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Skandinavisk Impregneringsservice

Essay 1

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


Essay 1
An introduction to paint, varnish and the Lignu Resin on wood
Essay 2
Clear coatings on wood
Essay 3
Essay 4
How to get more life from paint on old, weathered wood
Essay 5
Essay 6
Essay 7
Essay 8
What's the Matter?

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