Chalk paint isn’t durable or moisture-resistant because it’s water-based. So, can you apply polyurethane over it?
You can apply polyurethane over chalk paint. Polyurethane will produce a glossy moisture-resistant layer that will protect the paint from moisture, water, scratches, and other damage.
For indoor surfaces, sealing chalk paint is optional. But, for outdoor surfaces, sealing it is mandatory because the paint isn’t durable enough to withstand outdoor elements.
Types of Polyurethane To Use:
You can use three types of polyurethane: oil-based, water-based, and exterior polyurethane.
Oil-Based & Exterior Polyurethane
For outdoor surfaces, using oil-based or exterior polyurethane is better for chalk paint. That’s because they are more durable and can withstand outdoor elements.
However, applying them is harder because they take longer to dry and are thicker, and their finish tends to yellow over time. In addition, you must thin oil-based polyurethane before applying it.
For indoor surfaces, use water-based polyurethane because it dries faster, is easier to apply, and you don’t need to thin it. Also, it doesn’t yellow over time.
Chalk Paint Dry Time Before Polyurethane
Chalk paint needs to cure for 24 hours before you seal it with polyurethane. If you seal it too soon, the sealant won’t stick, and the finish will turn sticky.
On average, chalk paint dries enough for a re-coat within 30 minutes. However, the paint must cure (oxidize) for 24 hours before you can apply a sealant over it. That’s because once the paint cures (fully dries), the paint particles harden and compact, meaning the paint will be strong enough to handle a sealant.
However, the dry time of the paint depends on room temperature, humidity levels, surface type, and thickness of the paint. You can speed up the dry time by increasing air circulation and improving the evaporation rate.
How To Apply Polyurethane Over Chalk Paint?
Polyurethane sticks over all types of paint. So, applying it on chalk paint isn’t hard. Here’s how to do it:
1. Clean The Surface
First, clean the finish to remove stains and dirt. The finish must be clean and even because polyurethane is a clear coat that shows imperfections. So, if you don’t clean it, imperfections will show once the sealant dries.
To clean the finish:
- Mix soap with warm water.
- Apply the mixture over chalk paint.
- Use a soft brush or clean rag to scrub the dirt or stains off.
- Remove the soapy water residue from the surface using clean water.
Before cleaning, wait until the finish fully dries (cures). If you clean it too soon, you will remove the paint. Also, if there aren’t stains or dirt over the paint, use a clean rag (without water) to remove the dust.
Related Read: Will Polyurethane Stick to Tacky Stain?
2. Sand Down The Surface
Sanding the paint is optional because polyurethane will stick regardless. However, sanding will remove bumps and imperfections and leave a smooth and even surface behind for the sealant to stick.
To sand chalk paint, use fine-grit sandpaper (220-grit). Don’t use lower-grit sandpaper such as 80 or 120-grit, as you can remove the finish.
After sanding, remove the dust.
3. Apply The Polyurethane
Once the chalk paint is clean, sanded, and dry, apply 3 coats of polyurethane over it. To apply it, use a paintbrush, roller, or sprayer. If you use a sprayer, you must thin it. Wait until the previous coat dries before applying the next one.
Optionally, you can sand between coats of the sealant (except for the final coat).
Polyurethane vs Wax (For Chalk Paint)
Polyurethane is easier to apply and maintain on chalk pants than wax. Wax will give the finish a darker shade, while polyurethane won’t change the color shade of the finish.
For high-traffic surfaces, polyurethane is better than wax. That’s because the wax is a low-durability finish that can’t withstand high use. If the wax finish gets damaged, you must re-apply the wax to fix it. And, re-applying wax over the paint is hard because you must remove most of the wax.
On the other hand, polyurethane is a durable finish that will last for 5-10 years and won’t get damaged easily. Also, if the coating does gets damaged, all you need to do is sand it and re-apply it.
Mixing Chalk Paint With Polyurethane
You can mix water-based polyurethane with chalk paint. The mixture will have a colorful and durable finish. However, you can’t mix oil-based or exterior polyurethane with chalk paint. That’s because chalk paint uses water as its solvent, and oil-based polyurethane uses oil. And oil and water don’t mix.
You can mix them to get a tinted durable finish. Polyurethane has a clear finish (no color) because it doesn’t have paint pigments in its formula. So, if you mix it with chalk paint, its finish will have the same color as the paint.
Applying poly over chalk paint is necessary for outdoor surfaces. When dry, it will form a thick glossy finish that is moisture, water, and scratch resistant. In addition, its glossy finish will protect the paint and the surface underneath from damage.
However, before applying it, the paint must cure (fully dry).
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,