What Causes Plaster to Crack?

Plaster is widely used as a wall covering because it is durable, does not absorb sound, and is resistant to fire and mould. Why then would a material with such high strength and durability fall out of favour?

Those who live in homes built before the 1950s will be familiar with the problem of plaster cracking, as it was a prevalent wall material until then.

Plaster can have many different ingredients, but the most common ones are water, sand, lime, and even horsehair. Contractors apply plaster to walls and ceilings by spreading a paste-like mixture. It can be applied thinly for a smooth finish, or thickly to create textured patterns. When the mixture dries, it becomes brittle and hard as a rock.

The good news is that most cracks in plaster are merely cosmetic and won't lead to any structural issues. However, if you want to be sure, you can have local plaster companies inspect any new or unusual cracks.

Plaster Cracks: What Causes Them?

Examining the interior of a cracked plaster wall can provide light on the problem. Plaster walls require horizontal lathes of wood to be attached across the studs. Next, plaster is put, and it seeps between the laths and into the spaces behind them.

The plaster used to cover and conceal the lath strips is known as the "key," and its hardened form is used to secure the strips into place. The key secures the lath and plaster boards. Another couple of plaster coats are then applied and smoothed over the top. There are a lot of fragile layers there that may break if the house shifted or if the wall was disturbed.

Plastering, first and foremost, is not the most malleable material due to its rigid composition. Plaster allows for some interesting design possibilities, especially when it comes to texture, but it has a tendency to break apart. Rapid fluctuations in the temperature, expansion, or contraction of a house are usually to blame for this kind of damage. While this is a common problem with plaster, there are ways to avoid it.

Older homes often have issues with plaster cracking. Several factors contribute to this phenomenon. Causes of cracks include temperature changes, foundation or sill work settlement, and prolonged contact with moisture. The depth of a crack varies from plastering to plastering.

But that's not the whole story. The following are some of the most frequent causes of plaster cracks:

• Shrinkage of plastering
• Debonding
• Dry shrinkage
• Grinning
• Structural cracks
• Popping
• Lack of hardness
• Expansion of plastering

Let's take a closer look at each of these.

Plastering Shrinkage

When humidity levels drop suddenly and dramatically, cracks known as plastic shrinkage cracking appear in walls and ceilings. Dehumidification is the process of removing moisture from an environment.

Dry Shrinkage

The liquid in plaster or stucco evaporates, causing dry-shrinkage fissures. Caused by the drying contraction of plant-based materials like cement and lime. These are stable, but you should fill them with filler before painting.

Structural Cracks

Foundation settlement, moisture expansion, brick wall contraction, and roof slab expansion are all contributors to structural fissures. These fissures typically manifest as parallel or perpendicular lines.

Debonding

The inner layer shrinks more quickly when it's dry, and the outer layer shrinks more quickly when it has sufficient ventilation, which is a problem with debonding. If you tap on a plastered wall, chances are there's a cavity behind it. The air pocket forms due to the disparity in thermal expansion between the outside and interior layers of plaster, which results in a hollow sound.

Grinning

When mortar joints are readily apparent through plaster, the walls have a grinning expression. The fundamental reason for this is the inability of brick walls to hold as much suction as cement mortar, which is used for plastering.

Inadequate Hardness

An excessive amount of sand and dust in cement mortar causes it to crack and be less durable. Because of the mixing of low-quality water and the addition of more water after the initial mixing, this occurs.

Popping

When there are impurities in the plastering mixture, the walls begin to pop. Conical bits of plaster break away from the surface as the popping occurs, leaving behind holes of varying sizes. It is frequently brought on by humidity and can be fixed by filling the holes with cement and painting over them.

Expansion Of Plastering

Plaster expansion is a moisture-related issue that can be avoided if caught early on. Wet wall coverings, poor ventilation, or persistently high ambient humidity all contribute to the problem. If this damage has already happened, it can be fixed by scraping off the existing plaster and replacing it with a more porous variety.

Weak Spots in Plaster

Plaster is especially likely to crack around structural elements such as door frames, windows, and floor joists in a stairwell.

As the earth moves, your house will eventually find a new level. Nevertheless, settling is not a friend to hard, brittle plaster. In its place, it breaks. A doorway or the framing could be potential weak points where a crack would begin. Sometimes it will spread in a straight line from there, but more often it will spread in a diagonal pattern.

Little fissures in a plaster wall are normal. Accidental wall damage is often the result of momentary inattention. Because of seasonal changes in temperature, certain cracks appear and disappear as the materials expand and contract.

There could be gaps at the frame's intersections with the floor, ceiling, and walls. This is because cracks mitigate the effects of settlement's stresses.

In order to prevent wet plaster from oozing and forming a key to keep it together, professionals will often nail lathes to solid wood in the void between floors. After some time, cracks begin to show up.

Another potential problem area for the plaster is the most sturdy part of the house. As the fireplace and chimney are made of stone, the room tends to revolve around them. This is why crevices frequently appear in the brickwork of chimneys and hearths.

New Cracks Can Indicate Foundation Issues

The majority of the settling of a house occurs in the first ten years. New plaster cracks in an older home may indicate a deeper problem with the structure's foundation. Cracks may be found in the subflooring of a building.

The presence of these could indicate a problem with the building's foundation.

The appearance of new cracks in walls after plastering is completed is an indication of possible foundation difficulties. Inadequate plaster mixing, improper application method, or a lack of drying time are just a few potential causes of cracks that occur immediately after plastering. But, additional fractures could indicate a more significant issue with the foundation if they persist.

A building's foundation is the underpinnings upon which it stands.

The walls may fracture or bulge if there is a problem with the foundation. As the walls move due to the foundation settling unevenly or shifting, the plaster can crack or buckle. This is especially true if the structure was constructed on sloping or otherwise unsteady ground.

Keep in mind that not all cracks mean there are problems with the foundation. Potential causes of fractures include temperature fluctuations and natural settlement. Nonetheless, it is preferable to have a professional evaluate the foundation if the cracks are wider than 1/8 inch or are growing in size. A structural engineer can determine what's causing the damage and give advice on how to fix it.

Why Does Drying Plaster Crack?

Plaster requires careful management of moisture levels. There is probably a moisture imbalance at the root of your project's cracking problems.

Drying plaster cracks for a few common reasons:

• There are chunky particles of sand or grain in the plaster mixture. This can be avoided by using a professional-grade mixer. This can lead to a separation between them and, ultimately, cracks in the plaster.
• Oxidation of the plaster might proceed more rapidly when it is exposed directly to sunshine. Cracks will form as the moisture is rapidly evaporated by the heat.
• Exposure to wind. Prolonged exposure to wind might result in excessive aeration, hastening the drying of plasters.
• Because the surrounding bricks can absorb moisture from the plaster, the material can dry more quickly in some cases. Because bricks are porous, it's likely that this will remove all the moisture.
• Surface re-painting before it has dried is a common mistake. Before you paint over an existing layer, make sure it has dried fully. As a result of the lack of ventilation, the paint would peel and crack.

Fixing Cracks in Plaster

Many houses and commercial structures utilise plaster as a wall and ceiling treatment.

Yet the foundation shifting, temperature swings, and moisture can all cause plaster to fracture over time. Wall or ceiling cracks like these are unsightly and may also be a sign of a structural problem. Plaster cracks should be repaired quickly to prevent severe structural damage.

Plaster cracks can be repaired by the homeowner, but a professional may be needed for more significant damage. Plaster cracks can be repaired if the underlying reason is identified. The plaster should be fixed only after the underlying cause of the crack has been fixed.

The crack can be fixed in a number of ways once the underlying reason has been identified.

Spackling paste or joint compound can be used to quickly and easily repair tiny cracks. Remove any loose debris from the fracture and its surrounding region by brushing it away or sucking it up with a vacuum.

The crack should be entirely filled with the joint compound or spackling paste before you apply it with a putty knife. In accordance with the manufacturer's directions, let the compound dry before sanding the area smooth.

A drywall fix may be required for wider cracks. Step one is to cut a piece of drywall that is just bigger than the hole. The remaining paper should be scored with a utility knife on the back of the drywall around the patch's perimeter.

Use some joint compound or spackling paste on the back of the patch and press it firmly into place over the crack. After the patch has dried, smooth away any ridges or excess compound. Once the compound has dried, you can sand it down to a smooth finish and add another coat if necessary.

It may be necessary to remove and replace the plaster in some areas. This is typically the case with cracks that are particularly long or frequent. In this instance, you should probably call in a professional plasterer to make sure the job gets done right.

How to Use a Sealant to Fill a Crack

Because it is not a perfect medium, the plaster will eventually crack. In the event that a small fracture forms in your plaster, you might be able to fix it yourself by following these instructions.

• Remove any dirt or debris from the area surrounding the split.
• Inject some glue into the split.
• The crack will be properly covered if the caulk is spread over it.
• Try it out for a while. The duration may change depending on the type of sealant you use.
• Apply as many layers as necessary to seal the gap.
• Layers that stick out too far can be smoothed out with some sandpaper.
• Please be patient; it will take time to complete, but the end result will be worth it.

Tips to Avoid Plaster Cracking

To get the best results from applying plaster, you should keep a few things in mind. Among these are:

• The usage of high-quality paint is essential, as low-quality paint typically leads to poor adherence. You shouldn't mix multiple brands together because that can cause the ingredients to separate.
• Professional mixers should be used so that the sand and other small particles are thoroughly combined. Similarly, a professional mixer can aid in the same process.
• Layer the plaster on carefully, using thin, successive coatings rather than slathering it on thick. Drying quicker, smoothing out, reducing cracking, and absorbing fewer air bubbles are all benefits of this.

Conclusion

Plaster is a popular choice for interior wall coverings due to its long lifespan, its ability to withstand heat and flame, and its resistance to mould and mildew. Water, sand, lime, and horsehair are the staples, but it can also contain other materials.

Plaster cracks are brought on by shifts in humidity, shifts in temperature, and shifts in the foundation or sill work.

A solution may be found by looking behind a cracked plaster wall. Plaster cracks are a common problem in older homes, but there are solutions to this problem.

Plaster shrinkage, debonding, dry shrinkage, grinning, structural cracks, popping, a lack of hardness, and expansion of plaster are the most common causes of plaster cracks.

Dry shrinkage results from the drying contraction of plant-based materials like cement and lime, while plaster shrinkage is brought on by a sudden and drastic decrease in humidity.

When the inner layer shrinks when dry more quickly than the outer layer does in a well-ventilated environment, debonding takes place.

Foundation settlement, moisture expansion, brick wall contraction, and roof slab expansion are all causes of structural cracks.

Popping occurs when there are contaminants in the plastering mixture and is easily fixed by patching the holes with cement and painting over them.

After the patch has dried, any bumps or excess compound can be smoothed out. A professional plasterer should be brought in to do the job properly if the crack is particularly long or common. Because cracks can form in plaster, it's important to use a sealant whenever the material is damaged. High-quality paint that has been mixed by professionals is necessary to prevent cracking. Plaster will dry faster, smooth out more easily, reduce cracking, and absorb fewer air bubbles if you apply it in thin, successive coatings rather than one thick layer.

Content Summary

• Plaster is widely used as a wall covering because it is durable, does not absorb sound, and is resistant to fire and mould.
• However, if you want to be sure, you can have local plaster companies inspect any new or unusual cracks.
• Examining the interior of a cracked plaster wall can provide light on the problem.
• While this is a common problem with plaster, there are ways to avoid it.
• When humidity levels drop suddenly and dramatically, cracks known as plastic shrinkage cracking appear in walls and ceilings.
• The liquid in plaster or stucco evaporates, causing dry-shrinkage fissures.
• When there are impurities in the plastering mixture, the walls begin to pop.
• Little fissures in a plaster wall are normal.
• There could be gaps at the frame's intersections with the floor, ceiling, and walls.
• Another potential problem area for the plaster is the most sturdy part of the house.
• The majority of the settling of a house occurs in the first ten years.
• New plaster cracks in an older home may indicate a deeper problem with the structure's foundation.
• Cracks may be found in the subflooring of a building.
• The presence of these could indicate a problem with the building's foundation.
• The appearance of new cracks in walls after plastering is completed is an indication of possible foundation difficulties.
• The walls may fracture or bulge if there is a problem with the foundation.
• Keep in mind that not all cracks mean there are problems with the foundation.
• Potential causes of fractures include temperature fluctuations and natural settlement.
• Nonetheless, it is preferable to have a professional evaluate the foundation if the cracks are wider than 1/8 inch or are growing in size.
• A structural engineer can determine what's causing the damage and give advice on how to fix it.
• There is probably a moisture imbalance at the root of your project's cracking problems.
• Drying plaster cracks for a few common reasons:There are chunky particles of sand or grain in the plaster mixture.
• Many houses and commercial structures utilise plaster as a wall and ceiling treatment.
• Yet the foundation shifting, temperature swings, and moisture can all cause plaster to fracture over time.
• Plaster cracks should be repaired quickly to prevent severe structural damage.
• The plaster should be fixed only after the underlying cause of the crack has been fixed.
• The crack should be entirely filled with the joint compound or spackling paste before you apply it with a putty knife.
• A drywall fix may be required for wider cracks.
• Step one is to cut a piece of drywall that is just bigger than the hole.
• Use some joint compound or spackling paste on the back of the patch and press it firmly into place over the crack.
• After the patch has dried, smooth away any ridges or excess compound.
• It may be necessary to remove and replace the plaster in some areas.
• Because it is not a perfect medium, plaster will eventually crack.
• In the event that a small fracture forms in your plaster, you might be able to fix it yourself by following these instructions.
• Remove any dirt or debris from the area surrounding the split.
• Inject some glue into the split.
• The duration may change depending on the type of sealant you use.
• Apply as many layers as necessary to seal the gap.
• To get the best results from applying plaster, you should keep a few things in mind.
• Layer the plaster on carefully, using thin, successive coatings rather than slathering it on thick.