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Re: Aquatic Plants Digest V4 #1385--DIY Hood

Baker, Anthony asked about DIY Hoods:
> My questions:
> 1)   is the kiln-dried pine easy to work
> with?
> Inexpensive?  Will it take stain?  Or are there better choices?

The cost of pine depends on the part of the country you live in.  It's
somewhat expensive in the east but cheaper than hardwoods in the
western states.  Pine is relatively soft as wood goes and is very easy
to work my hand or to machine.  It sands easily.  Regarding staining,
because the grain changes direction often, it has a strong tendency to
soak up stains unevenly and look blotchy.  Gel stains are easy stains
to work worth and minimize blothches.  Kiln dried wood is usually not
more than 20% moisture.  The drier the better, because in your house it
will eventually reduce to about 8% -- or in constant high humidity
rooms, about 10%-15% moisture.  In other words, wet wood will
shrink--kiln dried wood will tend to shrink less.  Of course you can
dry the lumber for a few weeks indoors before building. 

> 2) Should I "seal" the inside and outside with polyurethane?  The
> outside of
> my stand is NOT sealed, and has performed very well for me over the
> years.
> I suppose I could seal it with the aquarium still on it if need be to
> match
> the hood...

The value of a varnish, petroleum solvent-based urethane, lacquer, or
water-base urethane is threefold:  to protect the surface by a film on
the surface that resists scratches, to give the wood a luster or shine,
and to reduce the effects of changes in humidity.

Each of the types of generally available finishes has different
combinations of strengths in these areas.  The all come in very low to
very high gloss.

Lacquer--easy to repair, scratches easily, doesn't do much to impede
moisture in and out of the wood--dries incredibly fast so it's best to
spray lacquer.  Even the slow drying versions made for brushing are
very hard to work with well.

Varnish -- very expensive these days but resists scratches, impedes
moisture in and out of the wood very well--dries very slowly.

Petroleum solvent-based urethane--same properties as varnish -- dries
very slowly between coats--between coats you should allow one day plus
an additional day for the number of coats.

Water-based urethane-properties are more like lacquer. It is the
easiest of all to apply; easiest to clean up.  You can put on several
coats in one day and be done .

All of these are reasonably good at resisting penetration by water as
liquid on the surface of the wood, although varnish/urethane is much
better than the others.  Water vapor in the air penetrates all of these
finishes, more or less.  In the more humid months, the wood then
swells; in the drier months, the wood shrinks.  Impeding the water
vapor reduces the wood movement, which makes the joints last longer and
keeps them fitting flush.

Applying finish to the inside and outside is a good idea to prevent one
side from gain/losing more moisture than the other, which promotes

There are hundreds of books on wood finishing.  The single best book
ever written on applying finishes to wood is 
Understanding Wood Finishing 
by Bob Flexner.   I know that is claiming a lot, but I have been on the
lookout for many years for good books on finishing and no other book
covers so much so well with such good guidance and tips.

> 3) Does anyone have a website with pictures of a split-type hood
> design
> and/or more detailed drawings than provided on Mr. Booth's page?

Sorry, I do not, but I will point out that you are basically building a
5-sided box when you make a squared hood.  Put two together with a
piano hinge connecting and then either one can be tilted up onto the
other.  I think that's along the lines of what I remember of George's
> 4) Should I try to remotely mount the ballasts in the stand, or leave
> them
> in the hood?  (I am going to use a cooling fan regardless.)

The ballasts dissipate very little of the input energy as heat compared
to the bulbs, but they can impede airflow of cooling fans.  I'd say
that where you put them depends on how much room you have in the hood. 
Be sure to leave room for an exhaust port as large or larger than the
fan intake opening.

> 5) Do I need to keep the cover glasses or can the light fixtures
> handle the
> increased moisture?

You should have insulation between the lamps and the water.  This can
be distance, glass, or clear plastic.

If you opt for plastic instead of glass, remember that the Lucite type
of acrylic (a.k.a. plexiglass) tends to absorb moisture (and can warp)
while polycarbonates, which are much stronger and highly resistant to
cracking, are slightly electrically conductive.  Both are much lighter
than glass and much harder to break.

Unless you have end caps that seal against moisture, you shouldn't
expose the end caps/socket to moisture.  Insulate.  If you're afraid
that it will consume some of the light, use slightly larger lights (for
example 2 x 55 instead of 1 x 96) and don't worry about light loss,
electric shocks, corrosion, early rotting of the wood, etc.  If you
want an open-air tank, affix the glass to the bottom of the hood or
keep the hood a foot or so above the tank.
> 6) Lastly, I really like the idea of a suspended hood (like the one
> Erik
> Olsen describes in That Darn Plant Tank), but am concerned about
> drilling
> holes in my apartment ceiling, and wonder about the weight of that
> design.

If you're worried about holes in wallboard or plaster, don't
underestimate the value of spackle.  ;-)   If you're considering
hanging something from the ceiling, don't underestimate the value of a
stud finder.

If you want strength with minimal weight and you can't do plastics or
sheet metal fabrication, then plywood is the way to go.  3/8" can be
plenty if it is quality plywood.  1/4" is adequate if the hood is not
too long.  Any moisture or water condition that will destroy plywood
will warp and rot away solid wood too.  Plywood with hardwood outer
layers is available that aren't too expensive.  Finnish plywood, which
uses many very thin layers is much easier to machine and is
structurally very "solid" stuff.  But it tends to cost more than other
plywood options.

Tip:  If you haven't done much woodworking before, make a drawing with
measurements, build a small hood first as practice.

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