# Does cement board require thinset to the underlayment?



## scheenstra (Jan 5, 2008)

Just finished installing a new subfloor & underlayment (3/4" and 1/2" plywood), old one was shot...looks great now, solid as a rock. Glued & screwed the subfloor...screwed the underlayment (UL) to the subfloor while avoiding the joists. Ready to start my first tile project. Need to lay the CBU in preparation. My question is: Do I need to set the CBU to the UL with thinset?

All the applications I have seen do this. My concern is...if I screw up, or sometime down the road, I need to pull it up...can I simply nail the CBU down w/o the thinset? Without the thinset, I can (relatively) easily remove the tile / CBU from the underlayment, if needed. I will nail (not screw) down the CBU to ensure relatively easy removal, if needed. 

I approach each project with a devils advocate mindset...if I mess up, how can I recover with minimal pain & expense. With the CBU "glued" to the UL, it would be very painful to recover w/o removing the UL / subfloor.

Bring it on...and thanks in advance!


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## Bud Cline (Mar 12, 2006)

> Do I need to set the CBU to the UL with thinset?


YES, absolutely. ALL cement board manufacturers require it. The TCNA requires it. The NTCA requires it.



> All the applications I have seen do this.


Well there ya go!!!




> I will nail (not screw) down the CBU to ensure relatively easy removal, if needed.


Yow-well....GOOD LUCK with that theory.



> I approach each project with a devils advocate mindset...if I mess up, how can I recover with minimal pain & expense. With the CBU "glued" to the UL, it would be very painful to recover w/o removing the UL / subfloor.


Don't use thinset under the cement board and see how long it takes the devil to come knocking at your door.

If you play by the rules and use unmodified thinset (as you should) you won't be "glueing" the cement board to the substrate to begin with.

The thinset is there to fill voids and firm the cement board, it's not there to glue it to the floor.


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## Floorwizard (Dec 5, 2003)

> All the applications I have seen do this. My concern is...if I screw up, or sometime down the road, I need to pull it up...can I simply nail the CBU down w/o the thinset?


Let's put it this way....

Bud is right...

However we put Ceramic tile over ROOFING FELT in our showroom which is on uneven concrete. That is so we can remove with very little effort to change out. This is not a recommended practice for homeowners. But all is doing very well.
Bud's point is that even though you MAY be o.k. installing outside of the box, chances are you will not be o.k. and it will cost you.
We are pro's here, so most of the time if you want exact pro answers, you will get it.
I would never install tile over felt in a home, but then again, it's supposed to be permanent right?
Maybe Vinyl is a better answer for you if you are looking at temp options.


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## Bud Cline (Mar 12, 2006)

> However we put Ceramic tile over ROOFING FELT...


For temporary installations that's the way it is done. Trade shows, showrooms, exhibits, displays, seminars. Then the tile is ripped up and thrown away. This is no place for that kind of information I don't think.

Three months from now someone will be here complaining that thier tile floor they installed over roofing felt failed and Florcraft said they could do it.:no::yes::no:


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## Floorwizard (Dec 5, 2003)

> This is no place for that kind of information I don't think.


This is a place for ALL info!



> Three months from now someone will be here complaining that thier tile floor they installed over roofing felt failed and Florcraft said they could do it.


That would be sad because I said...


> This is not a recommended practice for homeowners.


and.....


> I would never install tile over felt in a home


so I think I covered myself.
But I am not a lawyer.....

Just in case you are right though let me say this...

You will go to your mailbox and send Florcraft $1.00
Do it....
do it now.....


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## Bud Cline (Mar 12, 2006)

PM me your mailing address...I have something for you anyway.


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## Floorwizard (Dec 5, 2003)

Are you wearing a hooded sweatshirt and big dark glasses?
Do you live in a shed in the woods?

Now I am worried


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## Bud Cline (Mar 12, 2006)

Whatever.......it's your loss! I was going to send you a gift from corn-country but that's OK, others will appreciate it.

I do have relation in Anchorage just a hop skip and a jump from you.:bangin:


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