Poly-Vinyl-Alcohol. I learned a bit about it yesterday. I mounted the parting board and the hull to the cradles and started working in clay to the seam between the two to give a water tight seal. It took me a while to work out a method but I finally figured out that if I used my 1st grade “snake making” technique, I could put the snake at the seam and press it in using the rounded nose of a pair of forceps. I would fold the clay back on itself when the forceps pushed it out and repeat four times. Then I would press firmly with the forceps to separate the clay, peel away the upper and lower excess, and then run over the small fillet with a razor blade. It took me about 30 minutes to work up this technique but once I got it going, I was able to fill the seam in about another 30 minutes…it was frustrating work.
I then cleaned the plug to remove all the clay fingerprints using mineral spirits, gave it another coat of wax, and buffed again. I was able to find a mushroom polishing pad for my die grinder while looking for buffing alternatives yesterday morning at Northern Tools. The Partall wax simply isn’t reasonable to buff by hand – it’s very aggressive.
Now that all that was complete, it was time to spray the PVA. I’ve used this material in the past with relative no problems but I haven’t used the Partall brand (this time, I’m using a wax and PVA that are designed to work together – hopefully separation of the molds will go much easier). I loaded up my Divelbiss HVLP paint sprayer with about 2 oz of PVA and laid down the first mist coat and let it dry for about 15 minutes. I came back and shot the first wet coat and about mid-way through, some movement around the shop caught my eye. I looked up and found the air brimming with whisper thin “cob-webs” of PVA that were drifting around. For a few seconds, I was mesmerized at how they floated and then I realized they were landing all over everything – including the plug. YIKES! I started waving my arms at them catching them in the air but eventually a few found their way onto the surface. I let that dry for 20 minutes and came back with water and began wiping off the PVA since it had a bunch of these cobwebs in the surface. I also noticed that there seemed to be a lot of minuscule air bubbles trapped in the PVA and while most would come to the surface and pop, there was some fish-eyes left.
I researched a bit on the internet and found that the air was probably too dry and that some of the PVA was drying immediately upon leaving the paint gun causing the cob-web phenomenon. The website I found recommended adding up to 10% purified water to the PVA to avoid this. I did and the second round with the PVA went much more smoothly…except for the bug. A damn bug landed on the deck and stuck there. I tried to gently remove him while the PVA was wet but he started to come apart. I decided I would get him when the PVA dried. I came back tonight to pick him out and the moment I tried, the PVA lifted from the plug in an area about .25 inches in diameter. It also picked badly and left a ragged edge when the bug was removed. The good news is that the PVA separated very easily from the plug. The bad news is that I had to remove it yet again and start over. After realizing how easily the PVA lifted from the plug, I got smarter and simply peeled it off instead of washing it with water.
So now, after fixing some of the clay seams that suffered from the repeated stress of waxing, polishing, and spraying, 7:30pm Sunday night, I have another first wet coat of PVA on. With any luck, the second coat will be going on in about another 15 minutes.