One of an artist’s top priorities is making sure their paintings last. Varnish can protect these artworks from dust and ultraviolet rays while keeping them from yellowing. But what happens when you need to make some adjustments to a completed and varnished painting?
Sanding varnish off an acrylic painting is safe and will not damage the paint as long as you do it lightly. However, this action can pose a health risk due to inhaling airborne particles with constituents that may be carcinogenic 
to humans.
The rest of this article will explain how to correctly sand varnish off an acrylic painting and answer some of the most common questions related to this process with Is It Safe To Sand Varnish off an Acrylic Painting?
Table of Contents
How To Sand Varnish off an Acrylic Painting
Sanding varnish off an acrylic painting is relatively easy, and even a novice artist can take on the task. But it requires patience and care, using the right materials, and following the correct procedure. Here’s a list of the materials you will need and the procedure you should follow.
What You’ll Need
- Fine grit sandpaper
- Acrylic paints
- Varnish
- Paintbrush
- Mask or respirator
- Safety goggles
Procedure
- Make sure the varnish is completely dry. The first thing you need to do is make sure the varnish is dry and cured. This means that it is dry all through the layer and not just on the surface.
- Apply water onto the surface of the painting. Once you’re sure that the varnish has cured, dab a bit of water onto the surface of the painting. This will help trap the particles of dried varnish that would be released into the air during the sanding process. You could also achieve this by soaking the sandpaper in water before sanding the painting.
- Sand off the varnish. Using fine-grit sandpaper, begin sanding the varnish off your acrylic painting. This step can take some time and requires patience, as you’ll have to proceed carefully so that you don’t damage the paint underneath the varnish.
- Clean the painting. Once you have sanded off all the varnish, clean the surface of the painting using a rag or paintbrush. Be sure to remove all the dust and varnish particles.
- Retouch the painting. You can now make adjustments to your painting using acrylic paints. Once you’re satisfied with the retouches, allow it to dry and cure. It’s recommended that you wait a week after retouching your painting before applying the varnish.
- Apply a new layer of varnish. Lay the painting down on a flat surface. Using a paintbrush, apply the varnish in even, parallel strokes. Begin at one corner of the painting and work your way either downwards or sideways, always moving the paintbrush in the same direction with each stroke.
- Let the varnish dry. When the varnish has been evenly applied to the entire painting, leave it to dry. This can take a minimum of 4 to 6 hours. Make sure you keep the painting in a clean area to avoid dust and debris sticking to the wet varnish.
- Inspect the coat of varnish. A few hours after applying the varnish, look it over to see if the entire surface has been covered. Some artists opt to add an additional layer of varnish for good measure. You may also decide to do the same.
Note: Wear a mask or respirator when sanding varnish off an acrylic painting to avoid inhaling the particles that become airborne during the process. You can also wear protective goggles to prevent particles from entering your eyes and causing irritation.
Frequently Asked Questions
Is Sanding Acrylic Toxic?
The fumes and particles that become airborne while sanding an acrylic painting are toxic. The International Agency for Research on Cancer states that prolonged exposure to certain compounds found in acrylic acid can cause cancer in humans.
Sanding is the most common way of removing varnish from an acrylic painting. While it’s not outrightly discouraged for health concerns, it’s advisable to take precautions.
When sanding varnish off an acrylic painting, you should wear a mask or respirator and work in a well-ventilated area.
Will an Air Purifier Help With VOCs From Acrylic Paint?
An air purifier can help with volatile organic compounds (VOCs) from acrylic paint if it has a level II or level III filter. A level III filter is specially designed for the removal of VOCs.
If you paint occasionally, a level II filter should suffice. But if you paint almost every day, an air purifier with a level III filter is recommended. It’s more expensive than the models with a level II filter, but it’s also more effective at removing volatile organic compounds from the air.
Can You Paint Over a Canvas That Has Been Varnished?
You can paint over a canvas that has been varnished. However, this is not advised as it can cause some damage, especially to older paintings. It can also create noticeable differences on the canvas between the old paint and varnish and the new layer of paint.
If you choose to paint over a varnished canvas, you should do so only in small areas for minor touch-ups. Since you’ll need to varnish over these new additions to protect the paint, there is a chance that the painting will be noticeably uneven due to the fresh layer of paint and varnish.
If you’re committed to retouching your acrylic painting, the best course of action would be to remove the varnish from the whole canvas completely. Once the new paint additions have dried, apply another layer of varnish that covers the entire surface.
Final Words
Moments, memories, and visions can be frozen and locked into a canvas forever — or for as long as the archival qualities of the materials permit. But the downside to these timeless pieces of art is that you may eventually wish you had done something differently and want to make some adjustments to a painting that has already been completed and varnished.
If you decide to sand varnish off an acrylic painting, do it correctly so as not to damage the paint, and take precautions to protect yourself from the fumes and airborne particles you might inhale.