So I was looking at the RAW for Sculpt Spells and Sheild Master:

Sculpt Spells

• When you cast an evocation spell that affects other creatures that you can see, you can choose a number of them equal to 1 + the spell’s level. The chosen creatures automatically succeed on their saving throws against the spell, and they take no damage if they would normally take half damage on a successful save.

Shield Master

• If you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you can use your reaction to take no damage if you succeed on the saving throw, interposing your shield between yourself and the source of the effect.

Since Sculpt Spell states that you automatically save if you have shield master can you use your reaction to take no damage on the spell?

Shield master is not needed in this particular case, sculpt spell already reduces the half damage on the success to 0 (for the chosen creatures).

Not a better answer than Icon, but: I would also say that if you auto succeed, you are not "subjected to an effect that allows you to make a dexterity save."

Sculpt Spell is mainly an ability to eliminate friendly fire.  Shield Master is great against enemy fire.  Basically, if your party Evocation Wizard wants to send a fireball into a group of melee, they can exempt their friends from the damage.  

But if an enemy spellcaster wanted to do the same, Shield Master would work if you succeeded on the save, you could then use the reaction to drop the damage to 0.  That said, you still have to make the save, and the ability is not available for saves other than DEX.

I was just wondering. You know in case you fail the Dex save but have shield master.

I could see it going either way, but it is always good to get others' opinion.

Thanks

Quote from DxJxC >>

Not a better answer than Icon, but: I would also say that if you auto succeed, you are not "subjected to an effect that allows you to make a dexterity save."

 That would be wrong. The fact that you automatically pass your save, does not mean that you did not make one, or that the effect was not one that allowed you to make one.

Quote from Chicken_Champ >>

Quote from DxJxC >>

Not a better answer than Icon, but: I would also say that if you auto succeed, you are not "subjected to an effect that allows you to make a dexterity save."

 That would be wrong. The fact that you automatically pass your save, does not mean that you did not make one, or that the effect was not one that allowed you to make one.

 Yeah, maybe my brain didn't finish booting yet.

Still doesn't matter for the reasons already pointed out.