Laticrete has several sound reduction products available. Depending on your subfloor I would eliminate the CBU from the equation and use an uncoupler. It would be best to contact Laticrete Tech for their recommendation.http://www.laticrete.com/home.aspx

And I'd get a more learned contractor. He doesn't seem up to date on sound reduction products that have been around for quite a spell. Ceement board isn't a requirement as there are several products to provide a tileable surface. Since this is over wood framing, be sure to use the handy dandy deflecto-lator found in the blue bar of the John Bridge Tile Forum.

Agree with C&R http://www.johnbridge.com/vbulletin/deflecto.pl

We're using the proper terms to help you find the proper materials.

I for one, refuse to "dumb it down". The internet can be a wonderful learning tool. Please use it as such. If you don't understand the terms we are using, please highlight them, right click, then scroll down to "google search for this term" You'll be taken directly where you need to be. The Pro's on this forum give their precious time and hard earned experience for free.

If you elect to continue with the same contractor its your call. The advice given was to help not only the OP, but everyone else reading along with the intention to avoid problems in the future. We find there are at least 7 people reading along for every one person posting.

All the while, the question I asked remains frustratingly unanswered. Does it make any sense to put cork under cement board?

I appreciate the pros who freely give advice here but it is common for the pros on this website to make mountains out of mole hills. Additional information is always welcome but it's not always helpful when the question asked is not answered. Or the answer is something only another pro can understand. I can't tell you how many times I've asked a question that is ignored by pros who go off on tangents when another lay person steps in to answer the question. It is so common I have started threads with the disclaimer of "please just answer the question."

I know you guys mean well but so far I don't the information I'm looking for. And the next time someone has the same question they won't have the answer they're looking for either.

Uscpsycho... I bookmarked this thread to learn about the issue for my own education and for future reference. I completely agree with you! This is a site where pros can talk to pros, but it's also a site where people with no background on a subject can learn from people and increase their knowledge.

There's an old saying that is very true...

It's one thing to know a subject, but takes intelligence to explain it to someone else.

This idea of 'dumbing down' is ridiculous! What an arrogant thing to say! It's obvious that we're ignorant on the subject, if we weren't why would we waste our time asking here??? We could research it anywhere, but here is where people with experience and knowledge enjoy sharing what they know.

Some day, someone with the attitude some of these so-called pros show will need info about a subject of which they know nothing. That day they'll be the ones without someone willing to help!

Cork under cement board isn't an approved installation method by the ceement board manufacturers or by the TCNA. All ceement board manufacturers give clear installation instructions on their web sites.

To answer your question. No it does not make sense as there are better products for noise reduction although without determining the construction of your existing floor there is no way to suggest the proper method. First use the John Bridge link which I posted and C&R suggested. If you can go with tile then you can use the Laticrete Tech link for manufacturer specific products. The easiest way is to have your contractor present a manufacturer approved method for your situation. From the cement board manufacturer for example which will approve or decline the proposed method in one simple phone call. I was typing and didn't see last 2 posts.

The cement board needs to be directly on top of the floor joists, otherwise its purpose as subfloor is largely defeated.

Cement boards are not structural and are never installed directly over floor joists. Cement boards have no structural value and simply provide a tileable surface.

NEVER!!!! place cement boards directly on joists!!! It is not a subfloor!

Seemingly simple questions don't always have simple explanations.

That is not true -- there are structural cement boards. They are used all the time when plywood can't be used due to a non-combustible requirement. Sorry, I am mostly familiar with industrial applications and don't know anything about tiling.

Ah yes. I see your point. Such as USG structural cement boards. We deal with backer boards / underlayment. I retract the word never as there are similar products referred to by a similar name but with a completely different composition for a specific use. I've gained some industrial knowledge. Thanks Peter Also a good example of why using the proper terminology is important.

Sorry it is my fault -- I should have been paying more attention to the context here. :)

"Seemingly simple questions don't always have simple explanations."

True. But in this case a simple question had a simple answer.

Q: Does it make any sense to put cork under cement board?

A: No

Seems like this is one of those cases where it's a cut and dry answer with no wiggle room.

But this thread went to a hundred different places before I got the answer I was looking for. The people asking questions on Houzz appreciate the knowledge many of the people here have (which is why we ask questions here) but sometimes it makes sense to just simply answer the question. If we need elaboration we are smart enough to ask for it.

It's great if you want to offer additional information but please do it in a way that doesn't require us to become subject matter experts in order to understand you. And again, at the very least please make a conscious effort to answer the question that is asked.

Illtelluwhat, Perhaps set the parameters for acceptable responses right out of the gate.

I.E.

"I expect your response to use 3 nouns a proverb and be less than 63 characters.... No meandering allowed" etc. etc. you get the idea

Believe it or not, I have actually done that. Nothing as ridiculous as what you said but I've started threads with a request for people to just answer the question on its face without complicating things. I didn't do that this time but maybe it would have helped because I didn't get a straight answer for ten days.

In any case, it's not that I don't appreciate more information but sometimes you have a pressing question and you just need an answer. Is that so bad?

"Cork under cement board isn't an approved installation method by the
ceement board manufacturers or by the TCNA. All ceement board
manufacturers give clear installation instructions on their web sites."

This tile mechanic's advice (above) being the answer IMO. why so many homeowners fail to use MFG tech support as their first line of defense rather than random DIY sites for their answers ill never get that.

Yes, that is the answer and it took ten days to get that answer.

I'm not sure what your experience calling tech support is (Is cement board even considered tech support?) but the reason so many forums like this thrive on the Internet is because customer support/tech support is generally abysmal. Most of the time you can find a much more knowledgable person on a "random DIY site" like this than you can get on the phone. That's why.

I totally get what you're saying. And pretty much agree with you.

But this was a simple question. Never put cork under tile. Period. Nothing to go over my head, no need for manuals, no variables to consider. There was no need for much discussion as there is never a situation (as far as I can tell from what's been said here) where it is OK to put cork under tile.

If someone asked a mechanic "is it ever OK to put milk in the gas tank" the answer would just be no. The mechanic could go on and on about why you shouldn't put milk in your gas tank but the inquiry would have been satisfied with a simple no. That was the situation here.

So all the tangential stuff was frustrating because there was a simple answer to my question that took ten days to get. Know what I'm saying?

Actually you'd be surprised at the amount of products now being sold for tile underlayment that are intended for noise suppression and or insulating purposes. I think the industry is still figuring this concept out, but in the meantime you'll find products out there with various compositions being sold for use under tile. I'm personally not a gambling man though. :)

And the definition of synthetic is?:)