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humidity question

4K views 26 replies 6 participants last post by  69 widetrack 
#1 ·
I recently flaked a roof with sg100 and before I added the clear a notice the center was getting a haze look. I felt it and I was able to feel moist. Now I live in so cal and we don't get a lot of humidity around here. So my question is at what level of humidity should I stay away from spraying. Now I sprayed around 5pm and the day was around 95 I really hot day.
 
#2 ·
95 is extremely hot to be painting. A couple of questions, what temperature of reducer where you using? Also your compressor, with high temps you will get condensation in your tank and your lines. Usually the humidity in the air just adds to the humidity generated when spraying. With the heat and if you where using the compressor it could be a combination. Do you have a drier on your compressor?
 
#6 ·
When you paint you almost need to be a weather forecaster and anticipate what changes you may have as the day wears on. If I was in Southern California I would slow my material down. With a medium reducer and the temperature getting warmer any moisture is going to show up. Did your compressor work hard before any painting?
 
#7 ·
Checking the temperature on the roof is fine but, it's the ambient air temperature and moisture content you have that makes a difference. The higher the temperature the more moisture it holds. Fore example, I live in Canada and we get a pile of snow every Winter. If our humidity content in Summer would be what it is in Winter, most of Canada would be a dessert. I hope this makes sense.
 
#9 ·
There's your problem...5 HP is usually fine, it's your reserve capacity that's killing you. Now I said 5 HP is USUALLY fine. In the compressor world many manufacturers lie and call their motors 5 HP when they truly should be rated at maybe 3 HP. The other thing you need to look at on a compressor is CFM out put. Paint guns use a lot of air and your compressor should put out at least as much or more CFM than the paint gun manufacturer recommends. 10 or 12 CFM isn't enough unless your using an air brush. 25 gallon reserve is excellent for filling a tire, not painting. When you paint you will drain that reserve tank very quickly and your compressor will run constantly...causing heat, causing moisture in your tank, causing moisture in your air lines and ultimately hazing off your paint work.

I just checked my portable compressor for my air brush and it's running 8.3 CFM and I can almost put that compressor in my pocket.

So in short...it appears to be a moisture problem. The moisture is coming from an undersized compressor, coupled with a warm ambient air temperature to really heat up the air your using causing condensation.

The fix, acquire a compressor that will more than handle the CFM requirements of the equipment (if you get a compressor that will handle more CFM and reserve capacity than you need it will last longer, reserve capacity should be minimum 50 - 60 gallon) your using and your problem will be solved.

I understand, simple, if only it didn't cost so much right.

Hope this helps
Ray
 
#10 ·
Another thing you should be concerned about in SoCal is the quick drop in temperature in the evening. It usually drops below the dew point at night, and with those high temps, the dew point will probably be higher also. So spraying outside in the evening is not a good idea.
 
#11 ·
Absolutely correct, especially outside. When the air temperature dropped it condenses all the moisture held in the air from the earlier warm temperature. Think of it this way, an air conditioned car needs a condenser and an evaporator. Without these pieces when you turn on your AC you would get a cloud of fog inside your car. This is because you are quickly changing the temperature and releasing the moisture trapped in the warm air you're trying to cool.

Make sense?

Hope this all helps.

Best of luck
Ray
 
#13 ·
Ok good info guys. I have a 60 gallon compressor but I have no 220 in my garage. Now it I had to paint small parts like I still have two what can I do prevent this. I have a few pieces left that need to be painted. The thing is I work 7 days a week and get off till 500 pm. Will days with less humidity or using a heat gun during coats help.
 
#14 ·
OK, I'm going to try and give you a cheaper fix for your problem. You still have to paint small pieces and you have a 60 gallon compressor but no 220 in your garage. Why not run a line from your 25 gallon compressor to the tank on your 60 gallon compressor. Let your little compressor fill up your 60 gallon tank. Now, I don't know what CFM your small compressor puts out so you may have to run it for a little while, shut it down, let it cool off and repeat until the 60 gallon compressor is full. Let your little guy cool off completely and start to paint. This should help with your mechanical moisture issues.

Days with less humidity will help and would be recommended...heat gun...NO...NO...NO. Your asking for more problems. It's way to easy to surface dry and not cure your paint with a heat gun. Body shops with an air make up unit don't bake their paint in-between coats, and neither should anybody else. If you do this you stand the chance of top drying your product and when you put more product over top the solvents will react with what you just painted and crack and blister and mess up what you just painted. Even after your last coat, leave the heat gun alone. You say you paint after 5 PM, well, paint your pieces, go to bed, let nature and the chemicals do their job and admire your painted parts in the morning.

Thanks
Ray
 
#18 ·
What gauge wire did you use when you wired it? If you used 12-2, then you can easily put in a double-pole 20 amp breaker and put in a 220 receptacle. That's assuming your 60 gallon compressor has less than a 20 amp draw, which mine does. Or you can just run another circuit altogether. There are a few additional details but the point is it's not tremendously difficult, even to do it and still be in code.
 
#23 ·
OK, The compressor that you have is great for running a small air tool, filling tires or blowing parts dry after you clean them. I see that they claim 5 horse power but, like I mentioned earlier some manufacturers embellish this performance data. It is in all probability to assume that other performance aspects of this piece of equipment may also not be accurate. 5 horse power only means it has the power to maintain a certain performance, the crucial criteria is the CFM out put. 8.2 CFM at 40 PSI and 5.6 CFM at 90 PSI is not enough for a paint gun. Most paint guns require twice that amount. This means that your compressor is working beyond it's capability when painting larger projects causing it to create excessive heat and moisture.

Try my earlier suggestion of linking this compressor to your other compressor's larger tank. The smaller compressor will fill both tanks giving you a total of 85 gallons of compressed air. Depending on how many "small parts" you need to paint, you should be OK. If your compressor still is working to hard, shut it off in between coats, let it cool down, start, shut off, start until you reach your maximum PSI in the bigger tank (like 100 PSI as an example). Always remember to drain your holding tanks after each use.

For future large jobs you will need to wire the big compressor to avoid this problem.

Hope this helps.
Thanks
Ray
 
#26 ·
You cannot make 5 hp from 110 volts. If you do the math, even with assuming a 100% efficient motor, it's just about impossible. So there's no ifs, ands, or buts about that one.

I don't see what he gains from having that small compressor fill his big tank as well. That small compressor motor now has to fill four times its capacity. The air will be really hot and he'll have a problem with water vapor in the lines. As soon as his pressure drops in the system, the air compressor will kick right back on again, even though he has 85 gallons of stored air instead of 25. Those small compressors usually max out at 120 psi. It doesn't take very much to drop the pressure in the system, especially if your regulator is set at 90 PSI. I once tried patching my little 20 gallon compressor into a large tank and I think it literally bought me about another 30 seconds of time before the compressor kicked on, only the compressor then ran forever.
 
#24 ·
The last time I remember having a humidity problem was shooting lacquer. And it was because it flashed so fast, it doesn't seem to make sense but at least with it going to a SLOWER thinner eliminated it.

Brian
 
#27 ·
You are right. as I said in my post, this "may" eliminate the problem for "small" pieces and that if he was to paint a large area he would need to hook up his larger compressor properlyy. I also mentioned that the smaller compressor would need to be shut off when filling the 60 gallon tank when it got hot and given a chance to cool off before restarting to continue filling the 60 gallon tank or, like you mentioned he would continue to have a moisture problem. This would give him just a little extra spray time for what he said he needed to paint, his quote, "I only have a few small pieces left to paint". This suggestion was not a permanent fix, only a temporary band-aide.

Hope we are on the same Page...Ray
 
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