Waterproof Expert

Waterproofing tips & tricks

Is Plaster of Paris waterproof? Can I make it waterproof?

Plaster has long been valued for its versatility and aesthetic appeal. But when it comes to its resistance to water, one question arises: Is plaster truly waterproof?

Can it successfully withstand moisture? Let’s see if this is the case.

⇒ Key takeaways:

  • Plaster is not waterproof and can absorb moisture.
  • Applying sealants or waterproof coatings can enhance plaster’s water resistance, but you can’t make it fully waterproof.

Is plaster waterproof?

Plaster is not waterproof. Traditional gypsum plaster is a porous material that can absorb moisture and water. If exposed to prolonged or excessive moisture, plaster can become soggy and eventually deteriorate.

While you can apply wax or other sealants to enhance its water resistance, plaster will never be fully waterproof.

It’s crucial to address any underlying issues causing water intrusion to protect the integrity of the plaster and prevent further damage.

How to make plaster water resistant

Apply waterproof coatings

Applying a waterproof coating over the plaster can provide an additional layer of protection. For example, you can use elastomeric coatings or cementitious coatings to create a barrier against water intrusion.

Use sealants

You can also use silicone-based sealants around areas where water is likely to penetrate to delay water damage.

Plaster of Paris

Plaster of Paris is probably the most frequently utilized plaster type. It is made of dry white powder comprising calcium sulfate hemihydrate. Mixed with water, it transforms into a pourable fluid. As it dries, it solidifies into a hard, porous material that quickly absorbs moisture and water.

How do you make plaster of Paris waterproof?

You can’t make Plaster of Paris completely waterproof but you can increase its water resistance.

To enhance the waterproofing capabilities of Plaster of Paris, apply a layer of pure acrylic on top. Let it dry and then apply a second layer.

Applying two coats of pure acrylic will result in a film thickness of approximately 600 microns. This additional layer can provide waterproofing properties.

If there are any uncovered areas or holes in the acrylic coating, moisture and water can still penetrate the surface and cause the plaster to become soggy and collapse.

The color of the acrylic can be matched to that of the Plaster of Paris, ensuring a consistent appearance. Pure acrylic also serves as an agent for crack resistance and bridging.

Can plaster withstand rain?

Standard gypsum plaster is not designed to withstand direct exposure to rain or excessive moisture. It is a porous material that can absorb water. Prolonged exposure to rain can cause the plaster to become soft, and deteriorate.

Applying a waterproof coating or sealant specifically designed for exterior applications may provide temporary protection against rain. However, these measures are not foolproof. Long-term exposure to rain can still cause damage to plaster surfaces.

For exterior surfaces that are exposed to the elements, alternative materials such as cement-based renders or specialized exterior coatings are a much better choice than plaster.

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