mdf

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Old 02-19-07, 12:59 PM
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mdf

I have a few finishing projects ahead of me and I'm kicking around the idea of using mdf. Up until now I have used only pine moulding and haven't had any problems except for some hairline cracks on scarf and miter joints in long runs. From what I've read online mdf is impervious to shrinking and expanding during seasonal changes which makes it a perfect product for moulding but I find this hard to believe. Anyone have experience with it? thanks
 
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Old 02-19-07, 05:00 PM
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Unless you can somehow break the laws of physics, all matter expands and contracts with changes in temperature. So it would not be correct to say that "MDF is impervious to shinking and expanding." It would be correct to say that it shrinks and swells less than wood does.

MDF is usually painted and it paints up well beacuse it is so smooth. Sometimes wood-veneered MDF trim is used if it needs to be stained. Bare MDF can also be clear coated with varnish or polyurethane if that's the look you're going for.

When you nail into MDF, an air gun will usually leave a small pucker around each nail, which will need to be sanded flat before the nail holes are filled with putty. When nailing into MDF, it accepts face nails well, but it usually splits if you nail into the end grain (such as if you want to pin casing corners together). I also don't like to cope joints when using MDF, but some people do. MDF does not work well in areas where it will likely get wet. MDF creates a lot of dust when cut, and it's hard on blades if you work with it every day. When ripping MDF, cuts can be cleaned up with a belt sander quite easily to remove saw marks. It also is easily routered and shaped. It can be subject to dents and dings because it's basically just pressed glue and paper. Woods like soft pine also get dents and dings, so that's really no surprise.

MDF is really heavy compared to wood- a 4x8 sheet of 3/4" MDF probably weighs twice what a sheet of 3/4 plywood weighs.
 
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Old 02-19-07, 05:21 PM
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mdf

Because of mdf's "pressboard" qualities you have to be careful that it always stays dry. In fact to finish mdf properly you must seal with a solvent based primer. Mdf paints beautifully, mills nice, there are no knots or sap to deal with. But I know some carpenters who wear a respirator when milling mdf.
 
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Old 02-20-07, 04:03 AM
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I agree with both xsleeper and painter guy on their views of MDF. Do not use in a basement. Basements are inherently damp, and it does not play well with damp. Mills great, comes in nearly all shapes of molding, flexible to an extent, smooth finish, no sap or knots. You have to carry it vertically to keep it from breaking (long pieces). It copes well, too. It will shrink if installed in a humid unfinished, unheated house. The humidity will set up in the MDF, and as soon as the HVAC guys fire up the heat, it will have cracks at the joints. So it is best to trim after the heat/cool is activated.
 
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Old 02-20-07, 05:31 PM
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thanks for the advice guys. I think I will use the mdf for one room and see how it goes before I commit to doing every room on the floor with it. I'm not so keen on all the dust it creates but I like the fact it paints well. I'll have to see if it's worth it.
 
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Old 02-24-07, 08:06 AM
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Unless you want to lower costs there is no advantages to going to mdf, it is a lower quality product than wood.
 
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Old 02-24-07, 04:38 PM
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Who wants higher costs? That is the reason for the manufacture of MDF. But it is not all that inferior to wood, when you consider wood has a mind of its own, it will split, crack, expand and contract, whereas MDF is engineered not to do this under normal circumstances.
 
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