How strong is MDF?

[jsnell]

I have been working on some plans for a raised bed and am trying to decide whether to use MDF or plywood. Can MDF be used for support structures? Here's what the bed looks like.

[Greg.B]

Few questions.

Are you talking about making the entire thing out of it ?

Others could chyme in here, but isn't there a degree of toxic chemicals used in MDF ? I know the dust is very bad.

[siliconbauhaus]

Depending on the connections (ie confirmat screws) used I would say its fine but melamine chipboard would work as well and you wouldnt have to finish it.

[Alex Franke]

Others could chyme in here, but isn't there a degree of toxic chemicals used in MDF ? I know the dust is very bad.

It's urea formaldehyde - be sure to coat all surfaces to make then as gas impervious as possible.

[Garasaki]

I personally do not believe MDF has any redeeming structural value, but that is based purely on personal opinion and not fact (so take it for what it's worth...nada).

[cabinetman]

You didn't state what finish you were intending. For a painted finish MDF might be a good choice. In adding to what's already been said, IMO, MDF doesn't have the structural properties that you'll find in the same thickness of plywood. For the standing end to be in MDF, you should have solid wood vertical edges to stiffin the sheet. I wouldn't make that bed free standing in MDF. The left end could be attached to the wall.

MDF on edge in a single piece would have more flex than plywood. For the weight, odor, dust, and weak edges that have the ability to break apart, which are common with composite material, and its reaction to moisture, are my reasons for not using the material on a general basis.
.

[mschrank]

I don't know how strong it is...I just know you have to be strong to lift it

I think it's fine for small structures (speaker boxes, cabinet carcase etc), but I'm not sure I'd want to rely on it for spanning a large area like beneath the mattress. I suppose it would be OK as long as it has some additional support.

You might like to play with the Sagulator for help in determing unsupported spans:
http://www.woodbin.com/calcs/sagulator.htm

Also, I'm assuming this is for a kids room. MDF has a tendency to chip and dent on the edges and corners, such as when a big Tonka dump trunk rams into it.

[RayintheUK]

Your design is very similar to one I custom built to fit a particular space a while back (full story here)



I made it out of pine (to match existing furniture), but given a free hand in material choice, there is NO WAY I would use MDF as a structural material in a bed. I might consider it if laminating layers together, but then the cost will outstrip ply immediately and possibly pine or poplar eventually.

Laying still in a bed is one type of downforce, but children have a tendency to do anything but lay still, including jumping up and down with their friends!

Ply has more structural integrity, but the raw edges will need lipping, as splinters are very common from ply, even after sanding.

Keep us posted on progress.

Ray.

[crokett]

Another one to say no. By the time you make it strong enough to be used structurally you might as well use the ply or solid wood. Cost will be about the same and it will take less time to do.

[LarryG]

Ray covered it well. MDF is fine for fixed, dead-loaded assemblies like cabinet bodies, but it's ill-suited to applications in which the joints can be stressed by movement or suddenly-varying loads. And as mshrank points out, it's not durable at all ... VERY susceptible to edge denting and similar damage.

[LCHIEN]

MDF is made of wood particles glued together. it's claim to fame is the uniformity of the structure, density and due to the these the low and uniform expansion and ability to be stable and flat when not stressed.

Wood is much stronger along the grain - the grain gives it strength but also makes it expand non-uniformly and split and warp etc. Still, it's better for structures. Plywood gives it more uniform dimensional properties as well as strength in both directions.

[jsnell]

Thanks to you all.

I am going to be painting the whole thing. I was hoping to avoid having to band the edges of the plywood that's why I was considering MDF but I know better now. So I'll probably make the left support out of plywood and the right (steps/drawers) out of MDF. Thank again for all of your input. I'll try and post some pictures once I start.