I have tried nail varnish remover and don't know what else to try. Any suggestions will be gratefully received.
There's also a manual solution to this problem: Sticky tape.
It may seem counter-intuitive, but putting sticky tape on the mat and pulling it back off has a chance to pull the adhesive residue off as well. The glue on tape bonds with the adhesive residue on the mat. When you pull the tape off, the adhesive has only 2 choices: either stick on the mat or stick on the tape. If the glue on the tape is strong enough (like duct tape or wire insulation tape) it will pull the adhesive away from the mat.
To do this, cut a strip of tape roughly as long as your hand is wide. Hold both ends of the tape together, sticky side out. Now dab the tape onto the mat and pull it away again repeatedly. If this methods works, you'll notice the adhesive residue on the tape. Once the surface of the tape is covered with residue so much that it doesn't stick well anymore, discard the strip of tape and cut a fresh one.
I would avoid chemical solvents intended to dissolve the glue (like nail polish remover or mineral spirits), as those may also degrade the plastic in the cutting mat.
If you still have the adhesive can, check the label for cleanup instructions for the dried adhesive. If you don't still have the can but remember the product name, find the manufacturer's web site and look there for the cleanup instructions. Even if they don't have instructions, the web site is likely to have a link to the MSDS, which will list the components and provide a clue to what is likely to work if you add that information to the question.
If they say the dried adhesive cleans up with water, soapy water, or alcohol, try the manufacturer's recommendation. If they suggest a solvent like mineral spirits, hold off and first see if the suggestions below work (manufacturers generally don't offer specialized cleaning advice for every possible surface, or suggest things that take a long time to work).
If there isn't a benign cleaner suggested, there are a number of common household ingredients that may work. Some should be completely safe for the mat (as long as you don't damage the mat trying to scrub it), some may leave the mat discolored, and some may damage the mat depending on what the mat is made of. The fast, simple solution is just to buy a new mat. But if you're willing to put in some time, try these suggestions in the order of their risk until you find one that works (or you have to buy a new mat because either you damage this one trying to clean it, or determine that nothing will clean it that doesn't destroy the mat in the process).
I'm not sure what type of plastic your mat is made of. If you're lucky, it will be polypropylene or polyethylene, because adhesives generally don't bond well with those. Some adhesives bond with vinyl, but you still might have some luck. Rather than dissolve the adhesive, the approach here will be just to get it off the mat without damaging the mat, either by getting it to release from the surface or degrading it so it falls apart. A word of caution -- cutting mats can warp, so do any of the following suggestions with room temperature materials.
Self-healing mats have a lot of surface area for glue to stick to, so be prepared for a potentially slow cleaning process. They can also be easily damaged, so clean them non-aggressively. The way they work is that the surface is composed of tiny segments bonded together below the surface. A sharp cutting implement pushes segments out of the way and goes between them. When you remove the cutter, the segments move back into position. Those gaps between the segments will provide a lot of surface for the adhesive to stick to, even if it doesn't bond well.
Lay the mat flat in a plastic tray and submerge it in the liquid selected from the list below (use only one at a time, in the order suggested). If the tray has a lid, use it to minimize evaporation. You can minimize wastage by using the "paper towel" method instead of submersion. Wet a piece of paper towel with the selected liquid and lay it on the adhesive. Cover with plastic wrap to slow evaporation. Check periodically to see if the paper towel is drying out and add more liquid as needed.
With either method, let the adhesive soak for an hour. Then see if the adhesive has been affected (did it become soft, crumbly, or release from the surface). If it has, use a soft brush or sponge to try to gently remove as much as you can without applying much pressure. Then repeat as necessary on any residual. If the adhesive wasn't affected, try the next material.
- Alcohol (70% or higher rubbing alcohol).
- Soapy water (water with a little liquid dish detergent)
Cleaners that may discolor the mat
- Oil + baking soda: Make a paste by mixing equal amounts of baking soda and oil. Coconut oil is best but any cooking oil will do. You can also use mayonnaise instead of oil. Spread the paste on the adhesive and let it sit for an hour. Then gently scrub the paste with a sponge and see if any of the adhesive comes off. If it does, remove as much as you can and repeat the process for any residual. If the adhesive is unaffected or when you are done cleaning with the oil and baking soda, use the soapy water in a tray setup to remove all of the oil and baking soda.
Cleaners that might damage some plastics
The following contain hydrocarbon solvents that can damage some kinds of plastic. If you have exhausted the suggestions above and the adhesive isn't affected, the choice comes down to leaving the mat as-is or risking damaging it. If you're lucky, the plastic in the mat won't be affected (although there's a chance it could be discolored). So save these for when you would otherwise toss the mat and have nothing to lose.
Reduce your risk by testing these on an edge. If they attack the plastic, only the edge will be damaged. Note that the gaps between the segments will create capillary action that will draw these liquids into the mat. Put some on a cotton swab and wipe it on the edge, but don't create a puddle that can wick in. Check it after one minute to see if the plastic feels soft or sticky. Rub a dry cotton swab on the area to see if it leaves any marks on the plastic. If it is OK after one minute, repeat the application and test again after 10 minutes. If there's no sign of the plastic being attacked, try it on the adhesive. If the first one of these materials you try attacks the plastic, it means that the mat is made of a type of plastic that will probably be attacked by any of these materials.
When you're done, or if the material attacks the plastic, wash the treated area with alcohol, then wash it in soapy water.
I would try these in this order:
- Mineral spirits
- Goo Gone or WD40
The hydrocarbon solvents will evaporate pretty quickly. Apply the liquid to the adhesive spots with a cotton swab (with WD40, just spray the spot, or spray a little into a container and then use a cotton swab). Keep reapplying the liquid to the adhesive as the solvents evaporate (Goo Gone and WD40 will still look oily after the solvent evaporates). Keep liquid on the edges of the adhesive so it can wick under. Most adhesives will soften and or release after about five minutes of this.
Aside from your current situation with adhesive, it's generally important to clean the surface regularly to remove dust and fibers that get pushed between the segments as that distorts the surface and keeps the segments from returning to their normal position. There are videos online for how to do that (just search terms like "cleaning self-healing cutting mat" or "caring for self-healing mat"). Those videos deal with normal dust and fibers, not adhesive.