Water tank split/Plastic welding?

Submitted: Wednesday, Jun 30, 2021 at 14:43
ThreadID: 142066 Views:1108 Replies:12 FollowUps:7
Bugger! The water tank has split in our Patrol. A custom built 160 litre rectangular plastic (HDPE I think) jobbie, made professionally around 10 years ago. We discovered the split a couple of days ago when we had a full tank of water & the car was parked on an angle.

It has split along one of the top welded seams - a straight line around 150mm long.

I reckon the chances of finding a plastic welder up here on Cape York are probably around zero, so will try to use it by only filling it around half to two thirds full & accepting a little spillage if the silver plastic 'gaffer' tape I've put over the split is inadequate. Hopefully this work for us whilst we are up here, & we also have a 70 litre tank in the Tvan should the split seam lengthen or the tank become unusable..

My question is about plastic welding, or more precisely what sort of temperatures are involved. The reason I ask is that if I can avoid doing so it would be far more convenient to have a repair done in situ, without removing the tank. The nearest 'flammable' material to the split is some painted 3mm ply, (which doesn't matter if it gets scorched/discoloured in the process). There is a gap of approx 10mm between the tank & the ply.

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Reply By: jeff r - Wednesday, Jun 30, 2021 at 14:53

Wednesday, Jun 30, 2021 at 14:53
I think a quick fix would be to use silicon. I did this on a stainless water tank, a left it for 6 months with no issues before I had it welded. Give it a go the silicon will stick well to the plastic I imagine.
Cheers...Jeff
AnswerID: 636992

Follow Up By: Member - Cuppa - Wednesday, Jun 30, 2021 at 15:06

Wednesday, Jun 30, 2021 at 15:06
Thanks Jeff, I have considered doing just that, but have held off only because I know using silicon can make some repairs (paint) very difficult, if not impossible.

As I have no idea what effect silicon might have on a future more permanent plastic welding repair I thought it wise to be cautious. If any plastic welders (Peter Wright?) read this I would welcome advice as to whether silicon is ok or a 'no-no'.
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Follow Up By: Peter_n_Margaret - Wednesday, Jun 30, 2021 at 20:09

Wednesday, Jun 30, 2021 at 20:09
If you ever want to make a decent repair to the tank, DO NOT use silicone, EVER..
Cheers,
Peter
OKA196 motorhome
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Reply By: Rocket Rod - Wednesday, Jun 30, 2021 at 15:10

Wednesday, Jun 30, 2021 at 15:10
For plastic jerry cans I heard people have used heated grass tree gum and forced it into the hole or heat a screw driver and melt the surrounding plastic.
AnswerID: 636993

Reply By: RMD - Wednesday, Jun 30, 2021 at 15:17

Wednesday, Jun 30, 2021 at 15:17
Cuppa.
Perhaps you could repair it with the aid of a decent heat gun to warm the surrounding area along part of the seam at a time and use a flat 4mm wide but pointed, ie, wedge shape Electric soldering iron to melt the pre heated area and close over the seam. and seal the whole section.
I bought a brand new 50 litre red HDPE tank which had the filler neck driven inwards in transit. The neck completely detached from the top of the tank. By pre heating until soft and using an iron as described above, I circular plastic welded the filler neck to the top and used a little small thin cutoff bits of green home water tank material as a filler into the weld where some sag took place, and as a fillet to strengthen the 90degree weld. All good after 10 years and using it as diesel tank.

HDPE softens easily and melts and is workable at around 130C so any soldering iron will easily do it. Sometimes too hot and if able to regulate the iron heat to a sufficient temp then it is more controlled welding with no sudden OOPS involved. Too hot and it gasses and become oily and not good for a welded joint. Professional plastic welders will know more., I am just an apprentice, my Briggsand stratton mower tank still weeps a bit.
AnswerID: 636994

Reply By: Joe Fury - Wednesday, Jun 30, 2021 at 16:49

Wednesday, Jun 30, 2021 at 16:49
G'day Cuppa

A quick, simple and very effective way of You plastic welding your tank involves using a heat source to heat the split area and using a black cable tie as a filler rod, the heat source should preferably be hot metal and not a flame, or a gas torch.
If you are carrying an electric (240 V or 12 V) soldering iron it would be a super simple job, just don't concentrate the heat point in one spot for to long, just long enough to melt the tank plastic with the cable tie plastic.

Safe travels : Joe

AnswerID: 636996

Follow Up By: Michael ( Moss Vale NSW) - Wednesday, Jun 30, 2021 at 20:10

Wednesday, Jun 30, 2021 at 20:10
Don't use cable ties, they are nylon and HDPE are NOT compatible. if you have a go with a clean soldering iron, a filler like a thin strip off a 2 litre milk bottle will be compatible. Obviously the ultra clear milk bottles are PET and also not compatible. Michael
Patrol 4.2TDi 2003

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Follow Up By: Peter_n_Margaret - Wednesday, Jun 30, 2021 at 20:12

Wednesday, Jun 30, 2021 at 20:12
A black cable tie is likely to be made from nylon which is totally incompatible with HDPE.
If you want to try, use strips cut from a milk bottle which is HDPE.
Cheers,
Peter
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Reply By: noggins - Wednesday, Jun 30, 2021 at 17:47

Wednesday, Jun 30, 2021 at 17:47
A plastic bottle top carefully heat welded into the crack was how I was shown how to do it when I had a split water tank in Vic.
If there's a body shop plastic welder/ interior repair man in the next town you'd be right on the money, so many cars are all plastic these days.


Ron
AnswerID: 636997

Reply By: Darian - Wednesday, Jun 30, 2021 at 20:13

Wednesday, Jun 30, 2021 at 20:13
Just on tapes...you might be able to obtain better than silver gaffer...your first hardware shop encountered might have the fabric reinforced version. The adhesive is much stronger on those.
AnswerID: 637001

Reply By: Peter_n_Margaret - Wednesday, Jun 30, 2021 at 20:18

Wednesday, Jun 30, 2021 at 20:18
Hot air welding is a simple process, but needs a knack or 2 to be good.
I do some at home including spin welding, but I am no expert.
The air temperature is typically around 300C for HDPE.
Most people who are good at it use a carefully controlled heat gun with an outlet nozzle of about 6mm diameter to concentrate the area heated.
A soldering iron might give you a temporary fix until you find someone good at it.
Cheers,
Peter
OKA196 motorhome
AnswerID: 637002

Reply By: Member - Wooly - Wednesday, Jun 30, 2021 at 20:44

Wednesday, Jun 30, 2021 at 20:44
What about the self amalgamating tape, sticks underwater and all that?

10 bucks a roll at auto shops, maybe 20 bucks up near cape york?

Most people have a roll in the kit for just this type of emergency.
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Follow Up By: Member - Cuppa - Thursday, Jul 01, 2021 at 07:04

Thursday, Jul 01, 2021 at 07:04
I have some self amalgamating tape, but believe it needs to be wound around something (like a hose/tube) to stick to itself(self amalgamate). So didn’t think it would work along the edge of a water tank.
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Reply By: Mikee5 - Thursday, Jul 01, 2021 at 07:20

Thursday, Jul 01, 2021 at 07:20
I repaired my home rainwater tank by the careful use of an electic soldering iron. Not full heat and quick dabs. It was untidy but worked. Quality cloth duct tape should hold as a temporary fix though.
AnswerID: 637006

Reply By: thinkin - Thursday, Jul 01, 2021 at 09:58

Thursday, Jul 01, 2021 at 09:58
How about trying a non welding type of repair . Get light angle aluminium, pressed metal, colourbond greater than the length you want to repair. The thickness of the angle only needs to be 1-1.5mm x 30mm or so. The angle is used to give rigidity. Pre drill the metal on the both edges to take tek or phillipshead screws.
Clean up the split section, apply liberal amount of sealer (silastic) , place the angle firmly over ( wound) and lightly screw on the angle to the tank. (lightly so you don't strip the thread in the plastic).
I did this 10 years ago the tank is still going. Tank was made out of 4mm black poly stuff.
AnswerID: 637009

Reply By: Member - silkwood - Thursday, Jul 01, 2021 at 17:54

Thursday, Jul 01, 2021 at 17:54
Two part repair putty (Locktite, Selleys etc.) will provide a solid, leakproof repair which can be easily ground back when a permanent plastic weld job is needed. Should be available in Bamaga. In fact, the repair will probably not need more attention. I've used it in dozens of applications and it is (almost) invariably effective.

Example...

Selleys Knead It

Cheers,

Mark
AnswerID: 637015

Follow Up By: RMD - Thursday, Jul 01, 2021 at 19:07

Thursday, Jul 01, 2021 at 19:07
It has to ba able to bond to the polymer strings of HDPE to stick and work. Does it really?
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Follow Up By: Member - silkwood - Thursday, Jul 01, 2021 at 21:37

Thursday, Jul 01, 2021 at 21:37
Yes...

There are a number of types to suit almost all situations...
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Reply By: Member - Cuppa - Wednesday, Jul 07, 2021 at 17:44

Wednesday, Jul 07, 2021 at 17:44
Thanks for all the replies.

We found that our 10 year old Ritar AGM batteries were struggling & decided to return to Mareeba to get them replaced before heading further up the Cape. The water tank needed to come out to enable battery removal, so we will get a plastic welder chap in Malanda to repair the tank.

Turned out that two of the Ritars were good & one was cactus. Explains why we were ok if we had sun each day, but voltage dropping to levels previously unseen if we had a couple of cloudy days in a row.

Anyone travelling in FNQ & in need of batteries - I recommend Bruno's Batteries in Mareeba. Better prices than Cairns & online sellers, & excellent helpful service.

Hopefully we'll get the tank repaired on Monday & head back up the Cape next week
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