I’m planning on using a simple rectangular profile 3/4″ MDF for the trim in my house however for the top member across doors and windows I want to have them a tad wider than the verticals and 1/8″ or so thicker so that I get a nice shadow line (it may also hide lousy craftmanship! <grin>). Since my local yards don’t carry 7/8″ MDF is there any problem in matching the paint finish if I use poplar for these pieces? That is, does MDF take paint differently from poplar and if so what do I do about it? I’ve also heard that the edges of MDF need considerably more pimer than the faces. True? Thanks in advance.
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look for GP PrimeTrim.. it's an exterior MDF... 4,6,8,10,12 wide and 4/4 & 5/4 thick all 16' lengths
it loves paint..
Mike Smith Rhode Island : Design / Build / Repair / Restore
MDF looks more perfect than real wood... of course... so I would look for 1" MDF for your headers. Poplar will look like actual wood. Hell, you don't want that! The edges do take some work. The core of the panel is less dense than the face and soaks up paint. Sand the edges with a sanding block and 150 grit paper before you install if you want to get yourself a little bit ahead.
MDF comes in other thicknesses, but you won't find it at you local building supply house. You need to check plywood suppliers, a little calling aroung and you should be able to get it.
Be careful though! The 3/4" sheets weigh in at about 90+ lbs, so imagine what a 1" thick sheet weighs.
You should consider easing the edges of the pieces you make for casings. This material is more brittle than wood. A sharp corner edge will dent if wood but will chip off when using MDF
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Good thought. Thank you and thanks to all other respondants.
Sounds like a simple craftsman casing detail. This is what I did with salvaged clear fir from old 2x4's and some T&G flooring. The side casing is 3/4" thick and I planed the old 2x down to 1". All corners were rounded with a 3/16" roundover.
As far as the MDF, I have heard of using sanding sealer or a good sandable primer on the edges first and doing some sanding before installing to seal them up and get rid of the fuz.
http://www.mgit.com/izaak/interior/bathdoor2.jpg
(the black spots are nail stains from the wood's first 100 years of life as the kitchen floor)
Nice, can I touch it?
Not yet, there's one more coat of paint to do on everything, then it's carpetman time, then I'm done, we move in, and then...and then...I...I won't know what to do with myself! We define ourselves too often by our work.
my painter would say make sure you use the best primer you can find ...
and plan no less than one nice coat of primer ... maybe two ...
and at least two coats of paint .... maybe three.
I've built lotsa mantles ... columns ... and other such built up moulded pieces ...
and he takes extra time and caution when it's a mixed wood version ... more so if there's mdf in the mix.
I'm pretty sure he adds the extra top coat when mdf is thrown in ... to get the final surface to look more like real wood ... something about letting a slight bit of brush stroke show thru.
He also primes first ...
Then caulks ... everything but the nail holes ... those get DAP glazing ...
then top coats.
A good painter can really help a nice project shine.
Jeff
Buck Construction Pittsburgh,PA
Artistry in Carpentry
Just did my whole new addition trim in mdf except for the window sills. I hate working with the stuff, it's heavy as hell and makes an awful mess, it doesn't really handplane very well, it's hell on blades, but...once it's in and finally finished off, you can fugeddaboutit! It won't move and it is cheap! You should use a good oil primer, (oil penetrates nicely and hardens the core part but latex will make it swell), and let it really dry and then sand the sides and core part smooth. I think it's really worth the effort for many applications, oh and I totally agree about the inside edges, they should be eased well or even rounded, I made mine a 3/8" bead. Looks great