't get it done for now. Any suggestions??
  He asked me to weld it but.............. yeah right.  NOT going to happen!!! I mentioned he might be able to get by, since it's not a bad structural crack, to use some duct tape and visqueen (spell??) plastic, tape the plastic over the hole with a little room around it and some slack and use the expanding spray foam insulation under the plastic to keep it from leaking. He would need to scuff the tank up a bit to get the foam to stick better but my thoughts are that it's some bad a$$ sticky stuff, flexible and should seal for this trip.
  Thoughts??
  Chaz

[Ed Hackenbruch]

Tell him to not overfill it!

[Len Silva]

Hot melt glue might work s a temporary measure.

[Tenor]

piece of plexiglass with silicone?

Glenn

[chev49]

i would plastic weld it... after checking exactly what plastic it was - and thats easy. Otherwise if it was available to get at the spot to repair it, and i was afraid to weld it, i would get another thick piece of plastic, some black winshield stuff in the tube that one installes winshields with (i use it for lots of stuff - about $14 a tube at the automotive paint store), drill holes in the top piece for the screws and glue n screw. After it dried, i doubt that it would leak...or come apart for that matter.  since the tank was cracked, i would reinforce it in that area anyway, cause with plastic welding, it would likely crack again.

[JohnEd]

I have had a lot of trouble "welding" plastic tanks.  There are a lot of different tank materials and the rods don't seem to like any material other than the exact stuff.  The RV repair places have this down to a science and they don't charge an arm and leg.....most don't anyway.  Step aside and lets the pros handle it.

I have seen tanks that were a mere 15 years old and they were "crazed".  No way is that repairable.  My waste tanks are 39 years old and showing no sign of giving up.  Depends on the material quality, for sure.

I have repaired fresh tanks at the bottom "outlet" using a 2 part epoxy style resin that sticks to propylene and such.  It worked very well and held up for years.  i only changed out the tank to get greater capacity.  Waste tanks are made from the same plastics.  Again, I would call a repair outlet to get the best working type and "brand" for the job.  no substitute for experience.

John

[eddiepotts]

I would drill an 1/8" hole at each end of the crack to stop it. Use a die grinder with a debur bit in it and grind a valley into the crack. fill it with roof seal caulk and walk away from it until they get the new tank. Like Ed said. Just don't over fill it and it will be fine with out a fix unless it is at an inlet hole and leaking. Don't over engineer it.

[TomC]

When I was running cross country in my truck, I mounted my black and gray tank on the fuel tank lower supports with the drive shaft above.  The gray tank being rectangular was to tall to clear the drive shaft at the rear of the tank, so I cut a triangular section out from each side and used a propane torch to heat it to bend the rear of the tank to have a slope to it.  I cut it 1 inch below the crease to create a lip. I then drilled holes and screwed self taping screws to hold the two halves together (this is important since the plastic gets soft and floppy when welding).  I then just took some of the plastic I already cut off and used it as the welding rod and welded a bead both down the joint and over the screws again with a propane torch.  The tank never leaked and was in the truck for almost 700,000 miles of bouncing around.

Polyethylene is the only plastic I know you can weld.  If it does start to sag, throw some water on it to stiffen the plastic back up.  I suggest you weld up that crack in the tank-or weld a plastic plate over it.  I don't know of any glues that will stick because of the high patroleum level in the plastic.  Good Luck, TomC

[Ace]

Drill holes like Eddie said. That will keep it going further. If hes afraid if widening, put a ratchet strap around it.
Look at the bright side, it's vented out the top!

[Geoff]

I've had good luck using "Seal All" on leaking tanks.

[JohnEd]

"I don't know of any glues that will stick because of the high patroleum level in the plastic."  And Tom is right about thast....almost.  They do have stuff that sticks and works.  Seal All?  Dunno, but Geof has been a good source before.

I don't recall the trade name of the stuff I used in 94 but it worked and they sure as heck must have made some tech strides since then.  Look what they have done with the soup sandwich.

John

[Melbo]

go to Home Depot and get the epoxy that is made for plastic -- drill the hole at each end of the crack as recommended but do it with a small hole saw then use the the epoxy --- get a bunch and some sheet rock style mesh --- If the surface is really slick be sure to scuff it up with sand paper ---- I made a repair like this (without the holes at each end) on an oversize drain I had installed on my fresh water tank that was not welded correctly and it has held for years.

HTH

YMMV

Melbo

[Hobie]

JB Weld in a stick.  Prep it like previously mentioned, drill to stop crack, grind and clean.   This stuff is a 2 part epoxy putty that you roll to mix and form into the repair with your fingers.  Works great.  Handy for stuff like this.  

I used this on a gas tank and had forgotten about the repair until this reminded me of it!  

[luvrbus]

Ruff it up with 60 or 80 grit paper and apply bed lining material 2 or 3 coats it will hold forever same material best stuff since sliced bread,bonds to anything  

good luck

[Lin]

This thread just re-proves the old proverb, "There's more than one way to skin a crack."