Clear fog from overspray in booth causing dots in last coat of clear??

20mercury said:
Hi Chris and thanks for the response. Used 885 reducer and 80 85F when shooting clear so I would think ok. Compressor out goes thru a vertical serpentine (homemade) cooler with a column of desiccant at the end then 50ft 3/8 hose to diaphragm reg at gun. Only regulator is at gun. I have a couple of drain valves with collection pockets at the bottom of the serpentine bends. The first drain sometimes drains out a few tablespoons depending on humidity 2nd valve usually nothing. Dry day on clear shot.

Dumb question but what does solvent pop look like?

U right dots or flecks uniform on horizontal surfaces only sides look great me thinks
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This is solvent pop. This happened because I did not allow enuff time between base and clear, on a spot repair I did. This doesn't wet sand out. It will get Shiney but it will still be there, under the clear
 

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I don't know how fast or how long it took you to get around the car Mercury, but I'll be willing to bet you took longer than you should have. One reason for the dry spray. You got to move when doing an overall no time to be casual.
Adding some retarder will help with open time some. If you re-shoot it, plan it out how you are going to spray, Know the direction you want to go. Oh and verify that you don't have water or water vapor coming through the lines.
 
Thanks for the responses! Had to stop, mix and reload a couple of times, so maybe will mix up total needed next time, hmmm... and speed up.

Update: Just did a look see with a couple of bright bright flashlights 2 days after clear shoot. Euro was hard as a rock; good. I know the base was smooth because I learned from that uh oh last time. And 99% of these defects are bumps not craters and look like dried clear. Some of them you can wipe off with your hand, not stuck and some are stuck pretty good. There are some black dots and some obviously trash but not many, maybe 1% overall. And I know I laid the 4 coats of clear pretty heavy particularly on the hood as I wanted to have plenty to buff with. So I am thinking this overspray clear that was fogging up the booth was drying in the air and floating back down on my newly sprayed surface. Thanks for the solvent pop photos, but it does not look like it is coming up from below to me anyway. If anyone wants to come by and check it out, happy to provide beverages of your choice. I think I am going to speed up the air flow next time per RoharonRooster and maybe rig up exhaust fans per Lizer too. For this one, I am going to try to cut with 1200 first, maybe 1000 and see what happens. If not good, will check out the whole air system (likely need to do that anyway) and spray some more Euro and try to improve my gun technique.

Thanks again for all of the much needed help.

Will keep you posted.
 
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I’ve been doing this for probably 15 years - most of what I have learned came from this site - I remember my first paint job - Barry talked my through it over the phone ON A SUNDAY !! But I’m always looking for improvement . Something I’m ALWAYS trying to improve on is laying down clear. What has really helped is YouTube- not for knowledge but to watch techniques- mainly just speed and gun distance. What you hear from someone doesn’t always “click” until you see it . Way less runs, lay it down flatter and less wave - of course gun adjustment is something you’ll just have to figure out with whatever style you decide to spray
 
Yes as Chris stated 5000 RP in a 1.3 puts out more than enough material. I really don’t think the fog is causing it to look that bad. I’ve literally sprayed in peoples small home garages before with just a box fan. Actually no ventilation at all before. Blow a coat on and go outside and wait. Never had them look like that. Maybe lost a little gloss the next day but nothing like that. Maybe try again on some test panels and play around with different settings/variables etc and see what happens. Hey, if you don’t get a small run here or there your not spraying wet enough! :)
 
Lizer said:
Positive pressure just does not work in homemade booths. You really need negative pressure to evacuate the overspray as fast as possible. I’m a front yard hack and I use a negative pressure set up.
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I think this may be a good part of the answer. I was planning to set my homemade booth up as positive pressure. Can't suck in dust at any joints. Fan and motor in fresh air so no worries about spark proof or explosion proof construction. Perfect solution. Then I wondered if this is the best way to do it, why aren't commercially built crossflow booths set up with positive pressure.

After some digging, I found a couple booth engineering papers online, along with the answer to "why not". Seems smoke testing as is done in wind tunnel testing has shown a blow thru booth is likely to have areas with near zero air velocity even when the total air thru the booth would show a 100 ft/min average velocity. These swirling motions occur mainly across the top surfaces of the vehicle where changes of shape are most abrupt. OTOH, the same booth running as a draw thru and handling the same total air quantity doesn't have perfect air flow across the surfaces, but it's so much better that it doesn't present a problem with redepositing overspray on the surfaces.

Some theoretical stuff was presented to explain the difference in flow characteristics but it was beyond the scope of my 50 year old engineering degree. The smoke pictures were good enough for me.
 
metlmunchr said:
I think this may be a good part of the answer. I was planning to set my homemade booth up as positive pressure. Can't suck in dust at any joints. Fan and motor in fresh air so no worries about spark proof or explosion proof construction. Perfect solution. Then I wondered if this is the best way to do it, why aren't commercially built crossflow booths set up with positive pressure.

After some digging, I found a couple booth engineering papers online, along with the answer to "why not". Seems smoke testing as is done in wind tunnel testing has shown a blow thru booth is likely to have areas with near zero air velocity even when the total air thru the booth would show a 100 ft/min average velocity. These swirling motions occur mainly across the top surfaces of the vehicle where changes of shape are most abrupt. OTOH, the same booth running as a draw thru and handling the same total air quantity doesn't have perfect air flow across the surfaces, but it's so much better that it doesn't present a problem with redepositing overspray on the surfaces.

Some theoretical stuff was presented to explain the difference in flow characteristics but it was beyond the scope of my 50 year old engineering degree. The smoke pictures were good enough for me.
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Now this is interesting to me with a 48 yr old engr degree, ha! ha! thanks for the explanation and please post or PM the links. And makes sense, likely have dead spots of air flow or swirling areas which does nothing good for overspray getting out. Might go out with a couple of cigars (and quite a few beers) and investigate. And yes I thought positive pressure would be good for all the reasons you mention. Do not have any explosion proof fans (yet) and too old to blow myself up (LOL's!)
 
Lizer said:
Positive pressure just does not work in homemade booths. You really need negative pressure to evacuate the overspray as fast as possible. I’m a front yard hack and I use a negative pressure set up.

From the pictures your clear is going on really dry. I can see dry spots just in the thumbnails. This is prob from poor lighting and visibility once the room starts to fog up, and maybe overspray settling on the wet horizontal surfaces. It will probably help to change your set up and then just work on better gun control and overlap—-REALLY easy to say and hard to do.
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Gee, I have been using a homemade positive pressure booth for years now. Works great.
Most who have problems, that I have dealt with, never bothered to calculate their booth size, air flow requirements, filter surface area and fans needed to produce the correct amount of CFM airflow.
 
Your 5 ton blower is capable of approximately 2,000 cfm depending on what your static pressure is in your booth on Hi speed. Lo would be approximately 1600 give or take a hundred.
Your static is going to be determined by your exhausting cfm.
Basically, you need to have enough exhausting to keep positive inside but still remove the fog in a timely manner. Otherwise your blowing up a balloon and reach the blowers output and accomplish nothing.
Reason interior doors are undercut for return air. If not,your room 'blows up' and no air is exchanged becoming uncomfortable when closed.
Also,any blower of this type requires static restriction in order to function. You just plug it in and let it free blow,it will die shortly from over amping the motor and tripping the internal overload in the motor winding.
The typical furnace blower is not very likely to spark or catch fire unless miswired,loose power wiring,or obviously not sounding 'right being wore out. You have a belt driven old style with a internal centrifugal switch,possibly. Your call.
 
Yeah buddy. My fist painting was done with the door up and a,5 ton belt drive antique Coleman horizontal gas furnace blower with plywood blanking of each side to keep the bugs and trash out. Kept getting crap in the Clear and wth???. Then I went outside and realized the big arse gap above the door that went unnoticed because the top of the door hid it from view inside. Genius man,Genius.
I always say,
"My superior intellect is only surpassed by my complete stupidity "
 
Hell, unless I’m spraying base or clear, everything else happens right in the driveway.
 
Dean Jenkins said:
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I crack my roll up door and prop it up with two 24" HF fans turned on high. Open the screened window across the shop, and make sure my hat is on tight, we're moving some air!
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Yup. I wet down the floor too. It's not a production environment, but my shade tree paint job went to its first event yesterday and won Best of Show. Thank you Barry and SPI!
 

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rdransman said:
Yup. I wet down the floor too. It's not a production environment, but my shade tree paint job went to its first event yesterday and won Best of Show. Thank you Barry and SPI!
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Congratulations! Beautiful truck.
 
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Got time today on the hood to cut with 1000/1200/1500/2000 and then polish with Rupes 15 (speed 4-1/2, 2passes horizontal and 2 passes vertical on 2sqft patch at a time, blue/yellow/white 3 dots of polish on foam pad) and got results above which I am happy with. Few craters that did not sand out and some orange peel in spots I need to go back and fix.
As said above per Lizer, RosharonRooster and Metimunchr, a positive pressure home made booth is problematic to say the least with what kind of air flow you get. I noticed when wet spraying that the spray was getting sucked back towards the blower instead of out the back, wat???. So chasing down the various bunny trails, I finally concluded most all my bumps, dots, most of which were up, not craters, that the overspray was being uplifted, partially drying and then floating back down on the wet clear. Also likely did not have enough air flow as also mentioned above. So, for the next paint job will go negative pressure booth which I think is less likely to cause problems and hopefully avoiding all this work or most of it anyway of sanding off these dried clear specks.

Thanks again for all the help and feedback from everyone!! More opportunities are coming to paint Corvettes and hopefully continue to improve, but first lots of bodywork!
 
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