Expert: Jamie Yocono - 1/2/2005

Question
hi jamie, thanks for the very complete answer.  a followup question.  just curious why you would go with a veneered mdf over a veneered plywood.  i'm assuming i would only need to stain one side of either of these products?  also, how would you recommend i join the ends of the sheets (biscuit, butt, rabbet)?

thanks again, matt

-------------------------
Followup To
Question -
greeting, we're looking to convert one of our upstairs room into a full blown library (floor to ceiling, all walls with consideration for a window seat) and wanted to do a bit of leg work regarding the construction. the room is approx 16'x12'.

we'd like the end product to "high-end" and are considering cherry or mahogany as our wood of choice. in speaking with some shops, it seems
many use cherry veneer (atop mdf) with solid cherry only on front pieces. i suspect this is done to reduce cost and maximize their profits. if we were to do this ourselves we would save on labor and therefore could spend more on materials. is it a waste to use solid cherry all around for this library (i realize if cost were no object one could use anything however i wanted to know what makes better sense and would look polished in the end)? broken down, we have:

side panels (cherry ply?)
shelves (solid cherry?)
back (that pins against the walls) (cherry ply?)
flutes, molding, etc (solid cherry?)
the framing (support) seems to be 2x4 (pine?)

does this seem right?

for our window seat, there will be room to construct a box below the window. what type of spacing (support) would one need to have between
boxes to insure adequate support for 1-2 adults seated on the seat (width of window is about 5ft). a similar question for the shelving above the window, what type of reinforcement would we need to consider to insure structural integrity for supporting the weight of the books above the window?

finally we have hardwood flooring. would we simply nail the 2x4 frames directly to the wood flooring or should we pull it up first?

thanks, matt
Answer -
Hi Matt,

It's wise to do some research for your project before you start, so you're already heading in the proper direction by asking your questions here. I hope I don't get too wordy for you here, but you asked a lot of questions, so here goes....

In my opinion, it's a waste to use solid wood for the flat panels on your project. You're thinking correctly when you mention using solid wood on any moldings, baseboard, etc., as those are the areas where end or edge grain will show, so you'll want the benefit of solid wood there. But there are 2 distinct reasons NOT to use solid cherry in the panel areas. The first would be that solid wood is not as dimensionally stable as plywood or MDF veneered panels. Solid wood will swell or shrink with seasonal humidity fluctuations. And it's prone to cupping if it's not glued up properly. Properly means that the wood should be of uniform widths, say in 3-5" strips, with the annual growth rings of the wood alternated. (Any good woodworking book will go into detail about this procedure.)

But more importantly, solid wood will really react poorly when you apply your finish to only one side of your wall. For solid wood to stay nice and flat (assuming you've glued it up properly) you must finish BOTH sides in the same manner. Not doing do allows moisture to enter the wood from the unfinished side, and therefore, it WILL cup and warp.

Another reason I wouldn't use solid wood in the panel areas is that it's simply too labor intensive, compared to it's benefits. Solid wood will be more expensive per board foot, will require MUCH more labor, and it's not the best solution "stability wise" in this situation. So ... it's my recommendation that you use the veneered MDF.

Your breakdown of using cherry ply for the side panels and back, and solid cherry for the shelves and for the flutes and molding seems perfect.  The framing (support) of  2x4  sounds good too, and depending on how thick your hardwood flooring is, it's probably not necessary to take it up. I'm assuming you have a 3/4" layer of sub-floor, and then a 3/4" layer of hardwood. So that would give you more than enough to tie into. I would check to see what you have. I've come across a situation where there was a thin layer of subfloor, and a thin layer of cement board, topped by a thin layer of prefinished hardwood. That sort of composite wouldn't be my favorite, but still- it would probably be OK for supporting the 2 x 4's.

Your last questions are regarding the seat and shelving spans, and how to support them. The seat is a rather easy solution. I am assuming you're going to build a box roughly the size of the window, and then add a top to it for the seat. The top would be supported all around the perimeter by the box, so the only thing I would add is a center stretcher (sort of like a divider) in the box. That would add support in the middle, which is the only part unsupported. It's probably overkill, as the wood probably isn't going to flex that much anyway.

The shelving span is a little more complicated. There are span tables in some woodworking books that will show you how wide you can go with shelves before you get some flex to them. If the span table is a good one, it will break it down and show each specie of wood, and then break it down even further and give different span lengths based on the thickness of the board.

There are MANY solutions to this problem, however, without looking at span charts, and I will name just a few solutions:

1- The thicker the board, the less it will flex. So if your 5' shelf can be made thicker without sacrificing aesthetics, then you could simply make it so.

2- Once again- adding some sort of center support to it would beef it up. Now I understand that you might not be able to add a center support under it, but you might be able to tie the center support into the ceiling above. That would be another way to support the shelf and keep it from sagging.

3- If all else fails, you can beef up the shelf by adding a structural supports (i.e., 1 x 2) to the front and back edges. Remember- wood is a lot stronger in it's vertical orientation, rather than it's horizontal orientation. That's why floor or ceiling joists are run vertically, rather than horizontally. So if you add even a narrow (1 x 2) strip of wood to the shelf, it makes it very much stronger. But it will make the shelf appear thicker, so if you don't like that, here are even MORE suggestions- add the 1 x 2 only to the back of the self, by the rear wall. Or you could add the supports under the shelf, so that from viewing the shelf from the front, the shelf appears to only be a single thickness of the wood.

Good luck, I hope this helps. It sounds like you're on the right track with all of this, so have some fun and enjoy the building process. Feel free to write back with any other questions you might have after reading this.

Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV


Answer
Hi again, Matt,

I'm sorry, I must have misunderstood or read your first questions wrong. I would always choose plywood over MDF, simply because it's a better product. It holds glue better, and you certainly can't break a corner off accidentally. Or at least it's not very easy to do. So to answer your follow up question- I wouldn NOT choose MDF if plywood was available.

As far as joining the ends of the plywood sheets- since there is some edge grain there, plywood has decent edge gluing properties.  So there are times when I simply glue solid wood right to the plywood with nothing added, which would be the butt joint you mentioned.  But often- alignment is an issue when gluing something to plywood. If that's the case, a biscuit is always fast, easy and accurate. If I'm in a pinch for time, I'll cut the plywood about 2 inches longer than what I need it, and shoot a small brad on each end to hold it in place while I clamp it. After the glue is dry, I trim off the inch on each end, where the brad is, and you still have the size panel you need, only with no fastener in it. Did that make any sense?!

And yes, you can get away with applying finish to just one side of the plywood. It's still always better to finish both sides the same way, but plywood is light years more stable than solid wood, so even if you just finish one side, it'll probably be OK.

Good luck, you're really on the right track with everything.

Jamie