Decking over concrete slab

we are looking to deck our alfresco area, its a concrete slab with a 70mm step down - not much I know, what’s the best way to go about it with such a small step down to work with ?

does anyone also have a great program to work out deck plan / spacing etc ?

thanks heaps!

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Jason

Hi @Tracey113 ,

Welcome to Workshop. We look forward to seeing how this project progresses and trust that you'll get plenty of helpful information and advice from our members. Feel free to post whenever you need a hand.

I also welcome any feedback about how we might improve Workshop for you. Just let me know.

Thanks,

Jason

asarson

Mc Donald Jones Homes? I just built a deck over our concrete slab with "70mm" setdown. The main sliding door was even less than 70mm setdown, other bedroom door was more than 70mm, had plenty of issues getting it done, wall to the right was not square either.

70x35mm Pine subframe secured to concrete with screws / plugs. Levelled using window packers

5mm spacing, wanted 5mm minimum which worked out good as the board widths over the width of the deck worked out full boards the whole way across. Painted the subframe black to avoid the "see through" effect.

70x35 subframe secured to concrete using screws & plugs.140mm Merbau decking with 5mm spacing.

MPountley

https://www.workshop.bunnings.com.au/discussion/comment/5629#Comment_5629

Hi, Just a thought. Did you put down a moisture protection layer between the frame and the decking boards?
If you do, then this normally comes in back, which means you would not have seen through the decking boards.

Cheers, Mark

Tracey113

https://www.workshop.bunnings.com.au/discussion/comment/5629#Comment_5629

@asarson yes ours is MJH house - in hindsight wish we realised that the set down was only 70mm. Do you mind sharing a pic of what you did around the pillars and the edges / sides ??

asarson

https://www.workshop.bunnings.com.au/discussion/comment/64934#Comment_64934

Hey Tracy,

Well as I am building a built in bbq the outside edge of the deck is still unfinished however I plan to picture frame finish the edges. It’s a little difficult since we are using 140mm boards and I can’t get to a full board around the pillars without cutting one down.. I plan to just check in full boards around the corners of the pillars rather than cut down full lengths. Hope that makes sense.. the inner wall was out of square also so we had to taper one end down. Rear edge

Side edge

Deck off master bedroom to eventually connect alfresco deck

Jason

https://www.workshop.bunnings.com.au/discussion/comment/95155#Comment_95155

Hey @asarson,

Just wanted to extend an overdue but very warm welcome to the Workshop community. It was great to see you sharing your project and assisting Tracy. It sounds like you have a lot of knowledge and experience you can share with community members.

We look forward to reading more about your projects and plans. Please feel free to post whenever you need a hand with anything or have something to share. And please let me know if you ever need assistance with getting the most from the Workshop site, or have any feedback about how we can improve Workshop for you.

All the best,

Jason

https://www.workshop.bunnings.com.au/discussion/comment/64930#Comment_64930

Hi Mark (@MPountley)

Many thanks for joining in the discussion on Workshop. Really sorry for the slow reply, but I did want to welcome you to the community. We are really looking forward to reading about your own projects. Feel free to post anytime.

Thanks again,

Jason

pats6182

https://www.workshop.bunnings.com.au/discussion/comment/95182#Comment_95182

Hi @asarson,

Did you bolt the joists to the concrete at every 600 mm along the joists?

Thanks,

asarson

https://www.workshop.bunnings.com.au/discussion/comment/114190#Comment_114190

Hey mate,

I cant remember precisely the width is about 4500 I think I put them at around 800, I just used blue plugs and batten screws to hold in place. Since the weight of the deck itself and no upward forces I went easy on the fixings to the concrete. I have since made some additions for those who are interested.

Simple cantilever to support BBQ & stone benchtop, plywood flooring, cabinetry to come shortly.

Cantilever deck extension for built in BBQCantilever deck extension for built in BBQ

-Andrew

Jason

https://www.workshop.bunnings.com.au/discussion/comment/124808#Comment_124808

Looking fantastic Andrew (@asarson)

When you have a minute it would be good if you could Start your own new discussion and share your project. It deserves its own thread! I'm sure members would be really inspired by what you have done.

Thanks,

Jason

holmess

https://www.workshop.bunnings.com.au/discussion/comment/5629#Comment_5629

Hey could anyone tell me what the black material is on the top of the joists in the photos of this deck? I'm doing the same board over and alfresco area and am worried about cupping. Any ideas to prevent this?

asarson

https://www.workshop.bunnings.com.au/discussion/comment/65332#Comment_65332

The black material on the joists is just black paint, this is so that the joists cannot be seen through the decking spaces. Given you have sufficient gap between the concrete and decking with wide enough gaps between boards you shouldn't have a problem, we gapped ours at 5mm and the deck sits barely 45mm off the concrete. We also screwed in wider spacing the screws 30mm and 110mm on 140mm boards.

Just a photo update on the threat - BBQ complete. 3xba%6zqR0mDaWgSJSBJfg.jpg

Jason

https://www.workshop.bunnings.com.au/discussion/comment/95410#Comment_95410

The barbecue looks fantastic @asarson. Well done. I imagine you'll be spending a lot of time out there with friends and family as the weather warms up.

Jason

holmess

https://www.workshop.bunnings.com.au/discussion/comment/95410#Comment_95410

Cheers mate for the advice,

Your deck is mint 👌 and thanks again for the advice about the spacing.

How did you secure the joists to the brickwork? Last time I decked I used masonry anchors but I found that took a long time. Did you just screw straight to the brickwork with blue spaghetti?

What was the time frame to complwte the initial deck?

asarson

https://www.workshop.bunnings.com.au/discussion/comment/114286#Comment_114286

We just drilled into the concrete and like you said, blue plugs and used batten screws to hold it down. We didn't go nuts screwing it down to the concrete since there was a lot of weight in the deck holding it down and no upwards forces. Probably about a day setting out to get to screwing down boards.

Jason

https://www.workshop.bunnings.com.au/discussion/comment/114286#Comment_114286

Great to see you getting fantastic advice @holmess. Welcome to Workshop. We're looking forward to seeing your own projects soon. Feel free to post anytime you need a hand or have something to share.

Jason

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