spraying acrylic

[mic-d]

I have to paint about 5m of exterior timber balustrade with a sprayable acrylic. I just bought the paint and a cheap spray gun, ala Bunnings, hooked it up to my compressor and did a test run on some scrap. Although paint did leave the gun and stick in the general vicinity of the scrap there also seemed to be a largish plume floating off into the distance :eek: Is this normal when using an air spraygun? I had the pressure set at the recommended 65psi. Are there ways to minimise this via setting changes or would an airless spraygun be better? I am completey new to this spraying business :rolleyes:
Cheers
Michael

[PuppyPaw]

hehehe
Its normal, what distance are you holding the spray gun at?
if its possibly you might want to change the actual nozzel to a smaller one!

you want the gun about 15cm away from the peice.
This info is from an art spray gun so I don't know if its different for a more industrial unit!

I hope you are wearing a mouth/nose mask.

[JB]

there also seemed to be a largish plume floating off into the distance Are there ways to minimise this ...


Pressure is the main issue. Have it as low as possible, if the mixture is thin you could try 50psi.

You might try setting the nozzle so it sprays a flat 'stream' of paint rather than a round one (if you know what I mean). That's ususally controlled by the knob at the back of the gun above the air inlet.

[Richardwoodhead]

Getting a good finish by spraying can be tricky. (Check back on some of the threads in this forum..). Lots can go wrong! I'm a total convert to spray finishing - you get a GREAT finish - but it was a steep learning curve for me. And I'm still looking upward. But a few ideas from someone who's done it all wrong before getting some of it right.....

.Make sure you know how to use your gun. There should be 3 adjustment screws controlling (1) spray jet ("cone" or width of spray); (2) amount of fluid coming through (you don't want too much, or you'll get runs & sags - or too little as it'll look & feel "dry") and (3) amount of air - too much and it'll come out too strong and blast your fluid too vigorously onto the workpiece - too little and it'll be insufficient to carry the fluid onto the workpiece.. (Maybe the Bunnings gun does not have these settings / dials?)

. Keep your air pressure blow 50 psi.

. wear a good face mask / respirator and spray in a well ventilated area.

. Find out how to clean the gun after use - otherwise it'll be gummed up when you come to use it again.

. Ask a friend / anyone who has experience using a spray gun to show you / hands on demo - how to use & hold the gun and move across the workpiece. Try to get the spray coming in perpendicular and about 15 cm from the workpiece and overlap your runs by about 30%. I'm not familiar with spraying acrylics - (only lacquers & other solvent based wood finishes). But assuming it's thin enough to spray, it should be a similar process (??)

I hope you can get it to work for you, because when it comes together, the finish you achieve is really even and smooth. Worth the effort for sure. Good luck.

[Dean]

Too bad you missed Major Panic's OWE day in Brissie not long ago. Plenty of spray finishing information to be had.
Here's the full report with some photos
http://www.woodworkforums.ubeaut.com.au/showthread.php?t=14307&highlight=OWE

Basically the uninformed (myself included) discovered the great benefits of spray finishing and realised that it isn't really that difficult once you know the basics ;)

I have a S-770 gun bought from Bunnies a little while ago. Works a treat and has all the adjustments. I paid around $55 at the time, but you can get the same gun from Tradetools and other retailers for $49 these days.

[Harry72]

Yep too much pressure 65psi, overspray is an unfortunate side affect of spraying all types of gun will overspray to some extent even airless types.
The trouble with cheap guns is they dont atomise the paint very well, they need a higher pressure to atomise into finer droplets, I run my cheap gun at 35-40psi to get acceptable results and the good gun(samson s90, a midrange price)can run as low as 20psi up to 30psi.
The samson run at 20psi has less than half the overspray of the cheapy run at 35psi and gives a better finish result... but as your only painting outdoors the finish may not be as critical as say spraying a with full gloss like Cabots cabothane.

[mic-d]

Thanks to all who posted. Tomorrow I'll try with a reduced pressure and see how it goes. The gun has 2 adjustment screws for width and one at the back that seems to control the amount of paint (?)
Cheers
Michael

[Harry72]

"2 screws for width" one will be width the other will be for air flow(unusual for a cheaper gun), the one at the back would control how much the needle will open in the nozzle.

Im a bit peaved ATM, I broke a part on my samson gun:( and cant find a replacment part for it.

[mic-d]

sorry my bad... 2 screws, one for width and one at the back controlling flow...

[johnno402002]

[QUOTE=Richardwoodhead
Find out how to clean the gun after use - otherwise it'll be gummed up when you come to use it again.
[/QUOTE]
My experience is all with automotive acyrlic Lacquer's, so take this advice in that context only. It may be OK with the acyrlic your using as well though.

When I started using my first gun, an Arnold from CIG 1979 vintage, I would clean it thoroughly after each weekend's use, and store it empty. I had lots of trouble with the gun, I replaced the gasket on the cup lid three times in 6 months, and I had to put a new set of gland seals in it, because it started sucking air around the needle shaft and no amount of adjustment would fix it. I was spending more time cleaning the thing than using it, and most of the time it wasn't working properly.

Next I tried leaving it with some thinners in it, this was a bit better, but if I left it for several weeks, the gun 'dried out' again.

What I did next was to completely stop cleaning it, and just leave it with the primer surfacer in the pot and all up through the head.

It's now, what, 26 years old and still has the same lid gasket and gland packings I put in it when I stopped cleaning it. I used it for the first time in several years about three months ago, and it took ten minutes of cleaning to get it up and running perfectly again.

The paint seems to keep it sweet, it's less work, but the most important thing for me is that the gun works much better.

Of couse, when you do some two pack stuff, and you're in the habbit of not cleaning your gun, guess what happens :o

One of the worst things you can do to a gun is to completely submerge the head when cleaning it, as this gets the paint into the air passages. You should be prepared to completely rebuild the thing if you submerge it.

regards,

John

[soundman]

leaving paint in a gun can be catistrophic if its the wrong paint.
You could leave ordinary nitrocelulose in a gun indefinitely with little trouble as long as it doesn't dry out. I ( and others I know) have a gun that most usualy has GMH flat black in it all the time ( black is beautifull ).
Try that with spraying enamel & you have a sticky mess & a very serious clean up job in days.
Etch primer will eat the guts out of you gun & polyeurathane will turn to jelly & is worse than enamel to get out.
I have been storing my guns wet ( thinners ) for years, It works for me.

Back to the original post.
All guns are different & you need to play with them to understand their habits.
If you want minimum overspray & can tolerate a coarse spray try backing off the air till the gun splutters then edge up the preasure till you get an even atomisation with the minimum preasure. This will all vary with viscosity.
When working near the edge of the guns capicity the fan adjustment may cause some variation as it effects the airflow within the gun & effects the atomisation.

Playing with thinners, turps or water makes less mess for starters.

[mic-d]

Thanks to all who replied! The job is done now and the client is very happy, which is the main thing. I managed to get minimal overspray on a setting of 35psi.
Cheers
Michael