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You should wait at least 24 hours for drywall mud to dry before sanding or applying another coat. However, the exact drying time depends on several factors, including the thickness of the application, room temperature, humidity, and the type of compound used. Thicker layers, or projects in high humidity, may require 48 hours or more. Lightweight compounds tend to dry faster than heavier, all-purpose ones. You'll know the mud is ready when it feels completely dry and firm to the touch and has changed to a consistent light color. Sanding too early can cause smudging or gouges, so patience is essential for a smooth finish.

In most cases, no, you won’t need a permit to replace drywall. If you’re changing the floorplan of your home by adding or removing walls during the drywall project, then you might need a permit, but replacement or repairs usually doesn’t require a permit. Your drywall professional should be able to confirm whether or not a permit is required for your project. If it is, it’s likely to add between $50 and $150 to your total cost. Keep in mind that you will need permits if you plan to install new electrical wiring or plumbing lines behind your new drywall.

Drywall can be toxic to the environment and to humans in some cases. As drywall breaks down in a landfill and comes in contact with other organic chemicals, it can create hydrogen sulfide gas or leach into the groundwater. Additionally, the CDC recommends methods for controlling the inhalation of drywall dust when handled. While the common ingredients of drywall—gypsum, silica, and mica—are naturally occurring, they can cause irritation in some humans.

There are six levels of drywall finish, from 0 to 5, that refer to the amount of work performed during the finishing process.

Level 0: Drywall is hung with no finishing work.

Level 1: Tape is placed over the seams between drywall sheets.

Level 2: A thin layer of mud is applied over the tape and screw holes. This level is common for utility rooms or walls that will be covered.

Level 3: A full coat of mud covers the screw holes and tape, but the surface is not sanded. This is often used in garages.

Level 4: This is the most common finish for visible interior walls. It involves applying two coats of mud over seams and screw holes, with sanding between each coat, creating a smooth surface ready for flat paint.

Level 5: This is a high-end finish for luxury homes. It includes full taping, mudding, and sanding, plus a final skim coat over the entire surface before painting.