I have been using cleaner and brightener. I notice some black/grey inside the grain. Is it normal? or it is weathered grey? How can I remove it?
Might be mold? Hard to tell from the picture for sure. Watered down bleach will probably get rid of it. We are not fans of bleach for wood but sometimes this is the only way to get it off. 1 part bleach to 4 parts water. Apply and rinse well after 5-10 minutes.
can you not paint over it? i'm not a fan of bleach at all