Primer Paint for Outboard Lower Unit

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
mb159
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Primer Paint for Outboard Lower Unit

Postby mb159 » Fri Apr 27, 2018 10:02 am

I am going to re-paint my 2001 Johnson OceanPro 90-HP outboard lower unit. The paint has faded. I have the Moeller paint specifically for the Johnson-Evinrude white for the year of my motor.

What primer to use?

Self-etching?

2K epoxy?

Or both?

In reading various articles on the internet, it appears that opinions are mixed as to which to use. My lower unit is not pitted or rusted, but it is badly faded and a lot of the paint has worn off.

All instructions I have seen indicate that I should thoroughly degrease, scuff with green Scotchbrite pad, then prime and paint. There is a lot of experience on this board, and I am seeking advice.

dtmackey
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Re: Primer Paint for Outboard Lower Unit

Postby dtmackey » Fri Apr 27, 2018 12:00 pm

I would do the following:

  • Prep the surface with a sandpaper or scuff pad, about 180 grit if there's no real bad spots
  • spray with self etch as it will "bite" into the metal. If you can find self etch chromate, that's even better, but it's hard to find and potent stuff
  • when dry, light scuff to prep surface to maximize the surface energy bond of the next step, you can use 180, but a 220 - 320 grit is better
  • spray with epoxy primer to lock down the self etch. Many self etch primers must be coated with an epoxy or equivalent
  • when dry, light scuff to prep surface to maximize the surface energy bond of the next step, this time the grit should be in the 320 range
  • spray with your topcoat

I'm assuming these are rattle cans and that is fine, but the paint quality is nowhere as good as professional finishes where the paint is catalyzed, but you can make something pretty and not worry about the hassle of mixing and spray guns.

When spraying hold the nozzle perpendicular to the surface and make wide sweeps across the item being paint, starting the spray of paint before you pass over the material and stop after passing over the material - what I mean is do not start/stop the spray of paint over the material. You also do not want to "flood" the paint all in one application and by this I mean for the first of each paint step, the first coat should be a mist coat and then allow to flash so that it tacks up a bit, then follow with another coat, this time a little heavier. You may find that a 3rd shot with the paint will give a nice uniform coat, again allowing the paint to flash between and tack up. Then move on to the epoxy primer following this same practice

People make the mistake of spraying too much paint at once and the paint sags or runs.

D-

jimh
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Re: Primer Paint for Outboard Lower Unit

Postby jimh » Fri Apr 27, 2018 1:18 pm

See

Cosmetic Repairing and Repainting of an Outboard Motor Lower Unit
http://continuouswave.com/maintenance-logs/paintSkeg/

jimh
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Re: Primer Paint for Outboard Lower Unit

Postby jimh » Fri Apr 27, 2018 1:23 pm

As a general rule, the best instructions for using a particular paint are provided by the manufacturer with the paint. If you buy a particular paint, carefully read and comprehend the instructions for using it, then follow those instructions. If a primer paint tells you that a certain type of top coat must be applied to finalize the primer's work, then you should apply the specified top coat--or expect something to go wrong.

ALAN G
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Re: Primer Paint for Outboard Lower Unit

Postby ALAN G » Sat Apr 28, 2018 9:28 pm

A few years ago when I painted twin 1989 Johnson 120-HP engines I used Rust-Olem VK9300 System 2K Epoxy Primer Spray:

https://www.rustoleum.com/product-catalog/industrial-brands/high-performance/spray-paint/vk9300-system-2k-epoxy-primer-spray/

VK9300 System 2K Epoxy Primer Spray is relatively expensive.

Prior to this, I used to use a simple zinc-chromate type primer recommended for aluminum. The old primer worked fine, but it was very soft and subject to abrasion from use (beaching, hitting the bottom).

I found the VK9300 System 2K Epoxy Primer Spray was very hard once cured and had much better adhesion. Mixing the catalyst on the spray can is very interesting; following the instructions on the can you puncture the activator and shake the can to mix the two components.

My prep-work involved sanding the old finish and any aluminum which was bare of coatings. The Rust Oleum instructions are very good and the VK9300 System 2K Epoxy Primer Spray is compatible with both old paint and bare aluminum. I painted two lower units up to the parting line where the water pump housings are. One can was sufficient for this area on both lower units, with none to spare. I top-coated with an off-white one-part polyurethane paint. Three years after the lower units look like new.

VK9300 System 2K Epoxy Primer Spray worked for me so I would recommend VK9300 System 2K Epoxy Primer Spray to anyone looking to put on a durable coating that will last.
Al

jimh
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Re: Primer Paint for Outboard Lower Unit

Postby jimh » Thu May 03, 2018 8:40 am

How expensive is VK9300 System 2K Epoxy Primer Spray? Please mention the cost per can at retail.

I presume that once the epoxy hardener and resin are mixed in the spray can, there is a very limited amount of time for using the paint. The epoxy paint must cure in the spray can as it does on the workpiece. I infer that this is a one-time-use product. This suggests that each can will only provide one-coat of primer.

Please give more details about how you applied the epoxy paint. Were you able to apply more than one coat from one can?

Did you try to apply a thick coat of primer?

Were there any runs or sags in the paint?

After the epoxy primer cured, did you abrade the surface before top-coating with another paint?

After the epoxy cured, did you wash the epoxy with soap and water to remove any amine blush?

If there were any sags, were you able to sand them away and smooth the primer surface without sanding to bare metal?

dtmackey
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Re: Primer Paint for Outboard Lower Unit

Postby dtmackey » Thu May 03, 2018 10:53 pm

jimh wrote:...I presume that once the epoxy hardener and resin are mixed in the spray can, there is a very limited amount of time for using the paint.


Depending on the brand of epoxy paint, you may have to mix and let it set for a 30-minutes induction period before spraying. Pot life is generous and I've seen up to six hours of pot life if needed. If there's an extended period between coats, I've even put the paint in a sealed container overnight in the garage fridge with no degradation in paint performance. Again, it will depend on the brand of paint.

jimh wrote:After the epoxy cured, did you wash the epoxy with soap and water to remove any amine blush?.


Epoxy primer does not exhibit the same amine blush as West Epoxy or others used in laminating fiberglass, so no need to wash with soap and water. A quick sand and wipe with a solvent (pre-sol or equivalent) and you are ready to go.

D-

ALAN G
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Re: Primer Paint for Outboard Lower Unit

Postby ALAN G » Fri May 04, 2018 5:28 pm

Jim--to answer your questions in order:

  • I can't remember for sure what I paid at a local hardware store, but VK9300 System 2K Epoxy Primer Spray goes for about $20 a can on line.
  • [VK9300 System 2K Epoxy Primer Spray] is a limited-use product, but the [paint] that is mixed but unused in the can is usable for about four days. The technical data sheet will answer most of your questions.
  • One can apply multiple coats provided the coats are light and two to five minutes apart.
  • I put on two coats to each lower unit. One coat would have probably been adequate, but I had the paint in the can so I used it all. You can get some idea as to coverage by sensing how much paint is left inside the can as you heft it and shake it.
  • I did not try to apply a thick coat, as the tech data sheet indicates that thin coats are to be used to prevent runs or sags.
  • I did not have any runs or sags when done because I was careful to use only enough paint each pass to cover the coat below.
  • After the paint cured, I did abrade the surface by scrubbing the surface with just water (no detergent or other cleaner) and a ScotchPad--the green ones that are somewhat aggressive but not as abrasive as fine sandpaper, and not remove the paint on sharp edges, where surface tension tends to thin the coating while in liquid form. With the ScotchPad, there was no problem going to bare metal or through the epoxy paint coating. The epoxy paint is very hard and not easily rubbed or sanded away, and that is what impressed me.
  • I would definitely use it again, and recommend it to others.

    https://www.rustoleum.com/product-catalog/industrial-brands/high-performance/spray-paint/vk9300-system-2k-epoxy-primer-spray/

Al

jimh
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Re: Primer Paint for Outboard Lower Unit

Postby jimh » Sat May 05, 2018 2:12 pm

AL--thanks for replying with more details about your use of the Rust-Oleum paint.

The beige color of the primer looks like it might be useful on a Boston Whaler hull with a Desert Tan or Outrage Gray color scheme.