How to Repair Hairline Cracks & Holes in Plaster Walls

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 it gone kaputt?

Do I need to replace it altogether?

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

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

Yes, you can patch it 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 it is and how it’s made, before we get started on how to repair those hairline cracks in plaster walls.

What is plaster?

If properly mixed, it can provide a more durable finish than even drywall. In the early days, it was 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, it 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?

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 of it is that it tends to absorb water easily, increasing the risk of water damage. Also, repairing it 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 it has is that it provides better sound and temperature insulation. One major issue with it is that it cracks more easily. Without using top-grade construction materials, installing it can be complicated and messy. And when not installed correctly, the joints between the sheets tend to show, thus ruining the surface’s smooth and seamless appearance.

Okay, then. But how is plaster wall made?

It is durable, not because of the material it’s made of, but because of the way it’s constructed. It is made of flexible material you can mesh together, allowing you to create a multi-layered coat 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 wall. Three coats are then applied to the lath in an interlocking manner, resulting in a structural system that holds the wall together. Also, by layering three coats together, you’re getting a system with good insulation for temperate and sound.

The 3-coat system is comprised of the scratch coat, brown coat, finish coat. The scratch coat serves as the 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 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 they happen 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, it is a line that appears along the surface of a wall (not just plaster), indicating a split that appears as if it 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.

They 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 it. For instance, a construction professional might forget to rake the background surface before applying plaster on it. Another possible scenario is when he or she overlays it without applying chicken wire mesh in the masonry first.

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

Seasonal changes

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

Shrinkage

Water from freshly applied plaster has a tendency to evaporate rapidly, reducing the surface layer’s volume. This volume reduction causes it to shrink, resulting in the formation of cracks in the surface layer. To prevent shrinkage 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. 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. Ones caused by corrosion can even more annoying than the regular ones because of its rusty color.

Foundation shifts

Natural disasters such as earthquakes, hurricanes, and floods can produce stresses in the foundation of the wall, causing cracks not just on the surface but also the structure itself. Ones 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. 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. They are usually vertical and are likely to run along the home’s exterior. Ones caused by settlements are not to be taken lightly because they may lead to structural problems. It will be wise to have them investigated immediately upon discovery to ensure that the structure of the home hasn’t been compromised in any way.

Fixing lead-painted plaster

Before you start repairing any cracks or holes, 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 wall was painted before 1978, it’s highly likely that the paint contains lead.

Thankfully, all you need to do to check the presence of lead 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 it is about to break away from the lath? Simple: give it 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 it feels like it’s going to hold, then good on you. However, you still need to patch it up. Here are the steps to do that:

  1. Widen it.

The first step to fixing a small crack 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 dust.

Clear the affected area of 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 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

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 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 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 area. 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.

  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 washers into the holes by driving a 2” drywall screw into each one.
  1. Leave the adhesive to dry before removing the washers.
  1. Patch it up 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

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

Nails popping out

When a nail is not hammered right in the center of a joist or stud, it has a tendency to pop through the 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 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 wall for too long, it can cause the material to soften or loose. Allow that amount of moisture to have its way for too long and it will eventually damage it, 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 wall an ideal target for infestation. Once these critters gain access to the insides, they can do a significant amount of damage.

There are many signs to watch out for indicating that termites have invaded your walls, such as pinholes, hollow sounds, bubbling, 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 the 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 one behind it to crack open.

Damage from furniture

Moving around heavy furniture inside the home’s interior can cause scuff marks. These scuff marks weaken the 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. 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 area. 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 It

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 it like a true professional.

Mistake #1: Painting over it 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, it 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 it up 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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