Learn Portuguese (Portugal): Nós esperamos até que a tinta esteja seca.

The phrase até que (until) introduces a time limit that hasn't been reached yet. Because the paint drying is an anticipated future event rather than a current reality, Portuguese requires the present subjunctive (esteja).

Why use the verb estar (esteja) instead of ser (seja) for "is dry"?

The verb estar is used for physical conditions or states that can change. Since the paint goes from being wet to being dry, its dryness is a temporary physical state, which requires estar.

How do we know if esperamos means "we wait" or "we hope" here?

The verb esperar can mean "to wait", "to hope", or "to expect". You have to rely on context. Because this sentence uses até que (until) to set a time limit for a physical process, it logically translates to "we wait".

Can I express this exact same idea without using the subjunctive?

Yes! You can drop the que and just use até followed by the infinitive (the basic, unconjugated verb form). You could say Nós esperamos até a tinta estar seca. This alternative means the exact same thing and is very common in everyday spoken Portuguese.