Stress cracks in drywall are caused by movement in the framing to which the drywall is attached. Some are caused by "settling" of a new house, wood drying out and adjusting to the stress of it's new role in the structure of the new house. There are also stress cracks caused by poor framing and engineering of the house. The first mentioned type of crack can usually be repaired once for all. The second type of stress crack is hard to permanently repair without going behind the wall and dealing with the framing of the house. The second type will likely return in a year or two (or longer), if you don’t address the framing problem causing the crack.
Stress cracks are repaired with drywall tape, either mesh or paper tape. The only exception to this rule would be hair line cracks in a inside corner where the drywall tape has not been disturbed or blistered. Such cracks may be speedily repaired with painter's caulk.
Priming
If the cracked drywall is painted with a glossy paint, it will need to be spot primed where the crack repair is going to take place. Drywall compound will not adhere to glossy paint. Use a quick drying oil based bonding primer like Zinsser’s Coverstain to prepare the area for drywall compound. If the drywall is painted in flat paint, you can repair the crack and apply the drywall compound directly over the paint without priming.
Fiberglass mesh tape.
Cracks are usually repaired with fiberglass mesh tape because of the advantages it offers. Fiberglass tape is self adhesive and is applied directly to the drywall surface. There is no need to embed the tape into drywall compound , as with standard paper tape. This eliminates one step, and prevents tape blistering problems. Mesh tape is also stronger than paper tape in resisting tears which is important for preventing the return of stress cracks. There are really no disadvantages to mesh tape when it comes to flat taping of seams or drywall crack repairs.
Lay the tape down over the crack and press is firmly onto the drywall by wiping it down with a 6” spackle knife. Do all the taping in the room at one time before starting with the mudding.
Speed up the process with quick setting compound
I like to use quick drying compound for the first two layers of compound and finish off with easy sanding standard compound. Quick dry compounds come in dry powder and are mixed with water which activates the compound causing a chemical reaction to occur which causes the compound to set up. The setting up and drying of these compounds can be further accelerated by 1) using a hair dryer or 2) adding a accelerator to the mix. I will use Easy Sand 5 min set compound for quick repair of a hole. As a general purpose compound I find that Easy Sand 45 is about the right set up time when doing repairs in one room prior to painting. An advantage of using the quick setting compound is that you don't have to take it off the truck every night during the winter months as you do with conventional compound to prevent freezing. See Quick Setting Compounds and Taping and Mudding Drywall.
Inside corners
If the tape is not blistered or has not pulled off, you can repair inside corners without tape by using painter’s caulk. Simply apply a thin bead of caulk into the corner and wipe it smooth with your finger. Tip: Some flat paints will crack when applied directly over some caulks. To prevent this from occurring, you can prime the caulk (after it is dry) with an oil based primer prior to painting. Sheen paints, as a rule are not subject to this problem and can be applied directly over the caulk once it has dried.
Taping inside corner cracks
If the tape has pulled off or blistered, you will need to cut the damaged area out, remove the blistered tape, and replace it with new tape. Mesh tape, is a little harder to use with inside corners because the mesh itself can cause bumps in the drywall compound because the edge of the drywall knife will bounce up and down off the mesh when doing inside corners. For this reason, paper tape is often used on inside corners , but if you want the added strength of the mesh tape, it will work with inside corners with a little extra work. See Finishing New Drywall pt 2 for instruction on taping and finishing inside corners.
Using an inside corner knife
The fastest way to mud inside corners is with a special inside trowel made for inside corners which will smooth out both sides of the corner at the same time. Use this knife for the first and second layers of compound , and smooth out the final coat with a 6” spackle knife, doing one side of the corner first, then the other side after the first side is dry.
Repairing Drywall Crack with Mesh Tape
Taping a crack
You must use drywall tape to give the repair added strength or the crack will reappear in short time. Center the fiberglass mesh tape over the crack. It is best to use one uncut piece of tape for the whole crack. If you run out of tape or cut the tape short and need to splice two pieces of tape together for the crack, try not to overlap the tape. Overlapping will create a hump where the thickness is doubled, which will make an invisible repair harder to achieve. Use scissors to cut the tape to length and to trim off any excess.
Drywall crack repair
Applying drywall compound over the tape
Once the tape is down, you will need to smooth over it with drywall compound. As a rule, it will require three coats of compound to totally smooth over the tape. Each coat extends out a little wider than the previous coat, allowing for a gradual taper so that the tape is not a "hump" that abruptly starts and stops in the middle of the wall. Allow each coat to dry before applying the next. Lightly scrape off any ridges or bumps between coats with your 6” knife (don’t sand between coats) to allow the next coat apply smoothly.
Drywall Crack Repair
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