sealing MDF, a revisit
 

Hello Group,
I did a google search on this subject and most of the reasons were to
lock in the vapors. I want to use a very heavy (1&1/2 inch thich)
former computer lab desk for my router table. I have routed the cutout
for the insert but I'm reluctant to set the insert in without treating
the raw material. Do you think there is any chance the MDF could swell
when polyurethane is applied? (Also, if that were a problem, I suppose
I should avoid aqueous polyurethane.)
My insert fits very nicely right now (minimal tolernces) but I'm
concerned that it might become a problem if coated. Any comments?
Thanks in advance,

Marc

sealing MDF, a revisit
 

marc rosen wrote:

Hello Group,
I did a google search on this subject and most of the reasons were to
lock in the vapors. I want to use a very heavy (1&1/2 inch thich)
former computer lab desk for my router table. I have routed the cutout
for the insert but I'm reluctant to set the insert in without treating
the raw material. Do you think there is any chance the MDF could swell
when polyurethane is applied? (Also, if that were a problem, I suppose
I should avoid aqueous polyurethane.)
My insert fits very nicely right now (minimal tolernces) but I'm
concerned that it might become a problem if coated. Any comments?
Thanks in advance,

Marc

ok, we have 1.5" of MDF and you are wondering if a layer of poly about
the thickness of paper is going to make the whole panel of MDF swell??
I don't THINK SO!

Dave

sealing MDF, a revisit
 

ok, we have 1.5" of MDF and you are wondering if a layer of poly about the thickness of paper is going to make the whole panel of MDF swell?? I don't THINK SO!

I think the OP was asking whether sealant on the cutout section would
swell the MDF enough to affect the fit of the insert. In response to
that, I doubt that the amount of moisture in sealant would cause enough
swelling to cause problems with your insert, but I know MDF does swell
when wet, so I'd use a couple very thin layers of something oil-based
that polymerizes to seal and protect from water.
Of course if you have any scrap you could measure it with a caliper or
micrometer and test a few different finishes - let us know how that
turns out.
Good luck,
Andy

sealing MDF, a revisit
 

marc rosen wrote:
Hello Group,
I did a google search on this subject and most of the reasons were to
lock in the vapors. I want to use a very heavy (1&1/2 inch thich)
former computer lab desk for my router table. I have routed the cutout
for the insert but I'm reluctant to set the insert in without treating
the raw material. Do you think there is any chance the MDF could swell
when polyurethane is applied? (Also, if that were a problem, I suppose
I should avoid aqueous polyurethane.)
My insert fits very nicely right now (minimal tolernces) but I'm
concerned that it might become a problem if coated. Any comments?
Thanks in advance,

Marc


you're probably fine. even if the edge does swell a little from water
poly it'll stop as soon as it dries, and if the swelling is enough to
affect accuracy it will be easy to sand it back to size.

sealing MDF, a revisit
 

"marc rosen" wrote in message
ups.com...
Hello Group,
I did a google search on this subject and most of the reasons were to
lock in the vapors. I want to use a very heavy (1&1/2 inch thich)
former computer lab desk for my router table. I have routed the cutout
for the insert but I'm reluctant to set the insert in without treating
the raw material. Do you think there is any chance the MDF could swell
when polyurethane is applied? (Also, if that were a problem, I suppose
I should avoid aqueous polyurethane.)


A coat of two of poly won't swell it, but they will reduce the tolerances.
Are you sealing it for vapor? If so, that seems kind of anal to me.

sealing MDF, a revisit
 

Hey All,
No, I am not trying to seal in any chemical vapors. The entire sheet
has some type of very hard and slippery material (melanminre? ) top and
bootom. I want to seal the machined area to minimize material
fragmentation due to use. The recess I machined was a perfect fit for
my router lifter, and I anticipated that within several hundred hours
of operation that the metal (anodized aluminum) to MDF junction would
become sloppy from vibration if I did not seal the MDF. However, since
I never worked with MDF before, I was curious if the small region that
is sealed would swell, thus making my now perfect fit, not perfect. As
I type this I am thinking that even the polyurethane may erode after
hours of vibration so maybe I'll just go with the untreated recess and
see when if it needs any attention in the future.
By the way, the router lifter does have leveling and tensioning
adjustments, but the recess is sized perfectly for height, with a minor
amount of "slop" for lateral adjustments.

Marc

sealing MDF, a revisit
 

marc rosen wrote:
Hey All,
No, I am not trying to seal in any chemical vapors. The entire sheet
has some type of very hard and slippery material (melanminre? ) top and
bootom. I want to seal the machined area to minimize material
fragmentation due to use. The recess I machined was a perfect fit for
my router lifter, and I anticipated that within several hundred hours
of operation that the metal (anodized aluminum) to MDF junction would
become sloppy from vibration if I did not seal the MDF. However, since
I never worked with MDF before, I was curious if the small region that
is sealed would swell, thus making my now perfect fit, not perfect. As
I type this I am thinking that even the polyurethane may erode after
hours of vibration so maybe I'll just go with the untreated recess and
see when if it needs any attention in the future.
By the way, the router lifter does have leveling and tensioning
adjustments, but the recess is sized perfectly for height, with a minor
amount of "slop" for lateral adjustments.

Marc

The core of my router table is MDF and I've had no change in size in
the lift opening due to vibration in 4 years of usage. You MIGHT be
overthinking this a bit, Marc. :)

dave

sealing MDF, a revisit
 

David wrote:

The core of my router table is MDF and I've had no change in size in
the lift opening due to vibration in 4 years of usage.

Same here, and it's in a basement.

Barry