Spraying System 3 LPU

Discussion in 'Boat and Accessory Building' started by Greg, Apr 20, 2006.

  1. Doug

    Doug Paddler

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    hmmm isn't working and I can't edit posts right now...

    I am thinking about trying a bit more dilution for the LPU. It comes back to my inexperience with spraying. Are the thicker/smoother areas correct? Or are thinner bumpier areas the type of coating I should be aiming for? ie. do I need to dilute so that the thinner areas flow together?

    thanks
     
  2. andreas

    andreas Paddler

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    hi doug,

    from looking at your pictures, it seams like your layer is to thin. or your lpu is to thick--no idea i never sprayed lpu . but if it comes out of the can alright then it should be thin enough (that comes from my experience spraying gel coat)
    if you followed the instructions on the can then i would try and put more on , on you next run. i don't know if i would sand it smooth before the next coat..... if you are lucky it will smoothen out, i would give it a try with out sanding.

    good luck
    andreas
     
  3. Doug

    Doug Paddler

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    whatever happens, I don't think I'll sand between coats. Any bumps will either get filled in or not. If not, it makes sense only to sand at the end.
     
  4. Doug

    Doug Paddler

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    thanks Mark. I just put an underscore between the 1st and coat: 1st_coat...
     
  5. Robert_Meier

    Robert_Meier Paddler

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    I fixed the link Doug. Images are now displaying.
     
  6. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    Doug, I believe that you're supposed to use distlled water to dilute the LPU (I'll have to check the instructions to be certain). When I spoke to the fellow that will be applying my LPU, he told me that he would first apply a "mist" coat -- just a very light coat, not enough to fill.

    I wouldn't sand between coats -- I think you'll find that subsequent coats will fill in nicely. I found that the finish got glossier with each additional coat.

    *****
     
  7. Astoriadave

    Astoriadave Paddler

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    Why is that? Is it the chlorine in tap water or any trace minerals? Tap water on the NW coast here is very soft. Well water might have minerals, I suppose.

    I used tap water and it worked fine.
     
  8. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    I'm not sure Dave. But I do remember running out to get some distilled water when doing my double. I doubt that I would have done that if it weren't in the instructions. You're probably right however, about the water in this part of the world being OK -- but some places the water can be pretty hard, which might not bode well with the LPU. Just guessing, of course.

    *****
     
  9. Astoriadave

    Astoriadave Paddler

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    That sounds right. Any calcium in the water might mess up the LPU emulsion. Emulsions are notoriously sensitive to ionic components in water.

    In any case, I had no problems using local tap water. We run our drinking water through a filter that takes out the chlorine and any residual bacteria, but I just used stuff straight from the tap.

    Our water source is surface runoff from a watershed that gets 6-7 feet of rain a year, so it is very soft.
     
  10. Doug

    Doug Paddler

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    I put 4 coats on yesterday. Doing light passes actually doesn't work that well. It never fills in, the subsequent coats just adds more "drops" to the surface. What needs to happen is that enough lpu has to land on the surface such that adjacent drops touch and flow together.

    The last coat I applied has sort of worked out the best. I probably hit the boat with about 300ml of lpu, and it was enough for a film to flow together. However, there were more problems. First, the film dried with a bit of texture perhaps this is what is referred to as "orange peel". I never did see the smooth surface as shown in the photos above again... Secondly, there were quite a few runs caused from the significant increase of lpu that was applied. Coating conditions had changed slightly. The humidity dropped from 70% to 60% RH. The temp was constant at 15C. All the coats (except for the initial coat) were done with 15% water thinning.

    I'm at sort of a loss right now. For sure I will try and increase the humidity again prior to the next coat. Secondly, I will try and sand off the runs now. Thirdly, I will increase the thinning to 20+%. The reason is that I want the film to flow without having to apply so much lpu (ie too much lpu causes runs). The conundrum I have is that I'm ready to apply the final coat or two with crosslinker (which is why I want to get rid of the runs first). The problem is that if I screw up with the crosslinker I'll need to keep recoating within an 8 hour time period. This causes issues with sleep and work schedules!

    Maybe I'll try one more coat non-crosslinked to double check my process settings (humidity, % thinning). If it goes well I can do the crosslink.

    Or maybe I'll just do a couple of crosslinked coats and then sand/buff the finish.

    I guess I'll also try to phone S3 today and get their thoughts.
     
  11. Astoriadave

    Astoriadave Paddler

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    Doug, if it were me, I'd wet sand the whole thing, to get to a uniform surface, free of runs, and then I'd test a thinner mix on a portion (without cross-linker). If it does not work out, you will have little repair work. If it does work out, then all you have to do is wet sand that portion, and continue. Adding cross-linker just firms up the end product. Application seems to be the same.

    Don't know how familiar you are with wet sanding. It is the only way to go with "soft" surfaces, I think. I have wet-sanded epoxy just 24 hours after application. I used a Makita sander, used wet (yes, I know they tell you not to do that), and first did 120 grit, and then 220 grit.
     
  12. Doug

    Doug Paddler

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    Dave, I was thinking I just need to sand the runs. Is it also advisable to wet sand the "orange peel"? Maybe I'll be able to post a picture later tonight to show the surface texture I currently have.

    Come to think of it, maybe the "orange peel" I have is just a result of the previous bumpy surface (from not applying enough lpu). In that sense, maybe I would have had a smooth glossy finish w/ some runs on coat #4 if I started with a smooth surface. If this were the case, did coat #4 have too much water and run too easy?

    well, the good thing is that I knew this was going to be an experiment so I'm mentally prepared for it. I wish now that I had some epoxied surface I could do a quick test with. All I have right now is the kayak!
     
  13. Astoriadave

    Astoriadave Paddler

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    I don't think there are any short cuts here. Only sanding the runs will give you a discontinuity at the edges of the sanded area. The orange peel is there to stay, also, unless you sand. Best to sand the whole thing, or live with the runs and orange peel. If you are very careful with a carbide-blade scraper, you might be able to reduce the runs to almost nothing, in which case wet sanding wll be pretty quick, and wll yield a more uniform surface.

    Or, if some discontinuities are less objectionable than the runs, do the partial sanding after scraping the runs, and lay on another coat ... if this really is an experiment.

    It might be, just to throw another variable into the mix, that a cross-linked coat will sand better, because it will harden up faster. It is soft surfaces that gum sandpaper and make for difficult finishing, not hard ones.

    In a couple years of use, if it annoys you, wet sanding will give you a shot at the finish you really want.
     
  14. Doug

    Doug Paddler

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    How hard does the lpu get? I noticed this morning that it is soft, something like a durometer of 40.

    BTW, I'm not expecting a perfect finish by any stretch. The underlying epoxy isn't perfect either, and I know that the boat will be even less perfect after it gets used for a bit. 8)

    Doug
     
  15. Astoriadave

    Astoriadave Paddler

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    Don't know what that number means -- but with the cross linker, it is hard as a rock -- harder than epoxy when it is fully cured. You can scratch it with a sharp tool, but ordinary whacks with the backside of a screwdriver or similar do not abrade it.

    To locate my strut, I used permanent marker on the fully cured LPU, and it comes off with acetone, leaving no residue. This stuff is tough. I bet Dan and others can give a more authoritative opinion on its durability. I have yet to get the hull wet so I really can not say how it is in use.
     
  16. Doug

    Doug Paddler

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    Here's a pic of the current progress. The picture makes it look worse than it actually is (other than the run).

    [​IMG]


    I'm taking bets. Is the lpu too diluted? Or not diluted enough w/ too much applied?

    Doug
     
  17. Dan_Millsip

    Dan_Millsip Paddler & Admin

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    I'm no expert, but I'd guess that the LPU is setting up before it gets a chance to spread out adequately. Perhaps a bit more water is needed to slow the drying process a bit? Maybe the nozzle of the gun needs to be a bit closer?

    Contacting the experts at System 3 at this point might save you a lot of grief and frustration. I've found their tech support to be excellent. Their number is 800-333-5514.

    As for the durability of LPU, I'm completely sold on the product -- but it would be nice if it were easier to apply. The finish on my double lasted a full four years before I had to refinish, and if it were not for some bumps and scrapes that needed immediate attention, I'll bet the finish would have been good for another couple of years at least. As Dave mentioned, the finish is extremely durable against anything that is not tool sharp -- the deck on my double had absolutely no visible scratches at all -- the hull was a different matter but that's to be expected.

    Dave, I made the same assumption as you about the hardness of the LPU finish, however, the System 3 tech told me that epoxy is indeed harder than LPU. But the LPU is tougher and more resilient to impact damage. The tech guy also told me that LPU is actually a paint. I don't know what that means exactly with regard to my boat, but it does seem to work well and I've been happy with it.

    I guess the key to LPU is learning to apply it well -- but at the price of the stuff, that could be expensive if you're not a quick study.

    *****
     
  18. Doug

    Doug Paddler

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    I've tried phoning S3 several times the last two days, the tech support haven't been picking up the phone. They're usually pretty quick with responding to emails though, even on weekends. However, my latest query has so far gone unanswered.
     
  19. Oldpro

    Oldpro Paddler

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    Spraying LPU

    Dan said:

    Call me crazy, but after reading so much about the difficulty in achieving a furniture-quality finish with LPU, I've considered considering spraying my usual coats of Flagship (or is it Captain's?) on the boat I'm currently working on. I checked the Pettit website for directions, and in part they recommend first applying a thinned "mist" coat, then two coats of thinned varnish "wet-on-wet." Sounds like a formula for disaster, with runs on top of runs, but maybe???? Has anybody sprayed regular varnish? Are there any lessons-learned that might apply to LPU application?
     
  20. Astoriadave

    Astoriadave Paddler

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    I agree with Dan: the stuff went on too dry, and never had a chance to level. I bet thinning the full amount and light passes, in succession, quick enough that the first pass is not dry, might do it. You still might get runs on vertical surfaces.

    Thanks, Dan, for that bit of insight into the LPU: tougher is a better decriptor.

    I like the stuff, because it is the most durable water-reducible coating I can buy. It is tedious to apply, but I hate high-VOC paints.