The photo posted shows a well spalted wood. It will have some punky wood along with harder wood form the fungus giving the spalting. On wood of this type, either stabilize the blank or use CA Skew, CA Skew layers until you get to the shape wanted. It will be subject to tare out. On open pore wood (Red Oak, etc.) I usually sand with GOOD 600 paper and medium CA when I have to fill the pores. The fine dust along with CA fills the holes leveling the surface. A bit more time consuming, I ply layers of CA then take off some with the skew as a scraper. When the blank gets an overall dull finish, I know all the low spots are level so I can then apply the final finish. Again, this advice is worth exactly what you just paid for it,zip, nada, nothin.
Charles