Roll, Don’t Tip Two Part Polyurethane Boat Paint! – Boston Whaler Restoration – Part 14

Final Coat Rolling Two Part Polyurethane

I’ll be priming and finishing the hull in part 14 of this classic Boston Whaler 13 restoration. To get this hull to a perfect finish, I’ll be using TotalBoat two part epoxy barrier coat and Interlux perfection. Interlux is a two part polyurethane boat paint with a high reputation. Of course, there will be a LOT of sanding in between coats.

In the last article, I finished up the repairs and added one coat of TotalBoat two part epoxy barrier coat in gray. How to Fair and Prime a Hull with Epoxy Primer That coat of epoxy paint was a blessing! It showed up a lot of areas that needed more attention. I took care of that with more fairing compound and sanding which leads us to this next step.

TotalBoat Epoxy Barrier Coat

Prepping The Boat For the Primer

Before applying a two part polyurethane boat paint, you have to have a properly prepared surface. To get to this step, I first sanded the entire hull with 220 grit sandpaper to insure that the last coat of primer and repair was absolutely smooth. After that, I washed the entire boat down with a mixture of ammonia and dawn dish detergent.

Preparing the Epoxy Boat Paint

TotalBoat’s two part epoxy barrier paint is easy to use. It mixes up at a ratio of 3:1 base to hardener. I bought one gallon of the primer and for this phase ended up only using two quarts. It is packaged so that you can pour the entire can of hardener into the gallon container of the base. If you are using less quantities, you need to measure carefully.

In my case I aimed for mixing up a half pint at a time. A 8oz of primer will cover about half of a Boston Whaler 13 hull. This gives you ample time to roll on a coat on one half of the boat before the epoxy primer starts setting up. First, I made sure that both containers were well mixed. I cheated and took them to Home Depot, where they put in their mixing machines, no questions asked.

Mixing the Two Part Epoxy Barrier Coat and the Induction Period

To do this, I mixed 8 ounces of base to four ounces of hardener. I made sure that it was well mixed. Then I had to wait! Both the two part epoxy and polyurethane paints have an induction period after mixing. For the epoxy barrier coat primer, it is 15 minutes.

Painting the Boat with the Epoxy Barrier Primer Coat

After the induction period passes, I added 10% paint thinner (Interlux 2333N) and mixed it in thoroughly. Next, I applied a generous coat to the entire hull. There were some spots that I had to use a brush. The lifting handles in the back and right underneath the gunnel were the two key areas I had to brush in. Otherwise, I rolled out the entire coat of primer with a Wooster T1Z roller cover that I had cut down to 4-1/2 inches.
brushing paint into handles
brushing paint into handles
Rolling on Totalboat Barrier Primer
Rolling on Totalboat Barrier Primer

Sanding the Barrier Coat

After the barrier coat dries and cures, we’ll need to sand it smooth to prepare for the two-part polyurethane paint. The Epoxy barrier coat leaves a somewhat pebbly surface when rolled on. I’m a firm believe that the final finish will reflect the underlying preparation and coats.

I initially started to hand sand the boat with 220 grit paper. It didn’t take me long to realize that hand sanding would take way too long. So I upgraded to a random orbital sander. I did change the paper to 320 as I didn’t want to be too aggressive with a mechanical sander. Once I settled on the method of sanding I went over the entire boat until I had a smooth finish. I found that running my hand over the surface was a better indicator of whether it was smooth or not than simply eyeballing it.

Applying the Interlux Perfection Two Part Polyurethane

Preparing the Boat Hull for Two Part Polyurethane

 Before applying any finish paint, we have to clean the hull. I mean really clean it. It should be squeaky clean and dust free (if possible). Once the sanding is done the first thing I do is wash the boat down. I use a solution of dawn and ammonia in water. Using this mix, I scrub the boat down with a soft bristled brush and thoroughly hose it off.

Before applying any paint, I let the boat dry. Just before I paint I will go over the entire boat with a clean rag soaked in either acetone or denatured alcohol. I do this to insure that there is no grease or other contaminants that may have settled on the hull.

Mixing the Interlux Perfection Two Part Polyurethane

To paint the hull, I’ll mix up the Interlux perfection first and then clean the hull will acetone or denatured alcohol during the induction period. Interlux perfection is a two part polyurethane paint. The mixing ratio is 2:1. That is, two parts of pain to one part of catalyst. Once it is mixed up, you have to let it sit for the 20 minute induction period before thinning.

Mixing Interlux Perfection two part polyurethane

Thinning Interlux Perfection

Interlux recommends that when rolling brushing that you thin perfection to no more than 10%. However, there is an excellent book by Russell Brown that explains how he thins this paint to 15% to get glass like finishes. The book is called “Rolling Perfection” and you can get it on Amazon here, Rolling Perfection (Affiliate link).

Getting the First Coats of Two Part Polyurethane On

First a Warning! Two Part Polyurethane is Toxic

Two Part Polyurethane paints are extremely toxic. So much so that it is inadvisable for a DIY person too spray it. Professionals use positive pressure hoods to spray this. So take caution and make sure you have a good quality mask designed to remove organic solvents. If in doubt, contact the manufacturer!

On to Painting the Hull

To get started, I mixed up a 6oz batch of perfection. After the induction period. I added .9 oz of Interlux 2333N thinner and mixed it in thoroughly. Next, I started applying the paint to the hull using the technique described in Russel Browns book.

Using a Wooster T1Z roller cover that I cut down to 5 inches, I loaded the rolled with paint. Next, I rolled out a section about 2 to 3 roller widths. When rolling out the perfection, it’s critical to spread it evenly over the area you are covering.

To get this right, you’ll want to start the next section about 2 roller widths from the section you just finished. Roll it back towards the just finished section, lightly overlapping it to insure there are no gaps or “holidays in the paint you are laying down. Basically use this technique until you have completed the entire hull. 

The key is to just use the weight of the roller to lightly roll over the entire section you just finished. If you are doing a vertical surface, use just enough pressure to keep the roller on the paint. The final step in rolling a section out is to lightly roll over the entire section. You are basically flattening out any bubbles by doing this.

Where to Start and Stop Applying paint

When you are applying paint, you’ll want to pick areas where different coats of paint can meet and not be conspicuous. Areas like the keel and chines or any sharp edges are ideal for this. I ended up rolling the paint using the keel and the chines as borders for the area I was painting.

I ended up putting two full coats and one on the sides of the two part polyurethane on before I ran out of paint. I did find that when mixing the last batch, I was short on the hardener. This led me to believe that when I applied the first coat, I may have used too much hardener

Recovering from the Mistake

The net result of this is that the paint did not have a chance to settle down to a nice flat shiny finish. Although it had a nice shine, it was pebbly and did not have a smooth glass like finish. To fix this, I ordered another quart of Interlux Perfection. More importantly, I broke out the 320 sandpaper.

I ended up sanding the entire boat by hand with 320 grit sandpaper. The key objective was to sand the pebbly grained areas down to a smooth surface. Additionally, I wanted to get everything sanded down so that the next coat would have a chance to flatten out and leave a glass like finish.

Applying the Final Coat of Interlux Perfection Two Part Polyurethane

Once the sanding was done and I received the quart of perfection I ordered I prepped the hull. Basically, I repeated the prior steps of a complete washdown. This time, I used a small glass beaker to measure it. I did not want to make a mistake with the ratio of hardener to again! I also reduced the amount of thinner to 10%.

I also used a slightly different roller. I used Arroworthy foam roller covers, also known as “hot dog or sausage” rollers. Whatever roller you decide to go with, make sure that it has two key qualities. First, make sure that is is solvent proof or at least resistant. The solvents in Perfection will eat through most rollers. Even the ones that are solvent proof eventually swell up and start falling apart.

Second, make sure it has a fine finish. Most foam rollers already are designed to leave a glossy finish. The Wooster T1z I used had an 1/8″ nap on it. It was actually a very fine foam covering but held an amazing amount of paint when fully loaded.

Rolling on the Last Coat

I went ahead and mixed up the final batch of Interlux Perfection, accurately measured! During the induction period I went over the entire boat with acetone. Once the Induction period was over, I added 10% of the 2333N.

Applying the Final Coat of Interlux Perfection Two Part Polyurethane

Once the sanding was done and I received the quart of perfection I ordered I prepped the hull. Basically, I repeated the prior steps of a complete washdown. This time, I used a small glass beaker to measure it. I did not want to make a mistake with the ratio of hardener to again! I also reduced the amount of thinner to 10%.

I also used a slightly different roller. I used Arroworthy foam roller covers, also known as “hot dog or sausage” rollers. Whatever roller you decide to go with, make sure that it has two key qualities. First, make sure that is is solvent proof or at least resistant. The solvents in Perfection will eat through most rollers. Even the ones that are solvent proof eventually swell up and start falling apart.

Second, make sure it has a fine finish. Most foam rollers already are designed to leave a glossy finish. The Wooster T1z I used had an 1/8″ nap on it. It was actually a very fine foam covering but held an amazing amount of paint when fully loaded.

Rolling on the Last Coat

I went ahead and mixed up the final batch of Interlux Perfection, accurately measured! During the induction period I went over the entire boat with acetone. Once the Induction period was over, I added 10% of the 2333N.

I mixed up 8 oz of the paint, which is enough for half the boat. The idea being that I would do one half of the boat, then mix up a fresh batch of paint for the next half. 

You can expect to get two full coats of paint on a 13′ foot whaler with a quart of Perfection. After that, it was a matter of going over the entire boat using the technique I described earlier.

The Final Results

The end result of applying four coats of Interlux perfection were amazing. I think anyone would be hard pressed to tell the difference as to whether it was sprayed or rolled on. The paint really leveled itself out to a glass like finish. To say that I am please would be an understatement. The paint flows on and levels easily.

Next Steps in the Boston Whaler 13 Restoration.

The next step is to get the trailer ready. I would hate to have this great looking hull scratched or marred by a beat up trailer. I’ll be changing the rollers and probably adding some small side bunks to keep the outside chines from hitting the fenders. I’ll have an article up on that soon!. Thanks for visiting!

You can view the video version of this article here: https://youtu.be/MYR2WIjByrA

Below are affiliate links to some of the products I used in this video:

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