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Re: Board with MDF? and Finished with Paint

Tom Wood said:

> I've had a tank enclosure made of MDF in service for
> almost a year now. I
> used the 3/4" water resistant material and sealed it with
> an oil based
> sealer, then painted the inside surfaces with a black oil
> based paint. I was
> a little sceptical of the material being next to the
> humidity of a tank, but
> it has performed well and shows no sign of deterioration
> due to humidity.
> I'd originally planned to paint the exterior with an
> automotive quality
> finish but ended up using a dark rolled-on latex paint.

Water-clean-up paints more easily pass water molecures than
do paint-thinner-clean-up finishes.  So paint-thinner-based
paints and urethanes seal better against the mositure
content of the substrate (MDF, pboard, plywood, solid wood)
changing with seasonal changes in humidity.  But modern
water-clean-up finishes still do a very good job.

The water vapor permeability of water-clean-up finishes is
the key reason such finishes are better for exterior wood
applications-- the ability to pass the water vapor makes
the build up of moisture underneath the paint less likely
and the paint, therefore, less susceptible to blistering
peeling.  This virtue is somewhat compromised with an oil
based primer below the latex.

Interestingly, both types impede liquid water about

Indoors, either type of finish should prove adequate, even
around aquaria.  Although, for locations directly exposed
to very damp air (e.g., the inside of a hood right over the
water) a paint-thinner-clean-up finish might prove more
durable over the years -- but who's counting?

Scott H.

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