In the past I have used the pre mixed UV sanding resin without any issues. But I am doing a series of boards for friends so I bought a 5 gallon drum of UV cure lam resin from Fiberglass Hawaii. I am using this resin with surfacing agent for the fill and gloss coats. I followed the recommended ratio of SA (yes I shook up the bottle) and used my usual procedure of flashing it in the sun for 30s, bringing it inside for a few minutes, then bringing it back outside to cure fully.
The problem is that when the wax rose to the surface, it did so with a fine texture that didn’t provide full coverage. This caused the resin to not cure completely. I actually brushed on a thin layer of SA which allowed it to cure to a sandable surface. But that created a nightmarish thick layer of wax to get through. Is there something I can do to prevent the wax from forming that texture so that it cures properly?
I never go to the count of 30. 10 or 15 seconds in direct UV or a UV box. Then back inside until the surface starts to look cloudy/milky. Doesn’t matter how long it sits inside. You have to give it a good amount of time though. That is where and when the wax has the time to rise. It could sit inside an hour and it wouldn’t hurt a thing. I go by the look of it, not the length of it. When you buy premixed UV, there may often be a period of adjustment to get set times figured out. You may even have to add UV powder to your premixed UV resin. If you can’t get it to work the way it should , you may have to break out the MEK. The problem with premixed UV is that if it sits on the shelf a few months, it will settle. All the UV agent goes to the bottom and becomes a yellow goopy mess. During the months of March and April due to the Virus I sold out of everything and couldn’t get a fresh drum of Silmar. Completely out of resin with 8 or 9 major ding repairs for $$. So I bought a quart of Fiberlay UV from Englund Marine to do the ding repair. It was thick yellow goopy resin. Would not set without MEK. Leave it in UV for hours and it still felt wet, not tacky! Wet! Sure was glad when that drum of OB 3 showed up at the shop.
I brush it on and walk away for 5 minutes before taking it out into the sun. The only times I’ve had issues like you describe was if I was impatient. That texture you describe, you might want to run the resin through a filter. I’ve had issues with wax additive getting a little chunky. Guessing that texture is messing with the surface tension.
It definitely helps to let it sit for a few minutes before flashing it.
I did some tests yesterday afternoon:
First I did a control with the SA ratio recommended on the bottle. This did exactly what it did in my board. The wax rose but disturbed the surface tension creating ripply droplets of wax with exposed resin in between. Impossible to sand.
next I tried just doubling or tripling the surfacing agent. This appears to have worked. I think with enough volume of wax on the surface it prevents that surface tension from causing those droplets. The surface looks consistently cloudy just like the premixed stuff. It sands great as well. Although there was way more SA, the wax was still thin enough to not be noticeable while sanding. Im calling it a success.
even better results may come from a light catalyzation but it doesn’t seem to be necessary for me.