caulking the windows

Post up a picture. That is usually part of the glazing bead and designed, to some extent, to allow moisture that bypasses that area to drain out.

You would normally use a clear silicone there.

It's a little hard to tell , but I think your first pic indicates that you're talking about the setting material . Either foam tape or adhesive that the glass seats on . Unless you are getting noticeable air leakage , it really isn't hurting anything. AND , if you try to aggressively dig it out , you can break the glass in a hurry !

You probably should frequently clean the entire window & sash with a bleach solution to kill the mold .

thanks. so I should not caulk it? I hoped to fill it up so that water did not sit in it and cause mold.

It would probably be better to leave as is . Unless you can get the mold & moisture OUT , you would probably be sealing it IN .

However , if applying a small bead of silicone could , say , keep you out of divorce court , caulking would seem prudent !

:biggrin2:

thanks very much