Restoring Plaster Walls - Setting Type Joint Compounds

If you have ever owned an older home, you must surely be aware of the pluses and minuses of plaster walls. Their durability, smoothness, sound deadening qualities and sheer mass make them very attractive. Plasters only negative, as I see it, is that it tends to react like glass when subjected to stress. In other words, plaster cracks.

Random or Systematic?

Cracks in plaster happen for a variety of reasons. Lumber shrinkage, seasonal moisture changes, wind forces, foundation movement, expansive clay soil movement, excessive loading, etc. all can cause cracks in plaster. Some cracks can be traced directly to a certain cause while some are tougher to diagnose.

It is important to try to determine the cause of cracking prior to repair. The reason being that if your house, wall or ceiling is mobile or in a state of motion, the crack will undoubtedly reappear. Certain cracks are very interesting. These are the ones that plague many houses in climates that experience wide humidity changes from summer to winter.

Wood - Like a Sponge...

Wood expands and contracts in response to changes in the humidity of the air that surrounds it. In other words, wood is a hygroscopic material. Plaster, on the other hand, is very stable. It is very strong if you try to squeeze it, however it is very weak if you try to bend or stretch it.

Thus, if the wood framing members of your house begin to stretch or expand, the plaster can and will pop. There is very little you can do to prevent this, other than trying to maintain a constant indoor humidity level.

Plaster and Old Age

Remember your body and skin when you were 10 years old? I'll bet it was smooth and virtually blemish free. What do you think your skin will look like when you are 70 or 80 years old? Well, a house is not much different.

Houses develop joints just like your elbows and knees where they bend to relieve stresses. Walls and ceilings also react to the force of gravity over time, just as our skin. Thus, it is not unreasonable for an older house to exhibit wrinkles, cracks, and other blemishes.

Fixing the Cracks

OK, so now that the plaster is cracked it is time to fix it. Time after time I have seen homeowners struggle to fix a crack using spackling compound. They are told to chisel the crack into a V shape and fill away! Well the patch looks fine until the house or wall moves the next time. The crack reappears.

The most long lasting repairs are made when you bridge the crack with a material that can absorb the periodic movement that most cracks experience. This is achieved by using either a standard drywall paper tape or a fiberglass mesh tape. The crack is coated with a compound that adheres to the plaster and coats the tape at the same time.

In all but the worst cases, cracks repaired with tape remain smooth for a long period of time.

The Gop

One of the first jobs I did after I got married was the rehabilitation of an old farm house. I was helping some friends. Marcy was helping me apply some premixed drywall joint compounds onto new drywall. She used to call the material Gop. I feel it is a very fitting name as it sounds much like the product appears and reacts when dropped. Premixed joint compounds are wonderful products. For all intents and purposes, they are simply water soluble glues mixed with fillers. These premixed compounds work fine for drywall. However, for serious plaster repair you need to use either real plaster or a product that has the properties of both plaster and premixed joint compounds.

The Stuff

You can purchase some wonderful plaster patching compounds that come in 25 pound bags. They are powdered setting type joint compounds. These products actually grow tiny crystals as they dry. These crystals lock into the coarse texture of the plaster base and/or the smooth white or top coat plaster. You can even add sand to these mixtures if you wish to create a textured look.

These compounds come dry because when they are mixed with water they begin to harden. Some of these products contain higher amounts of gypsum. These tend to set up or get hard within 30 minutes of mixing. You can buy mixes that take up to two hours to harden.

An additional advantage of using these products is that in one day repairs are possible. Premixed joint compounds can take a day or more to dry. Repairs can stretch out. I have used the setting type joint compounds and repaired a plaster hole from start to finish in as little as two hours!

Where Do You Get Them?

That is one of the most frequently asked questions. Homeowners miss out on tons of great products. These special dry setting joint compounds are found at drywall supply houses or building supply houses that sell plaster supplies. Only on one occasion have I seen them in a giant home center store.

If you want to get some of these great compounds, you will have to find out where your local builder or remodeler buys drywall.

This column was shared with my readers in the April 4, 2013 AsktheBuilder Newsletter.

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Setting Joint Compounds Avoid Dust

Real plaster work involves minimal dust. The plasterer trowels the wet, white plaster until it is as smooth as glass. There is no sanding.

You can do the same with setting type joint compounds. As they get hard, you can work with them and trowel them just like real plaster. A rubber ceramic tile grout float works best. The joint compound needs to be very hard to achieve the best results.

Wet the compound slightly. Glide the rubber float across the patch with just the trailing edge of the trowel touching the compound. You do not want the entire bottom surface touching the plaster. If you make successive strokes much like you would squeegee glass, it will work. Trust me, it takes practice.

If you can't get the hang of it, you will have to sand. You may be able to rent some new wonderful sanding vacuum tools at your local tool rental shop. These tools have a sanding pad attached to a shop vac. They really eliminate 95 percent of the dust in most situations. The key is keeping the filter clean.

Makers of Joint Compound

Want to know more about these powdered setting plaster repair products? Just check out the websites of these manufacturers.

All of these products perform well. The key is to mix only the amount you can comfortably use in 15 - 20 minutes. If they start to get hard in your bucket or mud pan, do not add additional water. It will weaken the mix and fall from the wall or ceiling. Clean your tools well, as the compounds can stick like concrete!

• CTS Cement RapidSet
• DAP
• National Gypsum
• USG Corporation

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This small section of wall has just about every drywall finish challenge in it: flat and tapered seams, inside and outside corners and an archway! Photo credit: Tim Carter

Surely you have seen a miserable drywall finishing job. One of the first places to look is in a corner. Typically, you will see holes and lift marks where the finishing blade was pulled away from the wall. For some reason, finishers seem to get tired as they sand in or near the corners!

I have seen home improvement television shows that tell people how easy it is to finish drywall. Well, it is easy if you know all of the tricks and have had considerable practice. If you don't, you struggle. Drywall finishing is not as simple as driving a nail or cutting a piece of wood. It takes lots of skill to get professional results.

Wipe It Off

One of the neat things about finishing drywall is that if you goof up applying the mud you can immediately erase your mistake and start over. All you do is wipe off the mud from the seam. The only aspect of the process that is critical is the actual taping. Too much or too little mud under the tape can cause all sorts of finishing problems later in the job.

Think Snowplow

Have you ever seen how a bulldozer or a snow plow works? The blade is angled to throw the dirt or snow to one side. This is an efficient way to work. Removing the excess mud from beneath drywall tape uses the same technique. The trick is to make several repeated passes with the taping knife instead of trying to do it all at once.

Learn the secrets to a great drywall finishing job in this Drywall / Plaster Installation Checklist. I offer a 100% Money Back Guarantee.

Professionals tape drywall in any number of ways. They can use a device called a banjo that applies mud to the underside of the tape as it is pulled from the simple hand held machine. Even more complex machines can apply tape and a coat of mud to a wall in one operation. But if a pro is doing it like you will be, they apply the mud smoothly and at a thickness of approximately 1/4 inch. The tape is then pressed lightly to the wet mud. When you glide your knife over this relatively smooth assembly, the excess mud flows easily out from beneath the tape.

Drying Time

The joint compound or mud you use to finish drywall is water based. It dries fairly quickly if the humidity is low and the temperature is high. Keep in mind that this compound is simply a glue with lots of filler. The color of the compound tells you, to some degree, if it is dry. When wet, the compound is a light gray. As it dries it turns white. You can see this transformation very clearly halfway through the drying process as the edges of the joint will be snow white while the center of the seam is still gray. Do not attempt to sand if you see any gray coloration.

Patching a Hole

Let's say you have a hole in a piece of drywall that is about the size of a golf ball. It is too small to cut a patch yet too big just to fill with joint compound. There is a cool trick that really works well. All you do is take a piece of paper drywall tape and coat the underside of it with a 1/8th inch coating of wet compound. You then flip the tape over and center it over the hole. Gently scrape a little of the mud out from the tape. Once the mud dries in a day, the area over the hole is very stiff. If you want to make it even better, apply a second layer of tape over the first one. Align the second piece of tape at a 90 degree angle to the first one.

Nails and Screws

Professionals do not apply a little dab of mud to each and every screw or nail. They coat three or four at a time with one quick motion. The end result is a stripe of mud on the surface of the drywall. If you see dried polka dots of white on a sheet of drywall, you know a rookie is finishing it!

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Drywall Hanging Direction on Steel Studs

Reader email:

Tim,

How do you lay out drywall on steel studs? Should it be vertical across the studs or horizontal across the studs, and should I stagger the drywall?

This is for a basement that is studded with steel and I'm very confuuuuuused!!! Thanks,

Holley

My Reply:

Holley,

The best way to install drywall is horizontally. You should also stagger the seams. Installing it vertically requires that the spacing of the studs must be perfect and they are perfectly plumb. This is much harder to achieve that you might think.

Then wait until you are bending down to tape all of those vertical seams every 4 feet. With 12 foot drywall, you only have to do it every 12 feet. Since you rarely have wall runs longer than twelve feet without an inside or outside corner interrupting it, you might never have that flat seam in a wall run.

Tim

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The Big Sheets

Conventional plaster application changed radically in the 1960s and 1970s. Veneer plaster systems were developed at that time. Drywall was being substituted for plaster at that time as well.

Drywall offered a different approach to quickly achieve a finished wall surface. The 4' x 8' and 4' x 12' panels of drywall could be rapidly applied to framing members. A standard sized room could be ready for finishing in an hour or two.

During the 1950s, conventional plaster systems required the installation of "gypsum lath." These were smaller (16" x 48") pieces of material which looked, at first blush, like typical drywall.

However, these smaller pieces of gypsum plaster lath actually were covered with a special paper which absorbed the water in a special manner so as not to harm the inner gypsum core. The paper was also manufactured in such a way as to provide an excellent surface for the plaster to grab on to.

CLICK HERE to get FREE & FAST BIDS from local Contractors who can install your new plaster wall.

The traditional two coat plaster system (brown coat/white coat) was applied over this gypsum plaster lath system. However, it was quite labor intensive to nail on these smaller pieces of gypsum lath. It made sense to switch to larger pieces of gypsum lath and develop a one coat plaster system.

Veneer Plaster Systems

Although drywall was rapidly becoming popular, drywall did not have the overall performance characteristics of conventional plaster. Plaster surfaces offered better joint concealment, fewer nail pops, a hard monolithic surface which could be easily decorated, and plaster was more quickly finished than drywall.

Also, the joint compounds used to finish drywall, even after they dried, could be easily dissolved by water. Water applied to the surface of a traditional plaster wall for short lengths of time did not harm the plaster in any way. Veneer plaster systems changed this. They took the best qualities of the two systems and combined them.

Veneer plaster systems use a gypsum core panel as the base for the plaster coat. This panel has a gypsum core very similar to drywall. However, the paper used to cover the gypsum core is different from regular drywall.

It is a special multi-ply paper. The top ply has the capability to readily absorb water and provide a good bonding surface for the plaster coat. The bottom ply, however, is water resistant. This ply protects the inner gypsum core from being softened by the water in the wet plaster.

Some manufacturers use a special blue paper on this gypsum panel. Plasterers often refer to it as "blue board." Special plasters were developed which allowed a one step finishing process. This plaster is applied in a thin coat directly over the gypsum panel.

The plaster thickness usually ranges between 1/16th to 3/32nd of an inch. Conventional plasters were often 1/2 inch thick.

Advantages of Veneer Plaster

Veneer plaster finishes offer two distinct advantages over drywall - dust and money. Dust is kept to a minimum with these products. The veneer plaster is applied in a wet state and troweled to a smooth surface. No sanding is required.

A one step veneer plaster can cut up to 75 percent off of a similar drywall finishing production time. After the gypsum wall panels are hung, a one coat veneer system requires one step.

A similar drywall job requires four finishing processes. The last step of a drywall job, as many people know, involves the creation of massive quantities of dust.

Certain plasters offer tremendous durability. Some achieve compressive strengths of up to 3,000 pounds per square inch. This strength rivals that of some concrete mixtures! Drywall can not make similar claims.

Plaster wall systems offer greater decorating flexibility as well. Wall coverings can be applied to plaster as easily as they can be applied to drywall. However, plaster systems allow you to readily remove the wall coverings in the future without damaging the wall surface.

The paper covering of drywall is often damaged, or partially removed when wall coverings are stripped from drywall.

Veneer plaster is affordable. Often it costs just 25 percent more than a drywall finish. While this may seem like a large differential, it is, in fact, not.

This upgrade may only add one-half of one percent to the overall cost of a construction project. When you consider the long term durability that veneer plaster systems offer, it is a tremendous value.

Tips on Residential Plaster Patching

Plaster is a hydration product, just like concrete. When you add water to dry plaster mix, you begin an irreversible chemical and crystallization process.The water and air content of the mix is critical. Timing is important, as the plaster has to be "finished" at just the right time. It is not a job for the rookie.

However, several manufacturers have developed different plaster products. They are fast setting plaster compounds. These products are dry powders. You add water to them and they begin to crystallize or "set" just like plaster.

They are available with different "set" times. Some of these compounds, however, are sandable. They allow you to do quick repairs to surfaces in a one-step operation similar to plaster. You can teach yourself some basic plastering techniques by working with these materials.

CLICK THE IMAGE to get a Durable Taping Knife for Drywall and Plaster projects.

As they begin to 'set' or crystallize, you can trowel them to a smooth finish, just as you would plaster. Or, if you are unable to achieve a smooth finish, you can sand them after they dry completely (assuming you used a sandable compound!).

If you live in an older home with a conventional plaster wall and ceiling system, you should consider using these compounds to patch your plaster. Premixed vinyl joint compounds do not always bond well to the sandy plaster base coats.

The quick set joint compounds, because of the crystallization process, actually grab to the old plaster much better. As the crystals in these compounds begin to grow, they interlock in the rough, sandy texture of the fractured plaster.

Once you have applied the quick set joint compound, you can always skim over the patched area and existing plaster with a ready mixed compound to fill any small nicks or scratches.

CLICK HERE to get FREE & FAST BIDS from local Plaster Contractors who can repair your plaster wall.

Plaster Crack Failed Repairs

Most older homes that have cracked plaster are constructed using wood framing materials. In certain climates, these framing members react seasonally to changes in humidity. During warmer more humid months, the framing members absorb moisture from the air and expand.

During winter months, the wood dries out and contracts. The houses actually develop stress points or joints where the energy of this movement is released in a visual form that we see. This same movement can also be a result of soils which expand and contract due to changes in moisture.

Repairing these cracks, which move on a regular basis, is somewhat difficult. You must tape over these cracks with a paper or mesh tape. Simply filling the crack with patching plaster will not work. As long as the cracks move even a small amount, the paper tape in most cases will hide the movement of the crack.

Patching the cracks is just like taping a regular drywall joint. You need to feather the joint to hide the tape as in a standard drywall butt joint.

Fixing Plaster Cracks

Cracks are simple to repair. You will need a four, six and 10 inch flexible drywall taping knife and/or broad knife. A drywall mud pan or flat plaster's hawk will be necessary as well. These two things hold the plaster so you can work with it.

CLICK THE IMAGE to get a fiberglass repair fabric that will help eliminate cracks in your plaster walls.

Start the repair process by removing all loose plaster. Mix up some joint compound. Mix until all lumps have disappeared. Precut pieces of paper or fiberglass tape to cover the cracks. If the crack is curved (many are!), then you will need several smaller pieces to make the curve.

Apply a 1/8 inch thick layer of joint compound over the crack with your four inch knife. Embed the tape into the wet compound. Drag the knife across the tape and remove half of the compound you applied. If you remove too much, the tape will blister on the second coat! If you leave too much, you will have a giant hump!

Once the compound has set up (becomes hard), you can apply a second coat to hide the tape. I like to use the six inch knife for this job. I also use the 10 inch knife as well. You are trying to add just an additional 1/16th inch over the top of the tape. The larger length knife allows you to taper the compound so the hump is disguised.

When this coat hardens, you can apply the third and final coat. Before you do this, it may pay to scrape off any high spots or use a ceramic tile rubber grout float to smooth out high and low spots. Slightly wet the dried or hardened joint compound and glide the rubber float over the patch. With just the right touch, you will get ultra smooth results.

An essential part of finishing your repair on cracked plaster or drywall CLICK THE IMAGE to get All Purpose Joint Compound.

Patching Plaster Holes

If the lath board is still in place behind the hole, your repair is easy. Simply remove loose plaster and dust, wet the area to be repaired and fill with the setting joint compound. Do not use premixed joint compound for these repairs. These simply do not bond well to the sandy base plaster or wood lath.

If there is nothing behind the hole but air, you need to create a base for the plaster to stick to. There are many ways to do this. Let's say the hole is two inches in diameter. I would cut a one inch wide piece of wood that is six inches long. I would then tie a 16 inch long piece of string around the middle.

Apply a liberal amount of construction adhesive to each end of the stick. Smear the glue on the wide face. Insert the stick into the hole so that the glued side faces you. Position the stick so it spans the hole equally.

Pull on it with the string so that it comes into contact with the back of the wall that is being repaired. Use the string to hold it in place. The glue should readily stick. After several hours, you should be able to proceed with the patching process.

Manufacturers of Veneer Plaster Products

• Flexi-Wall Systems
• Georgia-Pacific Gypsum
• National Gypsum Company
• USG Corporation

Veneer Plaster Technical Information

If you would really like to find out more about the different veneer plaster systems which are available and which one might work best for you, contact USG Corporation (http://www.usg.com). They have an excellent book which is loaded with information about plaster and drywall systems. The book is actually geared to the construction industry, however, it is very understandable for the average homeowner. It is called the Gypsum Construction Handbook.

CLICK HERE to get FREE & FAST BIDS from local Contractors who can install your new plaster wall.

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The Plastering article previously on this page has been combined with new, up-to-date information and great product links. CLICK HERE now to get what you need.

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The Plastering article previously on this page has been combined with new, up-to-date information and great product links. CLICK HERE now to get what you need.

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