Plastic welding question

An elderly couple just down the road from me have a 1000 gallon plastic water storage tank that has developed a minor crack near the bottom.
They say they have access to rod, and I assume, a plastic welder, waiting to hear back on that. I offered to give it a go, but cautioned I am 99.999999% sure that tank will have to be emptied, and the crack dried out before it can be welded. Unsure of material yet, but IIRC, most water storage tanks are PP or PE. I just can't see getting a good weld with moisture in there. But, thought I'd ask, surely somebody here knows a thing or two about plastic welding.
I also suspect the stresses that caused the crack in the first place are going to make a real long term fix somewhat improbable, but maybe we can get it to hang in there until these folks don't have to worry about it anymore...
Jon
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"Jon Anderson" wrote in message
An elderly couple just down the road from me have a 1000 gallon plastic water storage tank that has developed a minor crack near the bottom. They say they have access to rod, and I assume, a plastic welder, waiting to hear back on that. I offered to give it a go, but cautioned I am 99.999999% sure that tank will have to be emptied, and the crack dried out before it can be welded. Unsure of material yet, but IIRC, most water storage tanks are PP or PE. I just can't see getting a good weld with moisture in there. But, thought I'd ask, surely somebody here knows a thing or two about plastic welding.
I also suspect the stresses that caused the crack in the first place are going to make a real long term fix somewhat improbable, but maybe we can get it to hang in there until these folks don't have to worry about it anymore...
Jon
no opinion on your particular problem, but I have a (so far unused) harbor freight plastic welder, it was $30 or so -
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Bill,
I haven't heard back yet, but think they have access to one. But I'm offering to do it for free, so not buying a welder for this one... But thanks, didn't know one could be had so cheap.
Jon
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Jon Anderson wrote:

a simpler and safer option is to do a mechanical repair. 1. empty it 2. dry the split area 3. cut 2 pieces of ali sheet some 3 in larger alround than the crack. 4. drill the internal patch with holes suitable for some stainless self tapping scews or 3/16th in thick bolts. 5.place patch over split and drill through the plastic. 6. Apply sealing compound to the inner patch 7. and apply to plastic. place bolts or screws through holes. 8. use the bolts/screws to mark outer patch . 9.drill through for bolts or smaller holes for self tappers. apply sealing compound to outside as well and bolt outside patch or pull in with the self tappers.
Have used this method on several plastic containers over the years. all are still holding up ok.
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On 10/22/2010 8:01 PM, Ted Frater wrote:

I rather suspect this is for drinking water. Many wells in this area are marginal and people have decent capacity holding tanks. I like your idea, but any sealant would have to be safe for potable water. Any ideas on that?
Jon
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Jon Anderson wrote:

were on our own water supply ,have been for 40 yrs. I use for any jointing clear silicone sealant. I put it on compression joints to ensure there are no drip leaks and on screwed threaded iron pipe work i use what we call boss white and flax strands called maiden hair. Ask an old plumber hell remember it. Thats not suitable for drinking water as its linseed oil andf white lead. but you can use ordinary glazing putty. thats linseed oil and chalk powder. thin it down with some more linseed oil into a semi runny paste. Of the 2 id prefer the silicone as it goes off in air.. wipe off any surplus that squeezes out when you do up the patch .it will be quite safe after its cured. 2 to 3 hours will do it. Plastic welding wont be reliable enough under the water pressure so you dont want to have to do it again just after you have filled up the tank!!. What are the tank dimensions? Round or square.? Ted Dorset uk
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On 10/22/2010 11:15 PM, Ted Frater wrote:

Don't know. The request for help came through the local Freecycle list and I offered my services gratis, but have not gotten a reply yet.
Jon
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On Fri, 22 Oct 2010 22:36:30 -0800, Jon Anderson

RTV comes in Food Safe versions.
http://bbs.homeshopmachinist.net/archive/index.php/t-39053.html
Get an Aquarium Safe grade. Wont take very much. A single tube should do the job if used with the OPs patching method..which is pretty damned good.
Gunner
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wrote:

Very good idea!!
Jon can scuba too!!
<G>
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Ted, you stole my thunder. An interior patch, properly applied, and using the internal pressure to keep it pushed in on the crack is a better fix. A weld would still have pressure trying to make it split. Or, even make a patch, put it on with some good sealing compound, and use the plastic welding to seal the edges. I have never used plastic welding, but I do weld. Considering you will end up with probably three different types of plastic (base material, patch, and filler rod), it would make me wonder if all three would melt and bond adequately. As we all know, it only takes a little hole for water to leak.
Steve
Heart surgery pending? Read up and prepare. Learn how to care for a friend. http://cabgbypasssurgery.com
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Steve B wrote:

Hi Steve, No intention of stealing your thunder!!. Asyou will have read elsewhere in this thread, im basically a metal man so most of my solutions to problems here on my patch are approached from the metal point of view especially as I have all the kit, tools, metal and rivets etc to repair any thing and make most things, already on the shelf. I wouldnt attempt to go down the plastic welding route as its not my interest, tho I know a chap who speciallises in plastic car bumper repair. He makes a good one out of two crashed ones and you wouldnt know where he had welded it. Earns a good living from it just as I do from metal work. Horses for courses we say here.. ted Dorset UK .
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On Fri, 22 Oct 2010 20:22:42 -0800, Jon Anderson

Ayup..it has to be emptied below the crack. Not necessarily dried out though.
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Gunner Asch wrote:

To help the silicone to stick it would help to dry the surface of the plastic. depends how deep it leaves the water in the tank bottom, you dont want to have to wear fishing waders!! and work in water 1ft deep. Any problems getting into the tank? youll need to work from the inside!!, yuoll need a good light and a safe ladder to get in and out. as for the patch you could drill both at the same time, when fitting to the plastic put in 2 screws opposite each other, then put the outside patch over these to locate the outside patch. bolt up the drill through the other holes. Might as well make it easy!! and accurate!! An extra pairof hands on the outside will speed things up as well. Ted Dorset UK.
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I wonder about you Yanks - you used to be good at improvising, making do, lateral thinking. What happened? - solutions dont need to be hi- tech to work.........whats with this specialised tool stuff to do a simple repair.....and you dont want to lose your summer water storage by draining the tank...
Bang a patch over it - if you can see/find the stress line, drill a 1/8th hole each end, will stop it spreading. Make up a patch plate out of....anything...fold it to the contour of the tank, silicon it up round the seams and pop rivet it on..... easy as.....
Andrew VK3BFA.
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Andrew VK3BFA wrote:

Yes pop rivetting from the outside is a way of not having to drain the tank, BUT do run some trials with the pop rivets throughtthe plastic above the normal waterline to make sure the plastic is hard enough to take the pop rivet pull. Generally speaking pop rivets are meant to be of softer material than the material being joined. now putting washers on the inside of the tank where the pop rivets come through is the way to rivet soft material with harder rivets. but youll need to be able to reach down into the water to feel for the pop rivet to put the washer on. Thats why I asked what are the tank dimensions. Most folk can reach down 3 ft. Just maybe the crack is not lower than that. interesting!!,,,
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I welded up a 1500 gallon tank that blew off of a stand during a storm, found it about a 1/4 mile away. I bought a Steinel heat gun / plastic welder. Bought some rod in bulk and welded up about 15 or 18 ft of separation. Welded both sides 2 or 3 passes depending on the crack. I put some silicone on the inside to seal and leaks I might have missed. It preformed well for about 3 or 4 months and started leaking. So I took some 1" poly pipe and made patches from the pipe by cutting a chunk off the length of the crack I wanted to patch. Heated it up and flattened it out and welded to the tank. I ran out of rod and took long slivers of pipe and used that for rod. It worked and it still holds water no problems. Plastic welding is like any other welding. Depending on the material and the temperature welding and penetration. I found out temperature and speed make a big difference. Do not listen to the naysayers " It will not hold" . I have welded cast iron and was told it will not hold. Anything can be welded if you find the right rod or pretreatment and post treatment. I was using hot air to weld. I do not know about hot iron welding, but polypipe is welded with a hot iron everyday.
Scott
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On 10/22/2010 11:52 PM, Andrew VK3BFA wrote:

If it's something of mine that needs fixing, I'll try most anything and can be rather creative at times. Often works out, sometimes not. That's just the way it goes...
This is an elderly couple with health issues on fixed income. I'm quite sure buying a new tank is not in their budget. It's not in mine either should I muff the job. Nothing wrong with asking a few questions and getting some advice from folks that have faced something similar.
Jon
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wrote:

Polyethylene is an extremely forgiving material and easy to weld with hot air or even a plain old soldering iron. Making it pretty is another story... Yes it will need to be empty to below the leak, but don't worry about the dry. Heat from welding will take care of that.
Hopefully it is leaking in a thick area (think corners) so you will have some meat to work with. Real thick and you may even want to "V" it out a bit first. If it is leaking from a thin spot you may want to consider the patches so many have suggested.
--
William

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    [ ... ]

    Except that it would be the *winter* water storage here. Summer is well over. (And depending on where it is, there may be plenty of opportunity to shovel snow in to replenish the water drained.)
    And people here *like* to consider all kinds of tools and methods. I'm sure that whatever is finally used will be reasonable for the task.
    Enjoy,         DoN.
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"DoN. Nichols" wrote in message wrote:
[ ... ]

Except that it would be the *winter* water storage here. Summer is well over. (And depending on where it is, there may be plenty of opportunity to shovel snow in to replenish the water drained.)
And people here *like* to consider all kinds of tools and methods. I'm sure that whatever is finally used will be reasonable for the task.
Enjoy, DoN.
--
You could get the pop rivets they use on Kayaks. Plastic and will not
corrode as aluminum may do.
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