Lacquer overspray

[allsport]

Hi,
I'm looking for some advice on finishing some large honour-boards I've been asked to produce.
Each board is a full panel (2.4 x 1.2 metres) of jarrah veneer on MDF and the equipment I am using is a conventional spraygun (Star 770 with 2mm nozzle) and Wattyl Stylwood 90% gloss lacquer.
I've usually achieved pretty good results on smaller items, but I find that I'm getting dull areas and a slightly streaky finish. I think that this is being caused by overspray from dried spray settling on a nearly-dry surface, making it slightly rough and with a sandy texture.
Is there a slution to this problem? I've tried more pressure and less pressure (from 30 psi), more and less fan, but the problem is still there.
Maybe I need different equipment? Any suggestions welcome, although I tend to think it's a problem with me rather than the equipment. I need to get these done, so if a new system is required I'll pick it up tomorrow.
Thanks for your time.

[Harry72]

lightly spray it over with some straight thinners, lay the boards flat and level so no runs occur, this will remelt the overspray and under lying finish together creating a smooth surface.
The problem may well the thinners as they come in differing evaporation rates fast medium and slow, this is to cater for weather conditions.

[wheelinround]

I think you'll find that its your movement more than anything else you need to spay at a constant distance not in an arc. So its you that needs to move not just your arm.

When you arc the gun from side to side your pulling the distance of the nozzle away and this causes overspray or a dusty spray as I call it.


Have a read http://www.buzzle.com/articles/spray...echniques.html

[rustynail]

Both of the previous suggestions are on the money. When doing large panels keep your elbow up and the gun pointing straight down.

[Heilander]

To avoid overspray,always overlap the coats by 50%
i.e. 'wet on wet' you shouldn't get runs using lacquers because the solvents evaporate too fast
If the coats are drying too quickly,use a 'retarder' thinner,but don't go overboard eh? maybe 10 - 15% total or you WILL get runs
Hope this helps
Scotty

[munruben]

Also with larger panels, try to spray "off the work piece" that is to say, continue with your spray motion until you have completely continued past the board and then before you come back onto the work piece, start your spraying motion as you approach the board so you don't stop the gun in one place even for a split second, As mentioned above, keep your distance from the surface constant and moving continually, don't flex or fan the wrist while spraying, Good luck.

[Cruzi]

Moisture getting into airline can cause dull spots but often with gloss the finish appears to cloud, go flat and look uneven whilst it is drying, just leave it and it all evens out.

With overspray you can pull the finish with a thinners dampened rag, not the best for full gloss finishes but great for satin and matte finishes, you can use very fine steel wool with some wax or you can use a cutting compound and buffer.

[The Bleeder]

I see you are in Perth (nice temps at the moment). Temperature plays a big part. As said before 'wet on wet' and this has a lot to do the the thinners. If the thinners are evaporating to quickly you won't get a 'wet on wet'. 'Retard' thinners (doesn't evaporate as quick) if the temp is high or lightly spray over with thinners.