How to seal cracks in plaster on the wall with your own hands

Plaster cracks are not only an eyesore; they may indicate more serious problems with your walls. Ignoring these cracks—which may be brought on by settling foundations, moisture, or temperature fluctuations—may eventually cause more serious issues.

The good news is that expert assistance isn’t always necessary to seal these cracks. You can save time and money by doing the repairs yourself if you have the correct tools and techniques.

You can repair your walls and stop more damage by following this guide, which will show you how to seal plaster cracks. Now let’s get going!

Methods and technology for sealing cracks

If there are many cracks but the coating is weak, the wall is cleaned and the old finish is removed. They are covered if there aren’t many cracks.

There are two primary techniques for plaster crack sealing:

1. filling with mortar
2. sealant.

In any event, we begin by making preparations, which consist of:

• grooving;
• removing debris from the crack cavity;
• tapping (with a wooden handle of a hammer) the nearby coating and removing the lagging (you will need a hammer and chisel);
• replacing unusable laths (if the plaster was made on wood);
• remove dust with a vacuum cleaner or a damp brush;
• degrease and wash the area;
• dry.

Using a sealant

The sealant’s quick polymerization is what makes it so popular. Because of the sealant’s flexible composition, which allows it to fit into even the smallest cracks, wall plaster cracks are frequently sealed with it. Furthermore, the sealant maintains its elasticity and can shrink with the gap walls as they dry. Verify that the chosen sealant and the plaster mix’s binder component work well together before sealing.

If the plaster coating’s composition is unknown, the sealant’s compatibility with it is examined in a discrete location.

Using a sealant to close the defect is a simple process:

• fill the prepared crack with a small portion of the sealant;
• fill the gap with a spatula (or another convenient tool, even just a finger), and compact the sealant;
• remove excess with a spatula;
• wet a rag with a soap solution, wipe the surface around the crack;
• let the sealant dry;
• stick a painter"s mesh over the sealed crack and apply putty.

When applying the sealant, put on gloves and safety glasses to prevent injury. Without the use of solvents, it is challenging to remove sealant that gets on the skin.

Sealing with plaster mortar

Plaster mortar takes several days to dry, in contrast to sealants. But this product is more affordable and readily available.

The following is the order in which to seal cracks:

1. removal of damaged areas;
2. reinforcement;
3. primer;
4. filling with plaster;
5. grout.

If the area that needs to be repaired is large after tapping and removing useless plaster coating layers, the area is reinforced with mesh (either metal or synthetic). The mesh is positioned in the middle of the solution layer after being cut out to match the area’s contour. Before the mesh is installed, the area is primed.

You will need a paintbrush, grout, and a spatula to repair damage. Apply the diluted plaster mixture to the area with a spatula. The void is completely filled, smoothed over, and any excess removed.

Long cracks are drilled with a dowel hole every 30 centimeters (dowels cannot be driven in).

At a deep depth, mortar sealing is done in two passes to prevent the buildup of a thick layer. Using a spatula, the main layer is cleared of protrusions and pellets once it has solidified. The dried layer’s surface is primed. After the primer has dried and been sanded, a finishing layer is applied.

In order to fix unstable cracks, metal connections between their edges are made using metal strips or staples. Mortar is used to seal it only after this.

You have to realize that caulking wall cracks in plaster is the same as eradicating the damage. To truly eliminate the emergence of new flaws, you must identify the root cause.

Why does plaster crack

Mineral plaster compositions that harden produce a coating that performs poorly in tension or bending situations but effectively resists compression. Even vibrations from a nearby railway can cause them to crack; this is especially true if the walls are distorted. Plaster cracks typically show up after wall cracks if the finishing coat is composed of elastic materials.

Apart from the shrinkage-induced deformation of the walls, there’s a chance that the plaster coating’s integrity is also weakened along with the wall surfaces’ integrity. Although the causes of plaster cracks can vary, they typically result from technological errors made during any stage of construction, finishing, or material selection. External factors, such as exposure to sunlight, can compromise the integrity of the plaster coating.

Violation of application technology

Even ancient architects developed sets of guidelines for working that prevented or minimized the occurrence of different defects, based on the findings of their analysis of the experience building and operating structures. This is how technologies emerged, and their infringements have a detrimental effect on the caliber of the output. Plaster mortar application technology considers even the smallest details to help avoid flaws from arising, like the ideal temperature for preparing, applying, and drying the composition. However, breaking these guidelines will necessitate caulking the fissures that form in a home or apartment’s plaster.

Let’s take the consequences of a technology violation when plastering drywall as an example. A network of tiny fissures in the plaster develops when a sheet of drywall is covered with an excessively thick layer of gypsum mixture or when the drying temperature is not met. It can no longer be sealed; a new gypsum composition, no thicker than 2 mm, will need to be applied after the plaster layer is completely removed. Once the first layer has dried, the second layer is applied if more thickness is required.

Poor surface preparation

Plastering requires different preparations depending on the type of wall and ceiling material. The adhesion of the coating to the base will be low if notches are not made before plastering concrete, the brick wall’s masonry joints are not expanded, grease stains are not removed, etc. The plaster layer will start to split and separate from the wall. If the wall is not dried before plastering, the same thing will occur. Moisture starts to erode the coating’s and the wall’s adhesion.

Plaster will unavoidably experience stress and cracks at the joints where dissimilar materials, like concrete and brick, are used in constructions, if the joints are not reinforced with mesh.

Neglect of the primer layer

Two issues are resolved by applying a primer: it improves adhesion and seals the base’s pores. High adhesion is necessary for heavy plaster coatings, and the strength of the mortar-to-wall bond will undoubtedly be impacted if a primer is not used.

Porous brick, cellular concrete, and other wall materials will start to absorb water as soon as the solution touches them if their pores—even tiny ones—are not sealed. This is essential for the processes of crystallization and polymerization, which are necessary to produce the hardness and strength of the coating.

One more subtlety. Not every solution’s composition gets along well with the base material; for instance, gypsum and cement react chemically when a gypsum plaster mixture is applied to concrete. The plaster layer expands and separates. Gypsum breaks down the cement layer from the inside out. It is not possible to apply lime plaster composition to gypsum due to differences in behavior during the hardening process. The volume of gypsum increases and that of lime decreases. A primer layer needs to be positioned between various materials if you need to connect them.

It is not advised to disregard the primer. As a result, it’s important to choose the primer composition carefully in addition to applying the primer mixture correctly and applying the appropriate number of layers. The manufacturer’s recommended drying time is spent with each coat of primer.

Processing the wall with only one layer

It is required to apply the coating in multiple layers. When the layer is extremely thick, the surface dries sooner and, as a result, there isn’t enough carbon dioxide in the air for the solution inside to harden. It thus hardens gradually over an extended period of time. There is an emergence of an uneven physical state that is prone to cracking. This unevenness is greatly diminished by splitting the thickness into multiple layers. In this manner, the coating becomes stronger overall and the hardening of individual layers happens more readily.

A freshly made solution with a lot of water weights a lot. When a thick layer is applied, the lower masses next to the wall are unable to support the weight and tend to slide down. A weak bond forms during the drying process, and when the plaster cracks, the layer easily separates from the base.

Ensuring the adhesion of the upper layers of the coating to the base material is the second reason layered plastering is used. Forced spray does not slide down the wall because it adheres to the base more firmly and weighs less. It dries fast because it is applied and made thinner. It adheres to the thicker-mixed primer more firmly, giving the impression that it is natural.

A thin layer of the topcoat is applied, and it is made thinner. Its integrity is no longer negatively impacted by the underlying dry layer. When a fresh layer is applied after the bottom of the previous one has dried, the coating becomes the most resilient.

Use of a low-quality or old mixture

Low-quality plaster is defined as having components or proportions that do not match the specifications. Such fixes don’t work very long. For instance, the solution behaves like fatty clay and bursts when drying if the cement content of the cement-sand mortar exceeds one-third of the sand volume. Less content won’t offer the necessary strength. Such a mixture is regarded as being of low quality since silt particles enter the composition along with unwashed sand, weakening the coating.

The condition of the binder, such as cement, which loses activity over time, affects the shelf life of SS (or dry mixes). Solutions made from an out-of-date composition lose strength. Use only mixtures whose shelf life has not yet run out.

A mixture that has too much or too little water in it is not really appropriate. The strength of the final finish decreases when there is insufficient liquid because chemical reactions require water. Excess prolongs the drying period, stops the solution from sticking to the wall without sliding, and interferes with the creation of crystalline bonds and strength gain with free water molecules.

Incorrect mixing of the solution

The proper order and method of mixing the solution also have an impact on its quality, which in turn influences how long the coating will last. The mixing instructions for the mixture should be followed before applying. Lump formation and undermixing can occur from not loading the components into the container in the correct order, which ruins the solution. It is not acceptable to use a lot of mixer revolutions, particularly when combining silicate compositions.

• mixing order;
• gradual introduction of components (all or in small portions);
• mixing speed;
• temperature of added water;
• standing time;
• consistency;
• periodic mixing of the solution during application (to lift the settling heavy particles).

Absence of a reinforcing frame

Reinforcement is required when applying the composition in a thick layer (greater than 30 mm). The mesh stops the solution from shrinking or bursting from different shear stresses during operation and hardening, as well as from sliding during application and hardening. At the joints between structures, mesh is also necessary, particularly when joining dissimilar materials. Plastering insulation requires the plaster layer to have bending strength, which is provided by reinforcement.

When plastering wood, a mesh of shingles also acts as reinforcement. The planks shouldn’t have more than 5 mm of thick sawn edges. The shingles must have a minimum mortar thickness layer applied to them to prevent cracking. Air pockets are prevented from forming in the corners and beneath the upper shingles by applying the composition in this manner.

Dust and debris on the walls

Failure to complete a crucial step like cleaning the walls of a layer of paint, whitewash, grease stains, dust, mold, and mildew can result in the coating cracking and peeling. In the event that the wall’s bricks were, say, removed from a stove chimney, it is essential to neutralize and remove any soot from them. Paint, soot, grease stains, and dust all hinder the solution’s ability to adhere to the wall.

Sun rays

The effects on the drying solution are more detrimental when plastering external surfaces. Even the mortar becomes obstructed by sunlight.

Sunlight intensely evaporates moisture from the hardening composition by raising its temperature. Increased internal stresses during shrinkage are a result of rapid drying.

A lack of water and an uneven layer’s drying cause cracks to form. The situation is saved by providing regular moisture and shade for the drying composition. To shield it from the sun’s rays, the container containing the solution is also set in the shade.

Moisture ingress

There may be too much liquid in the plaster mortar when:

• non-compliance with the recipe (too liquid consistency);
• abundant wetting of the base;
• undried, wet walls;
• carrying out finishing work in conditions of humidity over 75%;
• a large difference in the vapor permeability of the base and finish.

One or more cracks may appear as a result of any of these infractions. During operation, there is a risk of cracks and moisture penetration in addition to too much water entering the solution. The appearance of "wandering" moisture must be avoided. For this reason, finishing work is done after waterproofing, and the sequence in which external and interior surfaces are plastered is followed.

Cracks when load-bearing structures are damaged

Load-bearing structures may deform for a variety of reasons, and historically older buildings are particularly vulnerable to them. Consequently, the plaster on the ceiling and walls begins to fracture.

It is necessary to examine the structural integrity of the wall if, upon examination of the cracks (after the finishing in the affected area is removed), it is discovered that the cracks extend into the base material.

Determine the extent of the damage first, then fortify the walls to avoid being left with nothing but rubble. Don’t do the new finishing until afterwards. They also follow the fundamental guideline, which states that the base’s strength must be greater than the coating’s strength.

Cracks due to foundation deformation

If the application and preparation guidelines are followed but the finish still cracks, foundation deformation could be the reason. Investigating the causes and strengthening the building’s foundation are essential. All crack sealing is ineffective without it.

Shrinkage of the building

Within a year, new construction shrinks (at least). The cause could be attributed to the building’s base settling as well as the structures’ own shrinkage during the drying process, such as brickwork mortar. Consequently, it is best to use elastic compounds for plastering at this time or to postpone using mineral compounds until it is feasible.

Why does plaster crack when drying

Cracking occurs in the solution during the drying process for a variety of reasons. The primary contributing factor is the occurrence of internal stresses caused by shrinkage, which in turn depends on the proper operation of every technological link in the chain before the composition reaches the complete drying phase.

After everything has been correctly mixed, applied, and prepared, the only thing left to do is to watch the curing conditions. This entails monitoring the environment’s temperature and humidity while staying within the manufacturer’s recommended range. The hardening layer must also be shielded from sunlight and drafts.

General principles and rules of repair

We now have complete knowledge on how to patch plaster cracks in walls. Crack sealing is a process as well, and if certain guidelines are broken, new flaws could emerge.

Plastering follows the guidelines:

• we start repairing cracks caused by shrinkage of the structure, having repaired the supporting structures or having waited for the end of natural stabilization, otherwise the new coating may also soon crack;
• cracks that appeared due to dampness and high humidity are repaired after eliminating the causes;
• We do not cover up broken plaster of poor quality, but clean it off the walls and replace it with new one;
• we are looking for the same manufacturer and brand of the same compositions for repairs as in the old coating (if impossible, we select those with similar properties);
• if we apply a cement coating, we do it without interruptions on the entire wall in one pass;
• repairs (outdoor and indoor) are carried out at a plus temperature range of 5 – 35 o C, humidity up to 80%;
• when choosing a composition, we focus on those whose vapor permeability is the same or higher than that of the base material;
• if gypsum concrete partitions are made up of two layers of slabs, we connect them to each other with bolts placed in the middle of the slab in a row at a distance of 1.5-2 m (along the entire length of the partition).

Step	Description
1. Clean the Crack	Remove any loose plaster and dust from the crack using a brush or vacuum.
2. Apply Filler	Use a putty knife to apply a patching compound or plaster filler into the crack, pressing firmly.
3. Smooth the Surface	Level the filler with the surrounding wall by smoothing it with the putty knife.
4. Allow to Dry	Let the filler dry completely as per the manufacturer"s instructions.
5. Sand the Area	Once dry, sand the area lightly to achieve a smooth finish that blends with the wall.
6. Repaint	Touch up the repaired area with paint that matches the existing wall color.

Plaster crack sealing may appear like a difficult undertaking, but with the appropriate method, it’s a task you can confidently take on by yourself. It is possible to return your walls to their original smooth finish by identifying the kind of crack you are dealing with and taking the appropriate action.

It’s important to take your time when preparing because it will ensure a durable repair. To ensure a professional-looking outcome, clean the crack, apply a suitable filler, and finish with sanding and painting. Quality work is always worth the extra effort, so don’t rush the process.

You can avoid costly repairs and enjoy the satisfaction of doing your own home maintenance by adhering to these easy steps. Those ugly cracks can be eliminated with a little perseverance and attention to detail.

Anyone can seal plaster cracks on their own; all it takes is a few simple tools and materials and an easy process. Whether there are tiny fissures or more noticeable spaces, fixing them right away will stop additional harm and bring back your walls’ smooth surface. This tutorial will provide you with clear, step-by-step instructions on how to locate the source of the cracks, get the area ready, and use the appropriate methods to accomplish a flawless repair.

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