How to Patch Cement Board? 2 Easy Methods

Cement boards are widely used as backing for tiles or other things and protect them from moisture. Although it’s a very sturdy thing, with time, the board can be damaged and holes can be found there.

Having holes in the cement board can reduce its waterproofness ability. That’s why it’s important to patch the cement board as soon as you have noticed it. Patching cement board isn’t that hard and by following a few simple steps you will be able to do so. However, the steps or working procedure will differ from the size of the holes in the concrete board.

Read on and learn how to patch cement board and what need to do for different-sized holes in the concrete board. So, without any further ado, let’s begin!

How to Patch Cement Board

Procedure for Patching Cement Board

As aforementioned, the procedure for patching cement board will differ from different hole sizes on the cement board. Here we have provided both procedures for patching smaller or larger holes on cement board. Let’s start patching then! 

Method 1: Procedure for Patching Cement Board with Small Holes

First of all, you will need to clear off the hole area to ensure that there is no residual moisture and dust, or debris. Take a clean damp sponge, and moisten it with water. 

Now, clean the surface with it.

After that, if the hole size is lower than ½ inch, then –

  • Prepare the mix thin-set mortar and take a putty knife.
  • Now, with the putty knife, start applying the mortar to fill up the holes evenly.
  • Wait till the mortar dried, use sandpaper to make the surface smooth, and then start your further work with the cement board.

NOTE: Always use thins-set mortar that has a setting time of 10 to 15 minutes. So that you don’t have to wait for hours.

If the hole size is larger than ½ inch –

  • Create a V-shaped groove around the holes.
  • Now, fill up the groove with the thin-set mortar.
  • After that, take a 2-inch wide polymer-coated fiberglass tape, press it into the layer of thin-set mortar, and don’t forget to overlap the edges around the hole with a ½ inch of tape.
  • Lastly, apply mortar and fiberglass tape and wait till the mortar dries. Take sandpaper and start rubbing to provide a smooth finish.

Method 2: Procedure for Patching Cement Board with Larger Holes

If the holes are larger then you can’t follow the steps mentioned for patching cement board with smaller holes. But the cleaning process is the same. So, clean the surface and then follow the steps below. Here are the steps you will need to follow. 

  • First, you will have to cut the portion with the hole. Take a cement board cutter, angle grinder, carton knife, etc., and cut the damaged part.
  • Take off the broken pieces of cement board and dig until it is free of thinset mortar.
  • Take a new cement board, cut a piece according to the size.
  • Now, attach it to the installation place with the thinset mortar. Alternatively, you can use corrosion-resistant screws instead of thinset mortar.
  • Finally, apply mortar and fiberglass tape and wait till the mortar dries. Take sandpaper and start rubbing to provide a smooth finish.

Frequently Asked Questions and Answers (FAQs)

How do I fill holes in the Hardie board?

The Hardie board is a type of cement board. So, you can follow the aforementioned steps for filling holes in the Hardie board.

Can I use a broken cement board?

Yes, you can use a broken cement board for patching an existing cement board in your house. If you are asking whether you can use a damaged cement board, then the answer is no. Using damaged or broken cement boards can damage the tiles and walls as well.


Lastly, patching cement board is a very easy job to do and you can do it by yourself without any issue. Just you will need to follow the accurate procedure to get your job done. That’s all for now folks! If you have any further queries, let us know in the comment box.

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