Cold water cistern distortion

[toucan]

I replaced a 25 gall cold water cistern recently. I found it to be poorly supported on chipboard which had sagged from previous leakage, dry now. I was concerned that if I replaced the base only that the re-stressing of the distorted bottom of the CWS on a new ply base may cause cracking around the web supports. Was I right to do this or was it necessary work.

 

[PlumbBobBob]

the chipboard base needs changing as a matter of some urgency (with 25mm ply) and really the tank should the other way round, across the joists

 

[toucan]

unnecessary work.

 

[PlumbBobBob]

why? is it in a cellar?

 

[toucan]

I put new base in with noggins. It is in a loft.

 

[PlumbBobBob]

ah i see the pics are from before. sorry i misunderstood

 

[Best]

If tank distorted, I would change it. You would be responsible for damage if for a customer & tank burst later. Plastic base would have stretched, as would sides. Old tank may well have still been okay though, but how could you have been sure? Put the new tank in properly & with a proper new base & manufacturer is responsible, that's the way I see it.
Watch the woodworm don't put holes in the plywood (they love plywood) & bore through tank base! I am not joking.

 

[toucan]

Thanks best and steveb ..............woodworm through plastic ? ?

 

[jtsplumbing]

What part N Cornwall toucan ? how is work in your area ?

 

[Guest123]

Change the tank.

That's shocking, a CWSC on chipboard.

 

[WaterTight]

But ridiculously common. Around my area anyway. I'd say 1 out of every 5 ball-valve changes results in my warning the customer their CWSC isn't properly supported.

I remember one old guy and his was so bad I told him it could go any minute and he needed an emergency call-out (I was needed elsewhere.) I offered to give him some numbers to try and to drain it before I left but he refused saying it had been like that for years and I was exaggerating.

 

[Best]

Thanks best and steveb ..............woodworm through plastic ? ?

Fact is, for some reason woodworm really go for plywood, so better to treat the timber near the tanks, especially if the place is riddled in woodworm holes.
When I first heard of tanks leaking due to woodworm I thought it was a joke, but have now seen this on a couple of tanks. They not only "drill" holes in plastic base but also horizontal tracks along tank.
Chipboard seems not to suffer woodworm & is actually fine if fully supported & a heavy plastic sheet covered it to stop damp from any condensation or potential leaks from around tank & pipes.

 

[WaterTight]

building control wouldn't like it though

 

[Best]

But ridiculously common. Around my area anyway. I'd say 1 out of every 5 ball-valve changes results in my warning the customer their CWSC isn't properly supported.

I remember one old guy and his was so bad I told him it could go any minute and he needed an emergency call-out (I was needed elsewhere.) I offered to give him some numbers to try and to drain it before I left but he refused saying it had been like that for years and I was exaggerating.

What people don't seem to understand is the weight of 50 + gallons water!
If you criticise the work it puts people in bad form, but they then can't blame you if it later floods.
I see tanks just set on joists! Funniest one was a round 70gall tank ( the more flexible older type) set on top of a flat cupboard door, - which would have been okay if the round handle had been removed, as it was pushed into the middle of the tank base!

 

[Best]

building control wouldn't like it though

Absolutely! And you leave yourself wide open to redicule if you use chipboard. I wouldn't have any worries if it was in my house but with plastic sheet over it though.

 

[petercj]

Woodworm love the sweetness of pine timber, and being lazy little sods, they tend to avoid the hardwoods, which apparently don't taste as nice, as well as being harder going ... although I've never actually tried eating either myself.

Woodworm avoid chipboard because of the resin used to bond the wood particles together - as anyone who works with chipboard knows, it will take the edge of most cutting tools much quicker than natural timbers, including the hardest of the hardwoods.

As a bearer for anything that might spring a leak, the best board to use is an exterior grade strand board - which looks like this:-

[DLMURL="http://www.diy.com/nav/build/timber/sheet-materials/Oriented-Strand-Board-3-L-2440-x-W-1220-x-T-18mm-9276290"]Oriented Strand Board 3 (L)2440 x (W)1220 x (T)18mm, 5014957148673[/DLMURL]

As well as being highly resistant to water, it's not a favourite of the dreaded worm because of its high resin content.

I would go for around [FONT=&amp]¾" thickness.[/FONT]