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Old 13-12-2018, 08:00   #1
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Ripples in the paint. HELP!

When working on the boat to get it ready to launch last year I sanded down the stern to remove the old name. When I was getting ready to buff out the gelcoat for the new name I got the brilliant idea of painting the stern black to match the rest of the boat's color scheme.

After some extensive research, I settled on 2-part polyurethane. It was very expensive and I had never worked with it before. Some videos recommended rolling it on and some actually warned against spraying it. So, I followed the recommendations and used a roller and a brush to lay it out.

At first, it all worked fine. But after a while something weird happened. The paint started to show ripples. I couldn't understand out why. But after a while I figured that the angle of the transom was probably causing the issue.

If you look at the profile of the stern, you can see that the transom curves down and away.



Normally, you would paint using vertical strokes to lay on the paint and then follow up with horizontal strokes to lay out the paint. With good paints the brush strokes should disappear as the paint settles out. But that is usually on vertical or horizontal surfaces. I've never worked on a surface that was angled down and away like this.

Well, the result is that the paint formed ripples as if it was going to drip off the surface altogether. It looked very bad.



I tried buffing it out. I tried using compound polish. Nothing worked. Finally, I grabbed some 600 grit sandpaper and tried wet sanding. This worked partially but I ended up taking off the paint in some places. I was frantic. With only a few days left before launch I ran out and got some black tinted spray varnish. I touched up the areas that showed white gelcoat and accepted the rest.

Well, now I want to redo the stern and get it right. I need some ideas of how to paint the stern that will work. I have a compressor and spray gun. So, I'm ready to spray paint if necessary.
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Old 13-12-2018, 08:10   #2
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Re: Ripples in the paint. HELP!

First question would be, did you thin the paint to recommendations for rolling and tipping?

How many coats of paint did you apply? How many coats of primer?

Second. Check with your yard before spraying. Most yards won't allow spraying out in the open any longer.
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Old 13-12-2018, 08:24   #3
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Re: Ripples in the paint. HELP!

Quote:
Originally Posted by pcmm View Post
First question would be, did you thin the paint to recommendations for rolling and tipping?

How many coats of paint did you apply? How many coats of primer?

Second. Check with your yard before spraying. Most yards won't allow spraying out in the open any longer.
Yes. I followed the recommendations exactly. As for spraying, I set up tarps to completely cover the stern all the way to the ground. I would not spray in the open for a lot of reasons, especially since the wind likes to deposit all sorts of crud onto your freshly painted surface.

Personally, I'm thinking that thinning was the wrong way to go. Because of the negative angle I think the thinner paint was able to run more.
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Old 13-12-2018, 09:45   #4
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Re: Ripples in the paint. HELP!

Ultimately you want to leave a thinner coat on the surface. It will run less because it won't be as affected by gravity. Spraying too thick will make it run too.

Keep in mind that the roller contributes to the amount of paint left on the surface. I use a lot of those little 4" foam rollers, but they are not all the same. I used one the other day that wasn't my normal brand and it made my paint sag. Couldn't possibly have been my fault...
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Old 13-12-2018, 11:20   #5
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Re: Ripples in the paint. HELP!

Jim, the only way you get ripples is if you have too much paint. Forget about how the transom is oriented, if you spray LIGHT coats with the right amount of thinner/reducer, the paint won't be able to ripple. When in doubt, the are actually paint gauges (kinda looks like a coarse comb) to measure the thickness of a coating while wet. And sometimes it is simply better to use "light dustings" of paint, making sure each dusting is light enough to ensure it sets up without being able to run. That means having to apply more coats in order to build the final thickness, but ensures each coating won't be moving around while it dries.

You may want to pick up a piece of plywood or other material , hang it up in a similar orientation, and practice spraying on that, before you paint the transom again. If you can, earlier on the same day, and regardless of when you do it, remember that the weather (temperature AND humidity, amounts of sunlight heat or wind chilling) are going to make "the right" amount of thinner in the paint vary even from hour to hour.
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Old 13-12-2018, 12:05   #6
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Re: Ripples in the paint. HELP!

2 part polyurethane needs to be sprayed. If mixed right and sprayed through right gun with correct tip using nice even wet coats waiting for it to tack up nice between coats should be good not to light on coats unless you plan to wet sand and buff out orange peal. Maybe if not proficient with spray gun go with difrent paint roll it and tip it with brush.
Sounds like it sagged which can be from over thinning or applied to thick.
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Old 13-12-2018, 12:46   #7
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Re: Ripples in the paint. HELP!

In the "construction, maintenance,refit" forum, twelfth item down titled "painting the yacht" you will find basically the same conversation Ya'll about to have.
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Old 13-12-2018, 13:24   #8
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Re: Ripples in the paint. HELP!

You paint is "curtaining". It sounds counterintuitive, but you need to thin the paint even more, and apply it in thinner coats.

Don't bother with spraying - too much set up, too steep a learning curve. With two-part LPU's you can achieve spray-like results with good roller technique.

For this application, you want the paint almost the consistency of whole milk. For example, if you are using Interlux Perfection, this means using about 15% thinner. Roll it on with those cheap little "hot dog" rollers. "Stretch out" the paint as thin as possible using medium firm pressure, rolling over the same area several times. There will be plenty of bubbles and stipple, but don't panic. Once the whole area is covered, do a final pass with the roller with very light pressure to even it all out (no need to tip with a brush). The first two coats will look lousy (splotchy and transparent), but by the third coat, it will be fabulous. Don't sand between the intermediate coats (you need to build thickness), just knock the gloss off with a Scotchbrite pad (use the maroon or gray color one, but not the green). However, before the final coat, let it dry at least 48 hours and then sand lightly with 320 grit or finer sandpaper.

And whatever you do, don't attempt to apply any two-part poly in direct sunlight -your surfaces must be shaded or the paint will kick too early and the stipple and bubbles won't dissipate properly.
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Old 13-12-2018, 18:42   #9
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Ripples in the paint. HELP!

I have good success with roll and tip with the paint the consistency of milk as you suggest. A 4” foam brush makes a great tip brush, buy lots of them. There’s a magic point where it works just right, and then the thinner evaporates and you must rethin. Then it’s too thin and you must wait, With practice the magic time gets longer and longer.

It takes immense concentration but you can roll and tip to perfection!

With any oil paint wear a quality respirator and take breaks where you take big gulps of fresh air.
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Old 13-12-2018, 20:37   #10
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Re: Ripples in the paint. HELP!

If you are good, and have had a lot of practice spraying is the way to get the best finish.

BUT>>>> Spraying polyurethane paints is also a very good way to get very SERIOUS health problems. When they tell you to use air supply respirators, they are not kidding. A standard filter respirator is NOT good enough, even outdoors. You only have one set of lungs, don't risk them.

Most two-part polyurethane can not really be buffed and sanded to fix problems or patch scratches. The only one I know of that you can do this with is Awl-Craft. (NOT the more common Awl-Grip).

Rolling and tipping is an excellent, if labor intensive way to apply these paints. But you need to know what you are doing--REALLY know what you are doing. If you don't, you are far, far, better off using a single part polyurethane. They are much more forgiving.
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Old 14-12-2018, 09:06   #11
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Re: Ripples in the paint. HELP!

Awl Craft is not a polyurethane paint; its acrylic.
The benefit is that it can be easily repaired and buffed. The bad news it is not nearly as hard and tough finish as Awl Grip.
When you have your boat painted be sure you specify one or the other. If you want an awl grip look and durability you will be disappointed if you get awl craft instead. On the other hand if easy to repair is your goal awl craft is the ticket.
Tom
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Old 14-12-2018, 09:53   #12
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Re: Ripples in the paint. HELP!

Check out epifanes n.a.website
Great instructions and their foam rollers are made for 1+2 part paints.
I sanded between ALL coats. When you get to the 3D it really looks like new.
You should call epifanes 800 number and talk to a rep and get his 2cents
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Old 14-12-2018, 10:42   #13
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Re: Ripples in the paint. HELP!

Quote:
Originally Posted by SparkyDorado View Post
You paint is "curtaining". It sounds counterintuitive, but you need to thin the paint even more, and apply it in thinner coats.

Don't bother with spraying - too much set up, too steep a learning curve. With two-part LPU's you can achieve spray-like results with good roller technique.

For this application, you want the paint almost the consistency of whole milk. For example, if you are using Interlux Perfection, this means using about 15% thinner. Roll it on with those cheap little "hot dog" rollers. "Stretch out" the paint as thin as possible using medium firm pressure, rolling over the same area several times. There will be plenty of bubbles and stipple, but don't panic. Once the whole area is covered, do a final pass with the roller with very light pressure to even it all out (no need to tip with a brush). The first two coats will look lousy (splotchy and transparent), but by the third coat, it will be fabulous. Don't sand between the intermediate coats (you need to build thickness), just knock the gloss off with a Scotchbrite pad (use the maroon or gray color one, but not the green). However, before the final coat, let it dry at least 48 hours and then sand lightly with 320 grit or finer sandpaper.

And whatever you do, don't attempt to apply any two-part poly in direct sunlight -your surfaces must be shaded or the paint will kick too early and the stipple and bubbles won't dissipate properly.
Yes, it was Perfection.

I painted my 19' O'Day Mariner with 2-part epoxy paint back in the 80s with a sprayer. It worked perfectly. I did a lot of research and most people recommended 2-part polyurethane. But I had never worked with it before. My plan originally was to spray it but so many posts warned against doing that so I tried rollers.
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Old 14-12-2018, 10:46   #14
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Re: Ripples in the paint. HELP!

SparkyDorado +1
Perfection goes on thin with 3 coats. I have made this mistake of putting on too thick. Learned to sand and repaint.
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Old 14-12-2018, 12:50   #15
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Re: Ripples in the paint. HELP!

Painting is a science first and an art second. Type of paint, quality of paint, outside temperature, humidity, thinning, catalyst, mixing ratios, flash times, etc..all play a part in a successful paint job. Any one of those factors can be detrimental to application outside of ideal conditions. It sounds like your base coat didn't tack up enough before applying the second coat (low temp maybe). Inverse angles shouldn't make a difference compared a vertical surfaces. Seek local knowledge and follow the directions on the can exactly.
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