Crack repair is a common surface preparation task. Both drywall and plaster surfaces are prone to cracking as homes age and settle. You will likely have to repair one or more cracks in almost every room you are preparing for paint, decorative paint, faux finish or stencils.
Note: Plaster surfaces should be inspected by a licensed professional plastering contractor before any surface preparation work begins. For best results, damage that extends beyond the white-coat layer into the brown-coat layer (or beyond the brown-coat layer into the lath boards, lath rock or wire screen) should be repaired by a professional plastering contractor.
Crack repair basics
Cracks can often be found in the header area above doors and windows. Header cracks are common, as drywall or plaster covering the ends of headers is often exposed to greater amounts of movement than other parts in the wall framing structure. Cracks in the header area of doorways and windows are often the widest and deepest that you will have to repair. They are also the cracks that are most likely to re-appear, and need later repair. Cracks are also common in ceilings, corners and below windows.
Removing loose material and scoring an inverted “V”
It is important to remove all loose material over the crack, within the crack and around the repair area. This is important because loose material may prevent the durable adhesion of repair materials. Removal of loose material is accomplished in two steps. The first step consists of removing any loose material over and around the crack using a putty knife or scraper. Both the flat part and corner of the blade may be needed to pry and remove loose material. On drywall surfaces, such material may include drywall joint tape, dried joint compound and bits of cracked or peeling paint. (Figure 6.24, on Page 166; and Figure 6.25, on Page 167) On plaster surfaces, such material may include drywall joint tape, dried joint compound and bits of plaster or paint that has cracked or peeled. The second step involves the removal of loose material from within, and again around the crack. This is done by using the corner of the blade of a putty knife or scraper to score an inverted “V” into the crack.
Make the inverted “V”-shape in the surface around the crack by running the corner of the putty knife or scraper blade along each side and down the middle of the crack. Then use the tip of your putty knife or scraper blade to scrape flat over the top of the crack. These motions will loosen any unstable material from within and around the crack. Do not use excessive force in attempting to score an inverted “V.” If material is loose over, around and within the crack, it can be removed by using light, even pressure. Excessive force can lead to personal injury and damage to surfaces. The removal of loose material will create the inverted “V” shape. In some instances, the surface around the crack will be mostly solid and only a slight inverted “V” will result after scoring strokes. This is still good. Once any loose material has been removed, there is no need to continue applying force to remove stable material from around the crack. An inverted “V” shape can often be scored in a drywall surface with one or two stokes each to the left, right and middle of the crack. Plaster cracks will often require several strokes in each area to complete the scoring of an inverted “V.” The inverted “V” will usually be more pronounced in plaster surface cracks than drywall surface cracks. After scoring is complete, remove any dust and debris with a duster, and then wipe the surface with a wiping cloth.
Note: Consult a licensed professional plasterer should scoring strokes cause cracking in, or lead to the removal of, any piece or pieces of plaster white coat other than small granules.
Eye protection, either safety glasses or safety goggles, should always be worn whenever preparing surfaces for paint. Respiratory system protection should be worn whenever you are creating dust or working in a dusty environment. Respiratory system protection should also be worn whenever you are applying solvent-based materials. Eye and respiratory system protection products can be purchased wherever workplace safety equipment is sold
Crack repair technique
Begin by using a putty knife to remove loose material in and around the crack. Score an inverted “V.” Sand the surface around the crack with the medium-grit side of a sanding sponge or 80-grit sandpaper. Remove sanding dust and debris with a duster, and then wipe the surface with a wiping cloth.
Use scissors to cut enough self-adhesive mesh tape to cover the length of the crack plus two inches on each end, when possible. The extra length of tape should be applied in the direction of the crack. This preventative measure helps to keep the crack covered should it continue to spread. Center the mesh tape over the crack, pressing to smooth the tape and bond the adhesive side to the repair surface. Use fingertips to press mesh tape into corners (Using a putty knife or taping knife can split the tape). Cut the mesh tape into smaller pieces and center it over the crack should the crack changes directions. Some overlapping of mesh tape is acceptable. Use a utility knife to cut any portion of the mesh tape that curls or does not lie flat. This cut is similar to a relief cut when installing wallpaper.
Apply joint compound over and just beyond the mesh tape using a 6” taping knife. Remove excess compound. The mesh should be filled but still visible after the first coat. Allow drying. Apply a second and third coat of joint compound. Allow drying between coats. If the tape is still visible after the third coat has dried, then apply a fourth coat. Allow drying.
Use a fine-grit sanding sponge to sand the completed repair. Remove sanding dust with a wiping cloth or towel. Prime and paint.
More detailed coverage of the topic of crack repair can be found in the book:
The Homeowner's Guide to Surface Preparation for Interior House Painting, on pages 140-148
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