Using biscuits in primed plywood?

[Michael Donahue]

Hey folks. One of my upcoming projects will be building some bookcases that will ultimately be painted white. I was thinking of using screws and biscuits for the construction. I was hoping to prime the insides first as it can be tough to get a good finish (from my experience anyway) once everything is all together.

Will I have any problems if I prime the plywood first, and then cut the biscuit slots? I figure that the glue really only needs to be in the slots anyway.

Thanks for the help. :cool:

[Chris Friesen]

Shouldn't be a problem.

[Jim Becker]

The glue really needs to be on the edges, too...the biscuits themselves are more for alignment. The glue bonds the shelves to the sides. You'll need to mask off the glue area on both the bookcase sides and the ends of the shelves for best results.

[Karl Brogger]

This is just me. Many people love biscuits, they use them for everything. I can't stand using them. More often than not they limit the ability to get things straight. As in you may have to temporarily tweak one end out of alignment, to get another area aligned. When I have to glue sheatstock together on edge I typically clamp it and pocket screw it after the glue has set a bit. You have to cut the pockets first obviously.

That and modern glue doesn't need the surface area anymore.

[Peter Pedisich]

Michael,

For shelves that will hold heavy books, I'd pre-prime like you said (great timesaver), but then I'd dado them.
This creates a raw wood surface for a proper glue bond, and makes for a stronger shelf.
Just make sure it's not a latex primer that will gum up your blades and bits.
Or you could dado, then use 3/4 painters tape to mask off the dado.

good luck,

pete

[Shawn Walker]

What Jim said....

[Chris Friesen]

The glue really needs to be on the edges, too...the biscuits themselves are more for alignment. The glue bonds the shelves to the sides.

Maybe for really heavy books/magazines. For most usage I suspect that biscuits would be just fine given that my Ikea bookshelves have lasted through several moves so far and are held with just a couple of screws or pins.

Remember, the OP said he was also going to screw them.

[Keith Outten]

Some biscuits are designed to swell when they are wet with glue and may tend to spread and delaminate the plywood at the edges. I prefer to use hardboard biscuits that I make myself, often I machine a long spline along the plwood edge rather than using traditional biscuits.

[Prashun Patel]

Will I have any problems if I prime the plywood first, and then cut the biscuit slots? I figure that the glue really only needs to be in the slots anyway.
:cool:

I believe the biscuits are there to supplement the glue along the edge, not substitute for it.

If I was using biscuits, I'd either mask the glue line before you prime/paint or I'd sand off the primer along the glue line after.

That being said, I'd consider using shelf pins. With a jig, they can be easier than aligning all those biscuit slots. It also eliminates any gluing. It also allows you to completely paint the carcass and shelves independently b4 assembly. Oh yeah, and you can make them adjustable.

[Jim Becker]

Maybe for really heavy books/magazines. For most usage I suspect that biscuits would be just fine given that my Ikea bookshelves have lasted through several moves so far and are held with just a couple of screws or pins.

Remember, the OP said he was also going to screw them.

I missed the part about the screws. Thanks for pointing that out. And yes, I have a LOT of experience with Ikea's Billy bookshelves. The current lot does use metal fasteners in addition to the dowels and that adds to the weight support capability. This would theoretically be similar to what the OP wants to do given the screws. That said, I'd still glue the edges of fixed shelving if I were building my own! LOL