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Merbau decking over concrete slab

Usman
Budding Contributor

Re: Merbau Decking over concrete slab

Hi All,

I am also building a deck of size 11 x 3.5 m on the existing concrete. My clearance from the concrete to the flushed surface is around 120mm. Thinking to use 

90x45mm joist. to achieve 120mm my calculation is 11mm (gap between concrete and joist) + 90mm (joist) + 19mm (board) 

 

@Neo19 are you able to tell me (I see you responded to most of these questions earlier - sorry for my ignorance :bigsmile:

 

now i left with this only 

 

any other recommendations please?

 

Thanks

 

 

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

Welcome to the Bunnings Workshop community @Usman. It's fantastic to have you join us and many thanks for your questions.

 

What you have suggested sounds fine in regards to achieving your 120mm overall height. I trust @Neo19 will respond if they can see any other issues or had recommendations.

 

We look forward to hearing more about your decking project and would encourage you to let us know if you need any assistance or would like to share your progress with the community. I trust you'll find loads of other inspirational decking projects as our creative members are sharing their ideas here all the time.

 

Mitchell

 

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Neo19
Established Contributor

Re: Merbau Decking over concrete slab

Hi @Usman

 

My clearance from the concrete to the flushed surface was around 180 mm. And I've used 140x45 which gave me around 160 mm. Since the concrete slab wasn't perfectly level, there were some variations in the flushed surface height. I ended up using these ones to adjust the height. They come from 1 mm height onwards. Does that answer your question?   

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Usman
Budding Contributor

Re: Merbau Decking over concrete slab

Hi @Neo19 ,

 

Perfect and much appreciated. I am in a same situation where existing concrete is not accurately leveled so will be using most of these packers. 

 

- Do  I need to paste them with the liquid nails between concrete and joist?

- And to drill on the concrete (around 100 holes) which entry level drill machine would you recommend? Do I need rotary or just a hammer drill will be sufficient.

- I am thinking to use 140mm boards (total covering area is around 70 sq m). I was reading some where that if the board clearance from the ground (in my case concrete) is less then 300mm then there can be issue if cupping in the boards due to the limited airflow.

  

any comments / recommendation on this please?

 

Thanks    

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Neo19
Established Contributor

Re: Merbau Decking over concrete slab

Hey @Usman 

 

No need for any adhesives, you adjust the height of the joists with these packers and then bolt them to brackets and the packers pretty much stays there. Even if they come loose, it doesn't matter as your joists are already fixed at a certain height to the bracket. I hope this makes sense! 

 

For drilling holes into concrete, I initially tried with my Makita cordless hammer drill. My concrete slab was so hard that I gave up after 30 minutes. Went and bought this and the job became very easy. If you have that many holes, I'll definitely go with the rotary hammer. 

 

Re: your third question, I will leave it to the experts @MitchellMc to answer 😄

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Usman
Budding Contributor

Re: Merbau Decking over concrete slab

Excellent. You guys are awesome and what a forum. 

 

@Neo19 Got it. Sure I will buy your recommended 4J drill for this many holes. Might need to change the bits after certain holes. will let you know how I go.

 

@MitchellMc Please advise on question 3 i.e. use 0f 140mm board with the clearance of 120mm only.

 

Thanks Guys.  

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

Hi @Usman,

 

I apologise for the delay in my reply. A gap under your joists is essential for allowing water to drain and as you have previously mentioned allowance for 11mm has been made. If water is retained under the deck, with no drainage, then a very moist environment is created. You would then expect cupping of boards. 

 

You are creating a very low-level deck. Traditionally, decks were never created this low, partly because of styling but also due to issues that arise when building a timber structure this close to the ground. Times have changed and a low-level deck is now the go-to solution as they look fantastic and are easier to build. You will find many low-level decks which have been constructed within the community and to my knowledge, no one has reported cupping of their boards. 

 

The 11mm drainage gap is your biggest asset when it comes to preventing water/moisture build-up under a deck and the cupping/deterioration of the timber.

 

Please let me know if you have further questions. We're here to help.

 

Mitchell

 

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Usman
Budding Contributor

Re: Merbau Decking over concrete slab

Guys finally the decking project is completed. Thanks @MitchellMc and @Neo19 for your help , very much appreciated. Sharing some pics. 

@MitchellMc next project is to cover the area with bunnings bistro blinds. I have 4 panels with 3x2.32, 3.8x2.32, 3.8x2.32 and 4x2.32 m.

I see the bunnings bistro blinds are available in fixed standard sizes. For 1st panel 3m size is available however for other 3 panels I need to use more then 1 blind i guess.  @MitchellMc  Are you able help with what size I should use. 

Thanks for your help as always. 

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Neo19
Established Contributor

Re: Merbau Decking over concrete slab

Thanks for sharing the pics. Looks like you have done a fantastic job @Usman.

Good luck with your next project!

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

@Usman,

 

That is spectacular work and congratulations on achieving these results. You must be extremely proud of your efforts and rightly so.

 

We look forward to assisting with your next project.

 

Well done.

 

Mitchell

 

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