How and with what to plaster a bathroom?

A bathroom’s plastering is an essential component of any remodeling project. It not only makes your walls look better, but it also has a big impact on how long-lasting and moisture-resistant they are. Selecting the appropriate tools and methods can have a significant impact on the outcome.

Bathrooms are unusual spaces with a lot of humidity and sudden temperature swings. Plastering materials must be carefully chosen in light of these conditions. Because traditional plaster can easily develop mold and mildew, it might not always be the best option. The use of specialty plasters made to resist moisture is advised instead.

There are several options available, such as waterproof gypsum plasters and plasters based on cement. Each has a unique set of benefits and works well in certain bathroom areas. For example, plasters based on cement are very long-lasting and perfect for surfaces like shower walls that are in direct contact with water. However, waterproof gypsum plasters work well for upper walls and ceilings because they are simpler to apply and leave a smooth finish.

It’s crucial to prepare the surface properly in addition to selecting the appropriate plaster. This include giving the walls a thorough cleaning and, if required, priming them. A smooth, durable finish can be achieved by applying plaster in thin, even layers and giving each coat enough time to dry.

Although plastering a bathroom may seem like a difficult undertaking, it is possible to complete it successfully with the appropriate tools and methods. Knowing the fundamentals will enable you to achieve a stunning and long-lasting bathroom finish, whether you choose to do it yourself or hire an expert.

Step Description
1. Choose Plaster Type Select a waterproof plaster suitable for bathrooms, such as cement-based or lime-based plaster.
2. Prepare Surface Clean the bathroom walls thoroughly, removing any dirt, grease, or old paint.
3. Apply Primer Use a primer to create a good bond between the plaster and the wall surface.
4. Mix Plaster Follow the manufacturer"s instructions to mix the plaster to the right consistency.
5. Apply Plaster Using a trowel, spread the plaster evenly on the walls, starting from the bottom and working upwards.
6. Smooth Surface Use a float to smooth the plaster surface and remove any excess material.
7. Let Dry Allow the plaster to dry completely before applying any paint or tiles.
8. Final Touches Check for any imperfections and sand them down if necessary before finishing.

It’s important to use plastering techniques and materials that can tolerate high humidity and frequent exposure to water when plastering a bathroom. For better water resistance, consider cement-based or lime plasters instead of traditional gypsum plaster in this setting. A thorough preparation, which includes priming and sealing the walls, guarantees that the plaster will stick well and endure longer. The walls can be further shielded from moisture damage by applying waterproof finishes and additives, guaranteeing a long-lasting and appealing bathroom finish.

Why do you need to plaster the walls in the bathroom?

Professional builders and even inexperienced repairmen are aware that even the smallest imperfections in the wall beneath the paint are not only noticeable, but also stand out. Plastering the bathroom walls prior to painting is therefore required; this isn’t even debatable. However, many finishers—especially those who are new to the trade—avoid doing labor-intensive and dirty work on plaster surfaces beneath the tiles. They use tile adhesive to level the plane of the walls.

It is feasible in theory. But what will the outcome ultimately be? First, when a thick layer of tile adhesive is applied, the tile "floats" down the wall because the adhesive mass is moving. Second, the tiles either come off the wall or are drawn to it because of the adhesive’s shrinkage, which disturbs the finish’s flatness and usually results in a simple crack. Thirdly, the cost of repairs is increased because tile adhesive is significantly more expensive than plaster mixtures. Fourthly, the plaster dries much faster when a wall is adhered to in multiple layers, delaying the repair time.

Types of plaster for the bathroom

Builders use a wide variety of plaster mixtures to level walls (see work: "Plastering wooden walls inside a house with your own hands"). Grouts made of cement and gypsum work well in bathrooms. This is because of the unique microclimate in the space, which includes abrupt temperature swings and increased humidity.

Gypsum-based plaster initially cannot be used in such conditions (high humidity) because it is afraid of moisture. However, things are a little different in reality. Thus, we will take into account the advantages and disadvantages of the various solutions as well as their operational circumstances when deciding which plaster to use in the bathroom.

Cement plaster

Portland cement serves as the primary binding agent in cement plaster mortar, while fine river sand acts as a filler and a plasticizer (either gypsum or slaked lime).

TO experts This composition might contain:

  • versatility – no restrictions on use;
  • strength – withstands the heaviest loads of all types of plaster;
  • moisture resistance – the surface is not permeable to water vapor;
  • durability;
  • plasticity – can be rubbed into any crevice;
  • affordable price.

Furthermore, it is imperative to emphasize a crucial characteristic, such as the capacity to retain fluidity for an extended period of time, enabling you to promptly prepare a substantial amount of solution without worrying about it solidifying.

Among the flaws, note:

  • the solution has poor adhesion to concrete (relative minus – completely disappears after treating the concrete surface with the Betonokontakt primer);
  • dries for a very long time, which reduces the pace of repair work (the use of ready-made dry mixtures from well-known companies reduces this time significantly);
  • increase in room humidity – to accelerate crystallization, the surface of the plaster layer must be regularly moistened, which leads to an increase in the amount of moisture in the air;
  • the surface has a gray, nondescript appearance (for tiles and painting this drawback does not matter);
  • mandatory filling of the top layer of plaster (not carried out under tiles);
  • the surface is covered with a fine network of cracks (introducing fiber into the plaster solution eliminates the problem, as you can read about in the material: “Floor screed with fiber fiber”).

In summary, cement-based plaster is nearly perfect for bathrooms.

Gypsum plaster

The primary ingredient in gypsum plaster is a naturally occurring mineral called "gypsum" that is obtained by heat treatment and belongs to the sulfate class. Two types of material can be produced in this situation: alabaster with granular granules and selenite, which is actually what we mean when we refer to gypsum because the powder particles have a fibrous structure.

In addition to gypsum, the mixture also contains fillers made of natural or synthetic materials, which increase the strength of the plaster layer and decrease the amount of costly gypsum in the mixture; polymer additives also increase the plasticity and adhesion of the solution.

TO is meritorious Experts call plasters made of gypsum as:

  • high level of adhesion to any wall material;
  • manufacturability – the solution fits well on the wall and is leveled, which allows beginners in finishing work to more easily cope with plastering walls;
  • no finishing putty is required – the gypsum surface is immediately ready for wallpapering, and after sanding – for painting or whitewashing;
  • the ability to lay a plaster layer up to 6 cm thick, which speeds up work;
  • improvement of heat and sound insulation properties of walls;
  • lower consumption compared to cement mortar.

There are also shortcomings, which are also noteworthy:

  • porous structure – it will not be possible to lay gypsum as a monolithic mass. There will always be cavities and pores;
  • the ability to absorb and quickly release moisture, which is greatly helped by porosity. If a certain level of humidity is exceeded, water softens the solution, which leads to damage to the plaster layer, and in some cases to the appearance of fungus and mold. It is this point that raises the question of whether it is possible to use gypsum plaster in the bathroom;

  • low strength: does not hold heavy porcelain tiles well and is subject to destruction when subjected to pinpoint impacts (dents remain or chips form);
  • sets quickly – you need to prepare small portions;
  • Almost 2 times more expensive than cement mortar;
  • upon contact with tile adhesive, there is a high probability of the formation of ettringite – a mineral that destroys gypsum.

The solution’s shortcomings make it evident that the answer to the query, "Is it possible to plaster a bathroom with gypsum plaster?" is no. Nevertheless, in reality, gypsum mortar is frequently used to plaster walls in highly humid rooms, disregarding the need for moisture-resistant plaster in bathrooms. We’ll investigate the reason behind this below.

The best way to plaster the walls in the bathroom

There are particular requirements for plaster mortars because of the bathroom’s microclimate. They had to have:

  • resistance to high humidity;
  • resistance to sudden temperature changes;
  • environmental safety.

The aforementioned requirements are crucial, but the choice of finishing material—paint or tile—determines how to plaster the bathroom walls.

Under tiles

The bathroom walls beneath the tiles are plastered using a cement or gypsum-based solution. The strengths and weaknesses of this kind of solution make it evident that there is no need for commentary regarding the use of cement-sand mixtures. But there needs to be a reason for using plaster made of gypsum.

Three issues arise with gypsum mortar when it is used beneath tiles in moist areas:

  1. high probability of destruction under prolonged exposure to moisture;
  2. low strength;
  3. formation of destructive material when interacting with tile adhesive called “ettringite”.

Problem areas are also known to manufacturers of gypsum plaster mixtures. Deep penetration primers consequently made their appearance on the building materials market. Using this primer on walls enables you to:

  • stop surface pores of plaster;
  • create a waterproof film on the surface;
  • increase the strength of the plaster layer;
  • improve the adhesion of tile adhesive to gypsum;
  • block the possibility of ettringite formation (direct contact is prevented between the gypsum and glue – the primer film separates it);
  • additionally protect the wall from fungus and mold.

Additional barriers to prevent water from penetrating the plaster layer are created by silicone sealant, tiles, and glue. Gypsum is used to create waterproof plaster for the bathroom as a result of all the activities.

Plaster can perfectly withstand standard ceramic tiles if its surface is strengthened with a primer. The primary requirement in this instance is that the plaster layer’s thickness be limited to 2 cm over a sizable area (up to several m2), as this will increase the chance of the tile coming off.

In conclusion, it is difficult to determine which type of plaster is ideal for a bathroom with tiles underneath. The small details determine everything, including the availability of money, the timeliness of repairs, and the availability of plastering experience.

For painting

It’s not the cheapest finishing touch to paint the bathroom walls. First and foremost, you need perfectly level walls because any imperfections (such as holes, scratches, and concavities and convexities) will be visible through the paint. Further funding will be needed for the plaster to be finished and the walls to be puttied (tiles do not require these procedures). Second, only plaster mixtures made of dry cement and starting and finishing from reputable brands (Knauf, Cerozit, etc.) will guarantee high-quality work. You can create your own cement-sand mortar even on a tight budget.

Using other kinds of plaster solutions is not advised. Water can get through even moisture-resistant gypsum plaster that has been painted in a bathroom. The low strength of gypsum is the cause. Scratches and dents among other minor damage break the waterproofing film of primer and paint, turning the damaged area into a breeding ground for the slow, ongoing breakdown of the plaster layer.

In conclusion, plastering the walls with a cement-based solution alone is necessary before painting.

How to properly plaster bathroom walls

Plastering bathroom walls is done in the same way as with traditional technologies. consists of multiple steps (let’s use a cement-sand mixture as an example).

  • Old finishing is removed (in newly built houses such a technological operation is not necessary).
  • The wall is being repaired: loose bricks are removed, cracks, chips and potholes are sealed with repair mortar ("cement milk").
  • The surface is degreased and then primed with a deep penetration primer (for concrete it is necessary to use “Betonokontakt”).

As an example, applying "Betonokontakt" to different types of wall materials produces a nearly identical result at a significantly higher cost.

  • The point on each wall that protrudes into the room is determined by hanging it.
  • 3 cm is added to the found convexity, after which the plane of the plaster layer is constructed. The boundaries of the plaster can be fixed with beacons, which is very difficult (this technology is discussed in detail in the work “Plastering walls using beacons with your own hands”) or with chalk on the floor, ceiling and adjacent walls (a contour is applied), which can be read in detail in the material “How to level walls without beacons with your own hands". Note that a small area of ​​the walls allows even an inexperienced finisher to perform plastering work without beacons quite skillfully.
  • The necessary building materials are purchased, tools and devices are prepared (the types and purpose of each tool can be seen in the work “How to properly plaster a brick wall?").
  • Mix the spray solution with an equal ratio of cement and sand (proportion 1:1).

  • The first layer of plaster is applied a few millimeters thick (3-5) (its task is to ensure good adhesion of the leveling layer of mortar to the wall).
  • After the first layer has set, a leveling layer is applied (among plasterers it is called “primer”) with a solution with different proportions: Portland cement M500 (1 part) and sand (3 parts).
  • The wall is first plastered in a small area in the corner. Then successively in small sections around the entire perimeter. The level and the rule control the plane of the plaster horizontally and vertically. A reference point is a contour applied to the floor and walls. After the first row is looped, everything continues in the same sequence.
  • For tiles, plastering work ends here. The final stages are carried out before painting: a finishing layer of plaster (2-3 mm), called “covering”, is applied, and then grouting is carried out.
  • The process is completed by filling the surface with polymer compounds (they are not afraid of water), after which the wall is sanded with fine sandpaper (P100).

In order to achieve a durable and moisture-resistant finish, plastering a bathroom requires careful consideration of both materials and techniques. Choosing the correct plaster is essential; for managing the damp atmosphere typical of bathrooms, products such as moisture-resistant drywall or cement-based plasters are perfect.

Just as crucial is the walls’ proper preparation. Plaster will adhere more readily if the surface is clear, smooth, and devoid of any loose materials. Adhesion can be improved and an additional layer of moisture protection can be added by applying an appropriate primer.

The application procedure itself needs to be completed carefully. The quality of the finish will be greatly affected by the use of the right tools and methods. Not only does a smooth and even application look better, but it also offers a better seal against moisture.

In the end, spending time and energy selecting the appropriate materials and applying them correctly will result in a long-lasting and lovely bathroom finish. Whether you choose to do the plastering yourself or hire an expert, adhering to these tips will help guarantee a plastering job that is successful and resilient enough to withstand the rigors of a bathroom setting.

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Timur Kiselev

Professional builder with 15 years of experience. I know everything about the construction of houses, cottages, bathhouses and other buildings. I will be happy to share my knowledge and experience with you.

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