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Hi Varun (@arian10daddy),
By the sounds of it, if you have 120mm minus the 90mm framing and the 19mm for decking, you'll still have 11mm for airflow and drainage under the frame. You can use Carinya 40 x 80 x 40 x 5mm Hot Dipped Galvanised Angle Brackets fixed into the concrete and then bolt the Treated Pine Outdoor Timber Framing 90 x 45mm to them. You can use plastic spacers to help establish the 11mm gap.
You could use F5 graded hardwood timber, which might have some benefit over H3 treated pine MGP10 in your application. However, I haven't personally heard of F5 H3 treated pine. H3 treated pine MGP10 is the most commonly used structural grade timber for most exterior projects around the home. F grades indicate the basic working stress (in bending) for hardwood timbers, whilst MGP indicates a minimum threshold for stiffness and is used for softwoods.
Please let me know if you have questions.
Mitchell
Varun (@arian10daddy),
After further investigation, it appears the F grade system is sometimes applied to softwoods like pine as well. It sounds like what you can get your hands on would be suitable, but I would encourage you to have a visual inspection of the timber first to check if there are limited knots and no significant twisting or bowing.
I'll reach out via private message to get details of your location to check with our stores for available H3 MGP10 stock for you.
Mitchell
I thought I'll show a little more of the plan I've made, and gain some knowledge from everybody's experience.
I'm thinking of a 3600x4000mm deck using 90x45 F5 H3 TP and 90x19 Merbau which will run from left to right in the above pic, and will be picture framed (I love it un-framed but the Mrs. wants it framed).
The joists are at almost every 300-350mm, and should have a noggin every 1000mm. The 400x400 pillar with a circular downpipe will not be picture framed.
The window packers will run under each joist at 800mm on the afresco, and maybe 3 L-brackets every length. I will use the 100x75 offcuts I have from 200x75 H4 sleepers to make posts over the concrete pathway. I will paint those posts with the black tar paint at the bottom where it touches the concrete. The posts will in a similar pattern as the window packers.
To connect the frame together I'll use joist hangers and L brackets.
A few questions:
1. To connect the frame together using joist hangers and L brackets, should I use galv. nails or galv. screws?
2. What would be the best way to connect the posts to the frame?
3. I won't be screwing the posts to the concrete pathway. I'll only connect the frame to the alfresco concrete. Is that sufficient enough?
4. Any other insights?
Varun
Hi Varun (@arian10daddy),
Thanks for sharing more about your project.
Let me tag @Adam_W and @DIYgals who may have some advice and suggestions for you.
Stevie
Hi @arian10daddy ! It looks like your plans are well underway. 
We vote for picture framing also!
We can share with you a little bit about our experience to help you make a decision on some of those things you have questions about. There are probably a million of different ways you can do it though.
1. We started to use nails on our joist straps, but because we didn't have a nail gun we found it took too long. So we switched half way to galv screws. These are the ones we used: https://www.bunnings.com.au/otter-12g-x-25mm-matt-black-class-3-hex-head-screws-150-pack_p0162366 The screws also made it much easier to make any minor adjustments after attaching the joists and bearers if needed.
2. We used Galv Bolts to attach our frame to posts.
3. I would think that attaching the posts just to your framework which is secured to the alfresco concrete is sufficient enough to stabilise the step, is there any particular reason you do not wish to attach it to the concrete pathway?
Good luck with the build!
Thank you @DIYgals for sharing your experience, as well as @MitchellMc and @StevieB for helping me out.
I was not able to find the otter he head screws @DIYgals mentioned, and the ones I found were pretty expensive. I got my hands on some of the button head galvanised "stitching screws" with #2 Phillips head. I wonder if these would work to attach the joist hangers. Weird enough, I wasn't able to find these in Bunnings website.
I also bought 75mm external timber screws to join 2 90x45 boards together where needed, as well as screwing boards at right angle where joist hangers can't be used. I hope that works out too. (fingers crossed)
I also got the joist hangers and the big pack of window packers.
Its Good Friday tomorrow and everything will be closed. So I think at least that I am all set to build the frame.
As far as attaching it to the concrete, I'll work on that later in the week. While we're on that topic, I remember some discussions here that talked about using the plastic spegetti and screws to fix the L-brackets down into the concrete. I am wondering what kind of screws could have been used in those cases?
If using dynabolts, I'm looking at about $2-$3 per dynabolt. Wondering about a more cost effective alternative.
Regards,
Varun
It's great to see you are well on your way to a new deck, Varun (@arian10daddy).
Those screws look like they will be fine for attaching the joist hangers. The 75mm screws will only have 30mm penetrating the timber piece you are joining once they've gone through the 45mm thick joist. I'd recommend you drive them in past the surface, so they penetrate a little deeper.
I can't wait to see your deck taking shape. Ensure you take plenty of photos during construction as our other members will find them very beneficial and of great inspiration.
Mitchell
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