Thread: Should I convert to keg Pocket Holes or stay with Mortise and Tenons on Deck Bench?

Hi Barry

given the scale of what you are contemplating and your desire to incorporate a number of improvements, I suggest you bite the bullet and build a new version.

I have little faith in pocket screws holding for any length of time in weathered timber.

So I'm not an expert and happy to be corrected by others but it seems like you have several issues. The glue layer seems quite thick, perhaps indicating that the mortise and tenon joints are not very tight, which would lead to water collecting in the mortises, your tenons starting to rot and then disintegrating. And the glue selection may not have been the best? Some of the members also seem to have shrunk quite a bit (second photo).

I wouldn't think pocket holes would be a long term fix by themselves, since you'll still have ill fitting joints and exposed to the elements, the pocket holes and screws will give way as well as water gets into the screw holes and repeats the story of the mortises and tenons. The other issue you'll face with pocket holes is that if the piece with the pocket hole doesn't seat properly against the piece being screwed into and you only have 1 screw at each end, it's going to spin.

I would suggest a longer term fix would be scraping off all of the old glue, using a wood hardener to remedy the rot in the tenons and mortises, then a gap filling glue (epoxy) that can bridge the hopefully small voids in the joinery and stand up to exterior use at the same. Where the tenons are completely broken off, you could use a pocket hole and screw then fill any gaps with epoxy. Might be messy. Or cut a dado into the stub where the tenon was and insert a new tenon.

At some point it might actually be easier remaking the whole bench I think.

If the timber is sound, I would replace the tenons with loose tenon joinery. I would never go near screws for outdoors. If the timber is not sound, then as Ian suggested, rebuild the lot from scratch.

Regards from Perth

Derek

Many thanks gents!
Much appreciated.

I plan on using 2 screws per join.
I've been using stainless steel screws in my undercover boxes.
Wouldn't the kreg stainless steel screws be ok for the outdoor pocket holes?

And in conjunction with Titebond III?

I don't mind scrapping off the old glue to clean up and then the loose tenon solution.

And this time I plan on putting all together in the work shop on the work table clamped properly etc.


hmmmm

oops never mind.
I just recalled the fine threaded stainless steel search.
which ended up as Kreg only for 33c each.
Frak!
https://www.carbatec.com.au/joinery-...-fine-ss-100pc

Your biggest problem with any tenons that have come loose is that if the original glue was PVA then there will be a layer of PVA on the inside of both the mortise and tenon. This has to be totally removed as any new PVA will not stick to the old stuff. The alternative is to use epoxy which will stick and also fill any gaps left after the disassembly. Screws will only be a help during the glue going off and are not really suitable for something like chair construction as they tend to allow the timbers to crush and joints to move whenever the load changes.

My recommendation is to use lots of epoxy and clamps and to only use screws if you don't have clamps or they are unsuitable.

One of the reasons you're having problems now is the poor M&T's allowed water in, which sat and caused deterioration.

As for using screws (pocket or otherwise), well...

Originally Posted by Bohdan

Screws will only be a help during the glue going off and are not really suitable for something like chair construction as they tend to allow the timbers to crush and joints to move whenever the load changes.

...and this crushing/movement englarges the holes, which will let water in and...

So you'd still end up with similar problems further down the line.

The other problem also is when you sand/scrape or clean up the weathered exterior you will loose about 2mm per side so on all the small sections there won't be a lot left for any screw to get a reasonable bite or support.
Resin in the joints with loose tenons is the go or new timber and rebuild, at least you know what has caused most of the existing problems and you have gained experience since building it so now you have the perfect opportunity to do a first class job and impress you know who and she will be super impressed.

Whatever you end up doing, make sure you keep it covered when it's not needed. It's clearly been left fully exposed to the elements and you'll end up right back where you are now in a few years if you don't protect it.

Excellent advice gents.
Much appreciated.

Nixed on a new build.
I'm wondering if epoxy is expensive?

OK. Here's what I'm thinking.

Epoxy ( adhesive NOT resin ) as a gap filling glue between joints
Wood hardener
Loose tenons
wider mortise

remove joint glue by removing all existing tenons.
re-drill mortise wider and deeper to a standard size removing glue
making my own loose tenons to fit mortise properly
gluing using epoxy
Keep covered

sounds like a start

https://www.quora.com/What-is-the-di...d-epoxy-resins


https://www.artofmanliness.com/artic...iture-repairs/
https://www.carbatec.com.au/joinery-...de-237ml-brown

https://www.popularwoodworking.com/p...-tenon-joinery

Sketchup | 3D Warehouse | Woodworking Loose Tenon Mortising Jig

https://www.youtube.com/watch?v=zORuOdjasMo

Barry, to the above add fresh timber, and the old bench will be as good as new

Regards from Perth

Derek

Oops I did mean to say epoxy in my previous post (not resin)

any specific brand of epoxy adhesive?

Originally Posted by barrysumpter

any specific brand of epoxy adhesive?

Techniglue R60 is my go-to. It's quite thick so it's good for gap filling and won't dribble everywhere. Make sure you use the fast hardener, the slow one takes days to cure in colder weather, you'll still have to leave it over night with the fast one

I was thinking about this a bit overnight. My MIL had some ancient outdoor furniture she utterly refused to throw out despite the fact it was completely RS.

Any repairs on the timber were almost a waste of time. Once the wood has lost its density it simply didn't hold things properly. It could certainly be repaired enough for a sit or five, but two years? No way.

Despite glueing and screws (chunky ones from Kreg) is really didn't hold together too well. One more summer and it was time for the tip.

For this bench, perhaps you could use big dowels, the biggest that will fit inside the timber... such as 20mm. Drill them deep (50mm) and epoxy them in, then drill right through the benches side and make it into a split wedged-tenon... use gobs of epoxy. The wedged tenon will completely stop any pull-out or movement.

I look forward to seeing how this goes... but I suspect it would be better to use the old seat parts as templates and make new bits!

A Grandfathers Axe