How to Seal Plaster of Paris for Outdoor Use

Plaster of Paris is an excellent material for creating statues and other decorative items. It can also be used to seal exterior walls, but there are some things you need to know before starting this project. First, I’ll discuss the necessary steps to successfully seal the plaster of Paris against outdoor elements like rain, snow, and sun.

How to Seal Plaster of Paris for Outdoor Use

I’ll also talk about how you will want the surface on which the plaster is applied to be clean and dry with no cracks or crevices that could house water or cause mold growth. So, this article is for you. You will learn how to seal plaster of Paris for outdoor use with just one simple trick!

Step to Follow on How to Seal Plaster of Paris for Outdoor Use

Step One: Determine

First, you must determine if your plaster of Paris will be used for outdoor use. This step is important because the ingredients in this sealing mixture are harmful and should not be inhaled or ingested. Use plaster of Paris for outdoor use if used on an exterior wall or surfaces that may get wet.

Determine the Plaster of Paris

If your plaster of Paris will be used indoors, purchase a different product. If the finished surface is used on an exterior wall, you may follow these directions. The final product must be washed off of hands and any surfaces immediately after sealing.

Step Two: Mix Ingredients

Mix ingredients together thoroughly. You will use approximately 1/3 cup of each ingredient for every quart of plaster of Paris you wish to seal. Mix the powder and milk in a bowl to form a paste. Mix the other ingredients, such as dish soap and water, in a separate container.

Stir these items into the mixture of powder and milk. The ingredients must mix thoroughly to create a smooth paste. This mixture will be similar to the consistency of toothpaste and should not be runny.

Step Three: Apply Paste to Plaster of Paris

Cover the face of your plaster of Paris with a thin layer of this mixture before it is completely dry. The sealing paste will remain caustic and adhere well to the complete plaster of Paris figures. If you are using a piece that has been previously dried, lightly wet the entire piece before applying the paste.

Use a brush, sponge, or rag to apply the paste to the plaster of the Paris surface. The sealing mixture will smooth out as it is applied, so you can use more pressure to remove cracks and uneven spots in your finished project. Allow the paste to dry completely before moving on to step four.

Step Four: Sand Rough Areas

Lightly sand rough areas to smooth out your finished product. This step is essential if you wish to achieve a smoother, more refined surface. For example, if there are thick or jagged edges of the plaster of Paris figure, they appear even more prominent.

You can use fine-grain sandpaper for this sanding step to achieve a smoother finish. You can use sandpaper that has been used for woodworking or any other similar suitable grits. After the paste is dry, start with coarse-grain sandpaper and move from coarse to fine as you smooth out the rough areas of your plaster of Paris project.

Step Five: Cover with Sealant

This sealant locks in the fresh plaster of Paris smell. It also makes your finished product more resistant to water damage. This mixture is made up of 1 part latex paint and four parts mineral spirits. Mix both thoroughly before applying this mixture to your finished product.

Use Sealant to Protect Plaster of Paris

Please wait for it to dry completely before allowing children or pets near your finished product. The sealant must dry completely before it is safe to use near other surfaces or people. In addition, it should be noted that this mixture can damage certain surfaces, like finished wood or painted walls.

Step Six: Clean Up

Use mineral spirits to clean up any remaining sealing mixture on your hands or surfaces. Take care to remove all residue, as it will continue to irritate skin and damage certain surfaces. Wash thoroughly with soap and water after you are finished cleaning up the dried paste mixture.

Sealed plaster of Paris projects should not be used for at least 48 hours. The sealant must harden before it is safe to use for any other purposes. Packaging should state whether the plaster of Paris is meant for indoor or outdoor use. These instructions will teach you how to seal plaster of Paris for outdoor use.

Step Seven: Maintain Plaster of Paris

Use a light coat of sealant each season to maintain your exterior plaster of Paris protectors. This will help weatherproof your finished product and keep it looking fresh for years to come. In addition, you should keep it out of direct sunlight for extended periods. Direct sunlight can fade or damage certain finishes over time.

Maintain Your Plaster of Paris

For a more long-term solution, consider using a water sealant designed to be used on cement surfaces. This will provide the best possible protection from sun exposure and weathering. Remember that all plaster of Paris figures will become more fragile the longer they are exposed to the elements.

Try to keep your finished product indoors or sheltered in some way to prolong its life for years of enjoyment. If you need to move your new plaster of Paris figure, secure it with rubber gloves and protective clothing. Wear gloves and safety glasses as well if possible, especially when handling silicone molding material.


If you want to use plaster of Paris for outdoor purposes, seal it with a coating or paint. As an alternative, consider using cement as your base coat and applying the plaster over that. This will prevent water from seeping through onto surfaces beneath the plastered surface.

Plaster is an excellent material for exterior walls because it doesn’t absorb moisture like other materials, which can be problematic if exposed to humidity. You’ll need to account for how porous your wall is when deciding what type of adhesive you should apply, however.

Some walls require a thick application of bedding and then wire lath, while others may only need thin coatings that can be applied with sponges or brushes. The conclusion paragraph is informative and provides information on how to seal plaster of Paris for outdoor use.

You can also check it out: How to Glue Plaster

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