Using Hardwood as a Subfloor

Should you install Luxury Vinyl Flooring over Hardwood Flooring?

Lisa, my girlfriend, is readying for work one morning and says, “look, this thing is warped again; I wonder if it has something to do with the mirror?”

I’m laying in bed, eyes half open and truth be told, unlike my hummingbird of a girlfriend I’m not very responsive before noon…and that may be an understatement. I can barely muster an ‘uh huh’ response to what was less rhetorical than I would have liked. I’m not sure I actually verbalized my response. I may have heard it inside my own head and thought I said it out loud. 

Come about 1 PM that day I had a semi-epiphany as I recalled what she was trying to tell me. I’ll need to present some back story to make what I’m going to try to get across clear to the few readers of this blog.

Background

About a year ago Lisa bought a small, all wood, makeup vanity from Wayfair about 16 inches by 29 inches. It doesn’t appear that they sell it any longer otherwise I would have included a link. It looks to be primarily solid hardwood except for maybe a few parts like the drawer bottom. Upon close inspection the top is constructed in a butcher block fashion; inch-and-a-half (4 cm) strips of wood laminated together. There are three hinged sections that make up the top, the right and left both open to either side respectively and the center section (call it a lid), opens to the back revealing a mirror, laminated and slightly recessed into the bottom side.

A couple of months after the vanity was put into service the center section began to noticeably warp. The hinged side stayed in place but the front side raised or curled up more than half-an-inch. The center of the panel was approximately a quarter inch lower than the sides, which had not budged at all. It was starting to look pretty crappy. Check out the picture gallery below for some perspective.

The failure bothered Lisa mostly because she collects nice things and keeps them nice. Though, she was ready to bite the bullet and write it off because she felt, “it wasn’t very expensive.” On the other hand, I feel that it wasn’t abused so it should perform as designed for as long as it’s properly maintained. I thought maybe I can fix it, after-all I am a hardwood floor installer and have some wood tricks up my sleeve. Before I made a repair attempt I suggested to Lisa that she contact the vendor and get their input. If I see a problem with flooring I get in touch with the vendor who gets in touch with the manufacturer. Sometimes I buy something at Costco and the warranty says, “in case of a problem do not return to store, contact the manufacturer directly”. I’m a stickler for instructions, if the option is there to bypass the middleman, I utilize it.

Lisa emailed Wayfair and within 48 hours she got a reply that they were shipping out a new one and didn’t want the old one back. No questions asked. I’m thinking, yay, I don’t have to try to fail to fix it and disappoint her because she thinks I’m a superhero. No more problem, means no more thinking about what caused the problem.

Fedex delivered this fifty pound box which has got to suck for them because it has no handles; and we simply swapped out the warped center section with the new and left the other parts in the box as there was absolutely nothing wrong with the rest of the unit. I figured Lisa could give it away or sell it cheap to someone who didn’t mind if it had a warped top.  Alas, the unpacked unit is still taking up space in the garage partially due to new social distancing guidelines.  Though I did weigh down the warped top with 100 lbs. of weight plates to see if gravity and pressure over time would force it flat.

Fast forward six months or so, just after monsoon season ended here in the Sonoran desert, maybe the end of September 2020, the new lid is starting to warp as well! Every week it seems to get a little worse. It is regularly 10% relative humidity inside, low enough to make you want to scratch off your own skin. That leads me back to, what is properly maintained when it comes to solid wood? Whether it be furniture, decor, wood flooring or humans, a comfortable relative humidity [RH] is between 30-50%. The manufacturer of this vanity provided no such humidity requirements but the same cannot be said for wood flooring manufacturers. They have very specific requirements for how interior, environmental or ambient conditions (temperature and relative humidity) containing their wood flooring should be maintained. Generally, RH is in the 30-50% range and a temperature range between 60-80 degrees Fahrenheit.

Wood Flooring Has a Comfort Level Too:

As a general rule for solid wood flooring, with geographic exceptions, appropriate temperature and humidity conditions are defined as those conditions where the interior environment is controlled to stay within a relative humidity range between 30% to 50% and a temperature range between 60-80 degrees Fahrenheit. These ranges are likely to be the average of all types of wood products used in normal household environments, assuming common heating and cooling equipment is used to ensure human comfort. 

NWFA 2019 JOBSITE CONDITIONS Page 32 Part IV, § F.2

Now we’re back to square one; add in the latest newly discovered revelation – that we’re most likely not going to get a like-kind exchange because the piece has been discontinued. Now that I’ve presented some background I’m going to circle back to Lisa’s epiphany regarding the mirror.

What’s Happening to the Hardwood?

This particular vanity mirror is 1/16” thick glass; I’m quite surprised that it is not some sort of synthetic because it is bent quite a bit and has yet to break on either one of the lids. Glass has the lowest perm rating of any common building material with a rating of zero. That means it allows no moisture vapor to pass through. Vinyl flooring has a perm rating of .05 making it a a good vapor retarder as it permits very little moisture vapor to pass through. For some perspective, roofing felt, also known as tar paper commonly used under roofing shingles has a perm rating of 5. That means vinyl flooring is 100 times more effective at blocking moisture vapor than is roofing felt. You can view the chart here.

Cupping 

A concave or dished appearance of individual boards with the edges raised above the center.

NWFA 2019 Page 165 Glossary

It was suffering from a problem some people refer to as “dry cupping.” But the problem is really just cupping, which happens when the top of the board is drier than the bottom of the board. Typically the cause of the imbalance is excess moisture from the subfloor. But it can also happen because of excessive drying on top of the board.

Wood Floor Business

It is likely that the glass is keeping moisture from escaping on the bottom side of the lid. Consequently, the glass is upsetting the moisture content equilibrium of the hardwood vanity lid causing it to move in mysterious ways. The cupping of the extra hardwood lid has caused the bond to fail on the bottom side between the glass and wood. Take a look at the pics below and notice how the glass has broken away from the wood on the hinged side.

As the glass pulled away from the wood it allowed air to get in between. Over time the wood began to balance out on it’s own. At some point I decided I would help it along. At first I thought it possible to remove the mirror in one piece, since nature gave it a head start, how secure could it be? I was only able to get a spackle knife a few inches under before the mirror broke. That’s unfortunate but par for the course as I tend not to do well around glass anyway.

Once the glass was removed I clamped the lid to my workbench for 24 hours and then set a level on it to check for flatness. The gallery below shows that the lid is just about totally flat.

I’m confident that the lid will flatten out to an unobjectionable state. At that point I plan on attaching a new mirror in such a way that will allow for ventilation between the glass and hardwood. If and when I get around to it I’ll update this post for prosperity.

How does this relate to the installation of vinyl flooring over hardwood flooring?

I’ve stumbled across a luxury vinyl flooring manufacturer’s installation instructions specifying that their product has been approved for installation over hardwood. In the same manufacturer’s written warranty there was conflicting verbiage stating that the hardwood must be sealed prior to installing, though this was absent from the install guidelines.. It’s common knowledge in the flooring industry that moisture and wood don’t play well together, though they can exist in a controlled or regulated environment. Never say never, a low perm flooring like vinyl may perform successfully when installed over hardwood. But unless the person installing the floor has a better than average understanding on how such an encapsulation will affect the finished hardwood flooring that is now relegated to subfloor duty they’d be wise not to take the risk.

The moral of this story is, pay more attention to your better half.

Here’s a Facebook Post of LVP installed over hardwood flooring gone wrong.

https://www.facebook.com/100001311074201/videos/3520211268032541/