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.

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?

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")

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!!!!!!

I wouldn't want a bookcase that didn't have adjustable shelving, but you may not mind that.

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.