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Merbau decking over concrete slab

Jason
Community Manager
Community Manager

Re: Merbau Decking over concrete slab

Congratulations @Usman and many thanks for sharing the end results. I'm sure your work will inspire others, and will be something you and your family can enjoy for many years to come.

 

Jason

 

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Itai
Experienced Contributor

Re: Merbau Decking over concrete slab

These look great. How long has it taken most of you to build these?

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sachraj
New Contributor

Re: Merbau Decking over concrete slab

Hello everyone

 

as everyone has mentioned, this is the best source i have found throughout the whole internet for what i have been planning to make a deck (11x4m) over the concrete.!

 

as i am a total newbie on diy, i would really appreciate if you guys can help me with ideas and tips.!

 

from @Neo19 project i have gathered the materials i will be using ( such as this brackets, packers if needed for levelling, H3 or h4 timbers, dynabolts to secure on concrete, n other bolts to join h3 timber.)

my question is

1:) what size timber would you suggest if i wanna use this 90x19mm deck ?

my height from concrete to flush (entrance) is just 70mm.

2) can i use the same size bracket to also support the size of my deck and also to suffice the height from concrete to entrance.?

3) also, what is this black thing that is sitting Between the timber and deck in @Usman project? Do i need to use this? 

97F1223C-3C54-4DB1-A0CB-5174BF4B6406.jpeg

4) i have done a rough sketch of the deck planning with some measurements hopefully you guys can understand to help this poor newbie out.!

thanks in advance

251F94EF-FA4E-4335-941F-45701FE075DF.jpeg

76723A96-28CA-4490-9BDE-8241944CF4E3.jpeg

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

Welcome to the Bunnings Workshop community @sachraj. It's amazing that you've joined us, and many thanks for your questions.

 

It's great to see you've already done some research for your project. If you haven't seen it, make sure you read through @Adam_W's guide on How to build a low-level deck

 

70mm total height for a deck would be considered exceptionally low. If we remove the 19mm decking's thickness, you are left with 51mm to accommodate your joist thickness and a gap for airflow and drainage. Many would suggest that this is not enough room to build a deck. Your only real option would be to use 90 x 45mm H3 treated Pine laid on the 90mm face. However, this would still only allow a 6mm gap underneath. Since there is only a minimal gap, you should expect the deck's lifespan to be reduced. It's a bit hard to determine what repercussions you'll see from not having adequate airflow under the deck, but at the least, you're creating a moist environment that will encourage premature rot.

 

Since you'll be placing the joists on their side, you won't be able to use L brackets. Instead, you'll likely need to resort to packing out under the joists, and Dynabolting through the joists face directly into the concrete. I'll include an image below to illustrate.

 

It appears that @Usman has painted the tops of his H3 treated timber with an H4 in-ground treatment similar to Bondall 1L Inground Timber Protector. In your case, it might be best to paint the underside of the timber where it will be almost touching the concrete.

 

I look forward to following along with your project and providing further assistance with it. Please let me know if you have questions.

 

Mitchell

 

Dyna.png

 

 

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sachraj
New Contributor

Re: Merbau Decking over concrete slab

Thank you so much for getting back to me with such a detailed information. I truely appreciate your time and effort.

 

from the information i gathered, now i am thinking should i even go ahead with it, or if there is any other options for decking.!

But even if do decide to go with the provided information and mentioned materials, is there a way to calculate how many timbers and decking will i need to purchase for my 11x4 meters decking.! Trying to calculate the rough cost for this project if i can.!

cheers

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

Hi @sachraj,

 

You might like to consider Ekodeck, which is more resistant to rot, decay, mould and mildew than traditional timber. Does the concrete slab fall away from the house? The clearance under the deck is less of a concern in the covered area under the roofing. If the slab falls away, will there be more room under the joists once you move further away from the house?

 

According to the Specrite decking calculator, you'll need 510 lineal meters of decking or 90 x 5.7-meter boards if using 90mm wide decking. Generally, you'd space your joists at 450mm centres. Over the 11000mm span, you would have around 25 joists that are 4000mm long.

 

Mitchell

 

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Gregc
New Contributor

Re: Merbau Decking over concrete slab

Hi @Brad, is it better to use timber or steel framing for decking?

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Merbau Decking over concrete slab

Welcome to the Bunnings Workshop community @Gregc. It's fantastic to have you join us, and many thanks for your question on the best option for decking frames.

 

Hopefully, @Brad can help answer that for you and let us know about his experience with steel frames.

 

Some of the benefits of steel framing are that it is comparably lighter and stronger than timber, it's more uniform, and it's not affected by insect attack. Due to it being stronger than timber, it can span greater distances. This can be advantageous when cantilevering a deck or where there are no options to place posts supports.

 

Some disadvantages of steel frames are that they can be easily damaged, they can be slightly more difficult to repair and replace, and once their coating is penetrated, they can rust.

 

Are you planning a deck build shortly? I trust our community members would be excited to hear all about it, and we would encourage you to let us know if you have more questions or would like to share it with us.

 

Mitchell

 

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Brad
Trusted Contributor

Re: Merbau Decking over concrete slab

I have used steel where it is a damp area, run off from the shed and the overflow from the rainwater tank. It has minimal airflow but not showing any sign of damage yet but the Ekodeck does pick up some moisture over winter on the overflow end. I did watch the DIY video and they must have strong hands to cut it with snips. I gave up and used my metal cutting circular saw.

 

I much prefer wood as I can use hidden fasteners and it is easier to work with.

 

If there is good drainage and airflow I would go with wood.

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Gregc
New Contributor

Re: Merbau Decking over concrete slab

Thanks Brad, I will be low level. Half over a ground level concrete slab, half over the lawn I will dig out. Won't have the best drainage but air flow shouldn't be bad as it will be on the SW side of the house where majority of our wind comes from.

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