Nails can be left in plaster walls for an extended period of time, but it's generally recommended to remove them if they are no longer needed. The duration for which you can leave nails in plaster walls depends on various factors:
Wall Integrity: Plaster walls can deteriorate over time due to natural aging or environmental factors. If the plaster starts to crack or crumble around the nail, it's advisable to remove it to prevent further damage.
Rust and Staining: If the nail is made of a material that can rust, such as iron or steel, it may eventually cause discoloration or staining on the plaster surface. If you notice any rust formation or staining around the nail, it's best to remove it to avoid further deterioration.
Changing Wall Decor: If you plan to change the wall decor, such as rearranging artwork or installing new fixtures, it's a good idea to remove the existing nails and start fresh. This allows you to reposition the new nails more accurately and maintain the integrity of the wall.
Safety Concerns: Leaving nails exposed on walls can present safety hazards, especially if there are children or pets in the household. Accidental contact with protruding nails can lead to injury, so it's advisable to remove them when they are no longer necessary.
In general, if the nails are not causing any issues, such as wall damage, rusting, or safety concerns, they can be left in place. However, it's always a good practice to periodically inspect the nails and the condition of the surrounding plaster to ensure the long-term stability and aesthetics of your walls.