What Is the Difference Between Plaster of Paris and Drywall Compound?

To make better decisions and avoid future mistakes in home repairs, it’s essential to understand the differences between two common materials: plaster of Paris and drywall compound. These materials can be used for various jobs, but what sets them apart?

Plaster of Paris and drywall compounds have different compositions and properties. Describing these will help you choose the appropriate material for your project.

What is Plaster of Paris?

The product derives its name from the Montmartre area in Paris, where it is heavily sourced. However, plaster of Paris was first produced and used by ancient civilizations such as the Egyptians, Greeks, and Romans roughly 9000 years ago.

Gypsum is a mineral that humans have utilized for centuries. When heated to around 150 degrees Celsius, it transforms into plaster of Paris, a white, powdery, non-toxic, and fireproof material, making it ideal for various uses.

Due to its adaptability and affordability, it has found significant application in the construction industry. The primary ingredient is calcium sulfate dehydrate, which creates a paste when mixed with water that solidifies into a sturdy substance upon drying. It makes bricks, tiles, mortar, and other construction materials. Additionally, it can be used to patch or repair walls before painting.

What Is Drywall Compound?

A finishing substance for interior drywall seams and corners, a joint compound is sometimes called drywall mud, joint cement, or gypsum board compound. Its composition usually consists of basic material, often gypsum, mixed with water to create a paste. The paste is then applied to the drywall seam with a putty knife or trowel and left to dry.

Once the joint compound has cured, it forms a rigid, long-lasting surface that can be sanded, painted, or textured. Both powder and pre-mixed versions of joint compounds are available. Pre-mixed versions are more convenient since they do not require water and come in a range of colors to match the tone of the drywall. Typically, joint compound is used to complete drywall jobs quickly and can be used to patch holes, cracks, and gaps in drywall. After the joint compound has dried, the surface can be sanded, dusted, primed, and textured, and dust is removed before painting.

Plaster of Paris Vs. Drywall Compound:

Plaster of Paris and Drywall Compounds are widely used and great for different applications. Here is a table to compare both materials to see the difference between them:

Elements To CompareJoint CompoundPlaster
DefinitionIt has a muddy texture and is used to seal cracks, walls, holes, etc.It is a substance that is used to fill or join walls
Materials IncludedIt is based on gypsum aloneIt can be based on lime, cement, or gypsum
Time To DryTake a long time to dryQuick to dry
Application SkillsEasy to apply, does not require skillsThe application requires proper skills
Molding AbilityIt cannot be moldedPlaster is soft, so it is easy to shape
AvailabilityIt occurs naturally and is a mineralHumans mix up materials in accurate proportions to create it
Chemical NameCalcium Sulfate DihydrateCalcium Sulfate Hemihydrate

As you can see, both Joint Compound and Plaster of Paris are somewhat different.

However, deciding which one you’d need to go for should be much easier once we know the advantages and disadvantages. 

Here are a few advantages and disadvantages of these compounds and some of the most significant key differences:

Plaster of Paris Pros and Cons:

Plaster of Paris is a lightweight, easily spreadable material that mixes well with water has excellent adhesion with fibrous materials and a firm surface for paint, and offers great resistance to knocks and fire. However, it is highly porous and more expensive than standard drywall mud or other cement, unsuitable for moist spaces, and requires skilled workers for application.

Joint Compound Pros and Cons:

The joint compound is durable, easy to sand, and adheres well to drywall. It is also available in many variations for different environments and can be used for various purposes, such as repairing holes and cracks and concealing drywall joints. However, it takes a long time to dry, does not stick well on gloss paint, and might shrink, causing the structure to break apart.

Key Differences:

Here are some key differences to help you decide where to use joint compound or Plaster of Paris:

  • Composition: Joint compound is made with gypsum powder and is easily combined with water to make a muddy paste for application, while Plaster of Paris is a mixture of cement, gypsum, lime, and sand that needs adequate preparation.
  • Easy to Apply: A joint compound can be applied by anyone to cover corners, joints, or cracks while using Plaster of Paris requires skilled people to get a smooth finish.
  • Drying Time: Plaster of Paris takes around 60 minutes to dry and settle, while the joint compound can take up to several hours or a few days to dry.
  • Insulation: Plaster of Paris provides better soundproofing and insulation due to its thick layers, while joint compounds provide thin layers.
  • Molding of Material: Plaster of Paris is softer and easier to mold into different shapes than joint compound.
  • Cost: Plaster of Paris is more expensive than standard drywall mud or other cement due to its quick-drying and multiple layers requirements, while joint compound is readily available and affordable.

Plaster of Paris vs. Drywall Compound: Which to Use and When?

If you’re looking to manufacture building supplies such as bricks, tiles, and mortar, then plaster of Paris is the raw material you need. This versatile substance can also be used for wall patching or restoration and for creating artificial ceilings, sculptures, castings, artwork, chef hats, and even fractured bone casts. In dentistry and medicine, plaster of Paris is often used to create dental imprints and casts for bone fractures.

On the other hand, if you need to finish drywall corners and joints during installation, then drywall compound (or mud) is your go-to paste. It’s also perfect for filling holes and cracks, smoothing out dents, and even making medium or small repairs to plaster walls. So, the next time you’re faced with a DIY project involving plaster or drywall, make sure to choose the right material for the job.


Can You Repair Plaster With Drywall Mud?

Yes. Drywall mud adheres to many surfaces, including plaster walls. You must apply multiple coats of drywall mud on the cracks, joints, and holes to cover those areas so you can finish the wall.

Can You Use Plaster Of Paris as Joint Compound?

Yes, you can. Plaster of Paris is more effective than joint compound and can be applied as thickly as necessary to get a smooth look. However, sanding Plaster of Paris can be quite an issue for an amateur.

Is Plaster Of Paris Waterproof When Dry?

No. Plaster of Paris is not waterproof and is an extremely porous material. Even when the Plaster of Paris dries, it is porous and will absorb any water that touches its surface.

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