Is there any reason why I should not use pressure-treated pine to build/replace an exterior window sill?
I understand that cedar is probably the wood of choice, but for various reasons I would prefer to use PT pine, unless there is a major reason why I should not.
Thank you for your time.
Ed

If you were to go to any window company and ask them to replace a rotted window sill, they would use clear fir only because it doesn't have any knots in it, and that makes for a nicer paint job.

About the only reason I can think of not to use pressure treated lumber is that it's generally construction grade wood that gets pressure treated, and it just doesn't look as good on the exterior of your house as painted clear fir would. Also, only the outer surfaces of the wood are rot resistant. So, if you cut the wood to length, or whatever, you're exposing wood that doesn't have any preservative in it to make it resistant to the wood rot fungus, and that exposed wood will rot just as quickly as ordinary lumber. They sell "end cut preservative" specifically for this purpose, tho.

I wouldn't use cedar for a window sill because it's simply too soft to hold a fastener (like a screw) well.

I've found with the wood window frames in my building, that about the best way to make a wooden window frame maintenance free is to use a piece of thin PVC plastic to make an "awning" that covers the bottom of the window frame and use caulk to hold it in place.

After all, the ONLY place a wooden window will ever rot is at the bottom, and by having a piece of thin plastic sheet cut and bent so that it keeps the Sun and rain off the window sill, then the sill will never rot and the paint you put on it will last darn near forever too. Maybe see if there are any horizontal surfaces on your window that you could use double sided tape to stick a plastic awning onto and then caulk in place.

On the wooden window sills in my building, I have 4 inch wide pieces of 1/16 inch thick PVC bent 1/2 inch from one edge to an angle of about 15 degrees. I cut the ends of those pieces to fit against the sides of the window, and then use double sided tape to hold them in place until the caulk cures.

That 15 degree angle results in those plastic awnings shedding rain water and shading the painted wood underneath. So, bugs and air currents can still get under the awning so that if the wood gets wet for any other reason, it can still dry out just as fast as if the awning weren't there. And, the fact that the awning shades the window sill from both the Sun and the rain, any paint you put on those window sills will last darn near forever.

Every company that makes PVC doors and windows will also have thin sheet PVC in stock that they use for a variety of things, but you can buy it cheaper in 4X8 sheets from most plastics suppliers. Or, at least that's been my experience.

This message has been edited. Last edited by: Nestor,

Two comments:

1. Pressure treated is also not a good choice because it starts out with a fairly high moisture content (due to the pressure treated chemicals). With high exposure on a fairly small piece like a window sill, it is going to dry out and warp. This is in addition to Nestors points about the typical construction grade of PT pine.

2. Nestor - I am wondering if Canadian PT is a different process. The pressure treated we get is completely saturated with preservative. That's how the pressure treated process works - the wood is soaked under pressure so that preservative if forced completely through the wood. Cut a PT piece of lumber and all points remain treated, even the new exposed ends.

This of course, is based on the PT materials that we have available here in the SouthEast U.S. I know from trips out west that PT lumber in Nevada and California is much different from what we get. Out there the process includes machine punching hundreds of indents to aid in the chemicals soaking into the wood. Don't know for sure how far into the lumber the treatment goes with this method, but the material sure is ugly.

However, the PT we have available is treated to the core.

Well, whenever I've cut pressure treated wood, the thickness of the pressure treatment on the outside of the wood was anything from 1/8 of an inch to 1/2 an inch. So, for 1/4 inch penetration on a 4X4 fence post, say, that's only about 1/4 of the cross sectional area of the wood. Inside that treated zone, the wood isn't any more resistant to wood rot than untreated lumber.

So, if the treatment chemical completely permeates your treated lumber, then there'd be no need for anyone to ever buy end cut preservative, is that correct?

Pressure treated will not hold paint, you would have to wait months for it to dr y out and use soild stain not paint, will cause any fastners other then ACQ approved fastners to rust off, it's going to shrink a great deal when it drys out, if there's any aluminum (like aluminum siding) it will cause the finish to bubble up.
Over all a very poor choise for a sill.
They make replacement sills out of vinyl.
If the windows that bad it may be time for a whole new window.

quote:

Originally posted by Nestor:
Well, whenever I've cut pressure treated wood, the thickness of the pressure treatment on the outside of the wood was anything from 1/8 of an inch to 1/2 an inch. So, for 1/4 inch penetration on a 4X4 fence post, say, that's only about 1/4 of the cross sectional area of the wood. Inside that treated zone, the wood isn't any more resistant to wood rot than untreated lumber.

So, if the treatment chemical completely permeates your treated lumber, then there'd be no need for anyone to ever buy end cut preservative, is that correct?

I think that pretty much confirms that we are talking about two completely different methods of PT. If you cut one of our typical 4x4's in half, it is pressure treated completely through.

not necassary to use treated wood unless setting onconcrete pine and cedar on exterior usually wont hold paint as as well as poplar so unless fixed glass go buy a window replacement sill at lumber yard makeing sure ti meaSURE A MINIMUM OF 1 INCH PAST BRICK MOLD PRECUT SILL WILL MOST LIKELY ALREADY BE PRIMED REMOVE INTERIOR SILL AND TRIM UNDER SILL LEAVE ALL OTHER TRIM IN PLACE AND THEN CUT OUT SILL BY CUTTING AT CENTER OF OPENING PRY UP AT CENTER TO REMOVE IF WINDOW HAS NO DAMAGE AT BOTTOM ON SIDES CONTINUE IF SOFT REPLACE WINDOW OTHERWISE YOUR CAUSING MORE FUTURE PROBLEMS

Since I have installed the pressure-treated pine’s windows in my house I have seen many positive things of it. Best thing I like about these windows is that they provide long term protection from dry rot, decay and insect damage.
Home windows

This message has been edited. Last edited by: ralphtaylor,