Charlie:
Rudy down in League City says he is installing slate tile outdoors over an existing concrete slab, and he wants to know, what’s the best, cheap thing to use as grout? What should he use? Should he seal it? What?
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Tom:
When you use natural stone and you put it down, before you grout, you usually put a sealer on there. Not because of the sealer in the long run, but that the grout won’t get into the stone. You can put the grout in, you can wash it all off, you can make it look really good, and in about three months, the sealer’s gone. You don’t have to reseal it. Slate is slate, it’s meant to be outside.
Charlie:
Why are you sealing it? To keep the grout out?
Tom:
Keep the grout … The grout will stain it. Anytime you use a natural stone, you have to seal it before you grout it. People go, “Oh I’m sealing it.” Well, you have to or the grout, because it’s a cement product will make it all cloudy and get into the porous stone. Now would I use the stone outside? I would not but a lot of people do. Slate tends to crumble and start to flake, and sealers and all that stuff’s not going to keep it from doing that. That’s just the nature of slate.