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).

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.

Both plaster and drywall are durable wall finishes, but they differ significantly in installation, cost, performance, and aesthetics.

Installation & Cost: Drywall installation is faster and more affordable, typically costing $1.50 to $3 per square foot. It uses premade sheets, making it a more accessible DIY project. Plastering is a labor-intensive craft that requires specialized skills, pushing costs to $2 to $10 per square foot. It involves applying a wet paste over a lath framework.

Durability & Performance: Plaster is generally more durable, longer-lasting, and provides superior soundproofing. It is also a better insulator, which can help reduce energy costs. Drywall is easier to remove for future renovations.

Aesthetics: Drywall provides a smooth, uniform surface ready for paint or texture. Plaster offers a high-end, naturally textured look that can hide imperfections and is often preferred for achieving a classic or historic aesthetic.

Which is better? The choice depends on your priorities. Drywall is ideal for those prioritizing a lower upfront cost, faster installation, and DIY potential. Plaster is the better option for a higher-end project where durability, soundproofing, and a unique, premium finish are more important than the initial cost.

There are several warning signs that a ceiling crack is connected to a larger issue. For starters, if the crack is wider than 1/8 inch or longer than 12 inches, you might have a more serious problem. The same applies if you have multiple smaller cracks or cracks going across the ceiling and down the wall. In any of these situations, you should ask a professional to assess the damage.