Replies

1. 
   RedfordHenry | Jun 30, 2008 07:00am | #1

   Very common problem with exterior miters, esp on wood decking in sunny locations.  I always tell the clients to expect this.  Ordering the material weeks in advance and laying it out to cook on the jobsite before fastening might help, but that luxury is rare.

1. 
   rasconc | Jun 30, 2008 03:36pm | #4

   What about drilling and counterboring across, putting in a 1/4 or 3/8 bolt, pulling tight and plugging the holes?  Or maybe using a draw bolt underneath before setting on the post?

2. 
   Scott | Jun 30, 2008 07:08am | #2

   What Red said. The wood is drying, shrinking; this is to be expected unless it is acclimatized beforehand. Even if it is stablized, you should expect seasonal changes.

   I think butt joints show changes less. Perhaps you could carefully remove the caps and start again using butt joints. You'd probably need to buy some more stock though, so make sure you let it dry first.

   Scott.

   Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”

1. 
   jjwalters | Jun 30, 2008 02:34pm | #3

   I agree.......a mitre cut is gonna shrink and show up ugly no matter whatI like a half lap cut ...or you could cut a half lap/mitre I suppose.

1. 
   Scott | Jun 30, 2008 05:50pm | #8

   I stand corrected.... a halflap is going to show less shrinkage, although I have to wonder if it would be more subject to rot. Does water tend to wick inside the lap and rot from the inside?Scott.Always remember those first immortal words that Adam said to Eve, “You’d better stand back, I don’t know how big this thing’s going to get.”

3. 
   Danno | Jun 30, 2008 03:57pm | #5

   I agree with what others said--common problem. I think the last poster's idea about drawing the miter tight with bolts would cause stress somewhere else and bow the rails in or something.

   Could you cover the miter with a decorative block--maybe with a sort of finial, even a copper low-sloped pyramid, or a light? Or one of those glass prisms like they use on ship decks to get light below decks? Make it look like a planned feature ;-)

4. 
   Shep | Jun 30, 2008 05:14pm | #6

   Yes, that's a commen problem.

   I've had some luck minimizing the problem by first- using basically 1/4 sawn material for the top rail. Sort thru your material for the boards that seem closest to that.

   second- let them dry. I prefer a week or so, longer is better.

   third- I use 4 bisquits in the miter, with plenty of Pl Premium, or Gorilla glue. I also use a Chestnut Clam Clamp to draw it all together. I've also run long (4") screws thru the miter to hold it together.

   I haven't tried it yet, but I'd consider using pocket screws on the bottom side of the top rail to pull things together.

   Since I've been doing this, I've still had the miters open, but only 1/8" or so.

5. 
   gb93433 | Jun 30, 2008 05:28pm | #7

   If the typical 5.5" piece of wood that is flat sawn changes by 3% in moisture content it will change by about 1/32" to 1/16" in width. If you add the two together on a miter that amounts to 1/16" to 1/8"

   The typical piece of wood that is flat sawn will shrink from green to dry 6-8%. The wood will begin to shrink at 30% moisture content. If a piece of wood changes 3% in moisture content it will change in width by (3%/30%)x 6% -8% = .033"-.044"

6. 
   Piffin | Jun 30, 2008 06:01pm | #9

   it was wet
   now it is dry

   dry it before you use it.

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
   Excellence is its own reward!

1. 
   peedee | Jun 30, 2008 09:45pm | #10

   To all- <...using butt joints>Exactly, there are places where I used butt joints and they are fine (unnoticable changes).<The typical piece of wood that is flat sawn will shrink from green to dry 6-8%. The wood will begin to shrink at 30% moisture content. If a piece of wood changes 3% in moisture content it will change in width by (3%/30%)x 6% -8% = .033"-.044">Thanks, I recalled reading some figures like this and appreciate having the hard numbers and a clear reminder.<....a halflap is going to show less shrinkage, although I have to wonder if it would be more subject to rot. Does water tend to wick inside the lap and rot from the inside?>my thoughts exactly, I avoid laps in exterior work whenever possible, but especially cut laps.<dry it before you use it.>
   Pretty succinct (or, as some might say, ‘cut and dried’ ;), hmm, I wonder where _that_ expression came from? )Thanks to all, I appreciate all the thoughts, ideas, feedback and suggestions.