Stucco

[Hope]

was curious to know if others in the past have mixed their own stucco or purchased it pre-mixed to finish the oven. I think I would like to mix my own(since I already have portland cement) and was curious if the following is the correct "recipe" that can withstand the heat of the oven:
For a scratch coat, you will need this mixture:


1 part portland cement

1 part hydrated lime

2 1/2 to 4 parts sand


For a brown coat, you will need:

1 part portland cement

1 part hydrated lime

3 1/2 to 5 parts sand


Finish coat ingredients:

1 part portland cement

1 part hydrated lime

1 1/2 to 3 parts sand

I am also confused if I am suppose to mix a scratch coat, brown coat or Finish Coat. Or all three?

I am also curious if a Finish Coat serves the same purpose as Stucco Paint? Or does the Stucco Paint prevent moisture from seeping in?

I apologize if I am repeating questions, but I greatly appreciate any advice. I have never worked with Stucco before.

-Hope