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Old 21-07-2010, 12:06   #1
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Topside Paint Coming Off In Sheets

I WAS getting ready to sand and paint topsides but as I was chiseling off some caulk I inadvertently scraped off a large section of paint. I know that's not good. I have since found that the entire topside paint system has a weak bond layer. Looks like the boat has 5 coats of paint. The weak bond is between the 3rd and 4th coat. It must be under two categories: bad prep job and/or incompatible paint. Both can have a multitude of reasons. I am thinking the only way to be sure to get a good paint system back in place is to scrape down to the 3rd coat, clean that surface perfectly, then sand all the paint off to the gel coat, clean, prime, and paint. Does anyone have any other suggestions, cause I know how much work this is? Thanks. Pat
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Old 21-07-2010, 16:43   #2
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Some of the new "anti clog" sand papers will contaminate surfaces, unless it's washed off prior to painting the next coat. As a result of this new trend among the paper manufactures, I'm sticking with tried and true aluminum oxide and silicon carbide papers. Yep, they'll clog up faster, but you should change paper frequently anyway.

I've seen this personally with 3M "Fre-Cut" where huge sections of freshly painted surfaces came off in sheets. When the paint is $300 a gallon, it tends to piss you off. In my research, I found many companies are using animal fats and proteins to prevent clogging. Don't wash off these goos and you'll have contaminated surfaces. A tack cloth just doesn't get it.

Sand back to known good paint contact Pat. I know your pain, but it's cheap insurance compared to the alternative.
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Old 21-07-2010, 17:50   #3
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PAR,
Thanks for the sandpaper lesson. I did not know this. I will stick to the "clogging" sandpaper for sure. I guess I needed confirmation on my plan but was also hoping for some "magic". Thanks
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Old 21-07-2010, 18:01   #4
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Co-incidentally, we are painting Bluestocking to-morrow morning. The paint we are covering over is 12yr old Interlux Interthane Plus. We prepped the epoxy primer back then with the 2-rag system, one saturated with cleaner/prep followed by wipedown with clean lintfree rag. The paintwork was in good solid shape except at the waterline where the usual degradation takes place, here we have taken it back to gelcoat, and applied three coats of Dupont epoxy primer, with two coats above on the topsides.
We did the Awlgrip adhesion test (its described on their site) before priming by foam rollers (lots of them were used).
We rubbed back with 220 grade on hook and loop extractor type random orbit sanders to a good finish. We will roll and tip 2 coats of Imron MS600 EMBR Quality over the next 3 days.
Before the topcoat we will 2-process the hull wipedown with Dupont Sontara high temp cleaner, followed immediately with static control wipe.
I have no connection with Dupont Imron, other than as a user on the advice of my friend who is a professional marine painter (and is "tipping it" for me). If it was available, I would have used the Interthane again.
I have gone into detail, in total support of Par's comments.
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Old 21-07-2010, 18:59   #5
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Thirty-some years ago, when I first painted my hulls with LPU paint, I was so meticulous and terrified of applying the paint badly that I sanded everything to the point where I actually had a glass-like substrate. I primed it and sprayed three coats of LPU. It was absolutely gorgeous. Then I got greedy and decided to shoot one final coat within 24 hours, obviating the need for further sanding. So I took the water hose and began shooting water the knock off the dust and dew drips. Suddenly, whole sheets of plastic paint began blowing off. I discovered, the hard way, that one can be too diligent in sanding, actually to the point of "glazing" the substrate. LPU, as with other coatings, must have some "tooth" to adhere. I took it all down to the epoxy base and reprimed, then sanded with 120 free-cut, the non clogging white stuff. As long as you keep replacing the paper while it cuts quickly, you will be alright. The problem is when you try to save a few bucks by sanding a few extra square feet with tired paper. It merely heats up and melts the substrate, making it glass-smooth. This method has served me for all succeeding repaints, each lasting ten years, or so.
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Old 21-07-2010, 21:11   #6
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Silicone is evil!

Silicone spray, the kind commonly used on sail slides, can cause persistent paint failure. Just as it's evil cousin silicone caulk, it is very difficult (nearly impossible) to remove completely.

Sanding can drive the oil deeper into the fiberglass, chemical stripping of the paint may be your best bet.... would certainly get around a variety of possible causes of the failure....

..more work, but might be less work then an easier solution that might not work.
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Old 04-08-2012, 19:26   #7
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Re: Topside Paint Coming Off In Sheets

Am considering a 2010 Cat445 that has a painted hull (blue above the waterline) and a 2010 that does not. Should I avoid the painted hull, or is it OK if I can verify that the painting process was a good one? Would appreciate any wisdom on whether or not I'm buying trouble with a painted hull above waterline.
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Old 04-08-2012, 19:47   #8
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Re: Topside Paint Coming Off In Sheets

LPU painted hulls are superior to gelcoat. Top end boatbuilders offer it as a premium. LPU holds up to UV light better than polyester gelcoat, meaning colors last longer. When you bash the hull into a dock, or that Mexican panga with lobsters careens off you, the finish is more likely to survive. If you smash it enough, the paint can be repaired in the field. Gelcoat is harder to repair and color match. Ten years from now, the LPU will be looking shiny, the polyester will be dull. Unless, of course, you decide to polish two or three times a year with carnuba wax and lots of elbow grease.
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Old 04-08-2012, 20:04   #9
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Re: Topside Paint Coming Off In Sheets

Roy, so that's what 'LP' paint means in the listing. Sounds like good news. I thank you for this information.
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Old 04-08-2012, 21:24   #10
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Re: Topside Paint Coming Off In Sheets

Quote:
Originally Posted by Roy M View Post
LPU painted hulls are superior to gelcoat. Top end boatbuilders offer it as a premium. LPU holds up to UV light better than polyester gelcoat, meaning colors last longer. When you bash the hull into a dock, or that Mexican panga with lobsters careens off you, the finish is more likely to survive. If you smash it enough, the paint can be repaired in the field. Gelcoat is harder to repair and color match. Ten years from now, the LPU will be looking shiny, the polyester will be dull. Unless, of course, you decide to polish two or three times a year with carnuba wax and lots of elbow grease.

I paint and repair boats for a living, and my boat is all gelcoat. Wouldn't have it any other way for cruising purposes.
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Old 04-08-2012, 21:44   #11
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Re: Topside Paint Coming Off In Sheets

dcoe, LP or LPU stands for linear polyurathane. Two commonly used LP paints are Interlux Perfection and Awlgrip.
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Old 04-08-2012, 23:10   #12
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Re: Topside Paint Coming Off In Sheets

Quote:
Originally Posted by Roy M View Post
Thirty-some years ago, when I first painted my hulls with LPU paint, I was so meticulous and terrified of applying the paint badly that I sanded everything to the point where I actually had a glass-like substrate. I primed it and sprayed three coats of LPU. It was absolutely gorgeous. Then I got greedy and decided to shoot one final coat within 24 hours, obviating the need for further sanding. So I took the water hose and began shooting water the knock off the dust and dew drips. Suddenly, whole sheets of plastic paint began blowing off. I discovered, the hard way, that one can be too diligent in sanding, actually to the point of "glazing" the substrate. LPU, as with other coatings, must have some "tooth" to adhere. I took it all down to the epoxy base and reprimed, then sanded with 120 free-cut, the non clogging white stuff.
Thats what the suppliers of my topcoat said as well when I had similar issues on a build..
I use 180 grit now and never had an issue since
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Old 05-08-2012, 01:25   #13
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Re: Topside Paint Coming Off In Sheets

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Thats what the suppliers of my topcoat said as well when I had similar issues on a build..
I use 180 grit now and never had an issue since

I can't imagine how you could get a decent finish if you sand for topcoat prep with 180 grit. I always use 400 myself, every pro painter I know uses 320 or finer. Anything else shows through. From the Awlgrip Application Guide-


Application of Finishing Primer:
1. Sand the surface smooth with 120220 grit paper. Grit choice will
be determined by condition and make up of the surface.
2. Blow off the surface with clean, dry compressed air while dry wiping
with clean rags to remove sanding dust and residue.
3. Tack off the surface with
Deluxe Tack Rags #73009.
4. Mix all primers' parts A & B (base and converter) according to the
correct mix ratio and leave for 15 minutes induction. Reduce as
necessary for application method.
5. Apply the required coats of the final primer smoothly and evenly.
Thinning the product will reduce film thickness but results in a
smoother surface that will require less sanding.

NOTE: Awlquik
is easier to apply by brush/roll than 545 Epoxy
Primer
. However, 545 Epoxy Primer will provide a more durable
system.
6. Sand the entire primed surface with 320400 grit paper to a
smooth, flat finish.
7. Blow off the surface with clean, dry compressed air while dry
wiping with clean rags to remove sanding dust and residue.
8. Wipe with
Awlgrip Wipe-Down Solvent (NA: Awlprep T0008;
EU:
Surface Cleaner T0340) using the Two Cloth Method.
Repeat process as necessary until the surface is completely clean.
Allow the surface to dry.

9. Tack off the surface with
Deluxe Tack Rags #73009.
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Old 05-08-2012, 06:17   #14
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Re: Topside Paint Coming Off In Sheets

Quote:
Originally Posted by minaret View Post
I can't imagine how you could get a decent finish if you sand for topcoat prep with 180 grit. I always use 400 myself, every pro painter I know uses 320 or finer. Anything else shows through. From the Awlgrip Application Guide-
You can get a decent enough job if you are more interested in using your boat instead of having some shiny toy to impress your mates.

Not interested in the high end paintjob.
Cant stand boats where the owners are always worrying about their topsides getting some mark on it, no place in the real world IMHO

The anchor chain doesnt care about the type of finish you have as it scrapes across your bows unavoidably one day
Your hard dinghy cares little about it as you bang up and down on the transom in a swell while trying to board
The guy in his dugout has no respect for it as he bangs into your topsides.
The squid you caught have no respect for it as it hoses black ink over it
The tuna you caught have no respect as the piss blood everywhere.
The customs guys have no respect for it as the stomp over your boat in black kicker boots
The boats you are racing against have no respect for it as they kiss you on a rounding mark.

More than happy with the 80% finish and very slight orange peel.
Fools 99% of the people out there
And from my time building and fairing 100ft gin palaces in the 80's, that last 20% which makes up the perfect finish often takes more time to get at considerable expense than the 80% which you would have been happy enough with, especially when you are out there on the boat using it.

People who are on their boats using them boats don't actually see the outside paint job that often
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Old 05-08-2012, 08:10   #15
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Re: Topside Paint Coming Off In Sheets

The grit you use will depend on the type of paint you will use and the surface you are applying it on. The concern is the sanding scratches showing through the paint when the job is done. For a professional painter like Minaret, this is a sign of poor workmanship. Since he gave his word to the owner that he would use all his skills to give them a finish that "They" would be proud of, it is a personal goal for a painter like Minaret to achieve the highest quality. Cat man do has stated that he could care less for a "Yacht Quality Finish" so his input into a quality debate should be simply ignored.

Vertical Surfaces
If you are using a high solids (low VOC) paint like something that is used in aviation, 220-320 grit is the normal. If you elect to use a low solids (High VOC) paint like Awlgrip, you will need to use 320-400 to avoid seeing sand scratches. Since it has so much solvents in the paint, when it drys, the solids in the paint will shrink down and imprint the sand scratch which in some instances, can be seen at a distance.

Horizontal Surfaces
Lower grits can be used here because you put on a heavier coat of paint. The low VOC paint can fill the sanding scratch when it drys.

The delamination issue is generally caused by the applicator waiting past the overcoat window of the paint and a there is no chemical bond between coats. Another major cause is contamination.

The Cure
There is no need to sand all the way back to gel coat if the lower coat have good adhesion. Do a test for this by taking a razor blade and cutting a checkerboard series of cuts in the paint with the cuts being deep enough to test the bond at the gel coat. The squares should be about 1/4". Rub a piece of high quality tape like 3m 233 over the checkerboard and give it a good jank. If you have an adhesion problem it will show up with this test. Sand down to the problem and then seal the entire paint job with an epoxy primer.

Next use a guide coat over the epoxy so you can see how much you will need to sand off and then Paint to the level of quality you want.

Personally, if I had a gel coat that was in good shape, then I would cruise with that system since it is more resilient to little boats that go bump in the night. Here in the states, paint works best for me.
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