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Re: NFC: Tank Building.



"Joshua L. Wiegert" wrote:
> 
> Hey all.
> 
> Welp, most of my custom darter tank has come along pretty well thus far....  But, I've got a couple of questions for you all....  First off, I'm using an plexi-glass sheet for the front pane that measures 48" x 14" (I'd somehow originally thought this was a 36" long, btw, but, when I remeasured it, it was 48".)  The plexiglass is "medium strength" (whatever that means) and about a tenth to an eight of inch in width....  Did I do a dumb thing when I bought it?  :)  I have a few 2x2's I was going to use to reinforce it at a few places....  Will this help?  Someone told me that the standard silicon glues for fish tank's won't adhere very well to the plexiglass.  Opinions on this?

They will stick "sort-of" but I wouldn't count on any strength from such
joints. Use roughened surfaces and epoxy. The silicone can be a back-up
water sealant, if needed.

It may take a lot more than a 2x2 to reinforce it enough to stop ominous
bowing, unless you add cross members on top. Look at how commercial acrylic
tanks are made, with a thickness considerably more than equivalent-size
glass and a top that is so wide it makes up for the poor tensile strength of
the sides, hence prevents bowing.

You need much stronger joints than with glass, for one side of the plexi
will be exposed to air, and the other to water. It swells a *lot* when wet,
so huge bowing forces can be expected. I would bury all edges in dadoed
grooves in a strong wooden frame, so no plexi joint is ever in pure tension,
even with epoxy. Make the water pressure try to tighten the seal, not break
it.

Plexi has a bizarre surface chemistry that makes strong bonds almost
impossible. That's why plastic tanks are assembled with solvent to fuse the
joins into a solid piece of plexi.
 
> 
> Lastly, and most importantly, I couldn't find any marine paint.  Instead, I have a water sealent which uses petroleum distilate.  Is this stuff okay?  I'm hoping it'll cure and be suitable....  It does, btw, say on the label not to inhale fumes, etc. etc.  (Basically the same stuff you'll see on any paint.)

For underwater use, I would only use either a two-part epoxy paint, or
polyester resin and fiberglass with gel-coat last (exposed) surface. Most
water-sealant products aren't worth much if continously submerged.

I haven't ever done exactly what you are doing, but have some
boat/marine-hardware experience. Do keep in mind that free advice is worth
every penny. (^_^)

Wright

-- 
Wright Huntley, Fremont CA, USA, 510 494-8679  huntleyone at home dot com

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