Plaster walls are most commonly found in older homes, but can also be found in newer construction. Either way, there comes a time when they need a new coat of paint. Might it be because of stains, it’s untreated, or simply a change in the color scheme?
If it’s already painted and in good condition then no primer is usually needed. Otherwise, a primer is needed to improve paint adhesion and give the new paint a uniform appearance.
What is the best primer for plaster walls?
The best primer for dry interior plaster walls is a water-based acrylic primer. It dries quickly, is low odor, and provides a good base for paint to adhere to.
If your plaster has stains from water damage, nicotine, crayon, or similar, you’ll need to use a stain-blocking primer.
If your plaster walls are damp, such as the outer walls in a basement can be, then you’ll need a silicate paint.
If you’re planning to use an acrylic paint as your top coat and the plaster is untreated, you should first apply a mist coat to prime the walls.
What is a mist coat?
A mist coat is thinned out paint and it’s used prior to painting in order to prime the surface and seal porous materials. The mist coat will help the main coat of paint adhere better and create a more even texture.
To make a mist coat simply add about 30-50% of water to your paint and mix well. Apply with a roller and brush and allow to dry completely before adding your main coat of paint.
It’s very watery so make sure to mask and protect any areas you don’t want to be painted!
Recommended products for plaster walls
A primer that is commonly used by professional painters is Zinsser GARDZ. It’s a clear, water-based acrylic primer designed for interior application to porous surfaces prior to painting, texturing or wallcovering. It penetrates deeply into porous surfaces.
GARDZ is recommended for sealing problem porous surfaces such as:
- bare or damaged drywall
- plaster
- cement and cementitious coatings
- spackling paste and joint compound
- calcimine
- stucco
- acoustic and texture finishes
- uncoated wallpaper.
Another popular primer is ZINSSER Bulls Eye 1-2-3 PLUS Primer. It’s a water-based acrylic primer that can be used with any top coat and it has stain-blocking properties. This is a great primer to use if your plaster walls have any water stains or other types of stains that need to be sealed.
- Great for all projects – interior and exterior
- Completely blocks all stains – water, tannin bleed, smoke and more
- Penetrates and seals porous surfaces
- Low-VOC and low odor
SEAL GRIP is another primer with stain-blocking properties that is used and liked by professionals. It features:
- Outstanding Stain & Tannin Blocking
- Excellent Adhesion & Hide
- Fast Drying
- Provides a Mildew Resistant Coating
It’s also recommended as a whole-house primer for use on properly prepared:
- Interior or exterior wood
- Masonry
- Plaster
- Wallboard
- Cement
- Brick
- Stucco
- Cement composition board
- Aluminum
- Wall coverings.
What is silicate paint?
Silicate Paint, also known as mineral paint, is a water-based type of paint that uses inorganic minerals as a binder, such as water glass or potassium water glass.
It achieves its durability by chemically bonding to the substrate and it’s open for diffusion, meaning that it can “breathe”.
Along with its durability and longevity, the paint is non-combustible, fire retardant, washable, mold and mildew resistant, and water repellent.
Silicate paints chemically bond to all forms of masonry substrates such as brick, stone, mortar, stucco, and cement. Unlike latex paints, which form a film on the surface, it creates a permanent bond that works in harmony with the plaster.
I once painted the inner and outer plaster walls in a basement. I used an acrylic paint on all the walls but since the outer walls were damp they blistered soon thereafter.
I had to remove all the paint and start over. This time I used a silicate paint on the outer walls and since it’s open for diffusion it allowed the moisture to escape.
How to check if your plaster walls are damp
If you suspect that your plaster walls are damp, there are a few simple tests that you can do to check.
First, touch the wall in several places. If the plaster feels moist to the touch, it is likely that it is damp.
You can also use a moisture meter to test the moisture content of the plaster. If the reading is above 20%, the wall is likely to be damp.
Finally, you can tape a square of plastic film to the wall and leave it for 24 hours. If condensation appears on the underside of the film, it indicates that the wall is damp.
Wait until the plaster is completely dry before you apply primer or paint. For new plaster, it can take several weeks for it to dry depending on temperature, ventilation, air humidity and the type of plaster used.
Use the methods mentioned from time to time to check for moisture.
How to paint new plaster with primer
Read How to Paint Plaster Walls: A Step-by-Step Guide if you want to know how to paint plaster and what tools and materials you’ll need. You can also watch the video below on how to paint a newly plastered room. Use both resources to get the best results when painting a plaster wall.
FAQs for Best Primer for Plaster Walls
Here are some commonly asked questions when it comes to priming plaster walls.
What is the purpose of using a primer on plaster walls?
The purpose of using a primer on plaster walls is to prepare the surface for the topcoat. Primer seals the porous surface of the plaster, providing a saturated and uniform base for the paint to adhere to. This helps to enhance the durability of the paint, prevent peeling, and gives a more even finish.
What is the difference between oil-based and water-based primers for plaster walls?
Oil-based primers are known for their high durability and excellent adhesion. They are particularly good at sealing stains and can be used on a variety of surfaces. However, they take longer to dry and have a stronger odor compared to water-based primers. Water-based primers are easier to clean up (just water and soap), dry faster, have less odor, and are less prone to cracking over time. They’re also more environmentally friendly.
What safety precautions should I take when applying oil-based primer to plaster walls?
When applying primer, ensure the room is well-ventilated to disperse fumes. Wear protective clothing, including gloves and safety glasses, to protect your skin and eyes. Wearing a respirator with an organic vapor cartridge is a must when indoors. Always follow the manufacturer’s instructions on the primer can, and keep the primer and paint away from children and pets.
What happens if I don’t prime plaster before painting it?
If you don’t prime plaster before painting it, the topcoat won’t stick properly to the surface. This can lead to issues like bubbles, peeling or flaking paint.
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Conclusion
Priming plaster walls is essential for getting a good paint job and there are many different types of primers on the market, so make sure you choose one that is right for your needs.
The best primer for plaster walls depends on the condition of the plaster, but if it’s dry then any good quality latex primer will do, and use a primer with stain-blocking properties if you’re painting over any stains.
Check for moisture before applying any primer or paint, and make sure the plaster is completely dry before proceeding.
If the plaster is damp, then you’ll need to use a silicate primer that will allow the plaster to “breathe” and prevent the paint from blistering.
Once you’ve chosen the right primer, make sure you apply it evenly and follow the manufacturer’s instructions for the best results.