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An introduction to paint, varnish and the Lignu Resin on wood
All woods consist of cellulose fibers bonded together by
a natural resin which acts as glue. Typically seven to fifteen
percent moisture is present (chemically attached to the cellulose)
depending on average humidity. There is also a varying amount
of "sap", which is a complex mixture of different
oils and resins. Hardwoods such as oak have different resins
than softwoods such as fir. These resins and oils are very
water-repellent.
In order to obtain a good bond between wood and any paint
or adhesive, the fibers on the surface of the wood must be
strongly bonded to each other and to the adhesive or coating.
The surface of wood is microscopically rough, with many surface
fibers loosely attached to the bulk of the wood underneath.
Glues and the liquid portion of paints can soak into porous
wood surfaces. This can produce a paint with most of the pigment
on the surface and most of the paint resin soaked into the
wood, and such a resin-starved coating will soon fail. It
can also leave a glue joint starved for glue and hence weakened.
Therefore a sealer is important in order to obtain good adhesion
between wood and paints. Water-repellent [hydrophobic] resin
systems do not readily dissolve water, but Lignu(R) Impregnating
Resin contains a high percentage of alcohol in order to dissolve
not only the moisture in woods but also the sap and oils.
The fungus that causes dry-rot retains a lot of moisture and
inhibits effective penetration of sealers that cannot dissolve
water. Mildly dry-rotted areas can be impregnated very effectively
by Lignu Impregnating Resin since it can dissolve water.
It is not unusual for varnish to peel off of wood in six to
eighteen months, even when a top-quality varnish is used.
Varnish is a highly refined oil-base enamel paint without
pigments. Neither varnish, enamel or latex paints are particularly
aggressive adhesives. The Lignu resin is are very aggressive
adhesive, and chemically cures to become a tough, flexible
glue.
Now we have a very important concept: If we apply a varnish
or paint over a surface to which Lignu Impregnating Resin
was previously applied, but before the Lignu Resin is (roughly)
half-cured, the second material proceeds to cure first, and
the Lignu Resin film cures last, gluing down the second material.
This is why for thirty years these resins have been such an
effective adhesion-promoting primer for varnish. These resins
are designed to cure very slowly for just that reason.
The particular resins used in our products are substantially
derived from wood itself because these particular resins,
when they cure, will have a toughness and flexibility that
is comparable to the original wood. The fact that the surface
is dry to the touch does not mean that the resin is cured.
The time to a full chemical cure may be several days, depending
on temperature.
The modern use of the word primer has become a non-specific
term used broadly and irresponsibly by most paint manufacturers.
Literally, a primer was to be the prime coat, or first coat.
This derives from the Latin primus, meaning first. Products
now available in the marketplace include adhesion-promoting
primers, waterproofing primers used to seal a porous substrate,
filler primers, sanding and surfacing primers, corrosion -
inhibiting primers for metal, wood primers intended to block
tannin bleed-through of wood topcoats, moisture-diffusion-barrier
primers, and probably others. Adding specific adjectives to
the word primer conveys a clear concept.
When sufficient Lignu Impregnating Resin is applied to the
wood in one application to completely saturate the wood, a
thin film of the Lignu Resin is left on the surface. That
resin is a thin film of glue that glues down the varnish,
and the ultraviolet absorbers in the varnish protect the Lignu
Resin as well as the wood from degradation by sunlight. From
what our customers tell us, the typical life expectancy of
a good quality varnish, applied in this manner, is two years
or more.
When using clear topcoats such as varnish or polyurethane
it is important to know that the ultraviolet absorbers used
in all clear coatings are sacrificial. They will eventually
die. Therefore, more coats give a longer life. When the ultraviolet
absorbers finally "burn out", the ultraviolet from
the sun passes through the clear topcoat and attacks both
the Lignu Resin and the underlying wood, breaking down the
cellulose fibers. The coating eventually fails as the material
beneath it swells and decomposes.
In pigmented coatings the pigments block the ultraviolet.
Because the pigments are chemically stable minerals, they
do not "burn out" and so this failure mechanism
does not exist. Enamel and latex or urethane paints will therefore
last longer than clear urethane or varnish coatings, although
high quality clear coatings can last several years.
Latex paints, alkyd enamels, urethane coatings and varnish
can adhere better and last longer with Lignu Impregnating
Resin.
Paint formulations are often changed by the manufacturer.
Always do a small test with new product combinations to ensure
everything works together.
Copyright © 2002 Steve Smith All rights reserved
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