# Forum Home Renovation General Odds & Sods  poly tank repair

## dadof4

i need to repair a 3 inch long crack in a poly tank.when i spoke to a poly welding company they said they said the welding wasnt always sucessful.has any one any methods i can try.

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## Big Shed

> i need to repair a 3 inch long crack in a poly tank.when i spoke to a poly welding company they said they said the welding wasnt always sucessful.has any one any methods i can try.

  Don't know any other way of welding a poly tank. One of our tanks, a 22000ltr Polymasta developed a crack in the top and it was fixed under warranty, that was about 4 years ago and it is still going strong.  
Where in the tank is the crack?

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## Claw Hama

If you have access to both sides of the crack you could just bolt a metal plate to it with nice big washers on one side. Slip a lenght of flash tack or something food safe  under the plate to seal against the crack once the bolts are tightened.

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## BobL

> i need to repair a 3 inch long crack in a poly tank.when i spoke to a poly welding company they said they said the welding wasnt always sucessful.has any one any methods i can try.

  They will generally say that because they probably don't want to keep welding it over and over again if it does not take. This a somewhere between a rock and a hard place for any company, 9/10 times it will be OK but that 1/10 times will create more than the other 9/10 work so unless you bought the tank from them they will try to avoid it.  
Where is the crack, if it is on a seam or angled corner or in a place that cannot be cleaned or accessed properly, or can only be welded on one side the likelihood of it work goes down a lot. 
Maybe an independent plastic welder to do the job.

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## BobL

> If you have access to both sides of the crack you could just bolt a metal plate to it with nice big washers on one side. Slip a lenght of flash tack or something food safe  under the plate to seal against the crack once the bolts are tightened.

  This will work sometimes for a long while but if you have access both sides you might as well get a plastic plate of the same material welded on both sides

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## Buzza

Poly does not weld at all well if it is to be under pressure. A shapr wack will reverbarate the contents, and the welds will always let go with an audible crack  
One solution, is to purchase an inner liner. These are available for about $250.00 or so. Depending on your supplier and the size of course. They are essentially, a plastic sheet made into a bucket shape. 
The suggested solution, e. g. sealing the crack wih a plug can work as the other answer suggests, but I would utilise some neophrene (sic) on the wall inside and out, with the timbers over the top of them. Once the neophrene is squashed under pressure, it wll seal. Source neoprene from an old wet-suit or some runners that have been tossed away. :Smilie:  
I have just gone through the dramas of a leaking poly fish pond of 500 litres, and a rusting galv water tank.   :Cry:

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## prozac

Poly tanks do not weld well. 
Drill each end of the split to "stop" it. Just a small size drill, don't go bananas. Claw hammer is right on the button with his advice of using two plates bolted through. Instead of using SS for the plates perhaps two plates cut from a kitchen HDPE (High Density polyethylene) chopping board would be less likely to stress at the edge contact points? I don't know if Sika make a product suitable for potable water but an alternative might be soft butyl rubber which will squeeze to form a tight seal when some pressure is applied via the HDPE plates. 
prozac

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## Scarlette

There is a product out called Quickset Watercrete. It repairs cracks and holes in any kind of water tank, from galv to concrete to poly. It has a compression strength of 2000psi, also It sets under water in 5 minutes so you can go for a dip, fix the crack from the inside and scoop out the frogs at the same time. 
I agree you'll need to stop it from furthur cracking.

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## Plasticfusion

While this thread was posted some time ago, I can offer some extra advice that might be helpful.  My partner and I run a mobile plastic repair business that specialises in the repair of poly tanks, agricultural spray tanks and diesel fuel tanks.  I'm also an avid DIYer and understand the desire to tackle a range of jobs for self-satisfaction or to save money.  However, to successfully repair poly water tanks there is a need to use the right equipment to get a lasting repair.  Poly is very oily and difficult if not impossible to glue with success.  The large forces involved in a tank also need to be kept in mind.  A 23,000 lt (5000 gal) tank of water weighs 23 tonne or the equivalent to about 20 small cars.  The head pressure at the base of the tank and the expansion and contraction of the plastic make simple repairs using hot air guns, soldering irons, glues or screwed on patches unlikely to be successful as long term repairs.  We "V" out the crack line to within a mm or so of the thickness of the tank and fillet weld the grove with new plastic using a plastic extrusion welder.  These extrusion welders are specialist machines cost upward of $8000 and are beyond the handypersons tool kit.  It also takes some experience to use the welder and understands the mechanics of the repair proceedure.  My thumbs up advice is call an expert for this job.  :2thumbsup:

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## Plasticfusion

We now have our web site up with examples of poly repair work we have completed.  With the right equipment it is possible to repair extensive damage to poly tanks.  Check out www.plasticfusion.com.au  :Wink:

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