Why a soggy piecrust when I do rhubarb custard pie?

Answer 1

Because the dough pie shell wasn't cooked a bit first.
A) Poke several fork holes into the bottom crust, and
B) Cover with any kind of dry beans you have in the house, this keeps the crust flat against the bottom of pie dish.
C) Bake the shell at 350 degrees F., say maybe 10 minutes. Keep an eye on it, you want the shell to firm itself up, and brown just a bit.
D) Remove and let cool
E) Brush bottom & side with egg whites
F) Add Filling
G) Bake as you normally would
H) Say Good-Bye Soggy Crust.

Answer 2

What friend said, you need to "blind bake" the crust for 15 minutes at 350. You can also put a bit of egg wash on the crust before you bake it seal the surface.