The cedar railing on my deck has cracks and checks which I want to fill before giving it the semi-annual oiling. Art

I haven't used a sawdust mix for exterior use, but have for interior use - salvaged hardwood flooring with numerous defects. I mixed the dust with the finish that was used on the floor.

What sealing/finishing oil will you be using? Mix the fine sawdust with that oil.

If need be, sift your shop sawdust to obtain the finest dust possible. Sawdust from the/a sander's collection is sufficient. Course sawdust is not recommended, but I suppose you know this.

Sonny