49er advice please

[P.C.]

Hey 49er.

We're now in the process of putting in a pre-hung door.  We have read dozens and dozens of 'how to' instructions, and ALL of them say you must use shims to assure the jamb is plumb.  But not one of them says anything about not having to use them if the frame is already perfectly plumb.  Is there another reason shims must be used  ?  Help.  

[49er]

yes.....solid backing for location where you will drive nail, otherwise jamb will move or warp

[P.C.]

But why, if the frame is solid and square, would it...or could it move ?

lol....

[table bgcolor="#ffffdd" border="1"][tbody][tr][td colspan="2" align="center"][small]Anti-Spam Bot-Stopper
    Please type the text below into this field[/small][/td][/tr]    [tr][td align="center"]    [style type="text/css"]    TD.at_r1 (vertical-align:bottom;)    [/style] [table border="0" cellpadding="0" cellspacing="0"][tbody][tr][td]
[/td][td rowspan="2" class="at_r1"]ur[/td][td]
[/td][/tr][tr][td]abs[/td][td]d[/td][/tr][/tbody][/table][/td][td][input name="sauce_check" value="5ed5aadc2270d767952330ee41616f52" type="hidden"][input name="sauce" size="10" type="text"][/td][/tr][/tbody][/table]  [input name="post" value="Post" onclick="return scheck(); return submitThisOnce(this);" accesskey="s" tabindex="3" type="submit"] [input name="preview" value="Preview" onclick="return (typeof(document.postmodify.attachmentPreview) == "undefined" || !document.postmodify.attachmentPreview.value || confirm('You will have to reattach any attachments, continue with preview?')) && submitThisOnce(this);" accesskey="p" tabindex="4" type="submit"][img]Themes/default/images/blank.gif" alt="" id="fetchSessionTemp"]
 

[49er]

door jambs on prehung doors are usually soft pine.....most likely will bow when you countersink the nail if there is no solid backing

[P.C.]

The frame that the door jamb is going into is solid and square...you couldn't fit a piece of paper between the frame and the jamb at any point, from top to bottom.  Where would it bow ?  (sorry if I'm being thick here, but I don't quite get it)  

[49er@lunch]

OIC...I was picturing you have the normally 1/4"-1/2" gap.  The way you have now you cannot put in shims if you wanted to.  (Putting on my engineers cap).. With your situation of full contact with the house framing, your door frame will now tend to get out of square as your house contract and expand as the weather changes throughout the year.  In addition, new framing lumber contains around 19%-20% moisture and will loose this moisture over the years...so expect some movement by this process

[49er@lunch]

49er@lunch wrote:
OIC...I was picturing you have the normally 1/4"-1/2" gap.  The way you have now you cannot put in shims if you wanted to.  (Putting on my engineers cap).. With your situation of full contact with the house framing, your door jamb will now tend to get out of square as your house contract and expand as the weather changes throughout the year.  In addition, new framing lumber contains around 19%-20% moisture and will loose this moisture over the years...so expect some movement by this process
 

[P.C.]

OK...now THAT makes sense to me.

There is a quarter inch gap on one side...snug down the other.  So you would recommend shifting it so there is a small gap on both sides and shimming it.  

Thanks 49er.