Tuesday, January 30, 2007

Patching plaster cracks with joint compound

The upstairs bathroom remodeling project presents plenty of challenges. The most time-consuming project will be repairing the cracks in the plaster walls. There were plenty of cracks hidden behind the wallpaper, and since we’re going to paint the walls, each and every one of them needs to be fixed... and fixed right. The plaster walls are smooth, and any attempt to cut a corner will be amplified once the final paint is applied to the walls.

Over the next few days I’m going to show you the tools, materials, and techniques I use to repair cracks in plaster walls. There’s plenty to learn from this room, because the cracks appear everywhere: hairline cracks mid-wall; cracks where the ceiling meets the walls; cracks where the walls meet; and on, and on.

Joint compound of choice
When patching cracks in the plaster walls of my old home, I prefer a product that is durable and is going to stand up to the subtle movements and drastic changes in temperate and humidity. That product is Sheetrock-brand Durabond Setting-Type Joint Compound. Use in conjunction with (paper) joint tape or fiberglass mesh tape (depending on the type of joint, I’ll show each in future installments) and you’ll end up with a rock hard repair that’s not going to crack again for the foreseeable future.

I could write my own description of USG’s Sheetrock brand Durabond Setting-Type Joint Compound, but why not just use the word’s from their Web site? They state:

SHEETROCK® Brand DURABOND® Setting-Type Joint Compounds are chemically-setting powder compounds for drywall interiors and exteriors that permit same-day joint finishing and, usually, next-day decoration. They provide a hard, plaster-like surface when dry and are virtually unaffected by humidity. (They are difficult to sand after drying; must be smoothed before complete setting.) Also ideal for heavy fills. They provide low shrinkage and superior bond, which make them excellent for laminating gypsum panels to gypsum panels, to sound-deadening boards, and to above-grade concrete surfaces. In addition, SHEETROCK Brand DURABOND Setting-Type Joint Compounds can be used for filling, smoothing, and finishing interior concrete ceilings and above-grade concrete; for taping and finishing SHEETROCK Brand HUMITEK™ Gypsum Panels; and for taping and finishing SHEETROCK® Brand Water-Resistant Gypsum Panels under tile in bathroom wall areas. Other uses include finishing joints in exterior gypsum ceiling boards and presetting joints of veneer plaster finish systems.

To meet varying job requirements, a full line of SHEETROCK Brand DURABOND Setting-Type Joint Compounds has been developed to provide a choice in setting times. The suffix number identifying each SHEETROCK Brand Joint Compound indicates an approximate setting time. DURABOND 20 sets in about 20-30 minutes; DURABOND 45 in 30-80 minutes; DURABOND 90 in 85-130 minutes; DURABOND 210 in 180-240 minutes; and Durabond 300 in 240-360 minutes.


For me, the benefits of Durabond setting-type joint compound is that it’s easy to mix with water; it resists shrinking; and it resists humidity changes, which is especially important in a bathroom of a Midwestern.

The downside is sanding. Durabond setting-type joint compound is much harder than your traditional drywall joint compound, and thus, it’s harder to sand. You want to apply it in thin, smooth-as-possible coats to make sure you don’t leave yourself with a lot of unnecessary sanding in the end. Why not just use the pre-mixed, easy-to-work-with drywall joint compound? Because it’s not as strong and the chance of cracks re-appearing is much greater. Spend a little more time and effort doing it right the first time, and you’ll hopefully never worry about the cracks again.

When choosing the setting time (Durabond 20, Durabond 45, or Durabond 90 are most common), keep in mind that the higher the number the more challenging the sanding. Therefore, I typically use Durabond 45 for my first layer, and then switch to Durabond 20 for subsequent layers. I like to think this makes the finish sanding easier.

The other downside with using Durabond 20 is the quick setting time. While 20 minutes might seem like a long time, the clock starts ticking when the water first hits the product. After you’ve gotten the hang of mixing the product, the setting time shouldn’t be a problem. But in the beginning you will most likely struggle with getting the right mixture of water and the dry compound. You could easily kill five minutes mixing and then, if you have a long seam to repair, getting the entire mix of joint compound (or “mud”) on before it starts to harden can cause you to rush and make mistakes. Trust me, with the Durabond 20 you can literally see when the final grains of sand are moving through the proverbial hour glass. At that point it’s best to walk away from that batch. If you try to use mud that is starting to harden, you’ll likely end up with a result that will require additional sanding in the end.

One more thing on mixing: The consistency you’re looking for is similar to peanut butter. After some practice you’ll be able to tell if you have too much water in your mix. If there’s a glossy appearance to the mud, there’s probably too much water. If you try to put on mud that’s too watery, you’ll notice right away because you’ll see bubbles in the mud after you drag it into place with your drywall taping knife.

Next time I’ll cover the tools I use to apply the joint compound.

Visit USG.com and search for “durabond setting-type joint compound” for more details (including data/submittal sheets) on the Durabond line of setting-type joint compound.

7 comments:

  1. Thank you for these articles on plaster. I'm plastering too, in the tiny cottage we're building up here in Vermont. For the ceilings we're actually molding the plaster in place as one big unified part and then the concrete of the 2nd floor (loft & attic). The house is made concrete and stone. For the walls we'll be plastering the more traditional parge method.

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  2. to bergie of old home blog.
    have patched many cracks in plaster walls in kitchen with usg. durabond 90 a couple days ago. in week i will paint with latex primer and latex finish. the problem is that after walls dried i had to sand a little and also use the broadknife to scrape off small ridges left by broadknife. this left some white dust which can be observed by running your finger over the area. I need to get this off prior to painting.I took a damp sponge and went over the spots but I notice it seems to activate the durabond again as the durabond gets sticky and then redries. Im wondering if I should be using the damp sponge to get the dust off? Is this the right thing to do or should I just use a dry cloth to wipe dust off prior to painting? What way do you use?

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  3. ""Plastering with Durabond 90""
    I only use the Durabond 90 plaster for plasterin walls and ceiling small repair , the durabond 90 work's fine on plastering paching cracksand base coat plastering!

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  4. Durabond 90 is really good for plastering walls and celings repair!

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  5. I am using USG plaster bonder in the cracks, after preparing the cracks, and then using red top finish plaster for a permanent fix. Works for me! For the really deep parts that are to the lath, I'm affixing metal lath to the wooden lath and then using structo-lite until it is lower than the level of the rest of the plaster, but then leaving a srcatchy surface for the next coats to key to, then I'm finishing with the red top. These products can be mixed just with water and I am not finding them to be any more difficult to deal with than joint compound, but they are real plaster and will be just as durable as the rest of the original wall.

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  6. Cracks are not pleasant to look at , especially in bathroom walls. With plasters, you can prevent further occurrence of cracks - when done properly. Be sure that the plaster that you have acquired is the right kind for your walls and it is eco-friendly. Enrich your knowledge by reading blogs such as this as well as home remodeling magazines. If you have to consult building contractors, ask only the qualified professionals to give you reliable advice.

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  7. Great article! I’ve recently had a lot of home improvement work carried out. My advice to anyone looking for help is to shop around, whether you’re looking for a plastering quote, or any other work. Although cheapest doesn’t always mean best!

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