Got plaster cracks? Step by Step: Tape Plaster CracksI am going to walk you through this. For some, this may look like overkill. For others who have never known how to tape plaster cracks before, I hope this will make it clearer for you. You will be using regular pre-mixed all purpose joint compound and paper joint tape. Applying the tape A five or six inch wide taping knife, moderately stiff, works best. Cover about a three to five foot section of crack (provided it's all in a straight line) with a band of mud. You can do this in a couple of ways. Either put the mud on with strokes across the crack, or with strokes that follow the direction of the crack. If you use the second method, here is what I have found works well. Load a corner of the knife blade with mud, tilt the blade slightly so the mud doesn't fall off and run a narrow band of mud. Short strokes work best.
Two things to watch out for here. First, take care to see that the mud is centered on the crack. Once they are covered, of course, you can no longer see the plaster cracks. So. . . if the mud is centered on the crack, and the tape is centered in its bed of mud, that crack should be well-covered with the tape. This is worth stressing here, because if the joint tape is off target, your efforts are wasted. The second thing to watch for is -- skips! If the tape covers an area with too little mud on it, you will have blister problems showing up later when you apply the first topping coat. Be careful with this. This is the most common problem I run up against when I have to finish a job someone else started. Even tiny skips in the mud band are no-no's.
Center the tape with your left hand and pat it into place in the mud. (Be sure the crease in the tape is pointing down. This will happen naturally if the tape is unwinding from the bottom of the roll). It's probably best in the beginning to do no more than three to five feet of tape at a time (again, providing the crack is straight that long). As you gain experience, you can do longer strips at a time. Press the working edge of the taping knife hard across the tape near the end of your mud line, and with a pulling and twisting motion of the roll, tear the tape cleanly. If you find this method too awkward, there is an easier - more time consuming - way. That is to cut the tape to length first, then apply the piece.
Wiping out excess mud
Your next task is to anchor the tape firmly into the mud. Set your pan near you on a stool, bench, ladder etc. You will need both hands free. With your left hand, press down on the tape somewhere in the middle of its length. This will keep it from slipping as you draw out the excess mud. With the right hand, press the knife blade across the tape and wipe toward the end of the tape. Stop frequently to wipe off the mud buildup from the knife into the pan nearby. It seems to work best to hold the knife about 45 to 55 degrees angled to the plaster surface. If you hold the knife blade too steep, you will wipe out too much mud from under the tape and then the tape won't stick properly. Too flat an angle, and the tape will end up with too much mud under it. When that dries, you will have a bump and this will be harder to cover and hide when you do the coating process later. When the tape is laid just right, you will only have a thin band of mud under it. Note: when wiping down the tape, extend a forefinger onto the back of the knife blade. This stiffens it and gives you more control. Also insures that your knife will last longer before it breaks. Now, do the same going the other direction to the end of the tape, switching hands if that helps. Be sure the joint is cleaned of lumps or ridges of mud. You may have to wipe gently down the length of the tape several times to get them all. Taking time to do this now will reduce or eliminate the need to sandpaper the area later as you prepare for the first topping coat. In workable sections of tape, complete the plaster crack you started with. Since plaster cracks usually wander all over the place, you will probably end up with small taped sections running in all directions (especially when dealing with plaster over wood lath). Do not overlap the tape where seams come together from different direcions. You don't want any extra thickness to cover later. Let the taped cracks dry. With normal heat, this is 8 to 12 hours, depending humidity. Remember to keep a minimum of at least 50 degrees. A household fan or two set around the job can speed things up.
First Topping Coat
Tools: a 10 or 12 inch broadknife and mud pan. Or, plaster hawk and trowel. Be sure the taped cracks are dry. Check for lumps and ridges - anything that will interfere with you laying on a smooth first of mud over tape. Rough stuff can be sanded off with medium sandpaper (go easy on pressure. Don't scratch up the tape), or knock off with a taping knife held flat to the surface. Those grit covered sanding sponges work great for smoothing out roughness. Your goal here is a thin coat of multipurpose compound over the tape, to mute its outline. Once you start, do all the plaster cracks running in one direction, more or less. You can't cross a wet seam with another wet seam - leaves too many tool marks. Pick a taped seam and cover in short workable sections. When applying the topping coat, you will find that your broadknife or trowel will vibrate as its outer edges pass over the textured surface (though not all plaster is textured). This causes the mud swatch to have a rippled effect. Don't be too concerned unless the ridges are deep. If your plaster wall or ceiling is textured and needs extensive repair, you will probably end up mudding a sizeable portion of the surface. In that case, your best option may be simply to fill in the remaining areas with mud and shoot for a new smooth surface overall. You could then choose to leave it smooth or texture it before painting. Your main goal with the first topping coat over the taped plaster crack is to hide the tape with a thin layer of mud and feather out the edges as best as you can, remembering that a second topping coat is coming. Your seam will be eight to ten inches wide and you will usually be able to see the vague outline of the tape through the wet mud. When you complete all seams running in one direction, let them dry completely before you do the seams that cross.
Second Topping Coat
When all the seams have dried, you are ready to coat them the second and - you hope - last time. Prep as before, sanding or knocking off lumps, ridges etc. Coat all seams in the same way as before, but now make the mud a little wider than before. You are putting on a thin coat, remember. You don't want a big hump when you're done. Feather out the edges as best as you can. If you are doing cracks you plan later to retexture individually, you can wipe down the edges of the mud carefully with a thumb or finger. This will reduce the sanding you have to do later. To repeat an earlier point, if you have a lot of cracks you are repairing, it's often best to just coat everything with joint compound before texturing. This way, you avoid trying to match each individual patch to the existing texture (which can be a real challenge). Instead, you can end up with a whole new surface to texture or leave smooth as you choose. An easy way to coat a whole wall or ceiling is use the parallel strip method. Lay down the mud in strips, let dry then fill in the gaps later. You will probably have to do this at least twice or more, and going in different directions, depending on how rough the old texture is. This may seem tedious, but it will work if you have time and patience. For more on this, check out skim coating old plaster. ________________________________________________________ Sometimes when you are taping plaster cracks, you run up against one that just won't stay fixed. It keeps opening. What do you do? Try this super reinforcement method. _________________________________________________________ Return from Tape Plaster Cracks to Home Page
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