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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.

It doesn’t matter which way you lay drywall, and you can choose to install it horizontally or vertically depending on the size of the wall and how tall the ceiling is. It’s easier to lay drywall sheets vertically if you have a taller ceiling, but laying sheets horizontally makes it easier to apply joint compound.

Yes, you can apply new plaster over an existing plaster surface, such as a wall or ceiling, provided the old plaster is in good condition. Before you begin, check the stability of the existing plaster. The surface must be clean, free of loose material, and have no peeling paint. It is also recommended to roughen the surface slightly to promote adhesion. For older plaster, applying a base coat like a PVA emulsion or a specific bonding agent or primer is crucial. This step makes the existing plaster less porous and ensures the new and old layers adhere properly for a smooth, long-lasting finish.

This depends on how much plaster is applied and in how many layers, but a decent estimate is around 150 square feet. If you are applying only two coats on a small wall, there is a chance you may only need one or two gallons for the entire project. If you are plastering a large living room wall with high ceilings, using one of the more involved techniques–like Scagliola–that requires several coats, expect the project materials costs to add up quickly.