|Home » Forums » Professional Finishing » Message||Login|
You are not logged in. Consider these WOODWEB Member advantages:
bubbles and extra fine tips8/3
hello, friends. i'm struggling with bubbles again and wanted to know if kremlin extra fine tips will help. i use an 06 and 09 tip right now and both are regular fine (not extra fine).
yesterday - i sprayed identical pieces literally two hours apart with night and day differences. humidity was up a touch for the second round of spraying but nothing out of the ordinary. i'm spraying a 20:1 graco pump with an excite gun. ilva urethane, reduced 15-20%. i have an air dryer.
conditions today were reasonable and i got the same results - bubbles forming within 5-10 seconds after spraying (a was spraying small samples of various hardwoods as well as some small parts for a stained cherry cabinet). some bubbles go away as quickly as they form but some/a lot remain as the piece dries. not the end of world stuff but i would love to not have to depend on brown paper for an acceptable finish job.
samples were sealed earlier in the week so they have had plenty of time to dry. pressure and air are set right - i've been in a little groove with spraying, getting near perfect results for a few weeks now. hose is four weeks old. i'm spraying 3mils wet coats. i switched pumps, guns, and tips all with the same mixture. i'm 99% sure i'm doing everything the exact same as i was last week and earlier this week when i was getting great results. temps have been hot but not much different from last week and yesterday and today.
I didn't know that Kremlin had extra fine tips.
What wood are you spraying, and whose finish? Usually retarder solves the problem by slowing down the dry time enough to allow the air bubbles to escape. It is not the fault of the gun. It is the finish surface drying too fast to allow the solvent to flash off and the bubbles to escape. They get trapped in the drying surface film. It more often happens on open grained wood ei. Oak or mahogany. Try retarder and put on slightly thinner coats and you should see the problem go away.
Pumps can create shear in the finish and that causes micro bubbles. The Kremlin pump and waterbase finishes don't always mix well. MLC Resistant had this problem and it's a solvent based finish. They redesigned the finish and now it's known as Stealth and it works well in a Kremlin pump.
Also the bigger the pump, 20:25 vs 10:14 the less shear is produced because of the larger size of the piston.
leo - kremlin does have extra fine tips available. they have some sort of pre-orifice that helps to better atomize the finish. they are $12 more than the regular tips. i ordered one and will try it out and report back.
i didn't get a chance to spray today so it will be a heavy day of experimenting tomorrow.
Do you have a link to the fine tips?
the extra tips are shaded in yellow (not available in all sizes). my local supplier doesn't have them in stock so i won't have my new tip for a week or so.
i spray the same product. i tried a fine tip from CAT but did not make any difference.
chris - i'm retarding with tz4223 at 15-20%. i typically only use tz13 in the winter. are you getting these same results (inconsistent)?
i've been spraying liva for a couple of years now and things started great. i could shoot it with my eyes closed and get near perfect results. then, all of a sudden, i came in one day and started shooting and getting these bubbles. i'll get them and struggle through them, start to shoot perfectly again, and then back to bubbles. i've experimented with a full range of variables, trying to only change one thing at a time without being able to find the smoking gun.
i did talk with ic&s yesterday and they suggested a heavier sealer coat to more properly cover the wood. it was guessed that the wood is still exchanging air and a thinner sealer coat would allow air to escape when the top coat is applied, creating bubbles. this might be my problem for some of the solid stuff we spray, but the cabinet parts that i was spraying when the wheels came off we're sprayed the same and this stuff is mostly plywood (so no air coming off the material).
i'm in for a full round of experimenting today and will report back.
I am spraying a wide variety of veneers and the grain pattern varies a lot so for me it"s a question of slowing the sealer to allow the voids to be filled.
yes, ta0012. thinned 10-15% with tz33.
i'm thinking this isn't quite it. for the cherry plywood parts, we sealed one side, let it dry and sealed the other side - all within a few hours. i sprayed thirty or so hardwood samples (various woods) and the back/bottom side of these is unsealed (so air flowing out of the wood would go out the back - path of least resistance).
i'm spraying with an excite gun - 06 tip for my top coat and a box coat (two passes). i do the same for sealer but spray with a 09 tip.
I believe these products are designed to be reduced 20%, probably more with a fine tip. High viscosity would require higher fluid pressure, which could cause additional air induction into the material as it exits the gun. Normally a 0.9 tip is recommended, fluid pressure between 300-450 psi. Should also use a slow reducer.
friday's results are back to near perfect. i sprayed exactly as i have before with one exception. we shoot small quantities and use a hopper on our aaa set up. i have and typically do (and have gotten good results in the past) pee out the thinner i leave in the lines until the pump and hoes are near empty. load my top coat into the hopper. turn the fluid back on. continue to pee into a recycle container until i see the top coat come through. now, on friday, i didn't take the gun and pee top coat back into the hopper after i'd cleared thinner from the lines. otherwise, everything else was the same as i've done in the past.
i'll keep experimenting and report back.
i just got some thinner in as suggested by my supplier. It is TZ-425 a very slow mix.the TZ 4223 is listed as slow.
have you looked at the ILVA resource book at the IC&S website?
ILVA Resource Book