Veneering MDO for Stair Treads

A question about whether MDO could be stable if veneered on only one side, continues on into a deeper debate about the suitability of veneered material for stair treads. July 29, 2012

My understanding of the reason that veneers must be applied to both sides is because of the water in the glue evaporating and a balance being required during the drying process. I'm looking to veneer 1/4" thick shop cut veneers onto 1" MDO. If epoxy is used, would it still be necessary to do both sides?

Forum Responses
(Veneer Forum)
From contributor O:
1) Your understanding about why you need to veneer both sides of a panel is completely wrong. Veneered panels need to be balanced (unless restrained by framing) because veneer tries to expand and contract with seasonal humidity changes, and the panel will curl and warp unless those forces are balanced. This is a permanent requirement, not a temporary, assembly-related need.

2) 1/4" thick wood is not veneer. It's at least two or three times as thick as anything I'd call veneer. You're thinking of gluing a layer of unstable solid wood to a stable sheet good. Don't do it - not even on both sides.

From the original questioner:
You may be correct about needing to do both sides, however incorrect about 1/4" not working on both sides. Myself and others have had good results doing this. MDO is a plywood with a paper-like layer on both sides. I'm wondering if one more layer can be added to one side. Does it really matter if the plywood is 10 layers and not 9?

From contributor O:
As to whether 1/4" material on both sides is workable, a lot depends on things like the species of wood, the size of the piece, and the environment in which it's used. Generally speaking, thicker material will be more trouble-prone even if you can get away with it in some circumstances.

Although odd numbers of plies is a handy rule of thumb, it's not really the number of plies that makes or breaks a system like this. The problem you're flirting with is that the forces of expansion and contraction, due to humidity changes, of the veneer on one side of the panel won't be balanced by similar forces on the other side of the panel unless there's a similar veneer, oriented with the same grain direction, on the other side of the panel. When the panel is balanced, the opposite veneers push and pull against each other and maintain an equilibrium that minimizes deformation of the panel.

Think of it like an arm wrestling match. A balanced panel is like two evenly matched opponents; huge forces may be at work, but the grasped hands barely move because the opponents are equally strong. An unbalanced panel is like a bodybuilder arm-wrestling a weakling; there's no real contest, and the grasped hands slam quickly to one side.

From the original questioner:
Good explanation and you are probably correct for 99% of the applications. The circumstance which applies to me is treads and risers set into a housed skirt. So by and large it can be considered to be in a frame. Since the nosing is solid stock the portion veneered is less than 10" wide and 3' to 4' long. The piece which is veneered starts out 1/4" but by the time it is planed and sanded, is nearly the same thickness as the plies in the plywood which really makes me want to think of it as a face ply.

It may well be a failure but I'm going to glue up 2 and leave one in the shop for a couple of weeks on a shelf and the other in a mini skirt.

From contributor O:
I see; it does sound like your situation is more forgiving than most. I don't know what your machinery is like, but I'd encourage you to try sawing your veneers much thinner than 1/4", since most of that thickness is apparently destined for the dustbin. I typically shoot for 3/32", which wastes a lot less wood, and would also be less likely to deform your MDO after glueup.

From contributor J:
You must have a good reason for not using solid treads and risers. Making laminated composite stock is a lot of work. I am also assuming that the treads are not going to be walked on without carpet?

I have a stair book showing thick composite treads consisting of an inner lumber core and over-laid with two layers of wood. The first or sub-layer is applied cross-grain (or cross-banded) over the core and the exposed top face layer. The tread is completely wrapped. The layers are a minimum of 5 MM (a little less than 1/4").

From the original questioner:
You are right that it is more work than using solid material. The main reasons are ability to use woods that are either too scarce/expensive to use in solid and to sequence grain patterns. The only jobs I've used this on were homes where foot traffic would be light, however looking at composite flooring I don't see much of a difference.

From contributor J:
The difference between manufactured composite flooring with thin faced veneers and solid treads is that flooring can easily be pulled up and replaced. Your treads and risers are set into a housed skirt, therefore any replacement of a damaged or worn tread or riser would require a complete dismantling of the entire staircase (including the balustrade!). Veneered or clad treads can never be recommended for any kind of foot traffic whatsoever. The staircase you're constructing, in most cases, should be expected to last (at least) a lifetime.

I have replaced stairs in homes and public buildings that were over a hundred years old. The original solid oak treads were worn and hollowed out along the walking line by a half inch and more. These steps were unsightly but still serviceable. The risers all had deep dents and dings that would have punched through any veneer.

A glued-on nosing along the leading edge of a tread is another big no-no. There are tremendous forces applied at the nosing by just walking up the stair (let alone bounding up and down). A nosing piece that breaks off under the foot of a person bounding up the stair is going to be a serious issue!

Solid treads and risers should be the rule for professional stairbuilders. Engineered clad treads are mostly seen in modern riser-less designed stairs. These treads are often cantilevered or perhaps supported only by a single central beam. These laminated treads are often 4" thick and covered with a carpet mat along the walking line.

From the original questioner:
You have a very strong opinion on the subject so no point in discussing it. I first got the idea from Armin Gollannek, who does highly figured treads that are veneered.

From contributor J:
Very pretty indeed and maybe worth jumping through hoops for. When I look at those treads, I want to take my shoes off and step gingerly in my socks. They may even be a dangerous distraction as your eye focuses on the art of each step rather than paying attention to the climb. Next thing this guy will want to do is inlay each tread with elaborate marquetry patterns or cascading pictures.

"Artisan craftsmen" often throw reason out the window for the sake of their art. My points are still valid but who cares? This is gorgeous woodwork!

There's a recent picture posted in the Project Gallery of a custom made hand plane. Check it out and decide if you would use it or put it on display? You get my point? Anyway, I get yours. I am sure whatever you do will turn out great, so don't pay any attention to naysayers like me.

From the original questioner:
I do get your point. The use of something like this needs to be chosen carefully and doesn't lend itself to the vast majority of staircases. For the right customer it works, and besides, it is stunning to look at.

From contributor B:
It's unfortunate that none of the engineered flooring gurus comment on this. What you are proposing is not much different. I know most of them use a PUR adhesive, and hot presses that some of us simply cannot afford, but I think it can be done reasonably on a small scale.

I have been working on some flooring borders that use Tigerwood, and after milling a portion of the rough stock into blanks I realized I was going to run out due to excess wastage. There are many boards in the stack that I feel awfully guilty cutting up and I don't really want to order more stock due to my location, so I am doing a few mockup trials to test. I am using a 1/2" Baltic birch substrate, 1/4" wear surface and Unibond 800 in a vac press. I have applied a thin finish to replicate a worn out finish and am going to submerge the test into water for a few days in an attempt to replicate the effect of years of water abuse.

From the original questioner:
I've left a tread veneered 1/4" on one side, MDO core and 1/8" on the other side on a shelf for a couple of weeks now. Still flat and true.

Around here (Seattle) a 100 year old house is considered old and the ones I've been in don't show a 1/4" of wear. I'm sure that's not the case everywhere and the homes I'm referring to started as upper end and were well maintained.