[Public-List] Water tank

[Stephen Gwyn]

A few notes on the water tank. I took off the aluminum top to my
water tank a few years ago. The bottom side was pitted.  I
cleaned it, washed it with the aluminum prep stuff from West
System (product 860) and coated with two coats of West System
epoxy. The fibreglass liner bottom had hairline cracks in the
gelcoat. I opened them up with Dremel tool and filled them with
epoxy. In retrospect I wish I had coated the entire surface with
epoxy and I also wish the last coat had been carefully vetted
food-safe epoxy. (West System is a bit wishy-washy on whether
their stuff is food-safe).

To put the lid back I used screws.  Pop rivets are fine. There
may be a hole in the middle of the pop rivet, but since the
rivets do not go into the tank, but rather into a void under the
liner outside the tank, they will not cause a leak. But I used
1/4 inch screws because I did a bad job of removing the old pop
rivets and the holes were now slightly enlarged.

For sealant I called up BoatLife and asked them what to use. They
recommended LifeCalk, their polysulfide sealant. They said
polyurethane sealants (ie. LifeSeal, Sikaflex or 3M5200) leached
nasty chemicals into water. So do most silicone sealants (there
are food-safe silicones, they're just not very good sealants.
They also said water that comes in contact with the sealant
before it completely cures is not safe (1 week minimum).

The resulting tank produced water that did not have chunks in
it. It is also sealed very tight. At the last stages of filling
up, due to inadequate venting, the top of the tank flexes upward
with the pressure, but not a drop of water escapes. I have some
problems with green slime however, which I have fixed with a
combination of bleach (to get rid of the slime) and a carbon
filter (to get rid of the bleach). I also flush my tank fairly
frequently.

BTW, I'm pretty sure the lethal concentration for sodium chloride
is higher than 3500 ppm. That's equivalent to a tablespoon of
salt in a gallon of water.


Stephen
#495 Quasar


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  Stephen Gwyn                 |  Tel: 1-250-363-3136
  Dept. of Physics & Astronomy |  Fax: 1-250-363-0045
  Univ. of Victoria            |  Cell: 1-250-885-6969
  PO Box 3055                  |  E-mail: gwyn at uvastro.phys.uvic.ca
  Victoria, BC  V8W 3P6        |  http://orca.phys.uvic.ca/~gwyn
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