which of these joints is stronger?

[Wakahisa Shinta]

I am building legs for a garden trestle table. I am debating joinery methods for the legs. I worry that the joint might fail under the weight of a person sitting at the edge of the table. The rough Sketchup design is this:
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Between a traditional M&T and domino loose tenons (with 4 or 5 10mm x 50mm dominos, pictured), which is stronger do you think? The M&T joint is 1 1/4" deep tenon, width is 1/3rd lumber thickness.
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I think the loose dominos might be stronger given the increased gluing surfaces. No?

[daryl moses]

The dominos may be stronger but I think the M/T would be more than adequate.

[Peter Quinn]

Either is fine. Both stronger than the surrounding wood which will fail first. So it comes down to how much you trust your glue to resist the elements. The M&T can be draw bored and pegged, basically don't need glue at that point for a strong permanent joint, the domino is reliant on glue strength to a large degree. Domino is probably much faster than fitting perfect tenons.

[peter gagliardi]

More than likely a true mortise and tenon is going to be stronger. It is going to be awful hard to beat the integral strength of consistent fibers, and get more glue area to boot. However, if you go the Domino route, be sure to use the Sipo dominoes, the beech will rot quicker than.... once it gets and stays wet.

[Jim Dwight]

Fine Woodworking did a bunch of tests using 2.5 by 8 inch by 3/4 inch thick cherry pieces. They used one 10mm x 50 mm domino and it had about half the strength of the "real" mortise and tenon joints. Their loose tenon was effectively the same strength as the regular M&T joint so it was just a size thing. More gluing area = stronger joint. They got noticeably higher strength with a 3/8 tenon - half the material thickness - than they did with a 1/4 and a 5/16 tenon. Suggests we ought to use 1/2 the thickness tenons.

I think either will work fine. Whichever gives the most long grain to long grain gluing area should be strongest.

[Wakahisa Shinta]

Yep, I have the Sipo dominoes ordered just in case I need them. I am not too worried about rot from water damage. My wife is making a water-proof cover for this table and the chair/bench. She wants to cover them during rain season and when not in use.

By everyone input, I think 5 Sipo dominoes are likely stronger than a single M&T. Time will tell! :)

[Jack Jackson]

Dominoes will probably end up having more long-long grain glue surface.... at least it looks like they would. And it'd be WAY easier to do and that's gotta count for something.

[Robert Engel]

Looks like overkill with the dominoes, dude ....

My choice would be a through tenon with either draw bored pinning or wedges.

I would also consider epoxy glue.

[John TenEyck]

I don't see why you would be worried about the joint from someone sitting on the edge of the table. The greater risk is if the table gets racked and you have no stretcher between the two trestles. In that case, the traditional M&T is likely to be stronger because of it's larger cross sectional area. But I think either approach is more than adequate. How you attach the trestles to the table top is going to be really important if you aren't planning to use a stretcher between them. There is going to be a lot of tensile force on those joints if the table gets pushed sideways. I'd be more worried about that connection than the joints in the trestles.

John

[Wakahisa Shinta]

John, there will be a stretcher between the two trestles.

One trestle glued up. First time using Gorilla polyurethane glue. It's a bit messy! Is there any way to avoid the foam? Direction on the bottle read and followed.

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[jack duren]

Yep, I have the Sipo dominoes ordered just in case I need them. I am not too worried about rot from water damage. My wife is making a water-proof cover for this table and the chair/bench. She wants to cover them during rain season and when not in use.

By everyone input, I think 5 Sipo dominoes are likely stronger than a single M&T. Time will tell! :)

You would think but I'll take the one M&T over the Domino's. :)

[John TenEyck]

John, there will be a stretcher between the two trestles.

One trestle glued up. First time using Gorilla polyurethane glue. It's a bit messy! Is there any way to avoid the foam? Direction on the bottle read and followed.

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If there's a stretcher then it will be very strong against racking, meaning you shouldn't be concerned about which joint you use. As for Gorilla glue foam, I avoid it by not using it unless I'm working with wet wood. There's just no good reason to use it when working with dry wood. Titebond III is stronger, just as good for outdoor use, and much easier to clean up.

John

[Brian Holcombe]

Are you doing anything to raise the feet up off the ground?

[Wakahisa Shinta]

Brian,
Yeah, the trestles will be off the ground with swiveling and leveling feet/mounts. This table will be placed on top of a pavers patio that is uneven just because it is constructed with pavers.

John,
I have used Titebond III in past outdoor projects. It is indeed much easier to clean up. For this table, I wanted to try polyurethane glue because a lot of woodworkers believe that it is superior for outdoor use. I don't remember coming across a more scientific comparison between Titebond III and Gorilla polyurethane. I'd rather spend time, which is a finite commodity, building project than doing my own comparison/testing. I think I will go back to Titebond III in the future.

[Kent Adams]

There are numerous tests between gorilla glue and titebond on youtube. I'll be honest, I use to use gorilla glue a lot around the house, not with wood per se. I was shocked how weak it is compared to titebond. It was basically the weakest on wood, right up there with liquid nails. The titebond glue was even tested with being submerged in water and it never gave at the joint. The wood gave out first.

[Keith Hankins]

I think it would be application based and how much sheer pressure is applied. I built a hutch 10+ years ago with all domino, no issues what so ever, and they do tests with devices that measure strength till breakage. My point is unless you are putting tons of sheer pressure it won't matter. Your picture (in the first post) shows a strong joint. If you have the domino use it.

[Brian Holcombe]

Brian,
Yeah, the trestles will be off the ground with swiveling and leveling feet/mounts. This table will be placed on top of a pavers patio that is uneven just because it is constructed with pavers.

John,
I have used Titebond III in past outdoor projects. It is indeed much easier to clean up. For this table, I wanted to try polyurethane glue because a lot of woodworkers believe that it is superior for outdoor use. I don't remember coming across a more scientific comparison between Titebond III and Gorilla polyurethane. I'd rather spend time, which is a finite commodity, building project than doing my own comparison/testing. I think I will go back to Titebond III in the future.

Nice, good to see some feet in the works.

I have a table outside I built in padauk using titebond III at the joints, it takes some serious weather abuse and it's still standing without issue. Honestly I'm waiting for it to fall apart so I can built an updated version of it….no such luck.