Outdoor trestle table top - to glue or not to glue

[Wakahisa Shinta]

I am building a trestle table for outdoor use. The wood is doug fir, straight vertical grain, and knot-free. I finished jointing and planning the stock wood to final dimension of 1.75" x 5.75" x 9'. I plan to use 6 boards to make a top of roughly 36" wide. The length is ~80".

The top was modeled in Sketchup with each board spaced 1/4" apart and secured with three cleats and 1/4" diameter stainless steel lag bolts underneath. The spaces are there to allow for rain water to drip to the ground. Now, I am debating if I should glue the boards together to make a solid top and not be so worried about rain (given a good outdoor stain/finish is applied). I plan to use Titebond III for glue (the table sits underneath a pergola which has wisteria climbing on it).

So, to glue or not to glue?

[Peter Aeschliman]

My vote is to leave the gaps. No matter how good your finish is, less standing water means more longevity.

Maybe if you make a breathable cover for it for the rainy months, you could get away with it. Keep in mind I live in Seattle, so rain and rot are probably a much bigger concern where I live.

[Jerry Miner]

I would not glue. The spaces will not only allow water to drip through, but will also allow greater air circulation for drying out.

From my experience in repairing outdoor furniture, the weak point---where the rot will show up first -- will be the contact areas between the cleats and the top boards. If you are not against chemical treatment, treating these locations will make your table last longer

[John TenEyck]

I would leave the gaps if you plan to use the cleats and run lag bolts into each board. If you glue it up solid and lag bolt the cleats to it like you described it will buckle or break apart from seasonal expansion/contraction unless you make the holes in the cleats elongated.

John

[Wakahisa Shinta]

Hi and thank you for your advice.

The holes in the cleats for the lag bolts are going to be drilled larger than the diameter of the bolts to allow for the doug fir boards movement through out the year. I plan for two lag bolts per board, totaling 12 bolts per cleat. I think one lag bolt per doug fir board might not provide enough holding strength when the table is lifted when moving it. At 36" x 80", the top weighs 109 lbs per an online calculator.

I plan on using TWP wood stain for protection. It will need to be applied every 1-2 years, but I don't mind this maintenance schedule.

[keith wootton]

i work in a state park (for 39 years) where we have many tables i have built. my experience tells me you could build a top with three wider boards each made from glueing two of your existing boards. i use gorilla glue on jointed boards. titebond 3 should be good too. we use galvanized 3/8 carriage bolts to bolt the tops to the rest of the table. jerry's note on rot is spot on. using solid color stain and not a paint that seals the wood too well will keep individual boards from rotting from the inside out. water gets in and has a hard time getting out in a residential setting where you could cover the table with a sunbrella tarp in rainy weather, table should last a very long time. i have fir tables last 25 years and some redwood ones that were here when i started. keith

[keith wootton]

and keep the bottom of the feet off the ground on small blocks or bricks above grade. keith

[peter gagliardi]

I would not glue anything that is to become a flat horizontal surface such as a table for full time outdoor exposure. Leave the gaps, that is just good design.

[Andrew Hughes]

I made a picnic table for my house years ago,I spaced the boards on the top the spaces fill with leaves and acorns from my live oak.It was a pain in the ass to clean them out.So I say glue them up tight with gorilla glue!

[John C Bush]

The fir will likely cup when exposed to the hot Sacramento sun--more qtr sawn = less cupping. I would leave the spacing and anticipate dimensional change. I use cedar for outdoor furniture up here and had always used Daly's Seafin Teak Oil for the finish. It would hold its color for a couple of years before greying out. Now I use less expensive deck and fence sealer. lasts as long and less cost.

[Wakahisa Shinta]

Well, the consensus is to leave the gaps, so be it. CA is in the middle of a drought. I wish that there is enough rain that it becomes a problem for this kind of outdoor furniture.

John above mentioned cupping due to heat. I thought about adding breadboards to the end, but didn't think it is necessary given the cleats. Would breadboards help with anti-cupping?

[John C Bush]

Breadboards would be a nice finished look. My outdoor cedar tables--2 x 6's-- cup seasonally and is more visible at the ends. Tenons on the ends and pinning the center of each plank would work. Cleats in the middle of the table would work if you can fasten the edges of the planks and not limit wood movement. Humidity swing a bunch up here and may not be as much of an issue for you. The more qtr sawn the better as well. Send pics when you are done.

[Wakahisa Shinta]

A couple pictures. I finished attaching the cleats to the doug fir boards and trimmed the boards to final length. The center cleat is slightly larger than the outer ones. 1/4-3" stainless steel bolt and washer for each board to each cleat. I planned two lag bolts/board for the middle cleat, but changed to single bolt because it felt very secure after I attached one of the outer cleats.

I am thinking about breadboards using loose tenons. These will add about 10" to the overall length of the table. As of right now, I plan for 15" overhang at each end. This gives 50" between each legs.

Which species of wood is recommended for outdoor use and has a bit of contrast against doug fir?

garden table 01.jpg garden table 02.jpg

[Wakahisa Shinta]

I thought I'd update this thread with a picture of the semi-completed table. "Semi-completed" because I am undecided about the length of the cross brace. For now, I'm leaving it long. It actually makes a nice foot rest!

There are a few other threads I started after this one to ask various questions while I worked on this table during the few weekends that I can devote to this hobby. I wonder how long this table will last.

Thank you to the community for all the help!

IMG_3787.jpg

Doug fir SVG lumber, walnut pegs, General Finish 450 sprayed on (4 coats), stainless steel hardware.

[John TenEyck]

Good progress there. Redwood would go well with the Doug Fir. They will both turn grey if you don't put something on it, however. CWF Clear, or something similar, is about the easiest product to use.


John

Seems I missed your post of the finished table. Sorry about that.