Plaster Crack Repair

The Do-It-Yourself Plaster Crack Repair Guide

Have you ever wondered how to repair cracks in plaster? If the walls in your house are plaster, you should be prepared to do some type of repair work before every new paint job. Repairing cracks in plaster can be a simple repair or can take longer for larger cracks, but it is a chore that can be done by most do-it-yourselfers in just a short time.

Cracks in plaster walls and ceilings are bound to happen, especially in older homes. One of the biggest reasons that plaster may crack is caused by changes in humidity. As levels of humidity rise and fall, it can cause the wood frame behind the plaster to contract and expand. These changes, common with the changing seasons, create stress on the plaster, resulting in cracks. Another common cause of plaster cracks are weaknesses in the structure that creates shifting. These weaknesses can be caused by anything from poor workmanship to the settling of the ground underneath the structure after a period of several years.

How to Repair the Crack

Step 1: Examine the Cracks

If possible, determine the cause of the crack and do any necessary home repairs prior to repairing the crack. It may be necessary to repair any leaks prior to repairs.

Step 2: Clean the Cracks

Before repairs can begin, it is essential that the cracks be cleaned out. Remove damaged plaster from large cracks until the binding course is visible. Use a scraping tool to clean out the damaged plaster.

Step 3: Repair Large Cracks

If the lath and plaster have come apart from the wall, secure it by using plaster washers and drywall screws. This effectively secures the plaster to the wood lath. Secure them diagonally on either side of the loose area of plaster, approximately one and a half to two inches from the crack.

Step 4: The Base Coat

Proper plaster repair will require two coats. A base coat that will create a binding layer and a top coat that will provide a surface that is smooth. To mix the base coat, combine water that is room temperature to the base coat plaster mix according to the manufacturer’s directions. With an electric drill and paint mixer attachment, mix the plaster. You will mix it until it reaches the consistency of sour cream. Allow the plaster mix to sit until it begins to thicken.

Step 5: Apply the Base Coat

With a water bottle, lightly mist the wood lath with water. Do not over-saturate the wood. This step is essential to ensure that the wood does not draw water from the plaster, potentially causing more cracking. Use a trowel and fill the cracks with the base coat. Once filled, allow it to dry thoroughly. It can take up to 24 hours for the plaster to set and a couple of days to dry completely depending on the amount of humidity. After it has dried completely, sand it smooth.

Step 6: Apply the Finish Coat

The finish coat, finer than the base coat, provides the area with a smooth surface. Spread the finish coat over the base coat, once it has thoroughly dried and has been sanded smooth. Once the finish coat has dried completely, you can safely paint or wallpaper the area.

Tools & Supplies:

• Drywall screws; these will cost an average of approximately $20.00 for a five pound box.
• Plaster washers; these will cost an average of $12 to $15.00 for 100 pieces.
• Plaster; this product costs an average of approximately $45.00 for an 11 pound bucket.
• Bonding primer; this product costs an average of $22.00 for a one quart can.
• Gypsum wall compound; depending on where you purchase it from, this product will cost between $13 and $24.00 for a four and a half gallon bucket.

Quick Prevention Tips

Although nearly impossible to prevent cracks in plaster, there are some measures you can take to minimize the number and size of the cracks you see in the future. Maintain a constant level of humidity in your home using a humidifier and de-humidifier as needed. Use of elastomeric paint will also cover minor cracks and make them less visible.