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Thinning Oil Based Alkyd Paints for Spray Application

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 Spraying Alkyd Paints

Alkyd oil based paints are durable and can produce a high shine if proper preparation is taken.  Oil based paints are self leveling and this allows application with a brush without leaving brush marks.  Even so,  application by spray produces the best overall finish with little fuss. IMAG1176

Choosing a Solvent to Thin Alkyds

Alkyd paints are a solvent based finish.  They consist of a polyester resin and are crosslinked by drying vegetable oils and fatty acids.  The traditional solvent for oil based paint is mineral spirits.  This slow evaportorating solvent keeps the paint wet long enough to assist in leveling.  Mineral spirits are unsuitable for spraying alkyds unless it is very hot.  This is because it dries too slow and is suseptable to runs.  Therefore a faster evaporating solvent is desired.  The common choices are VM&P Naptha, Xylene, and Acetone.

Xylene, pictured above is an aromatic hydrocarbon solvent of medium strength.  It evaporates slower than acetone or naphtha but faster than mineral spirits.  The higher solvent strength allows the xylene thinned alkyd to bond better with primers.  It will produce somewhat glossy finishes but not that shiny and it still evaporates slowly at temperatures below 80 Fahrenheit.

Acetone is the fastest most powerfull solvent available.  In fact, it evaporates so fast that if you spread it on a smooth and warm surface it will dry while wiping it.  Using this alone to spray paint would be bad as it would evaporate too quickly.  Most spray paints in cans use acetone as the principle solvent but usually add in xylene or other petroleum distillates to keep the paint from flashing the solvent too quickly.

VM&P naphtha is a petroleum distillate much like mineral spirits but it evaporates much faster and leaves no oily residue.  It does not flash off as fast as acetone though.  It is perfect for spraying in that it limits sags and runs.  It also allows the alkyd paint to level out a bit as well producing a finish with a “wet” look.  Consider the photo below of a sculpture I am working on.  Notice the reflective quality in the finish.

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The disk shape is taped up so it can be painted a different color later.  Naptha thinned paint will usually produce this shiny look so long that it is not too hot or humid.  High heat can dull the shine a little.  It might be a good idea to add a little xylene or mineral spirits to the naphtha before thinning if it is near or above 90 degrees fahrenheit.

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Here is the completed sculpture.  When carefully applied with a Preval Spray Unit or the vfan airbrush, alkyd oil based enamel thinned with naphtha will give a near mirror shine. This composition is titled “Perspective”  and the central theme is the main triangle which is turquoise.  All the other colors and shapes were designed and picked out to find a harmonius balance in color and style.  Follow this link to the items listingin my Etsy shop for purchasing information.

Additives

A few words of discretionary caution are in order here regarding additives.  The first and most important, DO NOT USE PAINT HARDENERS without proper respiratory protection.  They are isocyanate based and will cause serious respiratory problems if you don’t.

Japan drier should be used according to instructions sparingly.  Do not add to thinned paint you intend to store.  Add only to thinned paint you plan on using at the time.  It does not take much because a little goes a long way.

Working with Quart Paint Cans

One of the most difficult parts of mixing and thinning your own paints is getting out of the cans to begin with.  This can be an extremely wastefull and messy process if certain techniques are not used.   You will need a few of the quart sized plastic paint pails like the one in the top photo.  You pop the lid off the paint can with a screw driver and raise up the can a few inches above the pail.  Never put the lip of the pail to the lip of the can. If you do that the paint will flow everywhere but inside the pail.  In a quick and assertive fashion, dispense the required amount of paint into the pail and quickly wipe off any drizzle from the side of the can.  If using a larger portion it is best to pour several small portions instead of holding the can there until you have the right amount.  When aiming the paint try for the center of the pail to avoid as much paint going on the walls of the pail creating more cleanup work.  These plastic pails are soft and are MUCH easier for dispening paint into jars and air brush containers.  Thin the paint in the pails before dispensing so the pails will clean up easier with less mineral spirits.

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