8 Common Problems When Applying Varnish & Solutions

By MWB-Team •  Updated: 05/22/23 • 

Varnish may be easy to brush onto a wood surface. However, it is challenging to get a flawless finish. Even if you’re an expert, different things can go wrong, and sometimes they might be out of your control. This article looks at common problems when applying varnish, their causes, and solutions.

1. Brush Marks

If you notice brush marks that have cured in the finish, the cause is you’re applying the varnish at full strength. If you’re applying the varnish at full strength, there will be no way to eliminate brush marks.

If the brush marks have already cured on the finish, sand the varnish once it cures and rub on the desired sheen. You can also reduce brush marks by thinning the varnish if you’re brushing at full strength. The more you thin the varnish, the lesser pronounced the brush marks will be.

2. Runs and Sags

Runs and sags that develop as you apply a varnish are mostly caused by applying a thick coat. To prevent this, thin the varnish to normal thickness on each application.

Remove some excess finish with your brush to fix runs or sags, and apply the excess to another part. You can also drag the rush over the edge of the jar to remove excess varnish.

3. Fish-Eyes or Crawls into Ridges

If you notice fish-eye or crawls into ridges, the wood you’re applying varnish to has been contaminated by silicone from a polish, lubricant, or body lotion.

The solution to this problem is to strip the varnish and reapply. Before reapplying the varnish, make sure to wash the surface of the wood with a silicone-free solvent.

4. Dust Nibs

Varnish can take around 12-24 hours in the right conditions to dry/cure. If there’s dust in the room, then it will fall onto the varnish and produce a rough surface once it cures. Because of the slow curing time, dust nibs can be a very bad problem. Before applying varnish, ensure the room is clean and dust-free.

If varnish cures with dust nibs, sand the surface and rub it with your preferred sheen. You can use steel wood or other rubbing compounds to achieve a smooth finish.

5. Air Bubbles

Air bubbles emerge when you apply a finish, and they don’t pop out before the varnish cures. The causes of air bubbles are turbulence when a brush glides over the surface, applying a thick varnish, or the finishing room is too hot.

If the varnish is too thick, it makes it harder for the bubbles to pop out before it cures. Sand the surface smooth, and add 5 or 10 percent mineral oils to thin the varnish when applying the next coat. Thinning the varnish will slow the curing process and allow air bubbles to pop out before the varnish cures.

If the problem is a higher temperature, then sand the surface smooth and work in a cooler room. This will allow the bubbles more time to pop out on their own before the finish cures hard.

6. Varnish Doesn’t Cure

If the varnish is sticky or remains tacky, it is because the room you’re applying varnish is too cold, there is uncured oil in the wood, and you’re using oily wood such as teak, ebony, or rosewood.

If you’re applying varnish in a cold room and notice the varnish is sticky, warm up the room and see if the varnish will cure. If it’s not cured, strip it and wait for a warmer day to reapply. The ideal temperatures for applying varnish are between 10 degrees Fahrenheit and 80 degrees Fahrenheit.

If the surface of the wood has an unsure oil finish or you’re using oily wood, warm the room you’re finishing the wood and give it more time for the varnish to harden. If you recently applied linseed oil, wait a few days for it to cure before reapplying the finish. For oily wood, first wash the wood with a non-oily solvent, such as naphtha, lacquer thinner, or acetone, just before you reply to the varnish.

7. Varnish Wrinkles

Varnish wrinkles are usually caused by applying a coat of varnish over another coat without letting it cure properly. If you notice this problem, strip the varnish and start over.

When applying varnish, allow more time for each coat to cure. Remember, varnish takes more time to cure, especially when applied in cooler temperatures.

8. Varnish Does not Flow

To produce a smooth varnish film, varnish must flow well when applied. You’ll notice problems like uneven surfaces, brush marks, orange peel, and more without a good flow. A thick varnish or varnish stored in a cold place can cause a poor-flowing varnish.

If the problem is a thick varnish, add a thinner to improve the flow and make applying easier. If the varnish is too cold, place the can in warm water to lower its viscosity. Because varnish is flammable, do not heat it directly under a flame because it can cause a fire.

MWB-Team

Hello there! This is the Make Wood Better Team. Here, we share informative how-tos and guides focused on making wood better. Whether it's finishing wood, maintenance, or restoration, there's something on this website for you to learn and improve your skills.