I need to install some MDF Baseboard, (5/8â€X 1-1/4â€) and run it around a outside radiused paper drywall corner. I can think of mitering the BB @ 22-1/2deg to get around the corner, or does kerfing the back of the MDF to bend it around the corner work.
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Big Er.
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kerfing will work, but if you leave it on a sawhorse overnight, I bet the bend will be ready for you in the morning
I honestly don't think kerfing and bending the MDF will give you satisfactory LONG TERM results.
As you're probably aware, MDF has a hard "skin" that covers the softer, more friable inner part. With kerfing and bending, the skin doesn't handle stress very well. I'd bet it'd fracture over time, even if you back-filled the kerfs with titebond to "lock" the bend in place. And, unlike wood, MDF isn't something you can wet or steam prior to bending.
For MDF baseboard, besides water, the outside corners are the weakest link. Even after painting, if something as non-threatening as a vaccum hose gets dragged across the outside corner, the crisp edge on the corner can abrade, eventually showing the primer or MDF underneath the paint.
To toughen the corner, prior to painting you can slightly ease the crisp corner, then wash the corner with a diluted titebond wash. That's a band-aid, and might help some.
Or, for your corner, susbstitute a small piece of 3/4" poplar for the double 22-1/2 degree MDF piece. Biscuits and gravy (titebond) to lock it all together. Then sand the 3/4" poplar to match the thickness of the 5/8ths" MDF baseboard. That'll put the exact location of the outside break of the corner all on the poplar, removing the MDF "edge" from even being exposed to the exact outside corner...if only by a fraction of an inch.
I just reread your post...is the baseboard really only 1-1/4" tall?
Oops, the MDF BB is 5-1/4" High, by 5/8" thick. Thanks for the input, I'd need to find a shaper bit to form the Poplar insert.
BigEr
If you are talking about a 90 degree outside corner with the bullnose round edge. We always cut a piece 22 1/2 to go around that, it is usually 5/8" wide across the top. Depends on the base profile as to the longevity of the corner standing up to abuse. Once it gets painted it holds up better, high traffic areas it might be better to do as was stated in the previous post.
Not sure that I understand what radius your working with here.
If its the typical bullnosed sheetrock than check out this thread.
Its been discussed a lot on here.
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Doug
Ahoy Doug,
Thanx for the link to the radiused corner thread.
BigEr
From Thornbury, ON (where it's snowing like crazy)
Depending on how much abuse the corner will get, what about using plywood as a backer, kerfing it to get the curve right and gluing 1/8" birch or maple over that so it's nice and smooth? The other way to get exactly what you need/want is using birch or whatever you want, making it thicker and cutting it on a bandsaw, then routing the top to match the rest of the trim.
"I cut this piece four times and it's still too short."