Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Sun 16, 2018 1:31 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 16 posts ] 
Author Message
 Post subject: Spraying technique help required... splotchy finish?
PostPosted: Feb Mon 26, 2018 3:10 am 
Member
User avatar

Joined: Nov Sun 16, 2014 9:43 am
Posts: 243
Location: Christchurch, New Zealand
I'd appreciate some advice on spraying - I'm getting this odd finish and whatever I try, this is what I seem to get. Is this normal? I'm fairly new to using a spray gun. I'm using a 1.0mm nozzle on a small spray gun and using NC lacquer. Any help would be appreciated.

This was the finish after the first spray - looks ok from a distance
Attachment:
splotchy1.jpg
splotchy1.jpg [ 117.46 KiB | Viewed 897 times ]


And this is the close-up - if I lightly sand and spray a second coat will this start to even out, or is this indicative of a problem with my setup / technique?
Attachment:
splotchy.jpg
splotchy.jpg [ 81.95 KiB | Viewed 897 times ]


Any help appreciated.

Cheers

Steve

_________________
There are no personal problems that cant be overcome with the liberal application of high explosives


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Feb Mon 26, 2018 4:23 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1327
Location: Jackson, TN
Hi Steve,

I'm more of a rattle can guy, but the picture shows a coat that has cured too quickly - didn't flow out.

I'd suspect too high an ambient temperature and/or not a wet enough coat.

I find that spraying in temps higher than 75 deg will cause too fast of a cure.

I'm sure others will weigh in on this.

PS: just checked NZ temps, not too hot, so I think you'll want to put on a wetter coat, subsequent coats should flow it out.

Tim


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Feb Mon 26, 2018 5:02 am 
Member
User avatar

Joined: Nov Sun 16, 2014 9:43 am
Posts: 243
Location: Christchurch, New Zealand
Thanks Tim- so more thinner? I think I was around 25% thinner to lacquer in this coat.

It was definitely a warm day here when I sprayed it - and where I am (near Christchurch) its not too humid.

Cheers

Steve

_________________
There are no personal problems that cant be overcome with the liberal application of high explosives


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Feb Wed 28, 2018 3:27 am 
Member

Joined: Jun Sun 01, 2008 3:43 am
Posts: 144
Location: Linn Creek, Missouri
Steve, it looks to me like you need a little more thinner. You may also try a little more air pressure.

Steve

_________________
M R Radios C M Tubes


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Feb Wed 28, 2018 3:40 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4189
Location: Sunnyvale CA
In addition to the other good inputs (essentially, that the coat is going on far too dry), it might be that your thinner is too "fast". Check with your manufacturer's recommendations for your conditions, but in a pinch, a *small* amount of retarder (like 5%, displacing some thinner) will slow it up enough to flow out. The problem is exactly what it looks like, the droplets are semi-dry by the time they hit the surface. Usually that only happens when it is extraordinarily hot and dry and this looks like a rather extreme case.

Brett


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Feb Wed 28, 2018 9:47 pm 
Member
User avatar

Joined: Nov Sun 16, 2014 9:43 am
Posts: 243
Location: Christchurch, New Zealand
Thanks Steve and Brett - I did a second coat, much more thinned out, and it was still not really smooth, but a lot better.

I tried spraying a third coat last night but it was quite humid (right on the fringe of drizzle) and the black I was applying to the grill bars and feet went almost immediately cloudy white. Lesson learned there. I was able to buff the cloudyness out with a light rub from 0000 steel wool fortunately. I'm assuming that it was the humidity that caused that?

I've stopped and reassembled the set now because I need to take it along to a local vintage radio meeting tonight but I have about 100 more radios in my restoration queue, so I'll call this one done and continue to try different things, ask questions and learn. The next one will be better... I'm not totally happy with how this one came out, but I'm possibly being too fussy. My partner thinks it looks amazing and since shes always right, it must be true :)

Here is is at 1:30am this morning when I finished it... I'll put some better photos in the restoration thread once I can get it out in the daylight
Attachment:
20180301_010246 (Custom).jpg
20180301_010246 (Custom).jpg [ 132.04 KiB | Viewed 821 times ]

_________________
There are no personal problems that cant be overcome with the liberal application of high explosives


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Thu 01, 2018 12:12 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4189
Location: Sunnyvale CA
kiwi_steve wrote:
Thanks Steve and Brett - I did a second coat, much more thinned out, and it was still not really smooth, but a lot better.

I tried spraying a third coat last night but it was quite humid (right on the fringe of drizzle) and the black I was applying to the grill bars and feet went almost immediately cloudy white. Lesson learned there. I was able to buff the cloudyness out with a light rub from 0000 steel wool fortunately. I'm assuming that it was the humidity that caused that?


Yes, it's called "blushing". The spray comes out the gun, expands, which makes it cold, and the thinner starts evaporating, cooling it further. Humidity in the air can condense in the spray, then get carried along to the surface. The issue is that this water got to the surface and got trapped. The solution - other than spraying only in the recommended temperature and humidity ranges - is to use some retarder to displace some of the thinner, which slows the drying of the lacquer, and allows the water to migrate to the surface before the lacquer dries. It's a particular problem when your thinner is particularly fast, which is still the cause of your first problem (no flow-out). The roughness is almost certainly because the thinner is evaporating on the way to the surface, then evaporates before the lacquer left behind can level itself.

Everything about this suggests that maybe 10-25% retarder is called for, I would start low and work up. Of course, you could just stop now, wait about a month for everything to stabilize (put it in a warm dry place), sand off any blushing and sand it flat with 600, then rub it out to the desired gloss. It looks like you have plenty of material on the surface already, near as I can tell, and this is one of the nice things about lacquer - as long as you build up enough film thickness, you can always fix it. In general, you never count on the quality of the sprayed surface for the gloss (although if you are really careful, you can), you get it coated as good as you can, then rub it out.

Brett


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Thu 01, 2018 1:10 am 
Member
User avatar

Joined: Jun Sat 18, 2011 3:36 am
Posts: 2041
Location: Milton, FL 32570
Technique will have a lot to do with it. If I were spraying and that happened I would add some air pressure and reduce liquid volume. We don't use retarder at all. We use a catalyzed water white sealer and catalyzed gloss clear Lenmar by Benjamin Moore. Today we averaged about 85% humidity, We have a hood vent which can be simulated with a window a box fan and a filter. Which pulls the humidity out allowing faster drying, We keep the front door open and if we start to get blush we shut the front dooor and just use the hood vent. When it starts blushing like that we kill the vent and spray with no ventilation, not much we can do about that if I'd like to have somewhere to still work.

Get some scrap wood and play with with till you feel comfortable. I had to learn by doing no one explained anything. Some days were good and some really sucked.

jason


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Thu 01, 2018 1:55 am 
Member
User avatar

Joined: Nov Sun 16, 2014 9:43 am
Posts: 243
Location: Christchurch, New Zealand
Thanks Brett - I guessed that was what was happening - although the detail of what happens is nice to know. I don't have a controlled environment to spray in, although my new property (an old farm) has an old small cinderblock killing shed (about 8' square) which I'm planning to convert to a spray booth... so I'll look at some way of maintaining a stable temp and humidity in there... maybe a cheap old second-hand aircon system.

Here it is in the background along with my custom bird-perch / distant station extractor :)
Attachment:
20180224_103249.jpg
20180224_103249.jpg [ 150.98 KiB | Viewed 810 times ]

_________________
There are no personal problems that cant be overcome with the liberal application of high explosives


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Thu 01, 2018 2:04 am 
Member
User avatar

Joined: Nov Sun 16, 2014 9:43 am
Posts: 243
Location: Christchurch, New Zealand
reeves03 wrote:
Technique will have a lot to do with it. If I were spraying and that happened I would add some air pressure and reduce liquid volume. We don't use retarder at all. We use a catalyzed water white sealer and catalyzed gloss clear Lenmar by Benjamin Moore. Today we averaged about 85% humidity, We have a hood vent which can be simulated with a window a box fan and a filter. Which pulls the humidity out allowing faster drying, We keep the front door open and if we start to get blush we shut the front dooor and just use the hood vent. When it starts blushing like that we kill the vent and spray with no ventilation, not much we can do about that if I'd like to have somewhere to still work.

Get some scrap wood and play with with till you feel comfortable. I had to learn by doing no one explained anything. Some days were good and some really sucked.

jason


Cheers Jason - yep - I figure the more I do the better I'll get. I have a lot of radios to get through - certainly more than I can probably do in one lifetime... so eventually I should be fair to average :lol:

And thanks for the venting info... I do need to have some kind of extraction system but I have a friend who does that commercially so I'll hit him up for some old gear I can use...

Cheers

Steve

_________________
There are no personal problems that cant be overcome with the liberal application of high explosives


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Thu 01, 2018 5:35 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4189
Location: Sunnyvale CA
reeves03 wrote:
Technique will have a lot to do with it. If I were spraying and that happened I would add some air pressure and reduce liquid volume. We don't use retarder at all. We use a catalyzed water white sealer and catalyzed gloss clear Lenmar by Benjamin Moore. Today we averaged about 85% humidity, We have a hood vent which can be simulated with a window a box fan and a filter. Which pulls the humidity out allowing faster drying, We keep the front door open and if we start to get blush we shut the front dooor and just use the hood vent. When it starts blushing like that we kill the vent and spray with no ventilation, not much we can do about that if I'd like to have somewhere to still work.

Get some scrap wood and play with with till you feel comfortable. I had to learn by doing no one explained anything. Some days were good and some really sucked.

jason


Catalyzed and other modern finishes are MUCH more forgiving for this sort of thing than lacquer. Basically, they are intended for semi-trained guys at car paint ships (or similar production furniture factories) to spray 10 cars a day and get them back the owners that afternoon. People stopped using lacquer for anything but restoration long before VOC rules started making them illegal or hard to get, it is pretty easy to repair and correct flaws but it comparatively flaky when it comes to gun setup or the temperature/humidity. Lacquer is also extremely fragile, catalyzed car paint in particular being designs to withstand gasoline dribbled on to it once a week for years.

Brett


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Fri 02, 2018 2:54 am 
Member
User avatar

Joined: Jun Sat 18, 2011 3:36 am
Posts: 2041
Location: Milton, FL 32570
So is lacquer superior to catalyzed lacquer? I tell you I can't see a difference between old clear jobs and what I do at work. So in my mind new guys around here would benefit from using it I would think. i mean I don't suspect many around here would learn to use a slide rule unless they learned on it just for the sake of how things were done.

jason


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Fri 02, 2018 7:11 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4189
Location: Sunnyvale CA
To preface this, I misread the post I was responding to - the difference between catalyzed lacquer and regular lacquer in regard to tolerance for temperature and humidity variations is not a lot different. I was actually referring to other catalyzed products that are universally used for car and other modern finishing applications, typically urethanes, epoxies, and acrylic. Those do tend to be more-or-less bulletproof when it comes to atmospheric conditions, or at least much more tolerant than lacquer.

reeves03 wrote:
So is lacquer superior to catalyzed lacquer? I tell you I can't see a difference between old clear jobs and what I do at work. So in my mind new guys around here would benefit from using it I would think. i mean I don't suspect many around here would learn to use a slide rule unless they learned on it just for the sake of how things were done.

jason


Lacquer (catalyzed or otherwise), is essentially obsolete except for applications like ours, i.e. restoration of old objects in the original way. Plain old nitrocellulose lacquer is what they used originally, so that's probably the choice here, too.

Brett


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Fri 02, 2018 1:14 pm 
Member
User avatar

Joined: Jun Sat 18, 2011 3:36 am
Posts: 2041
Location: Milton, FL 32570
So is there any benefit to using nitro versus a newer finish besides originality?

Thanks Jason
Not picking bones just trying to understand the whys.


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Fri 02, 2018 5:48 pm 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 4189
Location: Sunnyvale CA
reeves03 wrote:
So is there any benefit to using nitro versus a newer finish besides originality?


Not really. In any objective sense, modern materials are generally far superior in durability, ease of application, speed, etc. It can be an asthetic choice, lacquer has a certain look about it, and so does water-based polyurethane, oil-based polyurethane is different, etc. People here hate "poly" because it's hard to strip - which just means it's really durable. There are plenty of examples here that show how the various finishes look.

Brett


Top
 Profile  
 
 Post subject: Re: Spraying technique help required... splotchy finish?
PostPosted: Mar Sun 04, 2018 3:00 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1779
Location: Monroe, NC 28112 USA
I might have missed it in reading these posts.... Are you using GLOSS NC lacquer? Your lacquer in its can should be water clear all the way to the very bottom of the can. I first bought a gallon of Semi-Gloss clear and found it USELESS for duplicating radio cabinet finishes of the mid 20s to WW-II. After letting the can sit for over a year, I went back and carefully decanted the lacquer leaving the silica filler behind... At least I was eventually able to use most of the can..

Robert


Top
 Profile  
 
Post New Topic Post Reply  [ 16 posts ]  Moderator: Peter

All times are UTC [ DST ]


Who is online

Users browsing this forum: rugged and 3 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB