Built-in bookshelf questions

11 years ago

We are having a fairly large built-in bookshelf (w cabinets in bottom) made for our livingroom and the guy making it recently mentioned that he was considering mdf for the back panel (the rest of the bookshelf is plywood). Is mdf ok if it is just the backing? The is going to be a 90 inch wide unit, 8ft tall. We hope to have this stay strong and in good condition for many years? Just trying to understand if this is a bad place to use cheaper materials or if It ok?

Also, the 90" unit is made up of three columns of 30" wide shelves. We had imagined that he would have constructed 3 different segments -basically three different bookcases of 30" each and then attached them together. But instead he has started it as one huge unit - a 90" board all the way across the top and bottom. He is adding vertical plywood panels going down at 30" intervals. Aside from my confusion about how he will attach fixed shelving at the same height throughout the unit using this method, I am also wondering if the unit will be much weaker and less stable if it is made as 90" in one piece versus three separate smaller units attached.

I kmow he's done other carpentry projects but I don't think he's ever done something like this before so I'd like confirmation that this all sounds ok (and advice on mdf backing).

Thanks!!!!

Featured Answer

rwiegand

11 years ago

I'd also use plywood for the back, glued in place. Racking could be a problem with a unit that big. Lots of different ways to approach building such a unit, one giant assembly seems unnecessarily difficult. For something with cabinets on the bottom and a bookshelf on top I'd probably make them as at least two units (top and bottom) and maybe more. Partly it would depend on whether I was building it in place or making it in my shop and transporting it, as well as the style. In the shop I'd probably make it in four (or even six) pieces, a base cabinet and three bookshelves, applying a face frame on site. A non-face frame style would be need to be done in no more than two pieces.

I don't like to dado in fixed shelves on both sides of a piece of 3/4" ply at the same height, you probably want to keep the dados very shallow, perhaps 3/16"

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Comments (7)

klem1
11 years ago
Method is usually more important than material while constructing cabinets. I'm reluctant to advise someone about either without seeing the project in person. It would appear the back will determine resistance to racking of your cabinet. For that reason plus better apperance, I would likly choose 1/4" plywood matching shelves and sides.
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eastvillgal
Original Author
11 years ago
Thanks. He is doing two pieces - one whole piece for the top and one whole piece for all the bottom cabinets. I asked him about the mdf and he said it's actually "tempered hardboard" (but only 1/8 of an inch). He is saying that tempered hardboard is stronger than mdf and that even at 1/8 of an inch it will be strong. He would use something else if I insisted but I don't know if I am being unreasonable in doubting him. Also of course it is a little more money.

As for shelf installation he is not using dados. He showed me a picture - looked like thin discs? Are those biscuits- I'm not sure. He sent me a picture of one column w the shelves in and they were the wrong heights so he will have to redo that.

Unfortunately I think he is a bit less experienced than I knew when I first hired him. We've already paid half up front and paid a few hundred for materials so I think we have to just make the best of it at this point. It is a hard situation because I don't want to be insulting and question his judgement but at same time I want it done well.

Any thoughts on 1/8 inch tempered hardboard for backing here? (We will be painting it). Also any other "basics" I should make sure are being done?
rwiegand
11 years ago
You probably want to pay attention to loading of the shelves and potential sag. This page shelf_sag_measurements is pretty complete on the subject.

I, personally, would not depend on biscuits to hold up a shelf that could have 75 lbs of books on it. It will probably be fine (lord knows Ikea bookshelves work with less support than that), but I wouldn't do it on my own project.

If the unit is truly built in, and will be fixed to the wall at multiple points then racking is not so much of a concern. the hardboard is difficult to attach to the shelf in a rigid manner. In cheap furniture it is often used and just stapled in place, providing little, if any structural support. For a painted bookcase I'd use either 1/4" plywood, or for a really nice flat surface, 3/8" MDO (Medium Density Overlay, a high grade plywood with a very smooth paper surface bonded to it) (I don't think it comes in 1/4")
eastvillgal
Original Author
11 years ago
thanks so much. so I just found out that he is actually using 2" screws to screw in the shelves to the side panels. assuming he is using enough screws...should I ask him to also use glue or should these long screws be enough? and then ask him to either use 1/4" ply or 3/8MDO attached to all the shelves in the back for added support?

he will also do 1" solid pine edging on the shelves and 1.5" solid pine edging going vertically between the columns covering the side pieces. he said the edging would be attached to the shelves via nail gun - and wood filler over the holes.

all sound ok??

THANKS!!!!!!
annkh_nd
11 years ago
I wouldn't want a bookcase that didn't have adjustable shelving, but you may not mind that.
eastvillgal
Original Author
11 years ago
yes, I totally agree with you -- unfortunately my husband disagrees so I'm just going with that... he thinks fixed shelves will be stronger (probably true) and he also thinks it looks better (not sure I agree). We are having one very tall shelf -- 18" for very large books and also to display some statutes and other art possibility. than above that it will be three rows of about 12.75 each.