Backyard Aquaponics
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I have a 1000 gallon (us) PP tank that has a few small cracks in it.


1 is at the bottom 6 inches off the ground and about 4 inches long running up and down.

the other 2 are near the top and are about 3-4 inches long again up and down.


What i was thinking was some sort of marine type sealing tape for the inside, then bracing the outside by wrapping the tank tightly as to strengthen it and take the pressure of the tank.

It holds water it just leaks. so i figured if i can stop the leaks that would be great, and while i am at it i can wrap the tank to take away some of the stress where the cracks are.

The cracks are there do to the tank being tipped over not due to the water bursting it.


Couple tapes i looked at are foil backed with a water proof adhesive like butyl are extremly durable and capable of holding a seal submerged.


Thanks

Have a look at "plastic welding" them...

Tape or sealants will stop the leaks for the short term, but the problem with vertical cracks is they will just get bigger with Temp changes and such will and one day just let go. Your best option is to get it welded just make sure they know what they are doing and weld both inside and out

Weld and then wrap the outside of the tank in wire mesh and concrete render it.

I would weld, then get some plastic about 100mm bigger than the crack and glue over as a support to help reduce chance of cracking again along the weak point.

There are several ways you can fix this tank but some of the causes of the problem are going to prevent you from having the tank survive a full lifetime.
Polyethylene tanks crack and fail or develop small splits due to poor manufacture by the rota moulder.

This material must be correctly heated, formed into an evenly distributed thickness and then cooked or cured to an optimum point where it reaches its best impact and properties.
If you cut a x section and slice it with a very sharp knife you should observe a solid material with possibly some very small bubbles in the layer closest to the inside surface of the tank.
This indicates a close to correct cure.
if it has been incompletely cured you will see a lot of bubbles throughout or if it has been over cooked it will have none.
Either side of the optimum will result in poor qualities and wall failure will be the result.
Another failure will be due to the product being unevenly moulded with thick and thin areas throughout.

Polyethylene relies on correct curing to develop its best strength and impact properties.
If your tank is cracking it will most probably continue to and at some stage will completely split or unzip upwards.
If there are a lot of air bubbles in the cross section then this will be the cause, the product has not reached full cure.
To repair it, you need to have it welded professionally.
You may be able to brace it with a couple of straps and bolt them through the wall to support the area.

If you are handy with a soldering iron and can get or cut some strips of polyethylene, (plastic milk carton in the fridge is suitable) you will be able to heat the material and weld in some plastic.
First empty the tank though, if you heat it first it will expand and a large hole will burst through.
Cut the poly into thin strips and work the material with the iron and putty or bog fill it with the hot material.
Support the back of the tank as when the polymer is heated it expands and softens and will sag.
Work the iron deep into the wall split and get some penetration so you are not just smoothing over the surface and build a thick weld over the split area.
Drill a 8 mm hole in the tank top flange and practice filling it first to get the hang of it.

You will NOT be able to glue this material as it is oily based and other than a 3M product that is very expensive it will not hold glue or any sort of silicone material.
Paint, stickers etc will only adhere for a short time until the oil base lets the adhesive go.
Marine growth is similar, barnacles and weed can attach for some time but when the weight of the growth rises it can no longer stick to the material the oily base causes it to let go.

Polyethylene is capable of holding many dangerous substances but the worst material to affect the structure is simple detergent, simple plain detergent will cause bigger failures than things like caustic and acids.

The industry established Australian standards to ensure manufacturers are supplying approved products but it only applies to water tanks and aquaculture tanks are still a grey area.

There have been almost 6000 tank failures in Qld last year due to poor manufacturing techniques.
Government subsidies encouraged a lot of cowboy operators, who flooded the market with poor products, offered 30 year guarantees and went broke in less than three years, so much for your guarantee if you live in Qld...

Hope this helps

Gavin M McDonnell
Managing Director
Eagle Rota Moulding
Mandurah

PM me if you still need advice

Thanks Gavin,

Very informative, will keep this in mind