Biscuit joints with redwood?

[gugie]

I'm redoing parts of our outdoor deck, reusing a lot of old redwood. The older parts of the deck have 2x4 redwood as the top rail, with the corners miter cut. These have rather large gaps.

I'm thinking of miter-cutting the corners like the old section, but using biscuits and glue to join them. I'm wondering if these will hold up over time. Any ideas?

[JR]

I have had trouble when using biscuits outdoors. I built a bench out or redwood and used biscuits for some of the joinery. The biscuits broke down due to exposure to rain.

Here's what I have done in your circumstance. Run skill saw in the miter joint to even up both sides. Then drive some long deck screws in from the sides to cinch them together. Plug the screwholes if you feel compelled to do so.

HTH,
JR

[Black wallnut]

It seems to me that it would help. Added glue surface although a mitered half lap would be better if you have the extra material to do so. Nice seeing ya stop in! Twins must be 8.5 about now right? (I looked it up)

[cabinetman]

I would not use biscuits. There are several alternatives.

You could use half lap miters as mentioned.

Or you could make a splined miter, making the spline from crossgrain redwood.

Or you could do keyed miters.

Or you could use a loose tenon.

Or, you could glue/clamp the miter, and then drill for a dowel and insert with glue.

.

[gugie]

JR,

Thanks for the info! Since any issues probably wouldn't be seen for some time, your long term observations are very helpful. I am worried that the screw threads would pull out after a season or two, since they'd be driven into the end wood.

Mark (he says as a dog with a hare lip),

Your idea of a mitered half lap got me to thinking that using a spline. That way the reinforcing piece is covered on both sides, which would help with separation. I could glue up the corners and tack them together with 18ga pins using my airgun, let them set, then run my dado blade through them, maybe 3/8" thick. Plane down some redwood to a slip fit, glue them in, trim when cured. Luckily the rails aren't that long, else I'd have to wheel my tablesaw out of the garage.

Thanks for asking about the girls! Our twins are indeed 8 1/2, just about finished with 2nd grade. One is doing ballet, the other is really into art and drawing. Both are doing well in school.

L.D.,

Just saw your post after posting, so I'm editing this one. I think the spline idea is what I'll end up doing. Thanks for the confirmation.

[Tom Slick]

IMO forget about the miters, they'll open no matter what and they're a pain when your layout isn't square. You'll need to add quite a bit more framing in the corner but I'd lay them out like this:


no joints to open, plenty of room for shrink and swell cycles, they look good even if they are opening and closing, and if your layout isn't square you only have to scribe straight cuts to get the gap even.


Edit: I re-read (#3 reading) and it dawned on me that you're talking about the top rail, not the deck. My advice may not be applicable.

[cork58]

I agree with Tom on this one. His layout is great and his reasoning remarkable! I'll be using this when I finish our deck. It won't be Redwood as in Alaska it is soooooooo pricey. Probably Spruce out of our mill on site. Found some very nice trees on part of our property I haven't harvested yet last year. So might be a year or two or three before I get to it. Oh my, I better write that down so I don't forget it. Hey Tom P.M. that plan in a couple of years LOL.

Thanks Tom!

Corks

[pelligrini]

The Half Lap miter would be the strongest. Is there room to do the screws like JR suggests, but from below?

[cabinetman]

Is there room to do the screws like JR suggests, but from below?

If the glue joint fails, being screwed from below could allow the joint to separate. If this was the only form of a mechanical fastener it would not provide the joining force to the members of the joint as would other methods.

.