Preventing Sweat Marks on Work

Thoughts on how to affordably air condition a wood shop in a hot climate, and advice on preventing sweat from discoloring wood or finishes. May 23, 2011

So, when it's 90 to 100 degrees in your shop while you're working on a mahogany stain-grade project how do you prevent sweat from staining the job? Head bands work slightly, changing shirts (three-fives times per day) also helps, fans help except when you're milling or routing, then we become sawdust covered golems. I don't have the budget for AC, not in a 2500 sf shop with a 16' ceiling, it would be $400.00 per week - as much as my rent!

Also, are there any other ways to remove the sweat stains besides sanding? You can sand a job only just so much, and those grey blotches will show up badly if not removed. Any and all suggestions are welcome. We also tried starting at 5:00 am, doesn't really make a difference. There's a new term I learned, it's "residual heat". I really, really don't like it!

Forum Responses
(Architectural Woodworking Forum)
From contributor G:
How hot is it at night? Would going to night shifts help?

From contributor O:
When the first summer hit in my 1,000 s/f shop, I was final sanding a birds-eye table top to 400 grit. Three drips later, I was sourcing a window AC, and the next day it was 40% RH and 68 degrees in the shop by the end of the day. I was also much more productive. Absolutely the best place to be when the temp was over 80 degrees.

$400.00 per month is $2.50 an hour - pennies per man. I will bet lunch at a moderately priced establishment of your choice that your productivity will increase by that much per hour, and the quality of your work will be better if you don't have to deal with blemishes. Plus the shop and you will smell better (getting personal), and you will be a happier woodworker. Throw in safety, and you have no choice - it is a business expense.

From contributor G:

I have a 1300 sq ft shop and put a 12000btu AC under the garage door and blocked the rest off. My ceilings are 22'. Did it cool the shop - no, not really. Did it lower the humidity - yes, yes it did.

It staved off the high temps. We were going through a 95ļ plus with high humidity and dew point. Put the AC on in the morning and let it run all day. If I had no AC it would have topped 110 in the shop and the humidity would have killed me. With the AC I was there all week. Was it nice and comfy? Not really. Was I able to work - yep. If I didn't have it just about nothing would have been accomplished.

From the original questioner:
Actually I said $400.00 per week, per month would be fine, not per week.

From contributor G:
Nothing says you have to make it comfortable in the shop. Just nice enough to work without sweating up a storm. A little bit of AC and a bunch of well placed fans should take care of it.

From contributor D:
I have 4000sqft and built the place with a/c two years ago and never used it. We use the ceiling fans that I fought my electrician over and they do a great job. The thing that is worse than sweat is my 117lb yellow lab drooling and licking the finished sanded mahogany or cherry millwork or cabinetry.

From the original questioner:
Did your dog ever pee on any of the jobs? Iíve been through that too! Tomorrow it's supposed to 100 plus. I have to make 300 Lft of T and G and install it in the doors as well - not happy.

From contributor S:
I had a shop in Texas where 100 plus degree days are the norm. The humidity was not too terrible but the heat would sap my energy. I would work from 8 AM to 12 then take refuge in a restaurant until 4 and go back to the shop to work until 8 or 11 PM. This was not good for family life, but my productivity during those hours was horrible.

Now I live in the Philippines and have a 6,500 sqft shop. The heat here is not as bad (usually around 90) but the humidity is off the charts. I sweat so much! My shorts and shirt are completely soaked after three hours. We mostly process melamine and laminated panels so sweating on the materials is not a big deal. But keeping all the steel and iron in the shop from rusting is a full time job.

Giant fans and big windows mounted high in the walls help a lot. I havenít really had an issue with sweat stains in the finish. If I did I would separate the final sanding and finishing area and air condition it.

From contributor U:
I understand the problem of cooling a large volume of shop space. The few times I am happiest with my main shop area being on the small side is when we pay the rent and need to turn on the AC. Would it be practical for you to wall off a section and create a cool room that is for certain dedicated task? We air conditioned a 1/10th area of one of our larger shops, mainly for finish work. We constructed a wood stud/drywall room and stuck a window type air unit into one end. It made a big difference and we would actually let different workers rotate in and out to give them a break. Funny thing is, some preferred to stay in the hotter areas, rather than get cooled down and go back out. Just knowing the option was there made it less of an issue. On an earlier job I worked, my father made a room of studs and 6 mil bisqueen, stapled on double thick. We could never get it down to a real low temp, but again, it made a big difference.

From the original questioner:
Thank you to all whom have responded. I appreciate it. I think that more than anything I was venting. I wish that I had my old shop, there was room there to close off an area. Here though it wouldn't be practical. I work on jobs that are somewhat large, 8/6 x 9/0 is the norm and that would require too large an area to set up, and the landlord doesn't want any more holes in his wall than he's already got. One day I'll have my own bldg. till then I'll deal with the heat. Saturday it was 99 outside, by not opening my doors and keeping the AC on in the office with a fan blowing into the shop from the office kept it down to 85. I don't want to do that too often, I will when I need to.

From contributor O:
I did a little guesswork in a calculator as for your actual operating costs, and I have a hard time getting much over $12.00 per day, or $60.00 per week. I don't know your location or size of windows or energy costs, but guessed the worst case on all. On the upside, you can claim to be doing your part for a greener Earth, greener products and the sweat is organic.

From the original questioner:
What I really am looking for is a way to remove the sweat marks. I can deal with the heat, hell, I've been a carpenter and a fisherman for over 30 years so I will work no matter how hot, cold, rainy, and yes, in a few of blizzards too. I'm the guy who has been on an 8/12 roof tarping it off in a freezing rain storm. I even got off on that one once I got back on the ground. But I digress. If someone knows how to remove the sweat marks and blotches from Sapele without sanding it, please let me know. I believe that there's a chemical means, just don't wish to experiment on a nearly completed job.

From contributor G:
The problem is the difference in the surfaces. You either need to sand it to get rid of the sweat or sweat over the entire piece. Maybe wipe a sponge over the whole surface and them sand it very lightly only to remove grain raise.

From contributor E:
Contributor G's suggestion should work, although I would mist with a spray bottle as sponging can leave wipe marks. Something you can try instead - either a card scraper or a little cabinet scraper to remove the sweated-on spot.

From contributor F:
I don't have an answer, but one thing I might try if I was in your shoes would be a solvent wipe before finishing. I'd take some scrap, apply appropriate sweat stains and see if using a bit of DNA, or lacquer thinner, or similar will neutralize the sweat and eliminate the grey spots.

From contributor R:
I think you have two issues with the sweat stains. You have swelled the fibers with the sweat and the cells are more open than the surrounding area. The other issue is your body chemistry. I'm a very high acid person. I deal with purple stained hands when I work with certain woods, mainly oaks and walnut. I sure don't see a way to avoid the sanding.

From contributor F:
If the amount of tannin reaction is light, I have had success using lemon juice to ďwipeĒ the grey/purple reaction off of the woods most affected by it (oak, walnut, cherry, mahogany). Wipe is in quotes because you have to rub pretty hard to get it off, and you still need to sand lightly afterwards. While I have had no adverse results with finishing afterwards, you might experiment with your finish schedule to be sure. You may need some kind of neutralizer if you are use catalyzed finishes.

From the original questioner:
Tried the DNA and it worked a bit. Iím going to try the lemon juice next.