I have used watchuseek as a resource off and on dating back many years, and thought I'd give back a little by posting a recent experience cleaning my watch. I apologize in advance for not taking any photos! Of course the photos are one of my favorite parts of the forum.
The watch: Casio G-Shock G-9300-1 "Mudman" received from wife December 25, 2013, and worn 24/7/365 since that date
For those of you who don't have a rotation of watches, or gravitate to one watch, and are of the type that wears their watch for everything—sleep, showers, workouts, yard work, etc.—you are likely familiar with the smell that can accompany this behavior after a long period of time. It starts as a light, manageable, somewhat "biological" smell, and if left unchecked can develop into a truly funky, heady fungus smell. You can help stop or slow this down, depending on the watch, by taking care to dry it off after it gets wet, and periodically washing it. With my previous everyday watch, a Seiko SKX175, I only needed to simply soak the band in some sort of cleaner or solvent, and wipe off the soap scum/build up as best i could, and I would be set for a few months. But the G-Shocks, particularly the Mudmans, as I have discovered, have a lot of nooks and crannies that are simply inaccessible for cleaning without taking the watch apart.
ENTER THE FUNK
About a month ago, I started to notice it. It starts with a whiff, a passing smell that you think nothing of.
Then you notice it a few more times, and sniff around a little bit. You put your nose to your wrist and inhale. You realize you've let things go for too long. You take it to the sink, soak it in hot water and soap, maybe go at the nooks and crannies with a Q-Tip, and dry it off. It's worked before, why wouldn't it work now?
It smells less noticeable, but it seems to keep coming back, stronger and stronger yet.
You scour google and youtube, looking for solutions. You see a video of some well intentioned guy showing you how to wash your G-Shock under the faucet with soap. You look down at your watch, and together you laugh.
You find nice tutorials on watchuseek involving baking soda that help remove tobacco smells. These seem good, but they don't seem to be applicable to your problem.
Your watch is alive. It's a living, breathing, ecosystem. And you need to kill it.
You try a few things. You take an old toothbrush and scrub it with alcohol. Your G-Shock is not impressed. You try wiping it down with mineral spirits. Your G-Shock laughs in your face.
Deep within the watch's depths, there is something brooding.
You decide you need to get serious. You get a size #00 phillips screwdriver and take it apart.
With the bezel removed, you see what the problem is. all of the unexposed surfaces inside the watch are covered with "brown." You are accustomed to the whitish sweat/soap scum mixture that tends to build up on watch bands, and which wipes off easily. But "brown" is different. It visually resembles filthy, hardened ear wax, but smells so much worse. And then there is the semi-liquid build-up under the mud-proof button covers. I'm not going to describe what that particular area's smell reminds me of, because this is a family forum.
You take an old soft-bristled toothbrush, some alcohol, and start scrubbing. It seems to help a little, but it merely puts a dent in the smell. The soft bristles do little to abrade the brown build-up.
THE TOOLS AND SOLUTION
#00 Phillips Screwdriver
Firm-bristled toothbrush (soft will not cut it)
"Free and Clear" type liquid laundry detergent
Borax (sold as a laundry booster at grocery stores. Try it on your laundry when you're done, it actually works.)
Toothpick - wood or plastic
Paper towels/rag/Q-Tips/whatever else you have lying around
Silicone grease for the gasket
The detergent and borax are mild enough that they are not going to damage the watch in any way. I use them on all my laundry, as well as to clean bike helmets (I add bleach there, but do NOT use bleach on a G-Shock as it can ruin the surface of some plastics and you don't want to take that chance). Alcohol is used as a solvent because it leaves behind no odor, and helps the watch dry quickly, which is particularly important when cleaning around the seal area inside the case
Take apart the whole watch. In order to remove the caseback's plastic cover, you will need to remove the metal caseback; do so and screw the caseback back in place without the plastic cover over it. If you're not mechanically inclined, take pictures and write down where everything goes. It will be hours before you put it back together, and you may forget. Put all parts, including screws, into a plastic cup with a dash of laundry detergent, spoonful of borax, and hot water. The detergent is designed to break up biological agents, and the borax is anti-fungal. Let it soak for a few hours, to really soften up the build-up.
Then, take everything out one by one as you clean each piece, and rinse, taking care not to loose the screws. At this point, I would start by removing the bulky part of the build up by using a toothpick (or other hard, non-scratching implement). Then, repeatedly soak the firm toothbrush in rubbing alcohol and go to town scrubbing every surface until it is clean. There's no secret here, you just have to take your time and find the best ways to clean certain areas. There's just so many varied surfaces that you may find that some things work well on certain areas but not others. I found that Q-Tips really helped with the inside of the button covers, certain surfaces responded well to paper towels, things like that.
You'll need to remove the metal caseback again, and clean around the outside of the rubber seal (and the rubber gasket itself). Here I just used paper towels, because I didn't want to have alcohol spill into the case. You may also want to just lightly clean the underside of the crystal, while you're here. Lightly grease the gasket—just a thin film of it—and put everything back together. Be careful to not overtighten the screws. The rubber will do it's job keeping the water out. The screws need only be tight, not muscled-down. I've stripped a few bolts on cars in my day, and it's the worst feeling when it happens.
You put it on your wrist and take a deep but cautious smell. There's still something there, but it's faint and not something an innocent bystander would notice. You imagine that the baking soda trick you read about earlier could get rid of that lingering odor ingrained in the resin, or you could even do a second detergent/borax soak. But you feel secure that things are well in hand, and that the smell should not return for some time, and certainly not as the force of nature that you just slaughtered. This is your everyday watch; to get it completely clean would be an academic exercise, because its pristine state would soon be infused with water, sweat, and grit. It's a G-Shock.