About 30 years ago I bought a gaming mat. It's 3' x 4', made of heavy rubber with a felt backing and a 1" hex grid printed on the front. A few years ago it was stored in a garage near a leaky water heater. when I unpacked it, it was heavily stained and presumably ruined.
I'm about to run my first game in years and really wanted to use it but it was so bad I didn't even want to touch it let alone lean on it all night. Because of the material though I was hesitant to attempt to clean it. Finally, I came to the conclusion that I was never going to use it as is so I either needed to try something or just throw it away.
I should mention that I did look into replacing it. I remembered seeing one at a local store so I drove over to take a look. Theirs was double sided with hexes on the front and squares on the back. Unfortunately, it was only 2' x 3', was made of a very thin vinyl, the surface didn't look like it had any finish to protect the printing, and they wanted $20 for it. I concluded that it would be a poor replacement for mine even if the price had been more reasonable.
So I bit the bullet and grabbed some cleaner. I started with an all-purpose industrial cleaner. I sprayed the entire thing heavily, left it to soak a bit, and then scrubbed it thoroughly. Ten minutes of that and not a bit of difference. Dejected, I went to look for something stronger. Convinced now that it was a lost cause, I decided to give bleach a try. I was pretty sure that it would eat right through it but I couldn't think of anything else that would stand a chance.
I grabbed a large tub, folded the mat down to about one foot square, and set it in. I poured in about half a gallon of bleach and turned the mat over a few times to get it well coated. After a couple of minutes I started scrubbing and to my amazement it seemed to be working. Another ten minutes of this and it appeared to be looking pretty good. I pulled it out, hosed it off and set it out to dry.
It was spotless! Better than that, it was completely undamaged. I am still in amazement. From garbage to brand new in half an hour. I can't imagine what it would cost to find a replacement of equal quality so I am extremely happy to have recovered it. I don't know what we would have cobbled together to use otherwise.
My one suggesting if you decide to try this on something yourself. Don't follow my example and use your bare hands. Put on some gloves! Eight hours later and my fingers are all still red and raw, cracked and sensitive. A couple of spots look like they are on the verge of bleeding. I'm so glad I didn't work much longer. I'll be more careful next time but all in all I think it was a small price to pay to get my mat back.