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Re: Stand & Canopy Finish
> I think spar varnish is too soft for a
> furniture type finish that you would
> want on the outside of an aquarium hood.
> The main use of this stuff is in
> exterior applications where it is very
> U.V. resistant and very flexable and
> water resistant but these things are not
> really required on the exterior of the
ANY finish which provides a surface coat is going to be "soft" for a while.
A high quality, modern spar varnish WILL harden after several weeks. Many
people make the mistake of thinking that they can build up surface layer of
film quickly by applying fewer, thicker coats of finish. A properly applied
spar varnish finish starts with a 50%-50% wash coat (half varnish, half
thinner) which is allowed to cure for 36-72 hours and then sanded. The next
coat can be applied full strength or may be thinned 25%. Adding thinner
doesn't affect the quality of the finish, it just makes the "final film
thickness" thinner (more coats will be required to build up to a given final
film coat). It is important to allow each coat to cure properly and to scuff
sand each coat before applying the next (being careful to not sand thru at
the edges). Once the final coat is done, the whole thing should be allowed
several WEEKS to cure and "harden" before it is put to use. I have seen
finish "dents" on polyurathane finishes which were applied too thickly and
not given a chance to cure properly. It's a craft - you have to know your
tools and how to use them.
> Although I think you are correct that
> epoxy would be a good thing to use I
> believe all these marine grade epoxies
> are not U.V resistant. Even epoxy
> clearcoats containing U.V. inhibiters
> are sacrificial and must be renewed on a
> regular basis. Two part water based
> polyurethane is the finish of choice for
> use over top of epoxy. It is highly U.V.
> resistant and bonds very well to epoxy.
> Unfortunately, it is pretty pricy in the
> small quantities required for the
> interior of a hood.
Any finish, when used around water, heat and U.V. radiation is going to be
"sacrificial" to a point. The trick is buying from a knowledgeable dealer
and in reading the label (and/or contacting the manufacturer and speaking
with one of their chemists). Applying a compatible poly over a spar could
work - IF the manufacturer will guarantee that the poly will indeed bond
properly to the lower layer of spar varnish.
Finishing technology is moving rapidly - new products are always coming to
Most of the U.V. is going to be "reflected" off of the surface of the
ater - the lights should have reflectors which direct the light down, not
banging off of the hood interior. The prime purpose of the finish is to
protect the wood from the moisture which is generated by the aquarium. Wet
wood will swell, warp and rot.
> While oil base finishes are certainly
> more waterproof than latex it may not
> stick well at all to epoxy. Latex on the
> other hand adheres very well and does
> not peel as readily probably because it
> breathes better. Many boatbuilders on a
> budget use 100% acrylic paint to paint
> their boat hulls with good results
> although you cannot get a good finish
> with it. It does not matter on the
> inside of a hood so I say why not use
You don't WANT a surface finish which will "breathe" on the INSIDE of an
aquarium hood - you want one which SEALS the surface from moisture. You have
to keep the water vapour from entering the wood.
> finishes contain drying oils such as
> alkyd which will produce fumes for
> months. I do not know if this is harmful
> to the fish but I think that it could
All finishes contain "driers" of some sort or "catalysts" which can
potentially cause problems - that's why I recommend allowing the finished
hood to cure for several weeks before being put into service. They should
only be applied in well ventilated conditions.
> The 2 part epoxy you describe sounds quite toxic. Maybe not to the fish
> after it dries but what about me, while I am painting. Did you inhale? or
I _always_ inhale <g>. Makes me more "creative".
Epoxy finishes, once cured, are not going to be toxic. Uncured (as you are
applying them) is another story - work in a well ventilated room and wear a
respirator and/or mask. I can't recommend a brand - what I can buy locally
here might not be available where you live. Make sure that whatever brand
you use is certified as suitable for exterior (preferably marine) use.