How can repalce some broken tile and fill in the broken backer board behind the tile?

Asked By: askrick on Thursday, February 17, 2011
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Answer I am replacing some long overdue cracked/broken tiles in my bathroom shower. I've found some of the backerboard behind some of the outer edge tiles has broken away, about a three quarter inch to a half inch and about 2.5 inches in length in one area then at the upper corner after removing the corner tile the backer board corner was completely gone. The person just tiled over the missing corner. What is the best way to repair the edges and corner damage? I don't want to replace tile over broken or missing backerboard if I can repair it. The backerboard is the cement style as far as I can determine and it seems to be OK as far as the interior walls of the shower go. Appreciate all you do with your expertise and instructions.

I took the photos and sent them to you, showing an upper corner tile which I had removed because it was cracked and I discovered the cement backer as being broken and missing the very corner. The other two photos are the same area just slightly different angle showing cracked and missing backer board along the edge. My question is how to repair these areas of missing and broken backer board. In order to replace those broken tiles? Hopefully these photos are clear enough for you to be able to evaluate. And thank you for what you do.

Glenn, thanks so much for your question. First of all, I want to thank you for sending me the photos. They really helped me to understand your issue and I will be able to give you much better advice now.

The most obvious thing is that you need to be able to fill the area in so that the surface that the tile rests on is flush with the existing surface. Let's take a look at the first photo you sent me with notes that I added.

photo of top area of broken tile

You can see by the photo that there is a good deal of patching and prep to do before tile can be installed. The goal is to get all the tile to flush out the same. We don't want any tile protruding past the other tile surfaces.

So first make sure that if there are still any loose or broken pieces of mortar or cement in this area, you remove them. Once this is done and it is secure, you will be ready to fill in the area. Also, be careful not to take out any of this that is behind your existing tile, unless it would happen to fall out. What you are showing me here looks like you don't have this issue.

Now that the area is ready for patch or fill in, you will need you a cement based filler. The one I highly recommend and that is easy to work with is called Quikcrete Thin Set Cement Patch. You can also use SimpleSet which comes in a tub. Here are a couple photos of the product.

quickcrete quickset bag    quikrete thin set tub


The bagged product will have to be mixed with water and the one in the tub is pre-mixed. Either way, you will want to make sure the consistency is right for building the product up to make a good patch.

When I say this, what it means is that the deeper the area is that needs to be filled in the more coats it will need to fill in. You don't want any of it to sag on you. So be patient and take your time making the patch.

These both have an adhesive quality to them as well as being mortar based. So, they will not only fill the are in but also stick to the wall better. You can use a putty knife or small trowel to apply and spread the material. Make sure the area you are going to patch is free of loose grit or sand and you can use a damp cloth to wipe the area down before you begin the application.

The next photo shows the bottom area of the tile where it meets the tub.

lower area of broken tile

The same principles apply here. Remove any broken or loose pieces and then build up the patching material to fill in the area. Make sure you bring it up to the same surface level as the area that is behind the existing tile. You want all the tile surface to be flush. Make sure you use a good silicone caulking to fill in any cracks and seams where leaks could occur. 

Another thing to keep in mind is that you want to try and keep the thin set material behind the tile so when you come up against the edges of the tile, make sure you use drywall joint compound or Durabond to smooth out the wall area where the edges of the tile are going to meet the exposed wall. Sometimes this means to stop your filler just a little short of where the tile edges will meet the wall. Blend Durabond from that point out onto the wall and then after it dries, you can use drywall sanding pads to smooth it out prior to installing the tile. See the photo below.

patching area of wall tile

After your patching material is completely set as according the product instructions, you can install the tile. After the tile sets, you can then fill in your grout, caulk, clean off the tile surface and you should have a job well done.

I hope this helps. Rick

Rick Maselli is Founder and Editor of and Ask Rick


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