Wall unit bookshelf Shelving question - Warping walnut ???

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Forum topic by lepelerin posted 04-23-2013 02:04 AM 1644 views 0 times favorited 5 replies Add to Favorites Watch
View lepelerin's profile


495 posts in 2349 days

04-23-2013 02:04 AM

Topic tags/keywords: question shelf walnut bookshelf

Question about shelving,

hi all,

Here is the situation. I have been asked by a friend to build his wall bookshelf. It will be installed in a recessed wall. The bookshelf will be 12’ long (3.5 m), 8’ (2.44) high and 9” (23 cm) deep. I will make it into 3 pieces. For ease of explanation I will call them left, right and middle section. The left and right sections are 4’3” (1.3 m) wide and the middle section is 3’ (90 cm) wide. All of them 9” deep.

The frame (sides, top and bottom) will be made of solid walnut, 1” thick. There will be a total of 6 to 8 shelves in each section. Each section will have 2 or 3 fixed shelves and the rest will be floating shelves. Each shelf will be approximately 3’ to 4’ long by 8” wide, 3/4” – 1” thick

I mean resting on a pin similar to that,43648,43649

Here are my questions:

1) I cannot find walnut as wide as 9” wide. I will glue pieces together to get the required width.
Should I just glue them or use dowel to reinforce them. There will be a lot of weight and stress on everything.

2) At the store they told me that the floating shelves will be warping over time? What do you think? They recommended walnut-baltic plywood. The issue that I have with plywood is that my shop is in the basement, very unpractical next to impossible to cut a 8×4 sheet and the store does not cut plywood. Using plywood would require edging too. It might be more stable over time but my question is walnut prone to warp a lot? I have no experience with walnut. I do have a bookshelf build in pine with floating shelves (1’ wide, 55” long, ¾ thick) and they seem to be stable over time. I had this bookshelf for over 10 years the are still flat.

So the questions is should I use solid walnut or not? Would you use solid walnut for floating shelving to built your own library?

3) This is relative to how to anchor the unit to the wall. I was thinking to anchor (with what is to be determined) the left side of the left unit and the right side of the right unit to the recessed wall. The middle unit would be attached to the adjacent side from the left and right unit. Would it be ok?

Those are my main questions at the moment, but I am confident if this project goes ahead (and so far it seems it will) I will then have more questions.

I hope you will be able to help answer my questions. In advance thank you for your input, advice, comments and whatever I did not think of.


PS: If this topic is more appropriate in another forum please let me know.

5 replies so far

View pjones46's profile


1001 posts in 2667 days

#1 posted 04-23-2013 03:40 AM

First, you can use dowels or biskets. There will be less warping / sagging with glued up shelving if you take care to use opposing grain directions, however, the shelves over 36” will be more prone to sagging under the weight. IMHO, either rethink the widths or increase the shelving to 5/4 glue up that should be sufficient for the 4’ shelves . I have also seen what I call strong backed shelves where a strip is glued and screwed to the bottom centers of the shelves to make them more rigid taking care to cut those strips so grain is perpendiclar to the downward force. IMHO plywood would be worse on the 4’ expanse…

-- Respectfully, Paul

View Loren's profile


10476 posts in 3672 days

#2 posted 04-23-2013 07:23 AM

Walnut is one of the best cabinet woods. It is pretty stable.

There’s a lot of walnut in that job. Dowels are not needed
in edge joints for strength, though they can be used for
alignment. Biscuits are a little easier to work with in alignment

Plywood will sag over those spans without reinforcement.

Walnut ply doesn’t take a finish the same as solid walnut –
the glue in the veneer pores affects the color.

View Charlie's profile


1100 posts in 2310 days

#3 posted 04-23-2013 10:13 AM

Fixed shelves sag less than floating shelves.
At 1 full inch thickness, and assuming 12 inches deep, a 48 inch shelf may sag noticeably. The 36 inch span shelves should be ok.

There is a shelf sag calculator here

I use about 10 pounds per linear foot for bookshelf loading. Depending on the books, this number might be higher, but in most cases it’s fine.

The solid walnut is much better on the long span than plywood. Even plywood with an edge attached doesn’t come close.

View sprucegum's profile


324 posts in 2021 days

#4 posted 04-23-2013 10:50 AM

A couple of years ago I did a very large set of display shelving for a tile store. Some of it was built very similar to what you are doing with pin supports for shelves that were around 36” long. The plans were drawn by an architectural design company. They specified two layers of shop grade birch plywood glue laminated with a 3/4 X 1 1/2 hardwood edging. Tile is about as heavy as anything you would want to put on a shelf and they have held up well. Having never used walnut for a large project before I really am not qualified to advise you on whether or not it would work well for your application. As for cutting the plywood buy one of the many circular saw guides or just use a strait edge and a couple of clamps to break it down into manageable pieces before you move it to your basement.

-- A tube of calk and a gallon of paint will make a carpenter what he ain't

View lepelerin's profile


495 posts in 2349 days

#5 posted 04-23-2013 02:31 PM

Thank you all for the input and advice.

pjones46: I would definitively use dowel for alignment. The width is fixed. I cannot make then larger than 9”.

Charlie: Thank you for the sag calculator. Very useful. I will use 1” thick if we go ahead with this project.

A question I should have asked. If you had to build a similar bookshelf, which wood would you use?

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