How to Fix Bubbles in Polyurethane Using a Torch?

Polyurethane may cause bubbles on the wood surface due to many different reasons.

This can be from using an incorrect brush, not preparing the brush correctly before starting to apply the polyurethane, or shaking the container of polyurethane instead of stirring it softly.

Taking these things into account and ensuring that they are followed correctly will reduce any chances of bubbling.

But what if you have already applied the poly, and bubbles have formed on the wood surface?

Worry not; there are two common ways that you can fix this problem. One way is using a blowtorch, and the other is using sandpaper.

While the torch method is recommended for fixing bubbles on only water-based polyurethane, you can sand either type of polyurethane – water- and oil-based.

How to Torch Polyurethane?

If you’re a woodworker, you know that polyurethane bubbles can be tricky to eliminate.

But a small handheld propane torch usually does the trick – simply pass the flame over the bubble until it melts.

You should use a torch on water-based polyurethane bubbles immediately after applying the topcoat but before it dries.

Be careful not to go too fast or hold the flame in one place for too long, as this could burn the surface and ruin your overall project.

If you plan to put another coat of poly, make sure each coat is fully dry before applying the next one, following the product’s recommended drying time.

The final layer of polyurethane should be smooth and glossy with no bubbles using this torch method.

Torch Alternative to Fix Polyurethane Bubbles

If you don’t have a torch or are uncomfortable using one, no problem! You can use a hairdryer instead.

Just turn it to the hottest setting and aim the airflow low–but be sure to do this immediately after applying the polyurethane.

If you’re having trouble getting rid of bubbles with a hairdryer, you can try using a heat gun on water-based polyurethane as a substitute.

Sanding to Get Bumps Out of the Oil-Based Polyurethane Finish

The torch method is not recommended when using oil-based polyurethane because there’s always a risk of the project catching on fire.

Instead, it’s better to use the sanding method.

But the problem here is with this method; you will need to wait three days for the layer of polyurethane to cure, then lightly scuff out any bubbles with 120 grit sandpaper.

Finally, you should apply another layer of polyurethane as desired to get a bump-free finish.

How Can You Avoid Getting bubbles Trapped in Polyurethane Project?

Preventing bubbles from forming in the first place is always better than fixing them later.

To avoid bubbles in the polyurethane, gently stir it inside the can.

Do not shake the can under any circumstances, as this will cause tiny bubbles to form that could ruin your woodwork.

When you’re ready to apply polyurethane, start cleaning the surface of your woodwork.

Use denatured alcohol to clean surfaces before applying water-based polyurethane and mineral oils for oil-based polyurethane.

Oil-based polyurethane should be applied with a horsehair brush, while water-based polyurethane can be used with a nylon brush.

I am against using sponge brushes for applying polyurethane as they often leave behind too many bubbles that are hard to fix.

Before applying the poly, “lay off” the brush to remove any excess polyurethane and avoid dripping.

Dip the brush only halfway into the can to control the amount of product applied to the surface.

Also, keep a rag handy to wipe up any drips before they have a chance to dry.

Remember that thicker layers take longer to dry thoroughly between coats.

So, applying thin coats of polyurethane is recommended to create a more even finish and avoid trapping dirt or bubbles underneath the layer.

The bottom line

Bubble-free polyurethane is not as hard to achieve as it may seem.

Using the blow torch method between coats is ideal if you want to prevent or fix water-based polyurethane bubbles from getting trapped between coats.

Please do not use the torch on oil-based polyurethane, as it could easily catch fire.

The sandpaper method is an excellent alternative in such cases and for those uncomfortable using a blow torch.

Be patient, follow the tips above, and wait for each coat to dry completely before sanding out any bubbles and applying the next coat, and you’ll be well on your way to a flawless finish.