Yes, you can install drywall over plaster, but there are important factors to consider. While it can create a smooth, flat surface, it is often not the best approach. Installing drywall over plaster will increase the wall's thickness, which can cause issues with existing window and door frames that may no longer fit. You might also need to adjust power outlets to keep them accessible. A better, though more expensive, option is to remove the old plaster and lath entirely before installing new drywall. Drywalling directly over plaster seals in the old material, and if any problems arise later, you will need to remove both layers down to the structural beams for repairs. Given the potential complications, this job is best handled by professionals.

Plastering lasts for around 15 to 20 years without needing repairs or maintenance in most cases, and with proper upkeep, plastering can last a lifetime—sometimes more than 100 years. Plaster repair costs between $1 and $3 per square foot, and you may need these services once every 15 to 20 years or so unless you have a harsh climate where humidity changes are a constant issue. You can also opt to skim-coat plaster for between $0.90 and $1.30 per square foot, which may serve you better in the long run.

While a normal moisture level for drywall is between 5% and 12%, replacement is recommended if you get consistent readings above 17%. At this level, the drywall is likely too compromised by extensive moisture damage to be considered safe. You can replace either the entire sheet or just the affected section. If you are unsure after a visual inspection, it is best to have a contractor or water restoration provider use a professional moisture meter to get an accurate reading.

You can put drywall mud over paint to even out the surface or entirely resurface it. Sand the surface with 280-grit sandpaper, vacuum the debris and dust with a shop vac, and clean it with a slightly damp cloth. Allow the surface to dry. Apply drywall primer, especially if you’re skim-coating an entire wall. Apply the right type of drywall mud over the surface and smooth it with a trowel. Allow the layer to cure fully, then sand it before applying another layer or painting it.