I have aluminum frame windows that frost up in the winter, thaw and discolor
the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the water
stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in the
sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the window
frame and the sill?

I know turning up the heat or using a dehumidifier could solve the problem,
but I'm looking for a cheaper (long term) solution. Replacing the windows
with vinyl frame is too expensive, however.

On 11/25/2010 7:35 PM james spake thus:

I have aluminum frame windows that frost up in the winter, thaw and discolor
the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the water
stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in the
sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the window
frame and the sill?

You could try epoxy. Specifically the marine stuff people use for boats.
I used it recently to coat an exterior door surface. Works well, though
there are some gotchas. Not cheap, but it should make the wood pretty
water resistant.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

On Nov 25, 10:01*pm, David Nebenzahl wrote:
On 11/25/2010 7:35 PM james spake thus:

I have aluminum frame windows that frost up in the winter, thaw and discolor
the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the water
stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in the
sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the window
frame and the sill?

You could try epoxy. Specifically the marine stuff people use for boats.
I used it recently to coat an exterior door surface. Works well, though
there are some gotchas. Not cheap, but it should make the wood pretty
water resistant.

--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

Was the polyurethane oil-based or water-based? If it was water-based,
I would try some oil-based polyurethane on a piece of wood, let it dry
thoroughly, and then put water on it to see if the oil-based
polyurethane works better than the water-based version.

There's a reason they don't recommend polyurethane for outdoor use. (I
don't know what that reason is, but there is one)

Spar urethane, however, comes in outdoor versions. I've used that on
windowsills in wet locations (over the kitchen sink, for example).
Alternatively, use something that's recommended for decks, although
you might have to recoat it occasionally (at least, the deck stuff
doesn't last too many years on a deck).

james wrote:
I have aluminum frame windows that frost up in the winter, thaw and
discolor the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out
the water stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain
in the sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the
window frame and the sill?

Polyester resin, AKA fiberglass resin. This would also allow you to
reinforce it structurally (with fiberglas cloth/matting) should you see fit.

Before you mix up the batch to use, mix up a test batch first, so you can
see how much hardener/catalyst to add (the instructions are just a guide,
each application has it's own requirements).

Jon

On Nov 25, 9:35*pm, "james" wrote:
I have aluminum frame windows that frost up in the winter, thaw and discolor
the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the water
stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in the
sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the window
frame and the sill?

I know turning up the heat or using a dehumidifier could solve the problem,
but I'm looking for a cheaper (long term) solution. Replacing the windows
with vinyl frame is too expensive, however.

I dont think you can since the window covers the woods edge, the edge
you cant poly, thats where water is getting in. Wood frames are best.

"james" wrote:

I have aluminum frame windows that frost up in the winter, thaw and discolor
the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the water
stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in the
sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the window
frame and the sill?

You don't want 'thicker'. You want an impervious bond. An oil
finish will soak into the wood better.

Someone mentioned polyester resin. I think I'd go with a marine
epoxy if this is a troublesome window.

I like these guys--
http://www.rotdoctor.com/ Their product is far from cheap-- but
you'll only have to do it once. Their resin will soak into the wood
a long ways and outlast the house.

I replaced a piece and treated the bottom of my garage door 8 years
ago & I still can't tell where the joint is- and the door is solid.

Jim

james wrote:
....

I know turning up the heat or using a dehumidifier could solve the
problem, but I'm looking for a cheaper (long term) solution. Replacing
the windows with vinyl frame is too expensive, however.

Storm windows or if really cheap, the stretchy film route.

Condensate is undoubtedly penetrating under the poly on the side more
than actually penetrating thru as ransley points out.

--

On 11/25/2010 9:35 PM, james wrote:
I have aluminum frame windows that frost up in the winter, thaw and
discolor the wood window sill.

Thinking that polyurethane would waterproof the sill, I sanded out the
water stain, restained the sill, then coated it with polyurethane.

But the next winter, the thawed water still discolored the wood stain in
the sill.

Is there something other than polyurethane that could create a thicker
waterproof coating on the window sill and seal the joint between the
window frame and the sill?

I know turning up the heat or using a dehumidifier could solve the
problem, but I'm looking for a cheaper (long term) solution. Replacing
the windows with vinyl frame is too expensive, however.

Spar varnish.

--
Steve Barker
remove the "not" from my address to email

On 11/26/2010 10:03 AM, dpb wrote:
james wrote:
...

I know turning up the heat or using a dehumidifier could solve the
problem, but I'm looking for a cheaper (long term) solution. Replacing
the windows with vinyl frame is too expensive, however.

Storm windows or if really cheap, the stretchy film route.

Condensate is undoubtedly penetrating under the poly on the side more
than actually penetrating thru as ransley points out.

--

A single coat of clear finish is generally not enough to seal up the
grain. More coats (2 or 3)would likely be the answer, and thinning it
slightly may help it penetrate. With clear coat, the wood may still
darken from the sun.