Since varnish has a thick flow and a slow dry time, applying it is hard. It’s common to run into problems before, during, and after applying it.
Let’s check common varnish mistakes, why they occur, and how to fix them. Sweet right? Let’s dive in.
1. Bubbles in a Varnish Finish
The main reason bubbles appear in a varnish finish is because of air trapped between coats. Once the coating dries, the trapped air will create (produce) bubbles in the finish. If the bubbles are popped, the air will rush out, creating tiny gaps (holes) in the finish.
Bubbles will also appear if moisture (or water) gets under the varnish coating, or if you apply it over a wet surface. Water contains air and water; both of these elements will cause bubbles. So, it’s recommended to apply the sealant over a dry surface.
Since the varnish is too thick, you must thin it before applying. While thinning, you must stir the mixture with a turning stick. But, if you stir too hard or fast, air will get trapped in the varnish and cause bubbles.
To fix bubbles in a varnish coating, pop them, sand the finish, and touch up the surface with 2 more coats. If that doesn’t work, you must remove the entire coating, sand the surface, and re-apply it.
Note: Bubbles can be fixed by laying another coat on the bubbled varnish, but this is only a temporary fix. If you do this, the new coat will eventually develop bubbles too.
2. Yellowing Varnish
Varnish will develop a yellow or amber-like tone due to oily deposits in the finish.
Since oil-based varnish is dissolved in natural or synthetic oil, there will be many oily deposits on the coating. Once the sealant starts to dry, these oil deposits will stay on the coating and tint it after a few weeks. However, yellowing isn’t severe and is often unnoticeable because it blends into the tone of the wood.
Unfortunately, there is no way to fix a yellowing varnish. You can sand it to reduce its brightness, but you will eventually sand down the entire finish because each coating will turn yellow. You can also add another coat, but the new coat will turn yellow too.
If you don’t want a yellowing finish, use water-based varnish because it doesn’t contain any oily deposits.
3. Varnish Turning White
If varnish is exposed to water, its finish will develop white water rings that will spread across the entire coating. These white-water rings will develop if moisture is trapped in or under the coating. This usually happens while cleaning it.
Varnish can also turn white if you use bleach or the wrong cleaning products to clean it. In this case, the tone of the finish will gradually fade until it turns white or milky.
To fix a whitish varnish, find the cause, fix it, and re-apply it. For instance, if the varnish has a white appearance because of moisture, sprinkle baking soda over it, and wait 24 hours. The baking soda will soak the moisture and remove the whitish appearance of the finish.
4. Varnish is Cracking
A varnish coating will crack if you over-thin it (before applying) or apply light coats. If you over-thin varnish, the coating will become too light and crack from minimal contact. Since the coating is too thin, it can’t protect the surface and will start to crack.
The varnish will also crack if it dries too fast; this happens if the coating is exposed to increased heat. While drying, the paint particles of the varnish harden and compact. The longer it takes to dry, the more time the particles have to harden. But, if the sealant dries too fast, the paint particles don’t have enough time to harden and won’t be durable enough. This causes the coating to crack.
To fix small or light cracks, sand the varnish and buff it with polish or wax. However, if the cracks are too deep, you must remove the coating, sand, and re-apply it.
Here’s a guide to this:
- Scrape the cracked varnish with a putty knife.
- Sand the surface.
- Allow the surface to dry (if it’s wet).
- Re-apply it.
- Allow enough dry time to prevent cracking.
5. Wrinkles in Varnish
The varnish coating will develop wrinkles if you re-coat too soon. This happens when you apply a new coating before the old coating is dry. The wet undercoat will cause the new coat to move and shift since it’s not solid (yet). As the coating expands and shifts, it causes a web of wrinkles to appear on the finish.
Here are other reasons why this happens:
- Water Leak – If there is a water leak beneath the varnish, the bottom part of the coating will become wet, which causes it to absorb water and develop wrinkles.
- Cold Temperature – If you apply varnish during cold temperatures, the coating can shrink and develop wrinkles.
To fix wrinkles in a varnish coating, find the cause. For instance, if the wrinkles are caused by water, use a hairdryer to allow each coating to dry properly. This will work in most cases.
If that doesn’t work, remove the varnish coating, dry the surface underneath, apply waterproof primer, and re-apply the finish.
6. Varnish is Peeling Off
Varnish will peel off if the coating is too old (10 or 20 years) or if you didn’t apply it correctly. Also, if you apply varnish over a filthy, wet, or dirty surface, the coating won’t stick properly to the surface and will peel off. That’s because the loose particles of dirt will prevent proper adhesion. So, you must always clean and dry out the surface before painting over it.
The only way to fix peeling varnish is to scrape the finish off, fix the problem, and re-apply it. Here is a guide for this:
- Scrape off all of the peeling coats.
- Sand the finish with coarse-grit sandpaper to remove it.
- Remove dust, and apply a stain-blocking primer.
- Re-apply the finish and allow enough to for each coating to dry.
In summary, the varnish application takes some time to perfect, and you can face different problems while doing it. But don’t fret; you can fix most of these mistakes. If nothing works, you can remove the entire coating and re-apply it.
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,