some advice needed for my first decking job please

Hey folks I have just taken on my first decking job for a customer. I spent years working in the building industry so hopefully have the skills and tools to build a 30 sqm single level deck. However I'd like some advice from anyone who builds decking regularly. Firstly what size of treated joists should I use 6x2 or 4x2? One side of the decking (12ft 9" long) is fixed to a brick garage, I was going to use 12mm thunderbolts every 500mm with washers between the timber and wall to so as not to trap water which would rot the wood in time. The back edge of the deck (13ft long) butts up to a 6ft fence hung on three 4x4 posts concreted into the ground. I was going to fix the joist to these posts with coach bolts. The other two sides will attach to 4x4 posts concreted into the ground every 2 or 3 feet. I was going to attach these joists to the posts using threaded bar. That will give me my four sides from which I'll hand joists every 500mm centre to centre with noggins in between. I think I will also need a post or two in the centre of the decking to take any spring out of it.

That's the basic plan, if anyone has a better way of doing it or if i'm using the wrong materials please let me know. The customer has opted for the cheap greenish pressure treated decking, has anyone used this and does it shrink much as it dries. So should I butt each board tight to the next, or is there a risk of it expanding more in winter? I have done a bit of research online and it seems the debate was never settled. Also can cheap pressure treated decking be successfully sanded and treated to improve the appearance or does it maintain the greenish tinge, and can cut ends be coated with stain/varnish to stop them rotting? Sorry for so many questions, I want to do the job right.

Thanks, John

Sounds good John, I used 4 x 2 for the frame on the first one I did recently. I guess 6 x 2 would reduce the number of supporting posts needed. Would be wary of fixing frame to existing fence posts perhaps - would be a pita if you need to replace them later on ? I used coach screws rather than threaded bar to fix frame to ground posts, seemed the easiest way for me. Yes, you will need a couple of posts in the middle to stop it bouncing.

Timber shrinkage will depend on how well seasoned it is, you'll be able to tell by the weight. I used a 5mm spacer to give gaps between the deck planks to account for any expansion in the wet. The green tinge will weather off soon enough. Yes best to treat sawn ends with preservative.

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Russ Francis August 5, 2015 at 6:54pm

Sounds good John, I used 4 x 2 for the frame on the first one I did recently. I guess 6 x 2 would reduce the number of supporting posts needed. Would be wary of fixing frame to existing fence posts perhaps - would be a pita if you need to replace them later on ? I used coach screws rather than threaded bar to fix frame to ground posts, seemed the easiest way for me. Yes, you will need a couple of posts in the middle to stop it bouncing.

Timber shrinkage will depend on how well seasoned it is, you'll be able to tell by the weight. I used a 5mm spacer to give gaps between the deck planks to account for any expansion in the wet. The green tinge will weather off soon enough. Yes best to treat sawn ends with preservative.
- PRO
  
  Russ Francis > Russ Francis August 5, 2015 at 7:03pm
  
  Here's my first deck, the step was a bit fiddly, but quite pleased with how it turned out even if I say so myself !
  - john mcmaster > Russ Francis August 5, 2015 at 8:12pm
    
    Thanks Russ Francis very tidy piece of decking there, I hope mine looks half as good. I'll take another look at the edge against the fence and see if I can do something else. The reason for using threaded bar to join the joists to the posts is because I have metres and metres of the stuff in my shed and am looking an excuse to use some of it up! Thanks again, John
  - ChaseLandscaping > Russ Francis August 13, 2015 at 9:40pm
    
    How do you add a pic russ?
    - PRO
      
      Russ Francis > ChaseLandscaping August 14, 2015 at 5:57pm
      
      There's a little picture icon on the formatting bar, just click that and you're prompted to browse and upload your pic
ChaseLandscaping August 13, 2015 at 9:37pm

You can buy an end grain preservative which looks blue going on but dries with the same green tinge.
Have you looked at the swedish boards? Not much more expensive but much nicer. Atkinsons fencing and decking do it. Have a look at their website.
I use 6x2 joists with coach bolts but threaded bar will do the same job.
I put my joists 400mm apart and have plenty of posts in the middle but they can be rested on a bed of hardcore with a block/broken flag on top.
Screws are my main tip. Buy a quality screw and eliminate the need to pre drill every hole! Spax do a very good one with a hidden head.
Thats about it.
Id love to do a hardwood one or a bamboo one but finding a client with that kind of money is rare.
Benedict Simmons August 14, 2015 at 8:21am

Hi, I normally always use 6x2 joists at 400mm centers. I wouldn't attach it to the fence as it would be a nightmare to replace the fence. You are right to have an air gap between the timber and garage. Do a Web search for the timber decking association, lots of help there.
- Geoff Norfolk > Benedict Simmons August 14, 2015 at 11:48am
  
  Its a pity you can't persuade your customer to use composite decking boards...... I paid for a deck to be laid with them (millboard) and it looks great and no maintenance ever needed (well that's what they say!) The boards are much more expensive but reckon in the long run, they'll be a much better bet with not needing any treatment during its lifetime. They use special stainless screws with an unusual head which disappears below the surface of the board and then the board "closes" on top of it..... no sign of the screw to be seen.