sealing slate tile floors
To seal, or not to seal, that is the question. If you are about to install a slate floor, you have probably heard conflicting opinions about sealing your tiles. The conflicting advice comes from the different experiences contractors and homeowners have had with slate tiles.
Different experiences come from using different types of slate. Sealing slate isn't necessary, especially if you want to keep the natural look and beauty of the slate, but if the stone is porous and/or you aren't experienced at grouting, seal the stone first. Furthermore, sealing slate is important if you want a shiny or matte finish. You can buy chemical sealers at retail stone and home improvement stores.
Slate typically comes from Brazil, Vermont, China and India. The Brazilian and Vermont slates tend to have a low absorption rate, while Indian and Chinese have variable absorption rates. The softer slates need more attention with sealants before and after installation than do the harder slate tiles. Slate is a metamorphic rock, starting as a sedimentary rock and with pressure and temperature over time became slate. Because it has some porosity, you may want to seal it to keep it from staining.
A bit more about the origin of your slate will help you determine how you want to treat it. Brazilian slate is typically dense and has variegated colors while Vermont slate is typically dense, smooth and one consistent color (black, blue, green red). In contrast, Chinese and Indian slates are typically variable in density (soft to hard) and variegated coloring, with a wide range of colors. If you get a soft slate, typically Chinese or Indian, pre-seal with a porous stone sealer.
To help maintain better air quality, you want to use a water-based polyurethane sealer. To help give the stone it's best protection, a penetrating sealer is a good precaution. In addition to being low in VOCs (volatile organic compounds), water-based polyurethane is non-yellowing and non-cracking, giving you years of good looking slate floor tiles.
The preparation needed before installing your slate floor tiles is to clean the subfloor where the slate is to be installed, clean all slate surfaces, and let them dry thoroughly before applying two coats of the penetrating tile sealer. There are surface, or topical, sealers, but the penetrating sealer gives your stone tile better protection, and looks better longer. Apply the sealer in a thin coat, following the grain of the slate and let it dry for at least two hours and reapply (your specific product will tell you how long between coats to let it dry).
After you have laid the tiles, let the mortar dry and cure before grouting the tiles. To increase the bonding strength of your mortar and grout, mix penetrating sealant with grout instead of water. This recipe increases bond and tensile strengths and improves the water resistance of the installation. The increased water resistance is especially important if you are installing your slate tile floor on a concrete slab that can wick ground moisture into the room.
What look do you want your slate floor to have -- natural, wet, or glossy? You can get the wet-look without going glossy by choosing the right finish. There are finishes that will look natural after application, but many people love the wet-look for their slate floors.
After you grout the tiles (preferably with latex grout because it increases flex strength, reduces efflorescence, and has great bond strength), let it dry, ideally for a week, before cleaning the tiles. You want to wash the tiles thoroughly, several times, to remove all remnants of excess grout so that it won't become a permanent part of your slate floor. When the tiles are dry from the washing, you can apply two more coats of penetrating sealant. This step is to add further protection to the slate, but also to the grout and grout-tile interface.
After you have applied your last coat of penetrating slate tile sealant, let cure for at least 24 hours before walking on the floor. The longer you can let it cure before walking on it, the better protection you will have, and the longer the finish will last.
Maintaining your slate floor is easy. Just clean it with mild soap and water, and dry mop or vacuum in between washings. If you are accustomed to waxing floors, you are in for a treat because wax isn't necessary on slate. Wax won't hurt the slate, but will obscure it's natural beauty, turn the tiles a darker shade, and may yellow the grout; all good reasons to not wax your floor.
Slate makes a beautiful flooring. Proper preparation and care of it will keep it looking great for years to come. If you can't decide if you should seal your new slate tiles before installing them, error on the side of caution. Sealing them may not be necessary, but after you have installed them it will be a headache to seal them properly. And you may not be able to protect them soon enough, if they are porous and absorb stains.
To seal or not to seal? Go for it with a penetrating, water-based slate tile sealer and enjoy your natural stone floor for years.
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