How to Waterproof Plaster

Plaster can be found both inside and outside homes. Exterior cement plaster is used in the construction of buildings, and it doesn’t need to be waterproofed because it is made of cement. It is also a very strong material, and even without paint, it can withstand extreme outside conditions.

Plaster used on the inside of homes is a different material altogether. It is water-soluble and, without care, can succumb to moisture and humidity. Although interior plaster can never totally be waterproofed, there are some steps that you can take to create a stronger moisture barrier.

Painted Plaster

If you plan on painting your interior plaster, a traditional primer and paint treatment will create a sufficient moisture barrier against the elements. Remember, you cannot treat the plaster in any way to create a water barrier from the inside of the wall. If you have a leak, even a small one, you should repair it promptly to reduce the risk of water damage to your plaster walls.

Step 1 - Coat With Primer

Before painting the wall, apply one coat of heavy-duty primer. This will not only create a beautiful finished look to your paint job, it will also provide the foundation layer of your paint barrier.

Step 2 - Apply the Paint

A standard interior paint will work fine over your primer; however, if you are looking for stronger water protection, use heavy-duty exterior paint instead. Exterior paints have added ingredients that help them withstand the elements. This will fortify your walls even further.

Unpainted Plaster

If you don’t want to paint the plaster but still want to achieve a moisture barrier, you can apply a light coat of linseed oil to the walls. Again, this treatment will not eliminate the effects of water damage if water meets the wall from the inside.

Step 1 - Lightly Sand

Lightly sand the plaster surface to a beautifully smooth finish before adding the oil. This will allow it to absorb more efficiently.

Step 2 - Apply the Linseed Oil

When deciding on a paintbrush to buy, always try to find a high-quality variety. The natural bristles of a better brush will help the oil application remain even throughout.

Starting from the top corner of the wall, brush a very light coat of linseed oil over the entire surface. Apply sparingly—you don’t want to end up with a greasy wall. The naturally porous nature of the plaster will cause the oil to sink in. After a few hours, you shouldn’t be able to tell it was treated at all.

WARNING: Linseed oil is highly flammable, and paintbrushes or rags soaked in it will suddenly set on fire if put in a warm area. Carefully place any tools you use to apply it in water-filled containers once you're finished with them.

The process is as simple as that. In just a few steps, you have treated your plaster walls with the most effective waterproofing procedures available.

How to Waterproof Plaster

Can you waterproof a plaster wall?

Waterproofing compounds, such as paint-on resin, can be used to waterproof plaster walls. You must prime the walls before painting on the waterproofing materials, which must be allowed to fully dry.

What can you seal plaster with?

Resins are commonly used to create a waterproof sealant that can be painted right onto plaster walls.

Is there such a thing as waterproof plaster?

Waterproof plaster is made with polyethylene, a type of plastic that stays dry and resists moisture and dampness.

What is the waterproof liquid for plastering walls?

Many different types of liquid waterproofing formulas can be used on plaster walls. Many of these formulas are polyurethane-based.

How can I make my walls waterproof?

To waterproof walls, seal cracks and plug holes using caulk. Apply caulk around windows and doors to seal cracks.

Paint the walls with a waterproof coating to complete the waterproofing treatment.