Mistakes happen, and charging for the fix is standard practice in trades. My crew budgets for redos in every quote because materials and time aren't free. You're not ripping anyone off, you're just covering the actual expense to complete the job properly. Listen to your boss on this one.

For mixes like that, exact ratios avoid problems. Evan_burns' close enough way might work sometimes, but it's risky. Measuring right gives you the same results every time.

Knew a cafe sunk by a sneaky auto-renewal clause.