set width on ion-button code example
Example: remove ion button padding
You need to set the no-padding attribute on ion-col instead of ion-row and no-margin for the buttons.
<ion-row>
<ion-col col-6 no-padding>
<button ion-button full no-margin>Button</button>
</ion-col>
<ion-col col-6 no-padding>
<button ion-button full no-margin>Button</button>
</ion-col>
</ion-row>