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:

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.