Baseboard, Crown, Door/Window Casings - Wood Materials question?

[sanrene]

Originally Posted by bradykp

i thought i've been reading and have been told that MDF does NOT expand, but that regular wood does...

It will expand and contract with the seasons - slightly.

In the winter you might see a hairline joint mid wall if you have to use more than one piece for a long span. MDF comes in 16 footers though.

In the summer that crack will disappear.

It won't warp and expand like real wood though.

Also depends how you put it together. Don't use butt-joints going across a wall expanse - use spliced joints, glued together, and nailed (drilled first) at an angle that will catch both ends. The best option - one piece from corner to corner. Use coped joints in the corner, unless your walls a perfected square and your saw is in perfect alignment.

For finishing/nail holes - any water based material will "raise" the MDF and cause a dimpling effect on the material. Don't want that to happen.

[jimboburnsy]

Originally Posted by bradykp

i thought i've been reading and have been told that MDF does NOT expand, but that regular wood does...

Originally Posted by sanrene

It will expand and contract with the seasons - slightly.

In the winter you might see a hairline joint mid wall if you have to use more than one piece for a long span. MDF comes in 16 footers though.

In the summer that crack will disappear.

It won't warp and expand like real wood though.

Also depends how you put it together. Don't use butt-joints going across a wall expanse - use spliced joints, glued together, and nailed (drilled first) at an angle that will catch both ends. The best option - one piece from corner to corner. Use coped joints in the corner, unless your walls a perfected square and your saw is in perfect alignment.

For finishing/nail holes - any water based material will "raise" the MDF and cause a dimpling effect on the material. Don't want that to happen.

It may very well be the case that MDF expands "slightly", but I can't tell. I can tell with my oak floors, my pine door casing, my old heartwood joists, rafters and studs and the legs on my dining room table seem to go from tight to a loose between winter and summer. Haven't had to re-caulk or re-putty any MDF baseboard joints, FWIW.

[bradykp]

so it's that wood warps, and MDF doesn't. sounds like everything expands and contracts slightly...except maybe the PVC/Vinyle which i've been told to avoid completely.

[sanrene]

Originally Posted by bradykp

so it's that wood warps, and MDF doesn't. sounds like everything expands and contracts slightly...except maybe the PVC/Vinyle which i've been told to avoid completely.

My house is filled with crown/trim/door headers of MDF, but also with wood trim too. Like I said, might find a hairline joint in some of the crown in winter, but I imagine if I kept the house "even" all year, you wouldn't.

Best stuff for painting and working with, imho.

If you can, purchase long lengths to avoid having to splice with a given wall.

If you can't avoid that, DON'T use a butt joint to piece them together.