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Plywood "spacer" behind PVC exterior trim (OK or bad idea?)

Plywood "spacer" behind PVC exterior trim (OK or bad idea?)

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  #1  
Old 08-27-17, 09:27 AM
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Plywood "spacer" behind PVC exterior trim (OK or bad idea?)

Hello,

I'm trimming out my new windows with PVC trim. In order to bring the face of the PVC flush with the face of the window, I'll need to use a 1/2" think spacer behind the PVC.

At first, I was thinking of using 1/2" PVC, but that will certainly add to the expensive of, what already is turning out to be, expensive trim.
Then I thought; what about 1/2" exterior plywood? After all, that's what the exterior sheathing is. I'd paint all 6 edges prior to attaching the plywood spacers. Still, I wonder if the plywood will swell and I'll end up regretting the fact that I didn't spend the extra money to use PVC.

Thanks in advance.
 
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  #2  
Old 08-27-17, 12:31 PM
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Well, it all depends on if the plywood ever gets wet. If your trim is kept caulked, and you never have water behind the siding, the plywood shim would be fine. But you are right, plywood expands.

I have clad a ton of windows and 20+ yrs ago when I was first starting out, I thought 1/2" plywood was a good thing to use for exterior window stops, prior to covering it up with the aluminum cladding. That is, until one day where I came back to work to clad stuff I had trimmed with plywood the previous day. It had rained overnight and the rain had caused the plywood to swell so much that I could no longer fit a piece of aluminum trim coil into the space that I thought I had left. So since then I have made it a policy to never use plywood as a filler, even behind my cladding. I only use solid wood. You are right, a pvc shim would be pricy.

But you could buy a 4x8 sheet of 1/2" pvc and rip it on a table saw... if you wanted to use pvc, that would be the most economical way to do it.
 
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Old 08-27-17, 01:12 PM
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Thanks @XSleeper.
I think you're right. I'll hunt for a sheet of 1/2" PVC to rip. I'd rather pay now then pay a lot more later.
Thanks again.
 
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Old 08-27-17, 03:44 PM
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Some Home Depot's in NY carry sheets of 3/8" and don't cost an arm and a leg...

1/2" is harder to come by, you would probably need to get it from a lumber yard that is a dealer for Azek.
 
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Old 08-28-17, 06:05 AM
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Last time I bought a 4' X 8' sheet of 1/2" Azek it cost $95.00. You can cut whatever dimension you have down to 1/2". Window trim is a big spot for water leaks. I would use some thing that would not be affected by water. Check HD, I have heard they have less expensive brands of PVC.
 
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Old 08-29-17, 07:51 AM
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Thanks @JIMMIEM and thanks again @XSleeper.
After I assembled the basic surround of the trim and temporarily placed it around the window, I saw that I can get by with something thinner than 1/2" (maybe 3/8 or 5/16).
As I was looking for material, I came across something I hadn't considered. A local wholesaler had "scratch and dent" 1/2" PVC sheets for a bout 1/2 the price of a perfect condition new sheet. Used as shim material, "scratch and dent" would have been fine.
 
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Old 08-29-17, 04:34 PM
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Rip some thin strips to whatever shim width you need and glue to the backside of your trim. Make sure the shims provide good support to the trim so the trim doesn't bend inward when you screw or nail it.
 
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