Most colored concrete floors are finished with a sealer after the coloring process in order to protect the floor from everyday wear. However, this sealer is prone to some problems, including developing a hazy or cloudy appearance. This is caused by excessive moisture in the floor or high humidity during application. Water-based sealers are especially prone to this. If your floors have been finished with a water-based sealer, there are a few solutions you can try to clear it up.
Apply more sealer. The solvents in the sealer will temporarily dissolve the previous coating, allowing moisture to escape and eliminating the haze. This technique must be used with care, though, since it might cause more problems later. It's a good technique to try for a small area that is hazy.
Apply xylene or xylol to the floor. You can use a brush or roller, like paint, or spray with a sprayer. This will also dissolve the sealer, letting moisture escape, and is preferable to applying more sealer in most instances. Xylene is derived from mineral spirits and has some similar properties, and needs similar precautions. Protect your eyes and skin from this product and wear a respirator.
Remove the old sealer by applying a chemical stripper, then scraping off the old sealer and putting the mixture into a nonreactive container for disposal. Many solvents can soften or dissolve plastic; check the container for more specific information regarding disposal. Use a stiff bristled room to clean out patterns if you have stamped concrete. Clean the floor with soap and water, let it dry completely, and apply new sealer. This is your best option if the other options don't work or if you have a polyurethane or epoxy coating, since these can't be repaired if they are hazy. You should also determine if your basement has a moisture problem or if the sealer was simply applied during high humidity. If you have a moisture problem, try using a breathable penetrating sealer, which allows moisture to escape more easily.