What is "mortar"? Differences from concrete and points to note.

1-1. Mortar applications

• Finishing material Mortar is a soft, fine-textured material used mainly as a "finishing material" for walls and floors. Mortar can be finished in various patterns, such as by stretching it with a trowel or by daring to express unevenness in the application. It is also used for furniture tops and fixtures.
• Jointing material Because of its high adhesive strength, it is also used as a "jointing material" when tiling or piling bricks.
• Base material Because it can create a smooth surface, it is sometimes used as a base material before painting or applying cloth.

1-2. Mortar types

There are several types of mortar. Here we will discuss some of the most common ones.

• Cement mortar The least expensive, most commonly used, and most common mortar.
• Non-shrinking mortar (repairing material) Mortar that does not shrink when it sets and does not crack. It is less viscous and drier than cement mortar, and is used to fill gaps in concrete walls and to repair cracks that have occurred. Because of its high cost, it is rarely used extensively.
• Polymer cement mortar (base material) A cement mortar to which a polymer is added. It is often used as a base material because of its higher impact resistance and adhesiveness compared to cement mortar.
• Resin mortar (finishing and repairing material) Mortar using resin instead of cement. Because it is elastic, crack-resistant, and waterproof feature, it is often used in kitchen, vanity tops, and other water-using areas. Since its high performance comes at a high cost, it is recommended to incorporate it at key points in accordance with the intended use.
• Instant mortar Type of mortar which is a mixture of cement and sand that can be used simply by mixing with water. It is often used in DIY projects because it is easy to handle.
• Color mortar Mortar that is colored by mixing pigments with white cement is called colored mortar. Ordinary cement is gray because it contains iron. However, when pigments are added to gray cement, the coloring is not good, so white cement with minimal iron content has been introduced. Japanese-style buildings, for example, sometimes use "sumi mortar," which is a general gray mortar mixed with sumi(charcoal) ink to make it blackish.

1-3. Difference from concrete

The main difference between mortar and concrete is material and usage. The difference is whether or not sand (fine aggregate) is included. Concrete is made of cement + sand (fine aggregate) + gravel (coarse aggregate) + water. In other words, concrete is mortal + gravel (coarse aggregate). Gravel here refers to large pieces of gravel with a diameter of 5 mm or more. The gravel in concrete is combined with cement, making it more resistant to cracking than mortar. When reinforcing steel bars are added, the result is "reinforced concrete," which is used for building columns, beams, walls, and other structure. When gravel is added, the texture is rougher and more rugged than that of mortar.

2-1. High design quality

Above all, its high design quality is the secret of its popularity. It is a versatile material that blends easily into any space and can be finished in a stylish manner. One way of finishing can completely change the impression, from a modern look to a gentle atmosphere. In particular, "hand-rubbed" plastering, which is done by hand using a trowel, requires a high level of skill, and it is said that it takes a long time for a plasterer to become a full-fledged plasterer. The wide variety of finishing patterns makes it a very deep industry.

2-2. Fire-resistant

Mortar is made of cement and sand, which makes it fire-resistant. For this reason, it is also recognized as a "fire-resistant" or "fireproof" structure, which is required for exterior walls in urban areas.

2-3. Relatively inexpensive construction

Another advantage is that it is cost-effective. Because of the low cost of materials, mortar can be installed at a lower cost than tiling or flooring the floor. However, the cost can be higher if you are particular about the paint pattern or use high-performance mortars such as no-shrink mortar or resin mortar.

3-1. Prone to cracking

Although mortar replaces some of the cement with sand, the risk of cracking is inevitable. Cracks on the surface are not that much of a problem, but if there is a large crack on the exterior walls, rainwater can penetrate into the walls, causing deterioration and leaks. The skill of the installer will affect not only the finish but also the durability, so be careful when selecting a contractor.

3-2. Requires regular maintenance

Regular maintenance is necessary to prevent deterioration due to cracks, stains, and mold; we recommend that you have the builder inspect the site once every 10 years or so to repair or repaint. However, when there are large cracks of about 1 mm in width, there is a risk of leaks, so it is safer to repair them as soon as possible.

4-1. What is suitable for DIY?

• Repairing cracks (other than exterior walls) Minor cracks can be repaired by ourselves. We recommend using a product in a tube called "repair material." However, cracks on the exterior walls should be looked at by the builder, as there is a risk of leaks.
• Block piling Piling blocks to create flowerbeds and other exterior structures is one of the easiest DIY projects. However, when stacking blocks high, there is a risk of them falling over, so it is best to ask a professional to do the job.
• Part of an interior wall Mortar begins to harden at the water-mixing stage, so it must be worked quickly. It is not recommended to make a lot of mortar at once, so it is best to try a small area first.
• Making small objects Since you can freely create shapes, making flowerpots, objets d'art, and small objects in mortar is recommended.

4-2. What is not suitable for DIY?

• Interior walls (e.g., one large surface) If mortar is applied in several coats, the color may be uneven or the finish may vary depending on the area coated, and in some cases the finish may not be very beautiful. When applying mortar to a large area, it is recommended to have a professional do the work, as speedy and clean application is required.
• Exterior Walls The exterior walls are an important part of a house's performance. Since many processes and advanced techniques are required to protect the house from the wind and rain, leave it to a professional installer.
• Floors The floor finish is particularly prone to cracking. To prevent cracks as much as possible, we recommend laying mortar with a thickness of 2~3 cm and placing reinforcing wire mesh inside. A considerable amount of mortar is required, so leave this to the installer as well.

5-1. Floor

大島の住宅 ( architect：Yoshihiro Kono )

The floor of an entryway or mudroom space is one of the easiest places to incorporate mortar. In this example, a fireplace and plants are placed in the mortar earthen floor area, and the area is used like a terrace connected to the outside. We also recommend that the mortar earthen floor is easy to clean.

Stir ( architect：Ryu Mitarai )

When an entire floor is finished with mortar, it is possible to create a semi-outdoor, which is the open space. In this case, a carpet is laid on the mortar floor to create a place for each person. To preserve the soft texture of the mortar, a matte finish was chosen.

MA Residence ( architect：Eitaro Satake )

The living room is reminiscent of an overseas gallery. Not only the floor, but also the TV board is finished with mortar. Just by painting it with a wet glossy finish, it gives a cool and modern impression at once. Even the cracks in the mortar have a taste and fit in well with the space.

5-2. Interior walls

slash house　キッチンから生まれるリノベーション ( architect：Munenori Matsuo & Haruka Matsuo )

One of the interior walls is mortared as an interior accent. Mortar walls go well with wooden furniture and greens. It creates a natural and soft atmosphere.

Crown Heights Garden ( architect：Yoshiki Matsuda )

This is an example of a plasterer's work with an uneven application of paint. Line lighting illuminates the mortar wall, bringing out the shadows of the plaster patterns. The space is simple and modern, but with the warmth of handcraftsmanship.

surround house　団欒を囲う家 ( architect：Munenori Matsuo & Haruka Matsuo )

This is an example of colored mortar. The space is characterized by soft colors with green tints. It is fire-resistant, so it can be used around the stove without any problems.

5-3. Exterior walls

「 T 」型のボリューム ( architect：Hironobu Hosaka )

Mortar can be used for exterior walls to create a seamless, simple, and clean finish. In this case, two types of mortar, a common gray mortar and a black-tinted one, are effectively combined to create sharpness and a sense of depth.

ガレージハウス ｜ House with a garage ( architect：Takanori Ihara )

White is the best color to choose for a cleaner look. By using a beige-toned white instead of pure white, it is easier to blend in with the surrounding environment, and dirt will be less noticeable.