Humidity issues in our new shop

[Alex Jacobson]

We just moved into a fairly large shop and built a 13x23 enclosed spray booth for finishing our picture frames and installed a 13000cfm fan per code.

The issue is when the humidity is low, our waterborne white finishes are cracking if we put anything more than a very thin, almost dry coat on. We never had an issue with this in our old shop that would get down to 10% humidity in the winter but we there we had a dinky fan that hardly moved any air.

Our guess is that because there is so much air moving, it is drying the frames too quickly. Any ideas to counteract that? We have been putting wet towels and shirts in the intake filters to try to suck that into the air with mixed results. Any other suggestions?

We're using ML Campbell Agualente which dries very quickly as it is (which we love). We've tried target EM 6600 and love the finish but the dry/cure time was like 5 days, and we need a few hours. Any other products we should try?

[Steve Jenkins]

I’d suggest calling ML Campbell tech support and ask them. There may be a retarder you can use to slow the drying a little.

[Jim Becker]

Weird that you were having the dry time issue with the EM6600...dries fast for me, although not as quick as the clears.

That said, I agree with Steve that you may need a retarder given you have what sounds like a heavy fan system designed more for tradition spray situations where fumes need to be evacuated. Water borne finishes don't need that...it's primarily just a need to get suspended solids out of the air. The greater air movement you have is evaporating the water so fast that the finish suspended in the water isn't getting time to settle, resulting in poor results. Spray a couple of frames with the fans off to test this theory.

Perhaps you can also investigate if there's a way to regulate the air flow via slowing the fans for water borne finishes while still allowing full speed ahead for anything volatile. Your local code may not account for the differences that low VOC finishes bring to the table.

[Alex Jacobson]

Thanks Jim,

To respond to your suggestions:

I went back and checked and it was EM6500 not 6600, and the color was a dark black, not sure that changes your thinking. The stated dry time on the can is like 5 days which is way too long. We've had a bunch of issues where we've wrapped frames in foam after over a day of drying and it still made imprints. That's too slow for our production speed. I do love how it lays out though. Wish there was a way to speed it up.

We have tried Aquastar, the MLC retarder with very mixed results.

Unfortunately the only way we can think if to slow the intake of air is by cutting a hole in the intake ductwork in back of the booth and add a sliding opening to intake shop air. It's a 3hp 3ph motor and I don't want to play around with adding a dimmer to the van. The code was based on the fact that we have 25 ft ceilings and 10 ft above the roofline which necessitated 30" ducting and the big fan. We will definitely try doing tests with leaving the fan off on super dry days.

Thanks for these suggestions.

[John TenEyck]

How about installing a VFD on the fan? That would give you variable speed; low when spraying WB, full bore with solvent.

John

[Kevin Jenness]

You can easily add a variable frequency drive to the blower. I'm not sure what changing the intake is going to do for you as the fan will still be pulling the same amount of air through the booth. I'm guessing you have a closed, perhaps positive pressure system in the booth. Pulling shop air directly may well cause unwanted dust problems.

[Jim Becker]

I went back and checked and it was EM6500 not 6600, and the color was a dark black, not sure that changes your thinking. The stated dry time on the can is like 5 days which is way too long.

EM6000, EM6500, etc., are all the same product. Don't confuse dry time with cure time, either. Most products will take days to weeks to fully cure. And give Jeff Weiss at Target a call and discuss your concerns. He may have a solution, just as other manufacturers have solutions for their products, to both help it lay down nicely as well as cure enough to handle in a reasonable time period.

I agree with Kevin's suggestions and comments, BTW, relative to the ventilation system.

[John TenEyck]

I don't think the OP is confusing the dry time vs. cure time. But what he's after is the stack time, and that's not given on TC's data sheet. You don't need full cure before stacking or packing, but there is a minimum time required for the finish to cure enough not to block or have ghosting imparted by the packing separators.

An accelerator would reduce the cure and thus the packing time. The OP might need a dual solution in order to get what he needs. Less air flow in his booth to slow down drying and an accelerator in the finish to speed up the cure. I don't see an accelerator in TC's product line, unfortunately, but perhaps they can recommend one if that is the correct approach.

John

[Kevin Jenness]

It may be that you are on the right track in trying to humidify the air. It would appear that your blower is sized to give 100ft/min velocity through the filter wall which is an accepted standard, although you may well not need that high a flow given the products you are spraying. M L Campbell should be able to advise you on the issue, and there are plenty of paint booth manufacturers out there who would just love to sell you a humidification system.

[Steve Jenkins]

One of the reasons I like Valspar conversion varnish is it can be blanket wrapped in 24 hours. Of course it’s not water based

[Wayne Lomman]

You need to address the humidity problem. It is too low. When it is as low as you are experiencing, hose down the floor before you start and make sure it doesn't dry out too soon.

It is not widely understood that most precat products require moisture to cure correctly. Your extremely low humidity is stripping what little moisture you have right out of the coating. The effect you are getting is similar to trying to pour concrete is the same conditions - it cracks. Fix the humidity and your problem goes away. Ventilation is not the problem. Slowing that down will cause other problems. Cheers

[John TenEyck]

Yet again I've learned something from you Wayne. Very happy you share your knowledge here.

John

[Alex Jacobson]

Ok, I will look into this. Thanks. Yes, we have a closed booth, not pressure positive though. My idea was to open the hole in the ductwork in the back of the booth, so that it sucks in general shop air, reducing the flow of air through the booth.

[Alex Jacobson]

Don't confuse dry time with cure time, either.

Our critical period is how long until we can wrap it in foam and ship. MLC is 2-4 hours, TC is 2+ days. Not sure whether that is cure vs dry but either way, MLC is way faster. I will give Jeff a call again, and do more research to see if I can expedite the curing process with TC

[Alex Jacobson]

I don't think the OP is confusing the dry time vs. cure time. But what he's after is the stack time, and that's not given on TC's data sheet. You don't need full cure before stacking or packing, but there is a minimum time required for the finish to cure enough not to block or have ghosting imparted by the packing separators.

An accelerator would reduce the cure and thus the packing time. The OP might need a dual solution in order to get what he needs. Less air flow in his booth to slow down drying and an accelerator in the finish to speed up the cure. I don't see an accelerator in TC's product line, unfortunately, but perhaps they can recommend one if that is the correct approach.

John

EXACTLY. For me, it's packing rather than stacking but yes, that's the critical time period.