I think it s paint.
How to remove weatherstripping from bottom of garage door.
Or maybe from me dragging something into my shop and rubbing hard against it and marking it up or something.
This video explains how to remove and replace the rubber seal at the bottom of your garage door.
If the insert is stuck to the retainer you can use silicone based lubricant to loosen it.
Doorstop is made with built in weatherstripping specifically for garage doors.
If it doesn t come off easily you may need to use a knife or flat head screwdriver to help force it off.
If your stripping seems to be stuck on to the bottom of the door or if you can t see any screws or nails holding it on gently pull it off.
You can cut one side of the weather stripping insert moisten it thoroughly with your water soap mixture and then pull on the other side to remove the whole piece.
Learn how to do garage door weather stripping.
If you don t have silicone based lubricant you can use some dishwashing soap.
If so use a silicone based lubricant or water mixed with a little dishwashing soap to loosen it.
Pull the stripping off if it is attached with adhesive.
The weather stripping insert may be stuck in the retainer.
How to replace bottom weather seal on your garage door.
Wes door didn t have them so it s definitely something that i ve probably done perhaps.