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Thursday, July 11, 2024

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What is the most efficient way to take up cement board from the subfloor?

Usually in this feature, we simply present questions from NTCA Members and answers from the NTCA Technical Team as a whole. In this case, we present a dialog, to illustrate the kind of in-the-moment technical support NTCA Members are able to receive from Technical Team members and how that supports the successful work they do. 


What is the most efficient way to take up cement board from the subfloor? When they put it down years ago, they did a good job!

Thanks for any advice. This is the first time we have had to tear out flooring put down this way.

We have a lot to learn!


I have had a lot of success using a roofing shovel. Others may share their tips as well. 

– Matt Welner, NTCA Trainer

A digging bar can be helpful if you have the space. But if they used a good quality thin-set mortar under the board, you’ll likely just wear yourself out ramming it into a roadblock and scraping the top.  

Also, as long as you are remediating the dust correctly, you can pulverize the tile and part of the top layer of board as it seems you are doing now, sweep and remove big chunks, then scrape or grind. The diamond cup grinder need not be your favorite, as you are going to hit nails/screws and it should eat the board and mortar away easily – but I will reiterate again, use good PPE and good equipment to do this: demo hammer, properly guarded and vacuum shrouded grinder, HEPA vacuum, air scrubber, and negative air setup likely necessary.

If the thin-set mortar is well bonded, it could be that they used a proper ANSI A118.11 mortar. At that point, you do not need to remove down to the subfloor and can use prep products that will bond it to bring the floor into tolerance once the loose material is removed. That’s a decision you’ll have to make. 

– Brad Denny, CTEF Executive Director


We do have good ventilation in the room, a HEPA vac, shroud for the cup grinder and we are cutting grout joints with a blade that I used to use for repointing brick. It is working well.

Once we have the tile up, we are going to try a spade bit on a demo hammer and see where that gets us.

One thing we have learned is that when done properly, it will stay for a long time and when it does have to come out, it will be a pain for the demo team. We hope installers in the future have the same issue taking our work out!

Thanks again!


Okay. We have the tile off. We do not know if it is an ANSI A118.11 mortar or not, but this board is not moving! It took about 15 – 20 minutes to grind down 1 sq. ft. to mortar on the subfloor.

We know the loose stuff has to come off and we will vacuum the surface really well. 

At that point, can we prime the floor and self level to give us a good base for tile? We believe that is what we understood from Brad.


Why was this project occurring…was there damage or a previous failure that required this to be removed, or is this a design fix? 

At this point, whether we were enjoying brats, burgers, and beer in the backyard in shorts and flip flops or sitting a conference table with suits or replying to each other via the NTCA Technical line, I would suggest the same thing: always consult your manufacturer rep on issues like this.

Depending on the product line, each manufacturer may have a different way of dealing with an issue like this one. They may have a test for you to run before you take that next step. They may have a primer or reinforcement they would like to see in there. They may have a trick up their sleeve we haven’t thought about. They may even tell you to keep grinding. But over time, being diligent to ask questions, you will begin to see similar actions to take based on history and experience. However, having that phone call or email to the people that can easily help you replace products in the event of a mishap is HUGELY invaluable.

One of my reps said he loved getting phone calls from me because I asked before I plunged forward, and it would always untie his hands to help out if something went awry by having a “paper trail” that points to me seeking guidance. Put them on speed dial!

That being said, yes, I think you could likely prime and pour over this depending on the manufacturer and product, but double check to make sure. Without physically being there it can be difficult to evaluate just how sturdy and dense the remaining materials are. 

– Matt Welner, NTCA Trainer

Thanks for the discussion and photos. I agree with what Brad and Matt have already said.

For future installations: If, after doing some exploratory surgery and taking a sample or two by cutting/coring through the tile layer substrate and to the subfloor to determine the structure of the original system, it is possible to set tile over tile. It’s also necessary to determine if the substructure can support the weight of an added tile layer, but a couple of elevation changes created with a tile over tile installation might be preferable to the owner instead of going through all the effort of removing a well constructed installation.

An alternative approach I have taken is to hire (subcontract or have the client hire) a demolition crew to do this work. There are some that are fully set up with dust control equipment and experience in doing this sort of thing. Having someone else do this keeps you on task for what you do best – tile installation. 

– Mark Heinlein, NTCA Training Director

Response 3

Thanks everyone for the replies.

To respond to a few questions: we were the demolition team hired to do this job. It was part of the project and has been a good learning experience.

I am in contact with reps a lot and all of them are on my phone. They are helpful to say the least! I generally reach out to them, as I do you all, to get advice before a project begins. Again, the information that I have gotten from you all and my reps has saved/made back the NTCA membership fee multiple times over. We don’t like having to go back to fix something that was avoidable with a quick question on the front end of a project.

We will be self leveling over this. We will send pictures once we get it done.

Thanks again for how much you all help us out, even with what seems like mundane/simple questions.

Have a great finish to your week and a great weekend!

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