On May 7, 10:35 am, dpb wrote:
On May 7, 9:10 am, dean wrote:

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?

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...

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.