How To Fix Wood Holes, Knots & Cracks With Epoxy Resin

Industrial Clear is a liquid epoxy resin perfect for filling cracks, holes, and knots in wood. It has a medium viscosity that makes it easy to pour or inject into small crevices. Its high tensile strength and elasticity make it ideal for use in wood, as it can absorb into the wood fibers to create a strong bond that will not break under stress. Industrial Clear contains 100% solids and no fillers, which means it will not shrink as it dries.


Do I need to fill holes in wood before I apply epoxy resin?

Filling cracks in wood with a clear epoxy resin, like Industrial Clear, offers 4 main benefits:

  1. Prevents leaks
  2. Provides strength and prevents damage from spreading further throughout the wood
  3. Creates a smooth, even surface and prevents air bubbles in the flood coat
  4. Highlights the wood's natural appearance and beauty

Taking the steps to fill cracks in wood before applying a resin top coat will help you get consistently excellent results. 

fix wood holes with epoxy resin

What to use to fill in cracks in wood:

• A wood slab or board
• Sheathing tape or a piece of acetate and painter's tape
• A clear epoxy wood filler like Industrial Clear 
• Disposable nitrile gloves
• Plastic measuring cup and stir stick
• A syringe, dropper, craft stick or a small cup for pouring the resin into the hole
• A dustcover such as a clean cardboard box or plastic tote 
• An electric sander and a few grades of sandpaper, from coarse (80) to fine (1000)
• A mask for sanding

Skill level:  Beginner
Duration of Project: 2 hours, plus 24 hours of curing


Step 1: Prepare and seal the wood:

To prepare wood for repair, begin by flipping the wood over so the bottom side is facing up. Identify each hole, even the seemingly small ones, and mask them off with a good quality painter's tape or sheathing tape. Use your fingers to burnish the tape firmly for a tight bond to prevent any leaks.

Another option is to cut a piece of acetate to fit over the hole and secure it with tape. This will provide a reliable seal, preventing any epoxy from seeping through the hole.


tape the holes off
tape the holes off



Step 2: Fill the wood holes with epoxy resin.

After taping off the holes, flip the board back over so that the taped side is facing downward once again. 

Next, prepare Industrial Clear epoxy following the instructions on the label. 
Apply the wood crack filler epoxy by pouring from a small plastic cup, or use a dropper, syringe or craft stick. Allow the epoxy a few minutes to settle into the voids, repeating the process as necessary.

For holes deeper than 1/2", it's best to pour the epoxy in stages. You can wait for the first layer to gel up after 3-5 hours, or wait 24 hours for the resin to cure dry to the touch before pouring the next layer. Repeat the process until the hole is slightly overfilled with epoxy resin. Remove surface air bubbles with a heat gun or a quick pass of a flame torch after each pour.

If you prefer, tint the epoxy with mica powder or a specially-made resin tint. Once the epoxy has been applied, cover it and allow it to cure for 24 hours.

fill the wood holes with epoxy resin



Step 3: Sand until smooth.

Once Industrial Clear has cured, remove the tape from the board. Wearing a sanding mask, sand both the top and bottom of the board, starting with the coarse sandpaper to remove excess resin and to level out the surface. Gradually work your way up through the finer grits until the surface becomes smooth and polished.  Blow off any remaining sanding dust or debris. 


Step 4: Pour Your Final Coat

At this point, you can apply a seal coat, if you're doing one, or your final coat. To apply a seal coat, use either a foam brush or a gloved hand to apply a very thin layer of epoxy over the entire surface of the board. Cover and allow to cure for 24 hours. Sand lightly, remove sanding dust and debris, and then apply your final flood coat.  Industrial Clear will reach its full, rock hard cure at the 48 hour mark.

Once the resin has cured, the surface will be even and smooth and the imperfections in the wood will look beautiful.

There's always a way to get a perfect finish with Industrial Clear.

sand and pour final coat of epoxy resin


What kind of epoxy do you use to fill voids in wood?

The best epoxy for filling wood holes is a 2 part liquid epoxy resin that with a low to medium viscosity. The resin should be thin enough to penetrate the wood fibers and create a strong bond, yet not too thin that it becomes hard to manage or pour into small cracks. The best epoxy for filling holes in wood is one with excellent strength and some elasticity to accommodate the natural expansion and contraction of wood caused by temperature and humidity fluctuations. This will help prevent the resin from cracking or breaking under stress.



Why is Industrial Clear the best epoxy resin for filling holes?

Industrial Clear is an excellent wood crack filler for several reasons:  it has a medium viscosity that absorbs well into wood and is easy to pour from a cup or insert into narrow crevices with a syringe or dropper. Once cured, it provides a hard finish that helps strengthen and stabilize the wood. Additionally, since it contains 100% solids and no filler, it will not shrink as it dries.

One of Industrial Clear's most notable properties is its high tensile strength, which refers to the maximum stress the cured resin can endure before breaking. With a tensile strength of 7100 psi (ASTM D638), Industrial Clear is very strong and durable. However, it was intentionally formulated with some elasticity to prevent cracking, making it an ideal solution for filling cracks in wood.



Can you fill large gaps in woods with epoxy resin?

Yes, large holes in wood can be filled with epoxy resin as long as the bottom of the gap is properly sealed to prevent leaks. You can use a high-stick tape like sheathing tape to mask off the bottom of the hole, or cut a piece of acetate to size and secure it in place with tape. For very large cracks, place the wood in a mold or a frame built to the size of the wood. Once cured, excess resin can be sanded away.

It's important to note that for very deep holes or gaps thicker than 1/2", it's best to pour the resin in stages to avoid trapped bubbles or a flash cure. Bubbles can be removed after each layer with a heat gun or with a quick pass of a flame torch over the surface.



Is epoxy a good wood filler?

While there are various materials that can be used to fill holes in wood, using epoxy as a wood crack filler stands out as the superior choice. Unlike putty and other options, liquid epoxy is capable of filling holes of any size or depth with ease. Its exceptional strength and hard-curing properties allow it to penetrate deep into the wood fibers, providing a high level of stability and structural support. Finally, epoxy resin is incredibly versatile and can be customized by tinting or the embedding objects into clear resin. For tough, long lasting and reliable repairs to wood holes, cracks and crevices, clear epoxy resin filler is the way to go.



How long does epoxy last on wood?

With proper care and maintenance, epoxy resin will last decades on wood. There are a few factors that determine its longevity, including where the project is kept and the amount of wear and tear it is exposed to.

Allow Industrial Clear to fully cure for seven days before using your wood project. Be aware that sharp objects can scratch resin, however, damage can be repaired by sanding out the scratched area and applying a fresh coat of resin to the entire surface.  Avoid UV light and exposing the resin to temperatures beyond 350F (176C) which can cause irreparable damage. 

For best results, wood should be thoroughly dry before applying epoxy resin.  Moisture can cause the wood to expand and contract with temperature and humidity, placing stress on the resin which may cause it to crack over time. 

Learn more about how to use epoxy resin on wood.

Read our top 10 tips when using epoxy resin for wood projects.

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