connecting green oak beam to post

[rs6mra]

Hi
I plan on erecting a structure in the garden with green oak and the post and beams will be the same size 150 x150 of which the posts will be on a brick pier.
The beam has to seat on top of the post in order to get to the correct height. What is the best way to attach them as it is my understanding that fixings are likely to affect the oak?

The other thing is that the piers have rebar sticking out of them about 150mm; is there something I can paint them with to protect the oak timber as again it is my understanding that the tannins will react to the oak.
Thanks

 

[Jameshow]

How about a 150mm X 100mm tenon let into the top of the post at 45° which the beams attach too. Mitred at 45° and with a 100mm X 100mm X 25 mm cut out for the tenon.

Just a thought..

Epoxy or bitumen paint on the rebar too....

 

[rs6mra]

Thanks James but I'm struggling to picture what you mean.............
Any particular epoxy or bitumen paint you can recommend?

 

[Tris]

Bridle joints horizontal on the beam ends, then a blind mortice cut vertically 2/3rds through the bridle joint. That mortice fits on a tenon at the top of your post

Could just use a lap joint and through tenon but I would avoid the upward facing exposed end grain if possible

 

[rs6mra]

Bridle joints won't work as the beam needs to be on the post as in the photo below.
Would a wind brace like that in the photo help with mortice and tenon to fix in place but sufficient?

 

[Tris]

Sorry, I was assuming two beams coming together at right angles on the top of your post, not sure why I thought that.
A blind mortice and tenon, pegged, with wind braces should be fine

 

[JBaz]

Are you erecting a kit with pre-cut joints or making from scratch?

 

[Adam W.]

Hi
I plan on erecting a structure in the garden with green oak and the post and beams will be the same size 150 x150 of which the posts will be on a brick pier.
The beam has to seat on top of the post in order to get to the correct height. What is the best way to attach them as it is my understanding that fixings are likely to affect the oak?

The other thing is that the piers have rebar sticking out of them about 150mm; is there something I can paint them with to protect the oak timber as again it is my understanding that the tannins will react to the oak.
Thanks

Mortice in beam and tenon on post with a drawbore peg to keep it together. If you're feeling European, just plonk the beam on the tenon and forget the peg, as the weight of the beam will keep it in place.

Bracing is recommended to stop wracking.

 

[rs6mra]

Are you erecting a kit with pre-cut joints or making from scratch?

From scratch
Tried to get pre cut to the I want and no one seem interested

 

[rs6mra]

What I didn’t make clear is that with the upright post being 2.4m and the beam of 150mm resting on it (2.55m) that gives me enough fall for the flat roof.
With the mortise in beam method I lose 150mm.
The only other way I can see is to increase the height of the pier which would be a PITA for me.
Are fixings an absolute no no with green oak?

 

[Adam W.]

What I didn’t make clear is that with the upright post being 2.4m and the beam of 150mm resting on it (2.55m) that gives me enough fall for the flat roof.
With the mortise in beam method I lose 150mm.
The only other way I can see is to increase the height of the pier which would be a PITA for me.
Are fixings an absolute no no with green oak?

Use a 2"mortice and a 1 3/4" tenon. The tenon doesn't need to go all the way through the beam.

 

[Jameshow]

You and make the tenon out of an offcuts of oak surely?

 

[rs6mra]

Pardon my ignorance but if I have understood this correctly do you mean making a tenon out of oak or an oak peg, making a mortice in the post and beam and then driving the peg/tenon into the post then the beam onto the tenon/peg?

 

[Jameshow]

Yes...

 

[Woody2Shoes]

......
The beam has to seat on top of the post in order to get to the correct height. What is the best way to attach them as it is my understanding that fixings are likely to affect the oak?

The other thing is that the piers have rebar sticking out of them about 150mm; is there something I can paint them with to protect the oak timber as again it is my understanding that the tannins will react to the oak.
Thanks

The idea is that the bottom of the post has a hole drilled in it to accept the upwardly-projecting rebar - this will stop it 'falling off' the brick plinth. Last time I did this with pieces of M10 stainless threaded rod, to avoid the iron vs oak tannin-related business - the bottom of the post will be the wettest part over time. You could paint your rebar with red oxide primer, followed by some bituminous paint if you really wanted to be fancy. The rebar should be degreased with washing up liquid and water first (rebar often has an oily coating).

 

[Woody2Shoes]

Mortice in beam and tenon on post with a drawbore peg to keep it together. If you're feeling European, just plonk the beam on the tenon and forget the peg, as the weight of the beam will keep it in place.

Bracing is recommended to stop wracking.

+1 for the above

 

[JBaz]

If you are starting from scratch, I built a pergola from scratch last year.

Although I've been working with wood for over 50 years, this was the first time I'd used green oak, and soon found out it is very different to working with dry timber. For a start it is very heavy, about 1150 Kg/cu m, so a 150 x 150 x 2400 post weighs in around 65Kg. Not something you want to move too often!

I've got pretty decent static machinery (Felder) that would probably have planed up the 150 x 150 x 4200 beams, but over 100Kg each handling them was too much for 2 of us, so I bought a Triton 7" planer (sold it after completing the job and didn't lose too much - cheaper than hiring) and some plastering trestles. Also, green oak will stain/rust cast iron in minutes, so cleaning machines down all the time would have been a nightmare. The one static machine I did use was the chisel morticer. With an 18mm chisel I spent about 5 days solid cutting mortices - my arm still hurts.

As to joints, everything was pegged and the corner joints were quite complex. I didn't want any end grain showing vertically so that rain could soak down through the timber and I had to be able to assemble it. I spent some time investigating old joints and in the end I opted for this

This allowed me to make two portal frames for the ends and drive the pegs fully home on the ground, trim them then erect them with a Genie Lift. I could then lower the side beams onto the tenon cloaking the whole joint. The corner braces do most of the work, but I still gave the horizontal beam a 10mm bearing, plus the tenon.

I won't bore you with too much detail, but I'm happy to share my experience if you want me to.

 

[Jameshow]

If you are starting from scratch, I built a pergola from scratch last year.

View attachment 132496

Although I've been working with wood for over 50 years, this was the first time I'd used green oak, and soon found out it is very different to working with dry timber. For a start it is very heavy, about 1150 Kg/cu m, so a 150 x 150 x 2400 post weighs in around 65Kg. Not something you want to move too often!

I've got pretty decent static machinery (Felder) that would probably have planed up the 150 x 150 x 4200 beams, but over 100Kg each handling them was too much for 2 of us, so I bought a Triton 7" planer (sold it after completing the job and didn't lose too much - cheaper than hiring) and some plastering trestles. Also, green oak will stain/rust cast iron in minutes, so cleaning machines down all the time would have been a nightmare. The one static machine I did use was the chisel morticer. With an 18mm chisel I spent about 5 days solid cutting mortices - my arm still hurts.

As to joints, everything was pegged and the corner joints were quite complex. I didn't want any end grain showing vertically so that rain could soak down through the timber and I had to be able to assemble it. I spent some time investigating old joints and in the end I opted for this
View attachment 132497
This allowed me to make two portal frames for the ends and drive the pegs fully home on the ground, trim them then erect them with a Genie Lift. I could then lower the side beams onto the tenon cloaking the whole joint. The corner braces do most of the work, but I still gave the horizontal beam a 10mm bearing, plus the tenon.

I won't bore you with too much detail, but I'm happy to share my experience if you want me to.

Did you divide the 150mm x150mm into 5 (30mm) one way and 3 (50mm) the other way????

 

[Jones]

Why not just use a drift pin. A drift pin is a metal rod hammered into a predrilled hole. For that size timber I would use a 10" long 10mm piece of rebar or stainless threaded rod knocked into a 10mm hole. If you lubricate it with some glue it won't do any harm. Put the beam in place drill a little over depth then hammer pin in, two per upright will stop any twisting. If you knock the pin below surface this will allow for a bit of shrinkage and you can add a bit of mastic so water doesn't pool. If that doesn't appeal spax do some very long washer head screws.

 

[JBaz]

When you are working with green oak of these dimensions you buy it sawn to order at a nominal size. Unless you want the sawn finish, you then have to plane it, rather than thickness it, (unless you have a serious thicknesser and can handle 100+Kg timbers!). Because you are planing it, you invariably end up with every piece slightly different. Also, green oak is continually drying out and moving, so there is no guarantee that a long length won't develop a bow after it's been planed. If you look at the picture of my pergola, you can see that one of the top beams is missing. That's because one of the beams delivered was 20mm thinner in the middle and bowed by 50mm, so I rejected it and had to wait 6 weeks for a replacement.

It's up to the carpenter to mark out and cut the joints then fit each joint individually. You work to a reference face and size the joints accordingly.

I can't remember the exact dimensions of each joint, but I think we aimed at a minimum 30mm thick tenons and a minimum thickness of 20mm where the pegs went through.

As to drift pins, you use dried oak pegs because they will distort as you drive them into the offset holes and, provided you make them properly, in trying to align the holes the peg tightens the joint. Steel pins won't distort so all of the stress is taken by the holes and you can split the wood.

To make the pegs you take dried oak and cleave it to just oversize, so the grain runs along the length of the peg. You can then either plane or draw-knife it down to size, or make a tool like this

and drive the blanks through. We did try turning some on the lathe, but unless the grain follows the length, the pegs break when you try to drive them in.

We did make some drift pins from stainless steel, but they are only used as temporary fixings whilst the joints are fitted to each other and during erection. We made them as "tee's" so we could get them out.

Like I said, working with green oak and pegged joints was a whole new world for me.