You cannot nail thru cork and 3/4" hardwood needs to be nailed. See this link.

Are you trying to dampen impact sound or airborne sound? The cork might help with airborne sound but the impacts will largely be transmitted through the cork via the fasteners.

We have imitated old installations here that used a 1/2" thick wood/paper based product called hushboard and I can tell you that 2" fasteners barely get any penetration into the subfloor.

If sound deadening is a real priority you're better off going with 1/2" cork and gluing an engineered product over top.

As Timothy points out, noise is transfer through metal fasteners like nails, screws, staples, cleats etc. For that reason a glue down install is ALWAYS quieter than a nail in place.

And cork is NOT allowed to be pierced. The nails/cleats/staples will SHRED the cork underlay over time. It may not happen in the first couple of years...but it will happen. That's why cork pros (like me) do NOT allow a nail-down install over their cork underlayment. It defeats the purpose.

If you must have nail down then work with QuietWalk Plus AND acoustic 5/8" drywall on the ceiling below.

Thank you all so much!!! I had to make this call today for the framers and I was about to tell them 1.25" I am going the QuietWalk route.

SJ McCarthy I came across this post and your very helpful advice and recommendations, while searching for Quietwalk plus / cork. I wanted to request your kind advice and guidance. We are installing Mohawk engineered wood ( 9/16th inch) Tec wood and we have already made the non-returnable purchase. It’s uniclick wood that per manufacturer can be floated gluelessly. We have a family member with chemical sensitivities and medical condition therefore avoiding mold is very important. We are planning to use no glue.

We are in the Southwest ( no basements here) The house is new construction (was built about a year ago) with concrete slab. 1st Floor Subfloor is concrete ( hardwood will be installed in the bedrooms and closets only. The kitchen and common areas have porcelain tile installed).

The 2nd floor subfloor is OSB ( with a Gameroom that is open to below and catwalk/hallways) . All these areas were carpeted previously.

I am really confused regarding underlayment. Hardwood manufacturer sells their own underlayment and it’s about 2 mm thick, 3mil vapor barrier. Their tech support recommended that underlayment be no more than 3 mm thick because of potential to damage click and lock mechanism and if one is not using their own underlayment, then specs for different brand underlayment should be similar to or better than theirs.

Following are my questions/ concerns that I haven’t been able to figure out despite hours of research:

1. For 1st floor concrete subfloor: I am considering quietwalk plus, but it’s 3.175 mm thick and only has 1.5 mil of vapor barrier. I was interested in this due to the ability of wicking moisture from the perimeter that the Quietwalk manufacturer stated and it’s anti mold.

Do you suggest this would work for us? Or I should consider the Mohawk underlayment or any other you suggest? Would you recommend putting a poly 6 mil under the Quietwalk plus for additional protection? But I am worried about trapping any moisture between the poly and the concrete. Also doesnt the poly need to go up behind the baseboard couple inches up the wall? And quite walk plus needs to be 3/4th inch away from the wall. So wouldn’t the poly defeat the purpose of the quiet walk plus’s moisture management system??

Regarding checking moisture status of concrete: we are planning to do a calcium chloride test. But I am concerned that after self leveling cement that will be used to level the concrete, how long it will take for concrete to be completely dry for hardwood installation?

2. For second floor subfloor which is OSB: I was considering quietwalk plus, but it has vapor barrier and I am worried about trapping moisture between osb and underlayment. Or I could use cork. If I use 1/8th inch cork, I’ll be in compliance with manufacturer’s recommendation of not using underlay >3 mm. But will 1/8th inch cork provide any noise reduction? If I use 1/4th cork would that be better? How does 1/8th inch compare with 1/4th inch cork and quietwalk? Thank you so much again for all your help and very helpful information you have shared on this forum. Really appreciate it.

The good news is your new concrete slab *should have an intact moisture barrier below it. That's the best possible start. Traditionally you take the moisture readings BEFORE you go ahead with the Self Leveling Compound (SLC). We do that *just in case a primer/bonding agent is needed to get the SLC to stick.

You are using a click-together hardwood means you will be limited by the click system. The Uniclic system is one of two industry Gold Standard products. It has limitations. The deflection of a plank (when stepped on) is one of them. That's why Mohawk does NOT allow underlayment that is thicker than 3mm (foam or felt based products). The Quietwalk Plus 3.2mm *might be too squishy for the click system. If you can down grade it, then that's your best option over the concrete.

The OSB is another story. Wood subfloors are NOT allowed to have a vapour barrier laid over top. The one exception is QuietWalk Plus laid underrneath a NAIL DOWN hardwood (the nails pierce the underlayment thereby creating a vapour retarder not a vapour barrier...whew).

Cork underlay is different from the foam/fibre products. It does not compress. A 6mm cork underlay is equal (in acoustics) to QuietWalk Plus 3.2mm. It will not crush or cause any deflections that would disturb/damage the Uniclic system. I've used 12mm cork underlay underneath Uniclic floors before without any issues. The tech support suggested but I do not see anything against using 6mm cork underlayment.

I would use the thinner Quietwalk Plus over the concrete. Use it as per it's manufacturer's instructions and then install the hardwood over top of that. I would happily use 6mm cork underneath the Tec Wood. The Unclic system has the ability to handle 6mm cork underlayment. That's not my issue.

My concern is with the stairs. The riser heights must be matched very closely. That means the first step (from the main level) must equal the final step onto the second floor (the hallway). If you use two different underlayments on the main floor and the second floor, you may have to rebuild your stairs (very inconvenient...and very pricy).

Just be FULLY aware of what is happening on the top of the stairs. It isn't just door jams that have to be dealt with.

@SJ McCarthy I'm running into your name in a lot of posts. I have an old 3/4 pine subfloor, and I'm installing new 3/4 inch oak on top (2.25 inch wide). In this post you recommend the QuietWalk Plus, but I'm also seeing MPglobal's Insulayment product. This looks to be more dense (16 lbs/sqft vs 11) and have a higher compression resistance, but then I also see that it has lower IIC and STC ratings than QuietWalk Plus. That doesn't seem to make sense. Any thoughts? Also, what are your thoughts about this very thick QuietWalk carpet pad? Could that be used as a nail-down underlayment without the floor feeling "spongy"?

Thanks for bringing me back into the discussion.

First things first: you NEVER use carpet underpad under anything but carpet. EVER. So now that is out of the way, we'll move on.

The QuietWalk Plus is allowed to be nailed into. Very good. So too is the MPGlobal. Excellent. We are officially working with Apples to Apples. Nice.

Now onto ACOUSTIC RATINGS.....shise (German...allows me to swear without getting flagged!).

You are now into a WHOLE NEW INDUSTRY of trickery and crap...with some crapola on the side. And a desert of kaka pie! Nope not kidding. This is one of the LEAST understood parts of the building industry. And the underlayment manufacturers LIKE it that way....which is why they spend big bucks lobbying to KEEP the industry 'stupid'.

OK. That's my rant. Done. Onto SCIENCE (yah...big cheer!).

Always look for a Delta IIC rating. It is an expensive test that PROVES how good underlayment is. The cheep dudes will NOT do this test because it proves how BAD their product is. See where I'm going with this?

Right. QuietWalk Plus HAS the Delta IIC rating (22 dB). MPGlobal (made by quietwalk....ahem!) does not. For me that's all I need to know...but I also taught myself the insulation/acoustic rating industry. Only took me two years. Yep. 2 YEARS. And I already had a background in human hearing, decibels and neurophysiology of the auditory canal. It was teaching myself the CRAP the industry likes to do to HIDE how bad their products are, that took the longest. But I digress.

1. The QuietWalk Plus has a Delta IIC rating of 22 dB. That's EXTREMELY GOOD. That's BETTER than 6mm cork underlayment with a cork floating floor on top. This is VERY VERY VERY good. Personally I would stop there.

2. QuietWalk Plus is THICKER. Yes. I know. It is ONLY 1mm thicker...but the TOTAL thickness = 3mm. Compare that to the 2mm thickness of the MPglobal. It doesn't SOUND (haha) like a lot but STATISTICALLY it is 30% THICKER. WOW.

You have the difference RIGHT THERE. Quiet walk has DELTA IIC ratings that are ranked as very good to exceptional...and it is 30% THICKER.

My research is done. I'm still with QuietWalk Plus. I love my cork but it isn't always possible to use it. It cannot be nailed into. Which means my next favourite, QuietWalk Plus is the way to go.

Remember: floors are like roofs. It is the ONE surface that takes ALL the abuse. Do not 'save' money on the floor. You'll pull your hair out because you thought a few dollars saved on the flooring would be a great way to save a budget.

I'm not saying you are headed in this direction...it's just a statement I always make about floors.

I hope this helps....without having to give a two day lecture on the BS of the acoustic/insulation industry. Good luck. QuietWalk Plus is still the best that I've seen.

And no, I have no affiliation with them. I'm just impressed with their product.

Ben Schenck Why? What purpose is your underlayment supposed to serve? Any underlayment, when nailed through, will have it's performance degraded.

Yes, I understand that the nail down will decrease the performance of any underlayment (versus floating or glue), but that's a sacrifice I'm willing to make to have the hardwood floors.

So what is the purpose? Do you live in a multi-story building and you're protecting rooms below from hearing excessive noise?

Yes, it is a 3-story home, and there are a couple of bedrooms on the third floor that are above bedrooms on the second floor. You can hear both footsteps and muffled voices from these rooms.

Thanks @SJ McCarthy, I'm a little skeptical about your claim that you have no affiliation with QuietWalk ;). I'm having a lot of difficulty finding the QuietWalk Plus, especially a 360 sqft roll, which I would prefer. Think I can get away with using the regular QuietWalk in the naildown application?

The QuietWalk Plus is the ONLY one you can nail into. Right now the building industry is having a dastardly time getting products. So much relies on overseas materials...which have NOT been brought in for (roughly) the length of the pandemic. The bottle neck is the lack of humans in factories due to lock downs, etc.

Keep trying to find the QuietWalk Plus.

Your best bet for sound reduction is a sound control mat with an engineered floor floated over the top. Cut the jambs a tiny bit high, install the base or shoemold just off the floor and use an acoustical caulk. You can also use a foam product at the perimeter expansion space.

Should I use cork under my engineered hardwood at a beach front house? I'm concerned about the moisture in the air. Thanks!

@SJ McCarthy MPGlobal on this page of their site lists Insulayment's Delta IIC as 20:

https://www.mpglobalproducts.com/blog/best-acoustic-underlay-for-laminate-flooring/

Since Insulayment is much denser with higher compression resistance than QuiteWalk Plus, wouldn't it still be a better product for nail down installation to avoid board and nail movement potentially causing noise?