How To Seal or Reseal Tile Grout
The grout between tiles is naturally porous. Grout sealant is applied to the grout lines to make them waterproof. As the waterproofing wears away, water soaks into the grout which provides a breeding ground for mold & mildew. To keep grout looking clean and to keep it strong, it should be regularly resealed.
An easy way to check if grout needs to be resealed is to spill a little water on it. If the water beads up, the sealant is doing its job. If the grout absorbs the water or darkens, then it is time to reseal the grout.
For tile grout that doesn't see a lot of use, like a kitchen back splash, once a year or longer should be adequate. For high use locations, like a tile shower, several applications a year might be needed.
Before sealing grout, it is important to thoroughly clean the grout. Applying a sealer over dirty grout just seals in the dirt and grime. One effective technique for cleaning grout is to use a damp toothbrush dipped into dry OxyClean powder. It works best if the powder does not get too wet.
Select a grout sealant from your home improvement center or hardware store. We prefer the use of penetrating sealers for the best results. However, penetrating sealer should be wiped off any tile surface promptly or it will leave a difficult to remove haze. It is also unsuitable for unsealed tile because it will absorb the sealer, and change the tiles' appearance.
Applying tile grout sealant is easy, although tedious - especially on vertical surfaces. It should be applied only to thoroughly dry grout, otherwise you will seal in moisture. The sealer should be applied to the tile grout lines but it is best to avoid the tile surface. Use a disposable foam brush with a "V" tip to apply the sealer. The foam brush will hold a fair amount of sealer and the "V" tip makes it easy to get it only onto the grout. Because the grout is abrasive, have extra brushes ready. When bits of foam start coming off, switch to a new brush. Remember to wipe away excess sealer from the tile surface right away to avoid hazing.
Follow the manufacturer's instructions for the use and application of the sealer. Generally, the sealer will dry to the touch within a 15 minutes to 2 hours but must be kept dry for about 24 hours.