How to Repair Hairline Cracks & Holes in Plaster Walls & Mistakes to Avoid

Hairline cracks and holes in plaster walls are unsightly, aren’t they?

But that’s not what worries you the most.

You’re probably thinking:

Has my plaster wall gone kaputt?

Do I need to replace it altogether?

Can’t say we blame you. A damaged plaster wall has an aspect of finality to it. And the notion of carrying out repair or replacing your plaster wall sounds like it’s a lot of work, not to mention costly.

Thankfully, fixing a damaged plaster wall shouldn’t be a major cause of concern, at least most of the time. In fact, and if you can believe it, plaster wall is easier to repair than its more popular counterpart, the drywall.

Yes, you can patch up that plaster wall with minimal expense and effort. All you need is some knowledge on how to do it the right way.

As to that, we’ve got you covered.

Ready? But before we get started, here’s a bit of background on what plaster is and how it’s made.

What is plaster?

If properly mixed, plaster can provide a more durable finish than even drywall. In the early days, plaster is made by mixing lime, sand, cattle hair, and water until it’s turned to a putty substance. You get plaster once the mixture dries up and hardens.

What is the difference between plaster and drywall?

For centuries, plaster had been the go-to material when constructing interior walls for homes. It was not until 50 years ago when construction professionals started adding gypsum into the mixture, allowing the compound to dry up more quickly.

This mixture, as you might have already guessed, is called drywall. And it’s been the most popular material used for finishing interior walls over the last few decades. No surprise there. After all, modern construction practices favor the use of the material in terms of labor, time, and costs.

Which begs the question:

Is drywall really much better than plaster?

The answer, of course, largely depends on your priorities as a homeowner.

If you want a wall material with a durable surface and can last a long time, then plaster is the ideal choice. The drawback with plaster is that it tends to absorb water easily, increasing the risk of water damage. Also, repairing plaster can be difficult and expensive, sometimes even requiring you to remove big sections of the material when carrying out repairs.

As already mentioned, drywall is more cost-effective to use than plaster. Another big advantage drywall has over plaster is that it provides better sound and temperature insulation. One major issue with drywall is that it cracks more easily than plaster. Without using top-grade construction materials, installing drywall can be complicated and messy. And when not installed correctly, the joints between the sheets of the drywall tend to show, thus ruining the surface’s smooth and seamless appearance.

Okay, then. But how is plaster wall made?

Plaster wall is durable, not because of the material it’s made of, but because of the way it’s constructed. Plaster is made of flexible material you can mesh together, allowing you to create a multi-layered coat plaster system (sometimes called the three coat stucco process system).

So, how do they pull this off?

It begins with the lath, which are thin wood slats that are attached to the framing of your plaster wall. Three coats of plaster are then applied to the lath in an interlocking manner, resulting in a structural system that holds the plaster wall together. Also, by layering three coats together, you’re getting a wall system with good insulation for temperate and sound.

The 3-coat plaster system is comprised of the scratch coat, brown coat, finish coat. The scratch coat serves as the plaster system’s base coat and is, therefore, the first one attached to the wall. The brown coat is then applied after the application of the scratch coat, further strengthening the wall system. After the brown coat is cured, the finish coat is applied to give the entire system a nice finish.

Why Plaster Walls Get Hairline Cracks

While durable, even plaster wall can incur damage through wear and tear and poor maintenance. Before we delve into how to repair hairline cracks in plaster walls, let’s go over why cracks happen in plaster walls in the first place.

To be sure we’re on the same page, let’s define what a “hairline crack” is. To put it simply, a hairline crack is a line that appears along the surface of a wall (not just plaster walls), indicating a split that appears as if the wall is breaking apart. Small hairline cracks are not usually a cause for concern, but they must be addressed as soon as possible before they get worse.

Cracks in plaster walls can be caused by a wide range of things, and they are:

Poor installation

Sadly, some contractors won’t follow building codes just because they can get away with it, while some are simply not competent or diligent enough to do the job properly.

Either way, it’s you, the homeowner, who loses.

So many things can go wrong when constructing a plaster wall. For instance, a construction professional might forgot to rake the background surface before applying plaster on it. Another possible scenario is when he or she overlays the plaster without applying chicken wire mesh in the masonry first.

Whatever the reason for the poor installation, a crack on your plaster wall is something you can’t afford to ignore.

Seasonal changes

One drawback of using plaster is that it’s vulnerable to moisture. Moisture becomes prevalent in the atmosphere when seasons change frequently. Allow moisture to come in contact with the plaster wall regularly and it will seep through the plaster, causing it to expand and form hairline cracks.

Shrinkage cracks

Water from freshly applied plaster has a tendency to evaporate rapidly, reducing the surface layer’s volume. This volume reduction causes plaster to shrink, resulting in the formation of cracks in the surface layer. To prevent shrinkage cracks from appearing, always check if the plaster has been cured and sanded thoroughly before application.

Corrosion

Using concrete that is of poor quality contributes to the corrosion of plaster. Weak concrete has a porous surface, making it easy for the moisture to seep inside. Once the moisture comes in contact with the cement for too long, the protective layer holding the structure together becomes corroded, causing hairline cracks to form. Cracks caused by corrosion can even more annoying than the regular crack because of its rusty color.

Foundation shifts

Natural disasters such as earthquakes, hurricanes, and floods can produce stresses in the foundation of the plaster wall, causing cracks not just on the surface but also the structure itself. Cracks due to foundation shifts are more likely to expand since the source of the damage is coming from the subsurface.

Vegetation growth

Do you have large trees or vines near your home? If so, you might want to check if they’re growing into your plaster walls. If cracks are the result of growing vegetation, you can trim the “excess growth” with pruning shears.

Settlement

Cracks can occur when the house “settles” long enough to create stresses in the home’s foundation, causing the plasterwork to shift, which subsequently leads to cracks. Settlement cracks are usually vertical and are likely to run along the home’s exterior walls. Cracks caused by settlements are not to be taken lightly because they may lead to structural problems. It will be wise to have the cracks investigated immediately upon discovery to ensure that the structure of the home hasn’t been compromised in any way.

Fixing lead-painted plaster walls

Before you start repairing any cracks or holes in your plaster wall, you must check first if the paint used on it is lead-based. Why? For one thing, lead is a harmful neurotoxin that can cause many health issues. As you carry out repairs, you will need to perform steps that may cause the chemical to spread into the atmosphere, putting you and your loved ones at risk.

If your plaster wall was painted before 1978, it’s highly likely that the paint over your plaster wall contains lead.

Thankfully, all you need to do to check the presence of lead in your plaster walls is to use lead paint test kits. You’re also better off buying them in bulk, especially if the extent of the damage is huge.

Either way, children or pregnant women should steer clear from the work area before you get started.

How to repair hairline cracks in plaster

It goes without saying: the smaller the crack, the easier it will be to repair… at least as long as the plaster is still securely attached to the lath inside the wall cavity. How do you determine if the plaster is about to break away from the lath? Simple: give the wall a gentle push. Is it moving in a way that seems like it’s about to break away from its foundation? In that case, you must contact a specialist who can install a new plaster for you.

But if the plaster feels like it’s going to hold, then good on you. However, you still need to patch up that hairline crack. Here are the steps to do that:

  1. Widen it.

The first step to fixing a small crack in plaster is to widen it. Grab a putty knife (or a lever-type can opener), stick the point inside the crack, and open the edges to about ⅛ of an inch. That should give the joint compound some wiggle room for later.

  1. Brush off the plaster dust.

Clear the affected area of plaster dust or of any dirt sticking to it. Dip a medium-bristle brush in a TSP and water solution and gently brush away any crumbs or dust from the crack.

  1. Cut strips of tape.

Measure and cut short lengths of paper drywall tape or fiberglass mesh joint tape and then cover the crack with it. It bears noting that this should be done before applying a drywall compound to prevent folds and bumps from forming. Use scissors (not your hand or teeth) when cutting to ensure that the tape doesn’t have ragged edges, allowing for smoother application and preventing the compound from invading the crack.

  1. Apply the joint compound.

The application of a joint compound is an essential step to ensure a great finish. Dip your putty knife into the compound and then use it to smooth the tape over. Do this at least twice to make sure that the tape is adhering nicely around the crack.

  1. Apply the joint tape to the crack.

Apply the tape to the crack and then smoothen it out with your putty knife. Don’t overdo it or you run the risk of scoring the tape. Once the tape is evenly applied, leave the joint compound to dry for a few minutes.

  1. Apply another layer of joint compound over the tape.

You don’t want the taped area to be visible once you’re finished, so what you can do is apply another layer of joint compound over the tape, making sure that it extends a few inches past the tape’s edges. Once the joint compound is fully dry, sand it down with 8-grit sandpaper to make the joint compound blend nicely with the plaster’s surrounding areas.

  1. Prime it.

Apply latex primer over the area to make it easy for topcoat paints to adhere to the surface. Once the primer is fully dry (refer to the product’s instructions to determine dry-off time), apply the top coating (using the same paint color as the surrounding area, of course) over the plaster surface.

The Inverted V Method

  1. Open the crack to an inverted “V” shape (like a dovetail) and remove any excess dirt and debris. Doing this will give the patch a foothold to cling onto.
  2. Cut strips of drywall tape and adhere it along the crack’s length.
  3. Apply some moisture on the lath and plaster surrounding the crack. This will allow the patch to stick to the surface.
  4. Apply at least two layers of mixed joint compound over the crack and then sand it down with fine sandpaper until the surface is smooth enough.
  5. Gently push the compound with a trowel to make sure that the newly applied plaster is adhering securely to the lath.
  6. Apply at least two coats of joint compound. Don’t forget to sand the surface between coatings.
  7. Apply the final layer of joint compound to create a smooth and seamless base for the paint.
  8. Paint over the surface if you like.

How to repair wide cracks in plaster walls

For wider or bigger cracks, using a joint compound won’t be enough to patch up the damage. Do the following steps to repair bigger cracks in your plaster wall.

  1. Using a masonry bit, drill 2.54 centimeter-holes about 1.5 inches from both sides of the crack’s edges and 3 inches apart.
  1. Apply some adhesive along the holes using a caulk gun before removing any excess adhesive with a sponge.
  1. Secure plaster washers into the holes by driving a 2” drywall screw into each one.
  1. Leave the adhesive to dry before removing the plaster washers.
  1. Patch up the crack with a drywall knife.
  1. Install a crackstop fabric repair mesh over the damaged area.
  1. Apply two layers of coating and sand gently.

Common Causes of Holes in Plaster Walls

Holes in the plaster wall can be just as annoying as hairline cracks. Of course, a hole in the wall is not something you can ignore. But before you carry out the necessary repairs, it bears knowing why plaster walls develop holes in them.

Nails popping out of the plaster

When a nail is not hammered right in the center of a joist or stud, it has a tendency to pop through the plaster wall in due time. It can be incredibly tempting to just pick a hammer and drive it back, but this will only result in further damage. Besides, even if you drive it deep again, there’s a chance that the nail will pop out again. In this case, it’s always better to nail it through a different point so that it can be securely attached to another joist or stud.

Impact by accident

Holes in plaster walls can be caused by numerous things, but most are caused by impact from accidents, such as a door swinging too hard or someone bumping against the wall after tripping over his own feet.

Water damage

When a large amount of moisture comes in contact with the plaster wall for too long, it can cause the plaster material to soften or loose. Allow that amount of moisture to have its way on the plaster for too long and it will eventually damage the wall, leaving holes in their wake (an expanding plaster is a good indication that the material is about to pop). Water damage often occur because of roof leaks, causing water to run through the wall’s interior.

Termite Damage

Termites, as many of us already know, thrive in wooden structures, making your plaster wall an ideal target for infestation. Once these critters gain access to the insides of your plaster walls, they can do a significant amount of damage.

There are many signs to watch out for indicating that termites have invaded your plaster walls, such as pinholes, hollow sounds, bubbling plaster, and more. You’d do well to contact a pest control specialists as soon as you discover any of these signs.

Loose Joint Tape

Joint tape is applied to plaster wall to cover up seams in drywalls. A joint tape, however, may loosen up and separate from the wall because of moisture or poor construction practices, causing the wall behind it to crack open.

Damage from furniture

Moving around heavy furniture inside the home’s interior can cause scuff marks to appear in plaster walls. These scuff marks weaken the plaster material, which may cause it to crack open sooner or later. To avoid such damages, always be careful when moving the furniture around in your home, taking care not to apply pressure too much when you’re sticking them close to walls.

How to repair holes in plaster walls

Here are the steps to patching up holes in plaster walls.

  1. Remove any excess debris, dirt, or plaster from the hole. Cut off any dangling pieces of plaster. If the edges are rough or jagged, smooth them out with sandpaper. To remove remaining dirt, wipe the hole’s interior and exterior with a clean rag.
  1. Cut a portion of self-adhesive fiberglass mesh that is big enough to cover not just the hole but also the areas extending 2-3 centimeters past around its perimeter. Center the mesh over the hole and make sure that it’s at least in close contact with the wooden lath inside. If the mesh is non-adhesive, nail the mesh to the wooden lathe inside the hole.
  1. Apply a ready-mixed filler over the area with a spatula or a putty knife. Allow some of the filler to pass through the holes of the mesh until it’s all filled up. Make sure that the area around the sides of the mesh is completely covered. The idea here is to completely seal the affected area so that it will blend well with the surrounding wall. Once the hole is fully patched up, remove any excess filler by brushing at them with a downward stroke of the putty knife or spatula.
  1. Use fine sandpaper to gently sand the area until it’s smoothed over.
  1. Apply another layer of ready-mixed filler over the area. Wait for it to dry.
  1. Brush off any excess dirt or dust with a clean rag.
  1. Paint over the area if desired.

Mistakes to Avoid When Repairing Plaster Walls

Now that you know the steps on how to repair plaster walls, it’s time to get familiar with the common mistakes you need to avoid. After all, every human being has a tendency to get careless when he or she gets too comfortable with a process. If you can avoid committing the mistakes described below, you’ll be able to repair plaster walls like a true professional.

Mistake #1: Painting over the plaster even before it’s completely cured

Plaster, unlike most materials, takes longer to dry and cure. As a general rule of thumb, you need to wait several days for the material to cure before you paint over it. Paint it too soon and the moisture in the material will cause the paint product to fade, bubble, or bleed. This, of course, can result in a messy paint job.

Mistake #2: Skipping the patching process

Some homeowners (and surprisingly a few professionals) conflate filling with patching. They’re not in any way similar. As a result, many tend to skip the patching process, thinking that filling the breaks is enough to do the job.

That’s a big no, especially for big and extensive cracks. When you patch up plaster, you’re adding new material that will attach to the lath. Skip the patching process and the end-product isn’t likely to last long.

Mistake #3: Not carrying out the necessary structural repairs

As already mentioned, plaster is a durable material. In most cases, it takes something major like structural damage to cause the material to crack. If you fill or patch up the cracks without addressing the root of the problem, you’re likely to experience the same issue over and over. So, don’t just cover up the damage, get to the root of the problem and fix the wall once and for all.

Mistake #4: Ignoring the lath or wiring

The thing with a weakened lath or wire mesh is that it won’t be able to hold the interior plaster together even if it appears like it’s been patched up completely. Before you patch up those cracks and holes, don’t forget to check if the structure of your lath or wiring has been compromised. If they’re misshapen or damaged in any form, carry out the necessary repairs so that your patching and filling material will hold.

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