I read with much interest when FWW did their recent joint shootout (Fine Woodworking #203) But I’ve got a real world situation that invokes some thought. I built 2 exterior gates, one for each side of my house. Aesthetically they both look about the same. Long stiles with 3 rails, panels on the lower two-thirds, pickets across the top. The first one was made with half lap joints between the rails and stiles. The second gate was constructed with loose tennons. Both were glued and clamped using titebond 3. The material was pressure treated lumber (doug fir I would guess) to keep the termites at bay then primed and painted with exterior house paint.
After 3 years of rain and sun there is visible stress on the half lap joints. The lower rail is beginning to gap where the shoulder of the half lap meets the rail. Still strong but the paint has cracked along the joint and looks like the beginning of some wood decay. In contrast the loose tennon gate shows no joint issues.
My theory is that the half lap joint provides more places for rain to find its way to the joint and sit on the glue joint. The loose tennon is in essence sealed inside protected from the elements.
It’s too early too tell if the half lap will fail, but it appears it’s losing the race. Thoughts?
Mark
Replies
That's interesting Mark.
Do both gates get the same amount of sunshine on a typical day? Are either of them subjected to standing water? Are they both sealed with the same methods?--products, number of coats, etc.?
I like to hear from people who have taken it out of the lab and are using it in the field.
For the most part even sun/rain exposure. Both only get sun for part of the day as the neighbors house shades it (or my house). I live in Southern California so rain is just a few months a year. Both were primed and painted the same way using the same product. Both about equal usage. I should mention I did pin the half lap joint with two 1/2" dowels JIC. The joint surface area is about 3.5 x5.5".
"I live in Southern California so rain is just a few months a year."
You mean a few days a year.
-Steve
Yes. Plus the few days a year when a mis-adjusted sprinkler or two hits it :-)
Mark
mark,
ten years ago i made two 6'x8' shop/garage/shed doors. the joints were mostly half lap dovetails. there has been no separation. i did, however, pin each joint in three places with end grain wedged 1/2" dowels.
eef
There is currently a discussion on this subject on Breaktime - rain infiltration was mentioned as the big reason to avoid bridle joints or half laps.
You may want to take a peek - a lot of good info on that thread.
russs
You might be correct, but.......
In my opinion, pressure treated lumber is not a good wood when trying to evaluate joinery.
Few woods move as much as PT, and it continues to move years after you're done working with it. And one board might remain stable while others will not. This stuff really has no rhyme or reason to its twisting, shrinking, and swelling.
The changes that you saw on one joint, and did not see on another, might be caused by movement that was different in one board, as compared to another. That would be quite common with PT lumber, and does not reflect on the joinery being used.
FWIW, for such a gate, I have used half laps. My decision was based on my opinion of relative beauty, versus relative difficulty. And with the final result being a pressure treated gate, beauty (I knew) would be temporary at best.
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