Mortar vs. Plaster: Which to Choose?

Mortar vs. Plaster: Which to Choose?

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Though mortar and plaster are both used in modern construction, they have also been a vital part of building for many ages. Ingredients and mixing methods have changed throughout time, but the basic components and concepts have remained the same.

These materials each have unique benefits and advantages. They also have specific uses and generally shouldn’t be interchanged. We’ll clear up any confusion on the matter and define the practical uses for each.

Mortar and Plaster: The Basics

Before jumping into the differences, let’s start by taking a look at what each of the materials is.

What Is Mortar?

Mortar is used as a bonding agent that holds together building materials such as brick, concrete blocks, and other such substances. There are also special blends depending on what type of material you’re working with.

There isn’t a clear way to date how long mortar has been used in construction. Basic mud and clay mortars were used to build ancient structures, and eventually, it was discovered that lime could be added as a hardening agent.

It has been documented that lime mortar was used extensively in the construction of ancient Rome. It had a rigidness and strength that attributes to many ancient structures still being somewhat intact after so much time.

In the early 1800’s an English mason patented portland cement which was extremely durable but had low workability. Eventually, Portland cement was combined with lime mortar to create a balance of strength and workability.

Modern mortar typically consists of Portland cement, sand, hydrated lime, and water.

When combined properly, they create a highly workable substance that can be spread between the joints of various building materials, which will dry quickly and form a rigid, tough bond.

What Is Plaster?

Also commonly used in ancient civilizations, clay or gypsum plasters were spread over floors and walls to create a finishing seal on whatever they constructed.

The use of plaster has been found in ancient Asian cultures and in Egyptian tombs.

Plaster has seen many changes through the centuries, as new materials and methods were implemented to achieve unique visual effects and improve durability.

Plaster is basically reconstituted rock, spread over a surface such as a wall or ceiling. Modern plaster is typically made up of powdered lime or gypsum, sand, and water.

Reinforcement fibers used to be added to strengthen plaster, though it isn’t common now, as the texture of the reconstituted gypsum bonds together quite well.

Throughout history, this substance has not only been a means of finishing and decorating, but also a fire retardant and a common art medium.

Plaster has a few different applications, some finishes are textured and rough, and some are meant to prime the surface for a smoother, finer finish.

Stucco is a form of plaster, and has a variety of finishes, from very smooth, to quite rough and textured, depending on the style desired.

Plaster is not as common as it was in previous eras due to the growing popularity of drywall, or sheetrock, though a similar principle and product is used to fill and finish the seams when drywall is used.

In mid-century homes, it was common to have horizontally fastened wood boards making up the structure of walls, with a wire mesh tacked along the surface. Plaster was then spread over the surface and worked to a fine, smooth finish.

This made an extremely durable wall finish and was quite popular until paneling and drywall became more commonly used due to the convenience of quick application and finish time.

Similarities of Mortar and Plaster

The modern components are very similar in both mortar and plaster. Both contain cement, a fine aggregate, and are mixed with water until the desired consistency is reached.

The dry time for both mortar and plaster are similar, as well as workability.

The cost for mortar and plaster is very close since the ingredients are quite similar. This can, however, greatly depend on the quantity used based on the surface space being covered.

Differences Between Mortar and Plaster

Plaster contains much finer sand to allow for ease of workability and a smoother finished product. It is usually mixed slightly wetter to allow better manipulation on the surface.

Mortar can be stiffer than plaster, mixed with slightly coarser sand to provide good support for the concrete block or brick being laid. It’s important that the consistency be substantial enough to support a lot of weight and maintain a proper distance between blocks.

Mortar is applied with a triangular trowel along the edges of your block, brick, or other building material. Plaster is applied with a flat, rectangular trowel that is long enough to spread a generous amount on the surface while still being light enough to work into a smooth, thin coating.

Can You Use Mortar Instead of Plaster?

Though very similar in nature and makeup, the differences in aggregates and the mixing ratio are enough that you would not want to substitute one for the other, to make sure you get the best results for your project.

In the case of building a structure, for example, plaster would be too thin to properly support the building materials, and you would not achieve a proper amount of bonding for the strength needed using plaster.

Mortar vs. Plaster: Which of the Two Should You Use?

If you are building a structure, you will want to use mortar. Most premixes will provide the recommended ratio for mixing, and that can be adjusted based on your climate and customized for your preferred workability.

Laying block or brick will require mortar with coarse enough aggregate to support the weight. The consistency will be thicker, as you do not need to allow as much time to work with it.

Once mortar is spread on the surface to your desired thickness, no more manipulation is needed apart from possibly filling in gaps or spaces that do not have proper coverage.

If you are coating a wall with plaster, you will certainly want it to be mixed appropriately with very fine sand, and moist enough to allow more generous working time to get a more professional-looking finish.

Plaster can also fill in gaps and holes left in incomplete mortar joints, however, it’s best to fill all empty spaces with mortar as the structure is being built.

Additionally, plaster can be worked around a variety of shapes and is often used in round or curvy structures since it is easier to manipulate than other finishing materials.

Summary

Hopefully, we’ve cleared up any questions about mortar and plaster, and their differences.

Though quite similar in nature, following recommendations for proper material usage can make a major difference in your building or finishing project.