Re: Paint for inside of hood--Miscellaneous commments re

["S. Hieber" <shieber at yahoo_com>]

Dan Dixon said, in part:

<
> Porter Paints makes a product called Acrylic Bonding Primer that will
> work
> well. It's a latex paint 

It probaly has acrylic resin too besides latex particles, both ground
up quite finely.

> that contains a small amount of linseed oil,

Linseed oil won't do much to waterproof wood.  If it's cooked, then
when it cures, the polymerized material offers some inhibition for
water molecules to pass through -- but not a lot of inhibition --
linseed oil rates very low on the "water resistance/waterproofing"
scale for finishes.

> and it
> sticks to bare wood better than any other latex paint I've ever used.

That's what primers are all about.

> It has
> an ethelyne glycol vehicle and dries out pretty quick so it doesn't
> keep
> producing fumes for a long time like oil-based paints.

It also probably has propylene glycol, which is somewhat less toxic. 
The glycol ethers, as they are know, are made by reacting alcohols with
ethylene or propylene oxides.  They are the VOCs (volatile organic
compounds) used as solvents/thinners to carry the solids, latex,
acrylic, alkyd resin, or whatever the "water-base" paint or primer
uses.  So-called "water-base" paints and finishes are actually
glycol-based, with just a pinch of water.  Fearing that that might
sound nasty to shoppers and knowing that "water-cleanup" up sounds
wonderful, the makers stress "water" in the marketing and labeling.

These finsihes are great for house exteriors because they "breathe." 
They peel less because moisture can pass through more easily instead of
getting trapped behind and lifting the paint frm the wood.  So latex or
acrylic paints will never seal as well as petroleum-solvent-based
paints and finishes.  It is in fact one of their key features, for
better or worse.

> It also has a
> flat
> bright white finish.

Flatness in paints and finishes (e.g., varnishes) is achieved by adding
extremely fine silicate particles.  In the paint, these break up the
light so that "mirror images" aren't reflected back.  It's one of the
reasons you have to stir flat paints longer and more oftern than many
gloss paints and why you don't have to stir high g loss varnish or
thiner-based urethane at all.

> Even though it's a primer, it lasts a long time
> without
> a finish enamel over it, probably because of the linseed oil.  

It's durability definitely doesn't depend on the linseed oil, which
imparts very little compared to other polymers that are used in paints
and finishes.  The difference between a primer and paint is that
primers have less pigment (chiefly titanium dioxide) -- this helps them
to stick better, which is the sole intended purpose for primers, i.e.,
first coats.  You can make a primer by appropriately thinning your
paint -- but that's a tricky deal with "water-base" paints --
proportions are everything and how much glycol ether do you have on
hand anyway?  The next layer can more easily stick to a freshly cured
prime layer of similar material.  Primers sometimes lack the UV
barriers of top coat material since they are expected to be covered. 
When painting, a primer coat is always a prudent idea because and only
because it can helpthe next coat stick to the surface.  With varnish
and urethane and other transparent finishes, it's irrelevent since no
pigment is usually involved.

An excellent single source on finishes for wood is the book:

Understanding Wood Finishing

by Bob Flexner

It is the best single book on the subject.

Scott H.

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