Removing stain from multimeter case - Page 1
Forum section: electronics / repair

author: GregDunn
author_rank: Frequent Contributor
timestamp: September 24, 2018, 06:09:50 am
content: I'm cleaning up my newly acquired Fluke 8800A and wondering what this stuff is. It looks like someone had a large sticker of some kind that left adhesive behind when it was removed, and then they used something which only made the residue worse.The stuff resembles a hard, dried powder; in fact, it can be scraped off, but requires a lot of force so that would probably damage the case texturing. Obviously, I tried the usual suspects: Goo Gone appears to want to remove it, but after it's cleaned off and dry again, it's obvious that although darkened, the residue remains. IPA is no good; it actually makes the stuff whiter and causes it to stand out. That should tell me something, but my chemistry knowledge is decades in the past. Windex does nothing, and neither does vinegar. Overall, nothing seems to have touched it. Letting it soak in Goo Gone for a bit and then wiping it off at least reduces the visibility of it, but doesn't take it off.I can't figure out what it is, and why I can't seem to get it to dissolve. Has something actually caused the plastic to start decomposing?

author: GreyWoolfe
author_rank: Unknown
timestamp: September 24, 2018, 12:30:31 pm
content: No only do I use goo-gone and IPA, I have goof off, Mr Clean magic erasers and Simple Green. Maybe the last 2 might work?

author: David Hess
author_rank: Super Contributor
timestamp: September 24, 2018, 12:38:46 pm
content: Naphtha (lighter fluid) is safe on plastics and worth trying. The white residue might be old dried up label adhesive.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 24, 2018, 01:07:44 pm
content: What I think you’re describing is the adhesive used on some old labels. Most of the adhesives you find turn very sticky and can be removed with some sort of goo remover but some older adhesives seem to crystalize and now adhere strongly to the instrument but not to the label.What I use on regular goo is a paper towel with a small amount of white gas or Coleman camp fuel as it is commonly known. It doesn’t seem to hurt any surfaces and works better for me than “Goo Gone” and other removers. All these methods do require several applications to get the residue that turns into a substance that resembles rubber cement totally removed. I never have more than an ounce in a bottle available for safety reasons and most of these other chemicals have to be used carefully as well.I still use the same goo removal method with the crystalized crud but use a flat wooden or plastic stick as a mechanical scraper to try not to mar the paint surface. Wood or hard plastic are softer than the paint but removing this crystalized adhesive requires more work than the gooey stuff plus I think the crystalized stuff is generally older than the gooey stuff meaning the label has been on longer. I try to remove the crystalized stuff down to the paint level then go over the paint area a couple of times with the usual goo removal method to try to remove as much as possible, especially if the surface is textured. Even if you can remove everything down to the paint there will be discoloration where these older labels were because of paint fading so you will always be able to see the outline of where the label was.My gripe is when someone who is selling a piece of equipment puts a label right across the display area and you really have to be careful to remove it without leaving any marks on the display. There are some labels that are put in the worst location on the front panel and some previous owner has tried using a razor blade to remove the label and scraped paint away down to metal and that is very hard to repair. Bottom line is you can never make it look like new.

author: GregDunn
author_rank: Frequent Contributor
timestamp: September 24, 2018, 04:11:23 pm
content: Simple Green, unfortunately, had no effect; I left a puddle of it on the area for several minutes and scrubbed vigorously with a paper towel but it didn't even seem to attack the stuff.FYI, at the moment, what's left behind looks more like what you'd get if you let a saline solution dry out. Fortunately, it's on molded plastic rather than paint, so I don't have to worry about removing any coatings.There was some sticky residue on other parts of the case and display; Goo Gone worked a treat on those.Next stop: Home Despot for some naphtha!

author: In Vacuo Veritas
author_rank: Frequent Contributor
timestamp: September 24, 2018, 04:46:02 pm
content: Have you tried vegetable oil?https://www.dotit.com/blog/the-restaurant-safe-way-to-remove-sticky-labels-sticker-residue.htmlNo trip to Home Depot required, unless you really don't cook at home...

author: Shock
author_rank: Super Contributor
timestamp: September 24, 2018, 05:18:24 pm
content: Photo will help a little.

author: jancumps
author_rank: Unknown
timestamp: September 24, 2018, 06:29:37 pm
content: Quote from: Shock on September 24, 2018, 05:18:24 pm... and sometimes a hairdryer helps too. It can make some glues peelable.

author: Shock
author_rank: Super Contributor
timestamp: September 24, 2018, 06:57:24 pm
content: Quote from: jancumps on September 24, 2018, 06:29:37 pmI think this is where the top layer of the plastic has dried out and crumbled off with the sticker. But a photo should show what kind of damage, otherwise it's a bit of guesswork. The irony is sometimes heat can repair that exact problem.Similar to what has happened to this piece but the sticker rather than sun drying out the surface oils. That is my guess anyway.

author: GregDunn
author_rank: Frequent Contributor
timestamp: September 24, 2018, 07:46:18 pm
content: Well, I feel like a numpty now. I swear I thought I'd posted the pic with the first message.

author: ArthurDent
author_rank: Super Contributor
timestamp: September 24, 2018, 09:39:58 pm
content: Yup, a photo really helps.What I would try is your favorite goo remover with a brass bristle brush. Just don't go from one direction only and don't expect it to look new. It will leave most of the textured surface but remove the adhesive film. At least it is on the back.

author: tooki
author_rank: Super Contributor
timestamp: October 04, 2018, 12:37:10 pm
content: Honestly, try In Vacuo’s suggestion of vegetable oil. You can soak a piece of paper towel in oil to keep it from going all over the place. Leave this overnight. Then the next day, use Goo Gone.

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 08, 2018, 06:54:45 am
content: Sorry for the delay in replying. I wanted to try everything before reporting back again. Interestingly, of all the procedures I used, only one did the trick. I tried various cleaning methods as recommended above, and only Goo Gone made even a temporary difference - but the stain came back as it dried. Before I started the last trial, the case looked just as bad as it did when I received it.So I poured a thin layer of generic vegetable oil on the area, and used a cotton swab to make sure every area had some oil on it. Fortunately, the layer was thin enough that with the case level, it didn't run off or spread beyond the area I wanted. I let it sit for almost an entire day and then started wiping it off, rubbing fairly hard with a paper towel. A very small amount of dark stain came off on the towel, but the case stayed its proper color as you can see! I did not use any cleaner afterward, because wiping the oil off seemed to do an adequate job and the plastic did not feel moist to the touch. In fact, it had the shiny and smooth/satiny feel of the rest of the case.After the treatment, I've left it sitting for three days before taking the picture. There is no sign of recurrence. My opinion is that the stain was actually an area where the plasticizer was leached out of the case material, and the oil restored enough of it that the plastic resumed its original appearance. After doing some research online, it seems that vegetable oils are used for plasticizers in some substances to reduce the use of toxic substances, so there is some plausibility here. I may try another treatment as the original coat of oil gets absorbed into the plastic, because as it soaks up the oil the surface may dry out again. We'll see.

author: GreyWoolfe
author_rank: Unknown
timestamp: October 08, 2018, 11:50:57 am
content: Isn't it amazing what you can use vegetable oil for? I use it to lubricate my shredder. Great job and it looks good.

author: tooki
author_rank: Super Contributor
timestamp: October 08, 2018, 12:42:00 pm
content: Quote from: GregDunn on October 08, 2018, 06:54:45 amI'm glad to hear the oil worked.Hard plastics like that don't have much in the way of plasticizers. I think it's far more likely that the oil successfully hydrated (oleated? lipified?) the old adhesive that had dried out and attached very firmly, allowing you to remove it. I suspect that if you used dish soap or IPA to fully degrease the plastic now, that it would remain as it is.

author: GregDunn
author_rank: Frequent Contributor
timestamp: October 08, 2018, 02:54:53 pm
content: Could be - I'm not a chemist.But I think I'm going to leave it for a while and see what (if anything) happens, rather than attempt to clean it further; no one who was unaware of the prior condition would suspect it looked such a mess before, at this point. I'm just delighted to be able to put it back together and use it to help fix my next project...

author: tanveerriaz
author_rank: Contributor
timestamp: October 09, 2018, 01:36:42 pm
content: try with kerosene oil.