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How do I prep my boat for painting?

2009 August 1
Dear Boat Doctor,
I would like to paint my Johnson X Boat, and am looking for some tips. The boat is about 20 years old and in pretty good shape but it needs paint. The boat appears to have been painted a few times. The paint is scratched, dinged and peeling in a few places.

I started by sanding with a palm sander and 80-grit paper but this did not do much. I think I need to remove a lot of the old paint and smooth things out before I do any painting.

Do you have tips for me on how to properly prep and paint my boat?

Tim Boppre
Jackson, Wisconsin

Dear Tim,
I'm glad you realize that preparation is important. In fact, it is the most important part of a paint job and takes a majority of the time.

In simple terms, you will remove any loose paint and generally smooth the surface. You'll then want to prime the entire surface, repair any dings, and then prime again. At this point you will have a surface ready for paint.

I would start the prep process with a different sander. A random orbital (sometimes called a dual-action or DA) sander will work best for you. I would use 80-grit paper and change it often. I think you'll see good results. You want to remove any loose, rough or failing paint. Start with 80 grit and sand up to 120-grit.

Once the boat is smooth and clean, you'll need to choose a product line. I encourage you to choose one company and use its products all the way through. You could mix and match products from different companies but this is a tricky process. I have had good luck with the products from Interlux (www.yachtpaint.com, (800) 468-7589). You will choose a top coat and then work backward to specify the primers and prep components required. Since you are going over existing paint and probably want to brush or roll I would use Interlux Toplac. This paint is compatible with many surfaces and easy to use.

The priming process starts by cleaning the surface with Interlux Brushing Liquid 333. You want to completely clean and wipe down the surface. Once the surface dries apply one coat of Interlux Pre-Kote Primer. Once thoroughly dry, sand with 120 grit and repair any blemishes that are revealed. Wipe down again with Brushing Liquid 333.

If you see any blemishes in the primed surface, use Interlux Surfacing Putty to fill them. You'll first clean the surface with Interlux Special Thinner 216 and then apply the filler. Sand the finish fair. You may find that using a longboard-a roughly 2-foot long sanding block-may help smooth things better.

After you are satisfied with the surface, wipe down one more time with Brushing Liquid 333 and apply a final coat of primer. After the primer dries, sand with 120 grit and up to 320 grit, then wipe down with Brushing Liquid 333.
You are now ready for paint. Start again by cleaning the surface with Special Thinner 216 and wiping dry. Next, brush on two coats of Toplac. You should get a respectable finish after two coats.

You can use this same technique on the hull and deck, but you may wish to get a different finish on the deck. Often a deck looks and works better if it is less shiny-not so much for nonskid but to keep down glare. You can add Interlux Flattening Agent 715 to dull the paint down.

You may also want nonskid on the decks. I would mask and prep the areas that you want to nonskid, and paint them with one coat of Toplac. While the paint is still wet, sprinkle on Interlux Intergrip. Once the paint dries, blow off any loose Intergrip and apply another coat of Toplac over the top.