Preserve MDF

I just made a table saw sled using 1/2" MDF for the base.
MDF is very prone to expansion from moisture. I have some Minwax Polyurethane. Suitable to seal the MDF? Just around the edges, or all surfaces?
Thx, Will
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Do the whole thing. The poly should work, but as LJ says "stain and poly are their own rewards."
Puckdropper
--
Make it to fit, don't make it fit.

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Wilfred Xavier Pickles wrote:

Very much a false sense of economy.
MDF for a jig/fixture will come back to bite you.
Slap on a few coats of 1# shellac and pray.
Consider any service life you get as a bonus.
Lew
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I chose the 1/2" to keep the weight down a little, not particularly b/c it was cheap.
What would/do you use for such an application? The sled base is something like 24 x 32".
Will
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wrote:

a good piece of 1/2 or 3/4 ply - baltic pirch
shelly
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"Wilfred Xavier Pickles" wrote:

I like to use Birch ply AKA: cabinet ply, die board are some common names.
Standard sheet size is 60" x 60".
Thicknesses are standard US, not metric, available in 1'4', 3/8", 1/2" (9 ply), 5/8" (11 ply), and 3/4" (13 ply).
There are no voids.
For a sled I'd use 9 ply (1/2") for the base and 13 ply (3/4") for the verticals..
I like to seal my jigs with a wash coat of shellac, it helps to keep them clean.
I cut shellac with equal parts of denatured alcohol, then apply 3-4 coats with a throw away 2" chip brush.
Have fun.
Lew
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Sounds good. I may well try this approach next time if I can find a supplier that'll sell me less-than-a-truckload of the stuff.
Thanks, Will

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"Wilfred Xavier Pickles" wrote:

Forget Lowes & Home Depot.
ANY decent sheet goods distributor will sell you a couple of sheets at a time.
Lew
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On 26 Nov 2011 00:06:44 GMT, Puckdropper <puckdropper(at)yahoo(dot)com> wrote:

Not rewards, PUNISHMENT, Pucky, you shit-stirrin' SOB. ;)
-- Stain and poly are their own punishment.
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That'll teach me not to look up a quote. I thought you used "reward" in the sarcastic sense. A "you've been bad, so here's your reward" type of thing.
My apologies,
Puckdropper
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On 26 Nov 2011 20:40:08 GMT, Puckdropper <puckdropper(at)yahoo(dot)com> wrote:

Accepted, old sport, but with 2 demerits. Say 3 Hail Roys and cogitate on it. ;)
-- Progress is the product of human agency. Things get better because we make them better. Things go wrong when we get too comfortable, when we fail to take risks or seize opportunities. -- Susan Rice
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On 11/25/2011 5:03 PM, Wilfred Xavier Pickles wrote:

Shellac, right out of the can, works well also. It's what I use, but I usually have some used tins laying around.
Johnson's Paste Wax will also work and is much slicker than either poly or shellac, unless you wax them.
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Also, tell him to stop washing his sleds in the dishwasher.
-- Progress is the product of human agency. Things get better because we make them better. Things go wrong when we get too comfortable, when we fail to take risks or seize opportunities. -- Susan Rice
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"Wilfred Xavier Pickles" wrote in message
I just made a table saw sled using 1/2" MDF for the base.
MDF is very prone to expansion from moisture. I have some Minwax Polyurethane. Suitable to seal the MDF? Just around the edges, or all surfaces? ------------------------------------------------------------------------------------------------------------------------------
I have a saw sled made of 1/2" MDF also. No finish on it at all. It's still going strong after 7 years. It lives in an unheated garage in Seattle. Unless you work in the rain, don't worry about it.
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On 11/25/11 11:17 PM, CW wrote:

------------------------------------------------------------------------------------------------------------------------------
Me, too. More stable than hardwood in those conditions.
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-MIKE-

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No rain, just a basement workshop.
I'd probably take your advice, but, sooner or later we'll get the hard, HARD rain, the bsmt will take a little water, and ...
I got a tenon jig made with what I call waferboard years ago, and it just "ain't right". The waferboard is even less stable than MDF (I expect), but I figger the sled will get a chance to suck up some moisture some day.
Thx, Will
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On 11/26/2011 12:27 PM, Wilfred Xavier Pickles wrote:

Not all mdf is created equal. Temple-Inland has a product called "UtlraStock" that is "moisture resistant", and there is a product called Sierra Pine product called Medite that is also.
Both products are great for jig making. I've been carrying a piece of Ultrastock around in the back of my pickup, unfinished, for six months and it is still unaffected by the rain it has been subjected to.
Won't find them at the Borgs, but a hardwood dealer who handles sheet goods should have it.
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Thanks, that's good to know.
Looks like Home Depot has the 3/4" Ultrastock. Seems possible that my HD 1/2" is Ultrastock as well, 'tho it doesn't say so on the label. HD is great at mis- labeling, neglecting to label, etc.
Will
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