For years I thought that chlorine bleach was the only way to get rid of mildew stains. I knew of things that killed mildew, but left the black or gray stain. Straight vinegar with or without tea tree oil or grapefruit seed extract, let sit for hours. Straight hydrogen peroxide, apply and let sit for up to an hour. Then scrub, scrub, scrub to remove the dead mold. And rinse, rinse, rinse to get rid of any lingering spores. I preferred the magic of just pouring bleach on it. Pouf! both mildew and the stain of it were gone.
On the other hand, bleach is harsh on fabrics. Yesterday I tried Borax. I washed a mildewed shower curtain and curtain liner with Borax in the washing machine. The ratio for soaking fabrics is supposed to be 1 cup Borax per quart of water. I didn’t measure, just used a lot of Borax, maybe two cups, and the lowest water setting on the washer. With a vinyl liner, warm water is better. In cold, the liner stays stiff and awkward to handle when you take it out. If you throw in a couple of towels with it, they will help rub it clean.
It came out perfectly clean and bright, and smelled clean in a mild, non-perfumed way. The information I had said no need to rinse, the Borax left in the material will help stave off new mildew.I didn’t rinse, so we’ll see if it takes longer for the mildew to come back.
For upholstery, including outdoor furniture, dissolve ½ cup Borax in two cups of hot water and sponge it onto the mildewed area. Don’t use so much that it soaks the filling, this is only for the surface.