What turns a deck gray?

[dean]

Is it dirt? Sun bleaching? Something else?

Do deck sealers work by stopping the rain water and dirt from penetrating, or by coating with a UV filter?

[dpb]

Yes, and yes... :)

Much of the gray is oxidation and UV, but all of the effects mentioned plus molds, etc., are at play.

Sealers do a little against all of the above -- how much of what they do, specifically, depends on the product and the situation. What the wood is, the climate, etc., all are variables...

[dean]

Its cedar wood, in new jersey. I've got some penofin exterior stain which I'm going to lay down soon. I heard great things about it on here and other places, although consumerreports doesn't say too much good about it.

[Just Joshin]

UV light.

tom @