General Painting Tips
or
"Preventing Weak Links in a Chain"

       A good paint job is like a chain, it's only as strong as it's weakest link.  The first link is between the metal and the primer.  The second link is between the primer and the paint.

     A common misconception I have heard from many people is that they don't want hard paints because they chip easily.  Hard paints don't chip more easily than softer paints -- they chip less easily -- but only if they have been applied properly over the appropriate primer. You must have a good bond between the primer and the metal as well as the primer and the paint.  Only then will you get a strong chip free finish.

     Outboard motors are made almost exclusively from aluminum because it's lightweight and low priced.  As most of most of us know, aluminum is more corrosion resistant than steel.  Almost as soon as it is bared to the atmosphere an oxide layer forms on the aluminum. This layer is very thin and invisible to the naked eye.  It is this oxide layer that gives the aluminum its corrosion resistance and at the same time makes it difficult to get good paint adhesion.

Link #1
To get a good bond with aluminum a "self etching primer", also known as an 'acid etching primer", is needed.  The etching primer eats through the oxide layer and bonds with the aluminum preventing further oxidation.  Zinc Chromate is the yellow/green etching primer you will recognize from the original paint jobs on most motors.  Chromate's are banned in many places because of their toxicity. There are modern less toxic alternatives. If you can't find Zinc Chromate ask for a "Self Etching Primer".  I have had good results with Mar-Hyde's Single Stage Self Etching Primer.  Epoxy primers do a very good job of bonding to metals, and those meant for aluminum have Chromate's added. R.M.'s EP589 is a chromated epoxy primer.
Link #2

There are many different kinds of primers available.  One important thing to know about any primer is the "No Sand Time".  The primer I use has a no sand time of 8 hours.  This means that if I paint before 8 hours I don't have to sand before painting.  If I wait longer than 8 hours I must sand first or the paint will not get a good bond with the primer.
 
Some of the cheaper aerosol primers available from places like Canadian Tire and UAP/NAPA have no sand times of zero.  This means that they must be sanded before painting. These kinds of primers are not a good choice for painting outboards because there are many spots on an outboard that are hard or impossible to sand.  An easy way to determine if your primer has a no sand time is to do a test spray. Once it has dried look closely at the surface -- if it has some gloss it can be painted without sanding.  If it is flat, glossless and rough looking it must be sanded before painting.  This is not exactly a scientific approach but just something I have observed after trying many different types of primers.  The Mar-Hyde primer I mentioned earlier has a no sand time of 36 hours.  This leaves plenty of time to do any filling of cracks and gouges etc, before painting.  It comes in aerosols and quarts and works very well on aluminum.

Another common misconception I hear is that all old outboards were painted with lacquer paint.  Some were painted with lacquer but not all of them were.  I have documentation from OMC showing the use of an acrylic enamel two times to one over the use of lacquer.  I asked the technical representative at BASF how to tell which paint was on an old motor.  He said that anything painted with lacquer that was over 25 years old will have spider cracks running all through the paint.  If your motor doesn't have these cracks than it is probably has acrylic enamel paint.(see example) Notice the cracks in the decal which is made from Lacquer. You will notice the paint does not have these cracks, therefore it is not Lacquer paint.

Lacquer paint has been banned from commercial use because it dries by solvent evaporation and to be sprayed it is reduced by 100%.  A gallon of ready-to-spray paint has an equal amount of paint and reducer.  That's a lot of pollution going up into the atmosphere.  Enamel paint dries by oxygen absorption and requires relatively much less reducer.  You may have heard of some spray guns being referred to as "HVLP".  This means "High Volume Low Pressure".  Guns are rated according to their transfer rate.  This is a measure of how much of the paint that comes out of the gun actually ends up on the part to be painted.  A conventional gun operating at about 50psi has a transfer rate of about 35%.  That means that for every gallon of paint sprayed out of the gun only about a quart and a half ends up on the part, car or whatever.  That is not very efficient and it is also very polluting.

To be granted the rating of HVLP a gun must have a transfer rate of at least 65%.  Some go as high as 85%.  Most operate at about 10psi at the gun.  This all adds up to a savings of at least 50% on your painting costs.  For someone who will only paint the odd thing it probably won't justify changing equipment, besides, buying a new gun you may also have to buy a hose with a larger inner diameter and possibly change connectors (again to get a larger ID).  If you have no equipment and are considering purchasing some, going HVLP will certainly pay off in a relatively short time.
 
 
 
 
 
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