The Advantages and Disadvantages of Pure Oil and Oil Based Paints and Varnishes
What are Pure Oil and Oil Based Paints and Varnishes?
The binder for these paints is a drying oil or a blend of drying oils, or a combination of drying oil(s) and natural or synthetic resin called oil modified resin, for example Alkyd resin.
The dryer used can be any of the drying compounds that are based on metallic salts.
The drying is by oxidation (to combine a substance with oxygen) and partly polymerization (undergoing a chemical reaction in which two or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules).
The thinner is generally mineral turpentine but manufacturers often make a blend with other solvents to improve the paint’s properties, i.e. adhesion, working ability, penetration (in primers).
Today, spirit of turpentine, natural turps and wood turps are obsolete.
The pigments used are white or colored and include extender pigments.
Advantages of using Pure Oil and Oil Based Paints and Varnishes for Home Interiors
The advantages of using oil based paint or varnish are:
They are a well proven reliable coating
Their adhesion reliability, from penetration of part of the oil content. The penetration on new timber surfaces and when used on loose powder or chalking surfaces it binds to the substrate.
They are water and weatherproof. (With the exception of Linseed oil, which tends to absorb water when used on horizontal planes and becomes clogged.)
It produces a good finish with no brush marks, if applied by a skilled applicator, as it flows well.
A high level of gloss can be reached. This provides for a higher aesthetic value as it is easily cleaned, and doesn’t hold the dirt on the surface.
By using extender pigments like Mica, it provides a high sealing ability on new porous materials.
If using the correct resin and less oil content it is more heat resistant.
If using the correct resin and less oil content it is more alkali resistant.
There is no Minimum Film Forming Temperature (MFFT).
Disadvantages of using Pure Oil and Oil Based Paints and Varnishes for Home Interiors
The disadvantages of using oil based paint or varnish are:
It has a slow drying time. This depends on the oil content, the less oil the faster the drying time.
There is a long drying time between coats; this can cause an inconvenience, as the job takes longer.
A skilled applicator is required to apply it as it can be difficult to brush, it runs, curtains, laps etc.
It doesn’t have good sealing properties on “bleeding ” surfaces. Bleeding materials are mostly tar based and are easily soluble in oil. It is good however at covering water stains.
The heat resistant properties lower with increased oil content.
It is not alkali resistant through saponification (to convert oil into soap by decomposition with an alkali) of most drying oils but the resistance does increase by decreasing the oil content. Tung oil is very stable.
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