How to Patch Hardie Board

James Hardie fiber cement siding, trim, and fascia board are the strongest, most durable products you can put on the side of your home. They won’t warp or rot like wood and are much thicker and more resistant to heat than vinyl. However, we won’t say it’s indestructible: debris thrown around by a storm may cause some damage. If this happens to you, here’s how to patch Hardie Board.

Chances are, if there is damage, it will be kept to small areas of your Hardie siding. According to the James Hardie website, “dents, chips, cracks and other minor surface damage in Hardie® siding and trim products can be filled with cementitious patching compound.”

There are plenty of products on the market designed specifically for fiber cement materials, so you should be able to find what you need at almost any home improvement store. If there are large sections of siding that need to be repaired or replaced, you may want to reach out to Joseph Ketner Construction for a consultation.

If there are entire rows of damaged boards, there may be some water damage behind the siding that would need to be addressed. You don’t want to cover up any moisture issues because then it will be trapped in the walls of your home.

How to Patch Hardie Board

Patching Hardie board involves repairing or filling in damaged areas to restore the board’s integrity and appearance. If it’s just a matter of a few cracks, it’s easy enough to grab a small putty knife, fill in the cracks, and wipe away any excess. But for larger holes, here are some simple steps you can follow to fix things up.

Materials You’ll Need to Repair Hardie Board Damage Siding

  • Hardie board patch (cut to size if necessary)
  • Fiber cement patching compound
  • Putty knife or trowel
  • Sandpaper (medium-grit)
  • Primer (specifically formulated for fiber cement)
  • Paint (color-matched to the Hardie board)

How to Patch Hardie Board: The Process

Safety First
When working with Hardie Board siding, it’s important to prioritize your safety. While the material is durable and long-lasting, it can also produce fine dust particles that can be harmful if inhaled. That’s why it’s crucial to wear the appropriate personal protective equipment, such as safety goggles, gloves, and a dust mask, before beginning any patching or repair work.

Prepare the Area
Clean the damaged area of the Hardie board by removing any loose debris, dirt, and anything else in the hole. Use a soft brush or a cloth to wipe away dust and ensure a clean surface. This will help the patching compound to adhere to the interior surface. You may consider cutting the hole to a more uniform shape if needed.

Cut the Patch
Once the area has been cleared and prepped, cut a new piece of Hardie board to fit the damaged section. Use appropriate tools, such as a circular saw equipped with a diamond blade, to cut the replacement piece to size. If you are cutting a round piece of Hardie board, a jigsaw may work better.

Apply Patching Compound
Using a putty knife or a trowel, apply a thin layer of fiber cement patching compound to the damaged area or the back of the replacement patch. Make sure the area is clean first and spread the compound evenly and smoothly into place. Then firmly press the replacement patch into place.

If patching compound comes up through the edges, that’s fine: just smooth it into any small gaps. If the hole doesn’t require a patch, and you’re just using compound, use the putty knife or trowel to create a smooth and even surface. Feather the edges of the compound so that it blends seamlessly with the surrounding Hardie board.

Allow to Cure
Follow the manufacturer’s instructions on the patching compound for curing time. Typically, it takes several hours for the compound to dry and harden. Keep the area dry during this time. You can do this by covering it with thick plastic and taping it into place just under the siding above.

Sand the Patched Area
Once the patching compound is fully cured, use medium-grit sandpaper to gently sand the patched area. This will help achieve a smooth and even surface that matches the rest of the Hardie board. Run your hand over the edges to make sure there are no gaps and the surface is uniform.

You may need to apply another thin layer of compound to fill in little gaps or, depending on the type of siding, add little lines with the putty knife edge to mimic the grain of the surrounding areas. Let that dry and you’re done. Now it’s just a matter of priming and painting. Click here for James Hardie recommendations on how to do that and what products to use.

By following these steps, you can effectively patch Hardie board and restore the integrity and aesthetics of your construction project. Always refer to the manufacturer’s guidelines and product labels for specific instructions on using patching compounds, primers, and paints with fiber cement materials.