Good morning
I am using a Porter Cable HPLV spray gun with 95 PSI to the gun, and most of the settings (air volume, finish volume and overall volume) are all set roughly in the middle. The manual says max pressure to the gun is 100 PSI.
The spray head is set to about 80% wide (vs narrow spray pattern) which is producing some overspray, but allows me more even coverage.
I am using Flecto Varathane “professional Clear finish 900 clear gloss” varnish, and was thinning it with lacquer thinner and Penetrol.
I am varnishing 22 cherry kitchen cupboard doors, doing 3 at a time on a horizontal surface, and then moving them to a horizontal drying rack (all in what will, one day, be the dining room, right after I get done with the kitchen …) All the doors have been sanded in between coats with 500 grit – to take out the bubbles in the previous coat.
The last mix was supposed to be the last coat: was made up of 18-20% thinner, 5% penetrol and 75% varnish. Surface and room temperature both ~78 or so.
Two problems: First: the parts of the finish in between the bubbles looks great ! But the bubbles !!! Oh My Gosh !
Second, a few areas had a surface that looked and felt like 180 grit sandpaper
I think the second problem was caused by some overspray, and unless someone has any other ideas on that, I can fix that one pretty easily, but any suggestions on how to solve the bubble issue would be very gratefully received.
Some of the earlier coats seemed to have fewer issues with more thinner, but I may have adjusted the spray gun somehow as well by mistake.
How much thinner can I use ? Lacquer thinner or mineral spirits ?
Any thoughts on the gun settings ? More air ? less air ? More pressure ? Less pressure ?
Will spraying on a vertical surface reduce the bubbles ? I have a vertical rack set as well, but my inexperience in volume showed and I got runs, which the horizontal rack has eliminated.
Thanks in advance for any ideas. Meantime I’m heading back to the sander… It’s going to be a long day. Thought I had sanded these for the last time already…
Gavin Pitchford
“Sail fast – live slow” (build even slower)
Replies
Gavin:
Your post sent me running to my copy of Spray Finishing by Andy Charron.
His book cites a number of probable causes:
Material is atomized too finely. Decrease air pressure.
Trapped solvent breaking through surface of fast-drying finish. Slow down dry time.
There are some real experts here who may well weigh in (I have had considerable help in the past with my spraying problems).
As a first step you might want to reduce the pressure. If that doesn't work reduce the amount of solvent.
Regards,
Hastings
Without having a can of Flecto Varethane in my shop I can't say for sure, but I would think your problem is your solvents. I'm not sure any poly product should be thinned with lacquer thinner. Mineral spirits is the common thinner for that class of finishes. Penetrol is usually used in brushing applications as it is a retarder and causes the finish to flow out better and dry more slowly. I would try a moisture resistant cabinet lacquer like Sherwin-Williams or Campbell's. You could also try a top quality pre-catalyzed lacquer like Mohawk. If you are set on using Varethane, which I think is an excellent product for some applications, I would call Flecto and ask about using lacquer thinner as a solvent.
I'm going to agree with Terry that the lacquer thinner is a problem.
Although I've never used it, according to what I've read the Varathane 900 is supposed to be self-leveling, implying that no added retarders should be necessary. I would definitely contact either the manufactorer or whomever you purchased it from and find out what the recommended thinner is for your application.
Varathane is supposed to be reduced with hydrocarbon solvents, not lacquer thinner. Mineral spirits, or for faster drying, VM&P naphtha or xylol are the best choices. Penetrol is, IIRC, a slow evaporating glycol ether meant to improve flow out. I'm not sure how compatible it is with Varathane.
Spraying with conventional air or HVLP introduces air into the film. Lacquer thinner evaporates much faster than mineral spirits, so It may be coming out too fast, thus trapping air bubbles in the film.
An earlier poster said that too fine atomization may be the problem, but I doubt that. Too much air is the real problem, I think, and some possible cures would be:
1. Reduce air pressure (apparently you have a conversion gun) to reduce the amount of air introduced into the film (and reducing the fineness of spray as well).
2. Hold the gun farther from the workpiece so as to soften the impact velocity and volume of air per square inch. You will have to move slower to keep a wet edge this way.
3. Reduce the Varathane more and with mineral spirits instead of lacquer thinner. Lower viscosity will release bubbles easier and the slower solvent evap rate of MS will allow more open time for bubbles to release. You must be careful not to apply too thick a wet film though, in order to avoid runs.
If you call the manufacturer, you may get lucky and find someone knowlegeable, but you are likely to get some doofus with no knowlege of the product who is just working from a script - "If caller asks such and such, give him canned response #3". Ask for someone who has actually worked with the product.
Good luck
Thanks for all the help and the ideas.Left to my own devices yesterday afternoon, from another website, I decided that lacquer thinner was likely part of the problem, and equally that insufficient thinner was part of the problem.I reduced air flow, went to 25% mineral spirits, a brand new can of varathane (another website suggested that older material that had been exposed to air more often might need even more solvent / thinner because the open time caused solvent to evaporate) , no penetrol, and sprayed a much thinner coat than I had the coat before. Between the combination, and playing with variables as I went, I had a virtually flawless finish by the time I got to the last door, and while I have some minor sanding to do before redoing the LAST last coat, I think I may have nailed it. Fingers crossed.The notes for Penetrol suggest it is good to add as a thinner and to increase dry time, but from the results without it, I won't be adding it again anytime soon.Again, thanks to all.
Gavin
Gavin Pitchford
"Sail fast - live slow" (build even slower)
Congratulations, and thanks for letting us know what the outcome was.
BruceT
Gavin
I would be reasonably sure that the lacquer thinner is the problem. Back in my younger years when dealing with painting cars there was a very basic rule that, "you can put enamal over lacquer but you can't put lacquer over enamal" or there would be problems such as orange peel, blistering or outright delamination.
The Varathane lists mineral spirits as the thinner so I think that would put it in the enamal catagory. Once it is on and dry but not cured well, it does not seem to me it would take very much lacquer thinner to cause it to blister (or bubble). Spraying a final coat with lacquer thinner in it would likely be plenty enough to do the dastardly deed. It would be worth experimenting with using scraps and only lacquer thinner or mineral spirits as the variable.
RichThe Professional Termite
Gavin:
As you have found out, the lacquer thinner and too much air pressure where the cause of your bubbles. Your air pressure was way too high. I assume that you are using the pressure regulator that came with the P-C spray gun. I have the same gun. The regulator on the gun should be set to about 40-45 PSI without the trigger being pulled. The air volume control on the bottom of the gun should be set to wide open. That will give you about 10 PSI at the tip with less overspray. From there you can adjust your volume and fan pattern for best results. HTH.
The P-C gun has an air flow adjustment, but no pressure gauge. My compressor has a tank, and an independent output / hose setting (don't they all ? I don't know...) so while the tank is ~150, I set the hose to 96 or so. I like the idea of wide open on the gun and 45 at the hose, so I will try that too. I think the gun might be more able to do fine tuning, but there is no scale or gauge, so one has to do it and then hope it doesn't get knocked, or have a slight adjustment by accident etc. Whereas the setting on the tank is both protected, and the gauge tells you what you have, so far easier to replicate one time to the next.Wide open seems easier to control and then a gauge on the tank can actually govern the flow. Seems like an elegant solution ! Thank you!Haven't tried many other spray guns but I really like the P-C gun, although they could all use a stand to hold them steady while refilling.The other thing - going to mineral spirits proved a LOT less noxious than lacquer thinner. Thanks again for all the ideas.Gavin
Gavin Pitchford
"Sail fast - live slow" (build even slower)
Gavin:
You can pick up a small pressure regulator to use on the gun at any of the box stores (Lowe's, Home Depot, Menard's, etc.) or Harbor Freight for around $8-$25. Just make sure that it will adjust the pressure up and down (some don't - they only show what the pressure is). It just screws into the bottom of the gun where the air hose now connects. Just remove the quick connect coupling that's on the bottom of the gun now (assuming you are using one) and screw in the regulator and then screw the quick connect onto the bottom of the regulator and your good to go. Well worth the every penny. I also use one of those plastic disposable filters between the regulator and the quick connect fitting (also available at Lowe's, etc.). I like the P-C gun also. I have a Walcom FX gun ($400+) and it does a beautiful job (it should for the money!) but for many jobs I just grab the P-C, especially for colors. I reserve the Walcom for clears. If you attach a regulator to the gun, you can set the regulator on the compressor for approx. 90# and set the regulator on the gun for about 40 PSI or so with the trigger not pulled. When you pull the trigger, the regulator on the gun will fall to about 20 PSI or so and you will be getting about 10 PSI at the spray tip (which falls into HVLP measurements - 10 PSI max. at the tip.). You can then adjust your gun input pressure for different types of finishes. Good spraying.
Gavin:
Forgot to add: You can also pick up a stand for holding a gravity feed gun at Harbor Freight for about $8. Not sure if the box stores have them or not - never looked.
DPull
you are a font of useful information - THANKS !!There may be an upgraded P-C gun with a built in or add on gauge - or there could have been one with this model that was somehow out of the box, but I don't think so.I stole it ... $35 at Ocean State Job Lot, but I got the last one and the box looked like it had been opened so there may have at one point been a gauge, but the documentation doesn't look like it. Still, with or without the gauge, a great deal. The gun holder is a great tip - thanks again.Gavin
Gavin Pitchford
"Sail fast - live slow" (build even slower)
Yeah, $35 is a steal! I paid $89 for mine at Lowe's. It had the regulator with it even tho the documentation doesn't mention it. Not sure if you are aware of it or not but you can also buy additional needle/noozle sets of different sizes for different material viscosities. I bought a 2.0 mm set but have only used it once. I find the 1.5 mm that's standard on the gun is OK for most stuff if you thin it to about the same viscosity so that it sprays good. You just have to be careful with waterbased finishes and not thin them too much (usually no more than about 10%).
great info - thanks.
Gavin Pitchford
"Sail fast - live slow" (build even slower)
DPull,
Results improved dramatically - many thanks to you and others, for all the great suggestions. The doors are drilled, looking pretty, and about to be mounted - so 6 months of work about to see daylight ! Now for the drawers...Gavin Pitchford
"Sail fast - live slow" (build even slower)
I'm new to spraying as well. I noticed immediately that water in the air can cause problems too. I added a water separator and my results improved.
I agree - I get better results if I make sure the tank is well drained before I start but the water is back in shortly thereafter ....
But what is a water separator - where do you get one and what do they cost ?
ThanksGavin Pitchford
"Sail fast - live slow" (build even slower)
Is this gun (click) the type of gun y'all are discussing?
View Image
Sure looks like it. I'll try and find the manual and confirm the part number but 99.9%, "yes".
The only thing I don't love about it is the clean up of the exterior of the gun: there are lots of ridges which makes it easy to hold, but cleaning varnish out of the nooks and crannies gets old fast. I end up soaking the whole thing in a shallow tray of mineral spirits and then flipping it to the other side. Gavin Pitchford
"Sail fast - live slow" (build even slower)
Yes, that is the gun.
Thanks, Gavin(?). Here's something to try with the exterior problem. Look in the "food protection" section of the supermarket, where the Glad Wrap is, note the stuff called Glad Press 'n Seal. It has a sticky side, and the plastic is a bit heavier than regular Glad, and it's textured. Peel a portion of that off the roll and wrap it around the jar, smooth it on so the sticky stuff sticks. With any kind of luck, it'll work to keep the paint off, be "handle-able" and peel right off when you're done. I put it around the outside of quart paint cans when I'm pouring from them.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 7/4/2007 8:11 pm by forestgirl
Great idea for the gun - and the cans too, although personally I think the drips help save me from opening the can to check the colour! BTW, (sure you have tried this but just in case...) I've found pounding a blade screw driver through the lip of the can twice in close proximity, and then pouring over that spot seems to create some turbulence which causes the paint to "pop" out a little further from the can, and creates fewer drips. Then the finish drains from the lip back into the can which dramatically improves the seal on the can.Thanks for the idea of the glad wrap - I'll use it ! You should start a new thread with that one - "Great Tips & Techniques" or something similar.
Gavin Pitchford
"Sail fast - live slow" (build even slower)
Oooops! I gave you the wrong name. It's Glad Press n' Seal. That's the stuff you want.
I'll give the screwdriver-hole thing a try. I'm a bit chagrined though, the other day I put 4 nail holes in the rim of a quart of Benjamin Moore Satin Impervo to get it to drain back into the can, something I've done with several other cans of paint, no problem. However, when I opened it today, it had skinned over!!!! Oh, man, that was a bummer. I ended up transferring it to a quart jar using some cheesecloth to strain the yuckies out with.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Know what you mean - I've found the tin in some of the manufacturer's paint cans are getting thinner and putting the holes in can distort the lip so badly the lid no longer seals tightly. I've had a couple of those and needed to gently correct the problem with vice grips - and then really hammered the lid down when I was done. I have an old screw driver I sharpened sufficiently it now punches through the lip cleanly with less resistance - then I twist it with the widest part to open the hole.
Gavin Pitchford
"Sail fast - live slow" (build even slower)
I have found that among the variable listed: pressure, solvent, % spray cone of minnimal etc, that many issues including bubble formation could be solved by have extra material around to determine the optimal combination. Though daunting, a lot of the problems could be circumvented with some careful thought and logic that I am sure you are aware of. But making extra cabinents doors or facades from scrap as part of the construction plan has made wonders and saved a lot of headaches. Every sprayer is different as are the materials you use including the raw buliding materials, ambient conditions, and the list goes on. Have a scrap to adjust prior to spraying can narrow down the confusion.
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