# Forum Home Renovation Metalwork & Welding  Extending a deck post

## baileyboy

Hi, I want to specify to my welder to extend posts on a deck to build an arbor. Current posts are 75mm SHS. Post of the post has a metal rod to hold up the handrail and I think that will have to go. Like to know what I need to tell him, butt weld, backing etc...

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## baileyboy

Looks like this

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## baileyboy



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## Uncle Bob

Just explain to him what your intended outcome is then you both can discuss what needs to be done to make it happen.

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## baileyboy

> Just explain to him what your intended outcome is then you both can discuss what needs to be done to make it happen.

  Thanks. I'll do that. But thought I research it a bit before talking to him/her. Anyway, I have drawn up a sketch to show him.

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## baileyboy



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## Marc

What is the purpose of the 8 mm plate? 
Butt welding 4mm SHS is fairly easy for an experienced welder. For an amateur, perhaps internal backing would seem necessary. You could use 300 mm of 65x65x4 SHS for that purpose and plug weld the ends of the 65 to the 75, to increase lateral strength in case a hurricane and an earthquake hits simultaneously.  :Smilie:

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## baileyboy

> Hi, I want to specify to my welder to extend posts on a deck to build an arbor. Current posts are 75mm SHS. Post of the post has a metal rod to hold up the handrail and I think that will have to go. Like to know what I need to tell him, butt weld, backing etc...

  The 8mm plate is what's there. I can cut below it but that means I will have weld more brackets for the handrails

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## Bros

> Hi, I want to specify to my welder to extend posts on a deck to build an arbor.

   What's an "arbor" is it a sophisticated name for a trellis?

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## baileyboy

Basically a roof without the sheets

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## Marc

I see ... i would cut under the plate, bevel both edges of the SHS, butt weld and then add a pre drilled flat bar on each side to take the wooden handrail and screw from below. This weld is critical and needs to be done by a good welder with a good machine. If it is going to be done with a buzzbox by an amateur, you need to slip a backing inside and plug weld it and then weld the SHS

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## baileyboy

what is plug weld?

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## droog

> what is plug weld?

  It’s where you drill a hole in the outer material and weld to the lower layer of material, the hole drilled ends up filled with weld material and you grind it smooth.

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## Marc

:What he said:  
It is a way to weld material that is enclosed in an unreachable cavity. In your case, if I needed a backing I would go for 65mm SHS and drill a 20mm hole on each face at staggered levels, 4 at the top and 4 at the bottom of the backing pipe. 
Once the pipe is in position and the post is in line and straight. you tack weld each edge of each hole to the 65 mm SHS, check for alignment again and then proceed to weld the edge of each hole all around. 
Filling the hole in to conceal it is optional. This achieves a double purpose to give you additional bracing to a critical weld and also helps the welder by allowing the use of higher temperature for the main weld, achieving good penetration without blowing holes in the post wall. 
I use plug welded plates on each side of H beams' web, to join them end to end, and they remain rated as if in one piece.

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