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If you already have plaster walls and ceilings, adding new plaster costs $2 to $10 per square foot. For an average-sized room, that would come out to $1,200 to $10,000. However, the cost to replace plaster with drywall is higher—running between $720 and $1,250 for a 10-by-8-foot wall or ceiling (not including drywall finishing).

Although they are used for similar tasks, spackle and joint compound are not the same. Joint compound, also known as drywall mud, consists of limestone and gypsum and is primarily used for large-scale projects like taping and finishing seams on new drywall. Spackle is composed of gypsum and binding agents, making it a thicker compound best suited for small wall repairs like filling nail holes or cracks, as it dries quickly and is easy to sand. For small repairs, either product can be suitable. However, you can use joint compound for small jobs in place of spackle, but you cannot use spackle for large-scale taping and mudding projects.

All plaster walls will crack over time due to normal house settling and expansion and contraction from temperature and moisture changes. Small, thin hairline cracks are generally not serious and are mostly a cosmetic issue. However, larger or more significant cracks can indicate structural problems.

Here's how to tell the difference:

• Cosmetic Cracks: Cracks that are 0.5 cm (0.2 inches) or thinner are typically cosmetic.

• Structural Cracks: Cracks wider than 0.5 cm, excessive or deep cracks, multiple cracks in the same area, or cracks that span around corners can signify a structural or foundation issue. Cracks along the joints where walls meet the ceiling also warrant attention.

For cracks wider than 0.5 cm, structural repair is needed. If a crack is 2.5 cm (1 inch) or wider, or if you notice any signs of a structural problem, it is best to contact a plaster repair professional to assess the damage.

You can paint over drywall mud about 24 hours after application, but the exact timing depends on factors like humidity, temperature, and the thickness of the mud. For the best results, ensure the mud is completely dry to the touch and has changed from a darker gray to a lighter, chalky white. Don’t forget to sand and prime the drywall surface before you paint to create a smooth, even finish.