Spraying WR-LPU

I recently finished applying System Three’s WR-LPU to the Tern14. I chose to use this material primarily for two reasons. First, it is touted as being a very tough finish, longer lasting than standard varnishes. Secondly, it is a water-based suspension which means that it avoids nasty organic solvents. I had heard and read about some difficulties in applying the finish. Apparently it has a fine line between drying to fast and leaving orange peel or applying too much and causing runs or sags. Ultimately I wasn’t too concerned about getting a “pro” finish so I thought I’d give it a try.

I decided to try and spray the wr-lpu. System Three’s manual suggested that spraying the lpu would result in a better finish. Not only that, but it gave me a great excuse to buy a cool piece of equipment: a Fuji Q3 HVLP spray gun. Overall, my experience with the wr-lpu is mixed. I think it’s possible to achieve the almost-perfect finish by spraying lpu and not sanding/buffing. Unfortunately I wasn’t able to achieve this myself. Despite practicing on scraps along with coating several coats, I never applied the lpu in a way that gave a “check out that great finish” result. It is clear to me that lpu application process is not very stable and that small changes in application or perhaps formulation (ie dilution with water) or environment make big differences. With my own eyes I saw myself spray a surface that would go from glossy to patchy, all depending on small variations in moving the spray gun. One of the common things I see written about apply lpu is that it is very sensitive to temperature and humidy. I think these factors are almost red herrings. Providing that the temperature is down around 15C, I don’t think humidity is terribly important. 50%RH to 80%RH should give a similar result. I imagine that warmer temperatures could be very problematic.

My specific application settings were as follows. I used full air and liquid flow on the hvlp gun, along with a 1mm nozzle tip. Temperature was consistently around 14C, and humidity was 60-75 %RH. I tried various thinning of the lpu and most of it was done with 20% dilution. I kept the gun at about 6″ away from the boat and tried to move at a speed which maintained a wet edge while trying to avoid runs or sags. The video below shows me spraying the kayak.

Some parts of the kayak would get a fairly flat and shiny surface. Other areas would be textured because the lpu dried too soon prior to flowing together. Actually, I’m not clear on whether it dried too fast or perhaps there just wasn’t enough lpu applied. I also had lots of areas with runs and sags. Here is a picture that shows the balance between a smooth surface and a textured surface:
1st coat

Here is a picture of a sag:
typical run

Here is the kayak after finished spraying:
suspending

After I finished the boat I sprayed the hatches individually. The finish on the hatches was better than the rest of the boat, I think the smaller surface allowed me to easier control the amount of lpu applied.

With my inexperience in spraying finishes, for me it was quite easy to quickly go overboard and apply to much lpu. At some point I would like to do more experiments, such as lowering the air flow rate, carefully studying the effect of spray distance, and perhaps lowering the water dilution. The problem with this is that the lpu is extremely expensive. The cost sort of made me rush through the experiments. In the end though, I am satisfied with the material and plan on working with it again.

4 comments on “Spraying WR-LPU

  1. Hi

    I’m in the process of applying LPU as a topcoat for a furniture project I’m working on. These are a total of four rusted steel panels which form a set of folding screens.

    My first experiments with the LPU were with the satin flavor. I noticed at the time that the material did not want to flow together. I probably did not prep the surface well enough. It was rubbed out with maroon Scotch-Brite pads, but not wiped down afterwards. I assume the dust on the surface was the main culprit.

    By the way, the primer coat is a Sherwin Williams product called Corothane PrePrime. In contrast to the LPU, this stuff is really gnarly in terms of solvents. I honestly believe that taking more than a few breaths of it unprotected could cause immediate respiratory problems. However it works really well on the rust and sticks like glue, so I braved the process even though I don’t have explosion proof exhaust in my spray area.

    I continued in my finishing by spraying gloss LPU on the panels. The gloss seemed to go down relatively easily. It took 2 coats to get a nice even film.

    Then my plan was to mix the gloss and satin to arrive at the sheen I wanted. I settled on a guesstimate of 60% gloss and 40% satin. Now I have coats on 3 of the 4 panels and am not happy with where it’s heading.

    The first panel to recieve the topcoat ended up with a film that had several rough spots where the material dried to quickly and/or did not get enough build. I could see it happening during the spraying, but every attempt to cross-spray those areas or add more material would just keep drying the problem spots…

    On the next panel I tried to overcome this by lowering the air pressure and diluting the LPU more. At this point it’s about 10lbs of air pressure and diluted to about 40%. The tip I am using is 1.8mm. At this low pressure, the atomization is not so good.. I’m spraying very close to the surface and overlapping a LOT. I can achieve a nice flow with this approach, if I take care of any light areas as I go, i.e. not waiting until the entire panel is coated before going back to add material.

    HOWEVER, when the film dries, I am left with streaks of milky finish, matching the passes of the gun. They are on the subtle side but they are there. Now about 10 hours later and not seeming to change..

    By the way, the 2 coats of gloss were not crosslinked. The top coats I am currently spraying are crosslinked.

    So it seems I am having a problem putting down a successful coat either because of the satin formulation or the crosslinker.

    Since I am getting in the position of having to spray yet another coat onto each panel, I might spray my next one without crosslinker just to see if that could be effecting it. I don’t care quite as much on these parts about toughness since they are indoors.

    So I just thought I would write here about my experiences since after all, this is the glory of the internet..

    Anyone with thoughts can email me: ohronny at earthlink dawt neht

  2. That’s quite the experience there Ron. Are your panels horizontal or vertical when you’re spraying them?

    I think if anything it is best to spray dry as opposed to having a run. If nothing else, you can sand and buff out a slightly textured finish. That is a lot easeier than trying to sand a run.

    With your lower air pressure trial, is your tip is too big? I’m using a 1mm tip if I remember correctly. BTW, what kind of sprayer are you using? I don’t think my sprayer has a gauge where it monitors the air pressure. I spoke with S3 support a few times and they were pretty clear on some things. 1mm tip, maximum air flow, keep the gun close to the part. After that, they would be quite nebulous…. “depends on the temp, humidity, dilution, sorry but it should work…”

    Personally, I think S3 knows that this product is very hard to use. I wonder how well it sells.

    One other thing that I was surprised about was the amount of particles in the air after spraying. I know the LPU was water based which is better than solvent based, but there was a heck of a lot of particles floating in the air. I’d hate to be in the room without a respirator. I wonder if rolling and tipping with a solvent based polyurethane would actually be any worse… Well, we do what we can and avoiding solvents is something to aim for.

  3. I have been using the System Three paint on the deck and parts of my 22′ sailboat. It is the first time I have used a spray gun so this has been a totally new experience for me as I struggle to figure out what will work. I bought a super cheap HVLP system from Princess Auto which normally sells for about $140 but I got mine for $35 on a clearance sale. Making the deck of my sailboat my first project might seem reckless but that was the job I had to do and the paint is very expensive to spend a lot of time practicing.

    What I have learned so far:

    The System Three base paint goes on much easier than the finish coat. I really had no problem applying it at all. Even if I did not intend to use the LPY topcoat I would be tempted to use their base coat.

    The top coat is difficult to get perfect. In fact, I have not achieved anything close to that. I have, however, achieved a coat that looks pretty good and, I think, better than what I could achieve with roll and tip application f any paint.

    I can not achieve a totally smooth surface. If I apply very light coats the surface is textured (orange peel?) at best and rough at worst. If I apply enough paint to get a smooth coat, I also get runs. Runs are a real pain. Sanding them off is very difficult – which shows how tough this paint is – even before it cures. The best I got was a consistent texture that, oddly enough, is actually quite attractive and not out of place for the deck of the boat where a sheen Is not always desirable. As it turns out my wife really likes the looks and thinks I am a genius – so there you go.

  4. I just found about your comment, thanks for posting!
    Glad to hear that you’re happy with your finish coat. From what you describe, I think I would be happy with that too.

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