Polishing Linear Polyurethane Imperfections

[Epicurean]

uI have two DA sanders, a Bosch, and a Ryobi, I believe. The rubber pad melted on the Ryobi and I replaed it with some harder rubber.

TWo more questions I have:
1. If it's polished will the shine last thte same amount of time or will it need to be repeatedly polished?
2. If instead of polishing it's sanded with 320 and thenrepainted how many coats would it need? Could 1 coat be enough?

[minaret]

Originally Posted by Epicurean

uI have two DA sanders, a Bosch, and a Ryobi, I believe. The rubber pad melted on the Ryobi and I replaed it with some harder rubber.

TWo more questions I have:
1. If it's polished will the shine last thte same amount of time or will it need to be repeatedly polished?
2. If instead of polishing it's sanded with 320 and thenrepainted how many coats would it need? Could 1 coat be enough?

1. With an acrylic like yours, it'll be fine. LPU not so much.

2. No. You need at least 2 coats, but you need to understand the painting technique involved. The first coat is very light, you are not trying to acheive flow on it. A very small amount of peel is expected. This is called a "tack" coat. You only need to wait for this coat to tack off, not cure. The tack coat should be so thin it is translucent. Wait about 1 hr for it to tack, when you can barely leave a fingerprint in the tape and no paint comes off on your finger it's ready. Then very carefully shoot a nice flow coat. Interthane 999 requires a WFT of 5.3 mils to acheive the desired DFT of 2-3 mils. It should be quite thin. Study and practice with the rig you intend to use. A wet mil gauge may help you learn while practicing. Often a third coat is required to provide coverage, but you won't need that as long as you reshoot the same color. Pot life at your temps can be as low as 2 hours, do not accelerate. For Interthane 999 you need fluid tip E and air cap 704 or 765 in your gun. I prefer the 704. Adjust fan and fluid tip volume carefully. Reduce with International GTA 713 about 10%-20%. This can make a huge difference in flow, play with the ratio when practicing. Do a search on painting and study on this site. Oh, and run pot pressure at 12.5 PSI, cap pressure technically needs to be 45 PSI but I run it up to 65-70 PSI. This causes extra material loss in the form of overspray, but provides a nicer peel free finish. It can only be done on a conventional rig generally, which may be illegal where you are. Those cap pressures may be illegal as well. Local law may require you to use HVLP systems. Hope this info is helpful and not too intimidating. This can be done by a novice, at least much better than your last attempt. It just requires careful study, practice, and planning. You are on the right path, but I wouldn't blame you if you found a pro to do it for you if you decide to reshoot. It can be intimidating and materials are so expensive. Good luck! Oh, and don't prep sand your topcoat with 320, you'll see the grit scratches through the new topcoat if you do, at least where you've hand sanded. Use 400 dry. And guide coat to make sure you have all of the peel out.

[CharlieCobra]

Hmm, painted outdoors or someplace where a steady breeze was blowing I'm betting. Paint is funny. Cold airflow across it after spraying will cause massive orangepeel. Just think of it as goosebumps like ya get on yer arm on a cold, breezy day. That whole job needs taken down and re-shot but that's just me...

[minaret]

Originally Posted by CharlieCobra

Hmm, painted outdoors or someplace where a steady breeze was blowing I'm betting. Paint is funny. Cold airflow across it after spraying will cause massive orangepeel. Just think of it as goosebumps like ya get on yer arm on a cold, breezy day. That whole job needs taken down and re-shot but that's just me...

The OP is in malaysia, his average temps are very high. I doubt it was cold air, just a novice on the trigger. Though any wind never helps. He is shooting in an outdoor shed, from the pics. Probably didn't reduce either. Airflow can't cause peel, it can only prevent flow from occuring. The peel still has to be put there by the applicator.

[CharlieCobra]

Eh, I've seen this happen with cold air in my shop. I've watched perfectly smooth paint peel up with a draft. However, in high temps, it's likely pilot error exasperated by too fast of a set up time. Better application and some retarder would help.

[Epicurean]

Since I painted the cockpit and it turned out good I know that it's just my inexperience that is the problem. There were really ideal conditions; no wind and temp in the high 80's. I understand much of what minaret said but some of it I'll have to look up. Here, in Malaysia, nothing is illegal (except eating pork) but also much isn't available. I'm virtually certain it's not possible for me to change fluid tips or air caps. I haven't seen a Devilbiss gun but the guns here do work. I can only get 320 grit sanding discs, nothing finer. So, if I respray the hull (hopefully find someone) what can I do? Stop at 320 or block rub (dry) with 400? I ran the pressure into the pot at 65 psi (I hope in a metric country the guage isn't in Pascals or newton's per meter) but don't know how to tell what it comes out at. I read the wrong pressure can cause orange peel. You guys who are experts understand or have a feel for this but it's still a mystery to me. Anyway, I certainly appreciate all the response and will read some more to try to understand how to spray.

[minaret]

Originally Posted by Epicurean

Since I painted the cockpit and it turned out good I know that it's just my inexperience that is the problem. There were really ideal conditions; no wind and temp in the high 80's. I understand much of what minaret said but some of it I'll have to look up. Here, in Malaysia, nothing is illegal (except eating pork) but also much isn't available. I'm virtually certain it's not possible for me to change fluid tips or air caps. I haven't seen a Devilbiss gun but the guns here do work. I can only get 320 grit sanding discs, nothing finer. So, if I respray the hull (hopefully find someone) what can I do? Stop at 320 or block rub (dry) with 400? I ran the pressure into the pot at 65 psi (I hope in a metric country the guage isn't in Pascals or newton's per meter) but don't know how to tell what it comes out at. I read the wrong pressure can cause orange peel. You guys who are experts understand or have a feel for this but it's still a mystery to me. Anyway, I certainly appreciate all the response and will read some more to try to understand how to spray.

It is a big learning curve for a complete novice. Be careful, most pressure pots will explode if over pressurized. 65 psi is getting there. When the bottom of you're pot turns inside out, it's a sign! Pot pressure should be 12.5 psi, no more. Tip pressure, or the pressure coming out of the air cap is different. I'm guessing this is what you mean and you are using a siphon feed gun, not a pressure pot. A pressure pot will have an extra regulator on the pot itself. If it is a pressure pot rig which you cranked up that high, it certainly would explain the peel! If all you can get is 320, prep with that. You'll probably be perfectly happy. It just wouldn't fly at my pro yard, but we do megayachts and need a perfect finish for what we charge. A little 320 scratch barely printing through will still be 100 times better than what you have now. Sounds like it's definitely a reshoot for you, unless you want to import everything you need. If it helps the tip size you need is 0.33-0.45 mm or 13-18 thousandths, depending on your measuring system. The right fluid tip and air cap make a big difference.

[Epicurean]

OK I'm convinced to respray. It's just too difficult to get the things needed to sand and polish. It could be done here but it's a lot of work and wouldn't come out as well, I feel. Also, a first rate paint job will likely be downgraded after a short time by collisions with dinghys, etc. It was very interesting to get all this advice from some very knowledgeable people. Thanks

[vientoman]

Originally Posted by cat man do

I prefer NON marine specific urethanes like ameron coatings or Jotun

Far more affordable than awlgrip and sterling and tough enough for mining equipment and oilrigs, so certainly good enough for boats

Have seen them used on boats for over 20 years, easily buff able and re-coatable

Those paints may be cost effective, but it comes at a cost:

5/30/2001: U.S. Reaches Settlement of Cleanup Costs at Ainsworth Paint and Chemical Superfund Site in Baltimore

[cat man do]

Originally Posted by Epicurean

Here, in Malaysia, nothing is illegal (except eating pork) but also much isn't available.

Never had an issue finding and eating pork in Malaysia, mainly in more Chinese areas, but it is available
Malaysian cuisine - Wikipedia, the free encyclopedia

So, if I respray the hull (hopefully find someone) what can I do? Stop at 320 or block rub (dry) with 400?

The image below is my last boat being blown
That was dry sanded with 180 as have the majority of boats I have had any say in.

[cat man do]

Originally Posted by vientoman

Those paints may be cost effective, but it comes at a cost:

That has nothing to do with the paints performance.

[minaret]

Originally Posted by cat man do

Never had an issue finding and eating pork in Malaysia, mainly in more Chinese areas, but it is available
Malaysian cuisine - Wikipedia, the free encyclopedia





The image below is my last boat being blown
That was dry sanded with 180 as have the majority of boats I have had any say in.

That's hilarious, spraying in the dirt! Definitely amateur hour. Newspaper for masking not even taped down, one good gust of wind and it's in the paint. Funniest painting pic I've seen in years.

[bstreep]

Originally Posted by minaret

That's hilarious, spraying in the dirt! Definitely amateur hour. Newspaper for masking not even taped down, one good gust of wind and it's in the paint. Funniest painting pic I've seen in years.

Who cares? The dirt is has probably been dampened, and if there's no wind, there's no wind.

Not everyone wants/needs a professional job. Buddy of mine had his 40' trawler painted to the tune of $60K - which included completely stripping the boat. It's been a year. And the old hardware still stains the new paint.

[minaret]

Originally Posted by bstreep

Who cares? The dirt is has probably been dampened, and if there's no wind, there's no wind.

Not everyone wants/needs a professional job. Buddy of mine had his 40' trawler painted to the tune of $60K - which included completely stripping the boat. It's been a year. And the old hardware still stains the new paint.

How about the neighbors boat 3 feet away with no masking on it? How respectful is that, trashing someone elses boat out of sheer laziness or lack of know-how? Not to mention the cars parked right there. Here it wouldn't even be legal to do that, ground wet or not, and it doesn't look wet. Prepping for topcoat with 180 is just beyond ameteurish, any study would tell you that's a terrible idea. And so is shooting a boat that's not even blocked on bare dirt and masked with newspaper. Sorry but thems the facts. Next time tell your buddy to come see us, we usually do a 40' trawler for about half that.

[cat man do]

Originally Posted by minaret

That's hilarious, spraying in the dirt! Definitely amateur hour. Newspaper for masking not even taped down, one good gust of wind and it's in the paint. Funniest painting pic I've seen in years.

Laugh all you like but countless thousands of boats sprayed the same way around the world with not an issue.
The overspray cant tell if it is landing on free newspaper or purchased plastic.
and the proof is in the pudding with the 180 prep.
No sanding marks can be seen if you put on more that one layer of paint.

Oh, and paint job for this vessel cost less than $500 in labour and about the same in primer and topcoat, no runs, no dirt, no stuck paper.

My building and spraying sheds cost $0.00 a week in rent, how about yours?