Question
I'm shooting ICA polyurethane, opaque pigmented over MDF. Final finish hand cut and polished. We've always gotten a few tiny bubbles, but recently more and more appear. They aren't really noticeable until you're rubbing out. I thought it was the water compressor, so I got a new rotary screw with the cooled dryer, but I'm still getting the little bubbles. Any thoughts? Could this be a timing issue? We've tried about everything. We're thinking of trying polyester. After years with ICA poly, I'm still not nailing it
Forum Responses
(Finishing Forum)
From contributor R:
What kind of gun and solvents are you using?
I'm looking to get into new spray equipment if necessary. Any thoughts on the best solution?
It stands to reason in handcut surfaces that using the 39.00 cheapo guns and throwing them away is actually the most cost-effective. I don't condone the idea, but of the thousands we've spent on systems, they don't seem to work any better. We cut and rub out everything, and just want to get the product on securely.
When you spray the edges and then hit the flats, you get a double pass at the edges that is thicker than it should be. That explains the pattern of bubbles.
It could be your gun, could be you need to retard, but since it's only happening at the edges and places where the film is thicker, that says it is a spray technique issue. Trigger pull and release timing may be off as well as the distance between gun and surface at the start and finish of your stroke. I'm betting it's triggering technique and spray pattern overlap, though. Have someone watch you or set up a video camera to tape your technique.
The highest priced equipment and a chemical engineer on hand to vary your mixture according to a meteorologist's recommendations won't get you a good finish if your technique is off.
I agree with the technique advice above - your finishing speed of hand movement may be too slow on edges.
If I remember, the ECO gun is HVLP. You don't need HVLP to lay down the 2K PU. Sometimes it injects too much air into the product.
Also, what thinner are you using? In very hot weather, try two different solvent blends.
First try this - mix up a batch of just reducer that is 50% D1010 and 50% D1015. Thin your product with this and give it a try. Next, make a blend of 75% D1010 and 25% D1024. This blend is used to thin your product. The second blend is for very hot weather and should only be used as a last ditch option, as it dries very slow.
If your booth has a large amount of air flow pulling across the sprayed pieces, it could be causing the surface to skin too fast. Try shutting off the booth as soon as you are done spraying.
Another last ditch item is adding one of two different additives ICA can supply. The first one to try would be the AD3 anti-skinning agent. This product keeps the top surface open until all tail end solvents are out. It is not a retarder. Also, watch your air pressure - use just enough to atomize the product.
Comment from contributor L:
We did about 500 tops in the opaque ICA 2k. Heavy build coats catalyzed per ratio first, then used their dilutents about 5%. After the mix we let it steep (sit for about 15 minutes). We re-stirred the product and used the Kremlin pump/gun. Then every 15 minutes or so we would "cycle" the pump from the pickup buck through the drain tube back into the pickup bucket.
Coats were applied very heavy as it was all flat panel finishing - 4-5 mils wet coat. We used the same 2k ICA primer (white) and the same reducer ratio in that. Spray, sand, spray sand, prime coats over P-board substrate. Build coat pigmented 2k ICA as outlined above 4-5 mil wet. Sand and re-coat. 3rd top coat was thinned with 5% acetone and 5% reducer sprayed 3-4 mils.
Product laid out perfect each time and no issues whatsoever. We were replacing vinyl clad tops with a more durable non-cracking non-peeling finish for a call center.
I think your problem is air bubbles from the reaction in the catalyzation process or can be that it is flashing too quick not allowing off-gassing to occur properly in the cure. By letting the product steep 15 minutes before using will allow reaction to complete before stirring again and adding to your pump. By adding the ICA reducer for the product you are using will retard it slightly to allow off-gassing to occur (or air bubbles from wood pores to work through).
It worked perfectly for us with our big Kremlin pump as outlined above and about 500 tops came and went without an issue.
