Shimming Window Casing

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Old 11-30-08, 09:08 AM
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Shimming Window Casing

I am installing the casing around the windows in my basement and the sheetrock does not exactly line up with the window jambs. My trim carpenter that did the trim on the main floor used tapered shims behind the casing to fill the gaps. Should I cut the casing to the correct size and do a prefit to measure the thickness of the shims required or should I just build the shims and install them before cutting the casing? I want to be sure that I get a good fit on the miters am unsure which method would provide the best results.

I have read in previous posts where suggestions were made to outline the casing with a pencil and then beat the sheetrock with a hammer to crush it to eliminate the gap. Since this would create a compound miter cut, I am somewhat hesitant in doing this as I mentioned, I want a good fit on the miters and feel that doing this method would not produce the results that I desire.

Also, when making a tapered shim on the tablesaw, what is the best method for acheiving this as my windows are 65" tall and making a tapered shim 65" long is something I am not exactly sure how to do. The shims would vary in thickness from 3/8" to 0" and everything in between so making a common shim is not an option.

Any ideas on how to proceed?
 
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Old 11-30-08, 01:16 PM
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You can pre build the casings and install them provided you get really good measurements. Shimming is almost always required to keep things in line and tight until you get your case molding on.
 
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Old 11-30-08, 01:33 PM
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The shims I am talking about are between the window jamb and the casing to fill the gap between the jamb and the sheetrock which is proud of the jamb. I am thinking that I will need to make a shim to "picture frame" the window jamb so that the casing is then flush to the sheetrock. Since the windows already have extension jambs, I do not want to make new ones, I just need to extend them to the flush surface of the sheetrock.
 
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Old 11-30-08, 02:41 PM
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In some cases, the thing to do is to add an additional extension jamb onto the window that will be an appropriate thickness (like 1/4 or 3/8") so that the window jamb is flush with the wall in most places, recessed in some place and maybe proud in a few- in other words you have to split the difference. You would not make it variable thickness, you'd pick one measurement and make it all the same- If needed you can mud around the window where the new jamb extension is sticking out past the wall so as to level the wall surface out with the extension jamb. Once you do that, the wall will be perfectly flush with your new 3/8" piece that you added, and your casing will lay flatter on the wall. IMO, if a jamb is recessed behind the drywall no more than 1/8", that's perfect. When the jamb is proud, your miters open up and it's more difficult to get them to match.

In other cases, the window hasn't been installed straight with the wall due to the flexibility in the nailing flange-you might be able to move the window in or out a little, provided it isn't foamed in place... then run a trim screw through the window jamb to hold it in place. This is probably the first thing you should check if your window has a nailing flange- see if you can pull the window in, or push it out any- it might help.

Most trim carpenters have to compensate for the unevenness of the wall by tipping the casing, beating the drywall down, and creating a compound miter. Professionals have no problem getting these miters to line up, but I can imagine it might not be as easy for a DIYer.
 
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Old 11-30-08, 02:46 PM
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Bareftrz - If I understand what you are saying, you would end up with an exposed shim joint between the casing and the jamb Similar to a jamb extension. Is that correct?

How bad is the drywall fit? Usually you can just thump down the drywall a bit or even plane a little off the back of the casing. I've never had to add shims like that.
 
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Old 11-30-08, 08:31 PM
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Shimming Window Casing

Originally Posted by cwbuff View Post
Bareftrz - If I understand what you are saying, you would end up with an exposed shim joint between the casing and the jamb Similar to a jamb extension. Is that correct?
CWBUFF, yes that is correct.

Anyhow, I put a straight edge against the wall and it appears that the header and the sill plates were not installed flush with the King/Jack studs. So when the sheetrocker installed the drywall there is a noticable gap of between 1/4" to 3/8" along the vertical edges of the window jamb and about 3/8" gap along the sill and header jambs to the sheetrock surface.

Should I try to sand a bevel on edge of the sheetrock with a belt sander along the sill and headers to make them have the same gap as the sides? That seems to be the only way that I can use the same thickness extension jamb all the way around the window so that the casing will lay flat on the wall surface.

As I mentioned in my original post, in a post I read where someone mentioned to beat the sheetrock down with a hammer but I was hesitant to do this because I wanted to ensure a tight miter joint and it seems that this method would result in an uneven surface. Is this an acceptable method or would the belt sander produce better results.

One more thing, the windows were foamed in place and the exterior is bricked and the windows were caulked around the brick, I doubt that they would move.
 

Last edited by bareftrz; 11-30-08 at 08:34 PM. Reason: Forgot details about window installation
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Old 12-01-08, 05:13 AM
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Originally Posted by bareftrz View Post
Should I try to sand a bevel on edge of the sheetrock with a belt sander along the sill and headers to make them have the same gap as the sides? That seems to be the only way that I can use the same thickness extension jamb all the way around the window so that the casing will lay flat on the wall surface.
Not sure if you missed this part or what: Put on an additional extension jamb that is a consistent thickness.

If needed you can mud around the window where the new jamb extension is sticking out past the wall so as to level the wall surface out with the extension jamb. Once you do that, the wall will be perfectly flush
 
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Old 12-01-08, 09:53 AM
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Shimming Window Casing

I guess I did miss that part. I kept thinking about trying to get the casing flush and didn't catch the part about muding the sheetrock to make up the difference. I understand now and will proceed in that direction.

Thanks for the help.
 
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