how to retouch 2-part polyurethane paint without curling edges?

[paulo7]

Over the years, we noticed that no matter what brand of 2-part polyurethane topside paint we used, with corresponding primer as a first coat, we have small patches of paint flaking off from time to time???

Strangely enough, it is only the topside coat that flakes off, never the primer coat! Great that the primer sticks so well to what is under it: epoxy. What is not so good is that the topcoat does not stick everywhere on the primer!

First question is why the topcoat does not stick everywhere! After applying the primer, we sand it lightly and then clean it just before painting. Then we used the recommended thinner. to clean primer before painting the topcoat. When painting a large surface, you cannot avoid painting over areas you just walked over ... leaving perhaps small sweat particles??? Obviously if you drop an heavy object like a winch or tool, it might get some paint to flake off but again, only the topcoat, not the primer! Why??

Second question is regarding the touch up repair job! It seems that many times, where the new paint (same paint brand) slightly overlap the old paint surrounding the repair area, the new paint seems to provoke a curling of the edge of the old paint??? We slightly sanded and cleaned that edge before the touch up.

We have asked these 2 questions to several professional painters we met over the years but somehow never got any answers that solved these 2 issues on our boat painting projects! Perhaps this forum will get some real answers for us and whoever share the same frustrations!

[Tupaia]

Your issue is probably "lightly" sanded. PU paint requires a key and many times the prep is too smooth. Other reason could be contamination after priming.

It is very difficult to retouch linear paint (Awlgrip) - There are other 2 pack PU Awlcraft that can be retouched. Other conventional 2 pack PU like Stirling or Hempel Megagloss is very easily repaired.

[s/v Jedi]

First things first, watch how Frankie Bushong does this. Here’s just one video, he probably has better ones on his channel. (Especially how he cleans/preps for topcoat. Use the simple soap and denatured alcohol like he does)

So we can’t spray like Frankie and use a roller or roll and tip and have to deal with a curling edge at masking tape etc. Here is what I do… successfully because I am the only one who can tell and point out these edges

First, you just do one topcoat for these repairs? Then you tape once. For every extra coat you tape extra before starting, overlapping the previous tape but covering 3/16” or so of surface to be painted. This prevents a big step.

I try to find a place to hide the edge, like a curve, corner, anti skid section etc. and paint to that. After that you still have the next step but it will be hidden better.

After painting, I use a card scraper to shave the edge down. For working on a flat surface you want a curved card scraper so that you can work precisely without touching anything else.

https://www.youtube.com/watch?v=J8O7jROKwe8

[paulo7]

Originally Posted by s/v Jedi

First things first, watch how Frankie Bushong does this. Here’s just one video, he probably has better ones on his channel. (Especially how he cleans/preps for topcoat. Use the simple soap and denatured alcohol like he does)

So we can’t spray like Frankie and use a roller or roll and tip and have to deal with a curling edge at masking tape etc. Here is what I do… successfully because I am the only one who can tell and point out these edges

First, you just do one topcoat for these repairs? Then you tape once. For every extra coat you tape extra before starting, overlapping the previous tape but covering 3/16” or so of surface to be painted. This prevents a big step.

I try to find a place to hide the edge, like a curve, corner, anti skid section etc. and paint to that. After that you still have the next step but it will be hidden better.

After painting, I use a card scraper to shave the edge down. For working on a flat surface you want a curved card scraper so that you can work precisely without touching anything else.

Thanks for that, I will check the videos and practice