Building A Deck Over Concrete with TuffBlocks

Using TuffBlocks to build a deck on a concrete slab is one of the easiest ways to revolutionise your outdoor space. Even if you are building on uneven concrete, TuffBlocks are a simple foundation solution, whether you’re a DIY newbie or a seasoned building professional.

Let’s run through how to build a timber deck on concrete.

Before you get building

Let’s quickly cover what you’ll need before you start building a deck on concrete.


A weekend or two will usually be enough to complete a deck build like this. However, with any project, build time varies depending on your skillset, your build site, weather and other factors.


Varies depending on the size of the deck and the price of your timber. As a rough guide, most decks cost between $300 - $400 per square metre.


  • Circular saw
  • String line
  • Hammer drill
  • Level
  • Miter saw
  • Hammer / plam nailer


  • Timber decking
  • Fasterners
  • Joist hangers
  • Fascia boards
  • Joist tape
  • TuffBlocks
  • 45mm x 90 mm H3 treated joists
  • Optional: Decking hidden fixing fasteners
  • Optional: Timber preservative
  • Steps to building a deck on a concrete slab

    When using TuffBlocks, the steps for building a floating deck on concrete, whether it be a concrete patio or slab, follow much the same as building a conventional low-profile deck.

    Step 1 - marking out the deck dimensions

    Marking out the dimensions of your deck before you start building gives you a reference point throughout the build, and ensures your deck comes out straight, flush and stable.

    When building on concrete, a bottle of spray paint and a straight edge are all you need.

    Step 2 – Level TuffBlocks

    Place TuffBlocks in each corner of your deck build and ensure each one is level. On a concrete patio, where the slab is already level, this shouldn’t be an issue — but always make sure to double check. It is essential you confirm that the concrete surface is level before you start building anything.

    If you are building beyond your concrete slab and need to adjust for a change in level, use posts to accommodate for this; refer to steps 3 and 4 in our 10-step deck building guide.

    If your corner TuffBlocks are level, we can get started cutting the joists to the length of your deck. Once measured and cut, treat the cut ends of your joists with bitumen paint. This will prolong the life of your deck.

    Lay all four joists of the outer frame along the outside of your dimensions.

    Step 3 - Check your measurements

    Step 4 – Adding joists and overhang

    Now it’s time to add the joists. Each deck will be different, depending on the dimensions. However, as a guide, place the joists into the joist hangers, spaced out at around 16” to 18” between each hanger.

    Remember, TuffBlocks are 12” wide, so to prevent your TuffBlocks being visible under your deck, we need to factor in an overhang on the rim joist. This simply means ensuring your rim joists extend 12” beyond the first joist – as seen in the picture below.

    Your TuffBlocks will then sit underneath and support these joists. The number of TuffBlocks you will need will again depend on the size of your deck and the lengths of your joists.

    As a rule of thumb, the spacing between joist centres is typically around 18”; however, this is very dependent on the type of deck boards you’re using. For composite deck boards that have more flex, you’ll want your spacings around 16” to ensure a rigid deck. On the other hand, for firmer hardwood boards, the space between your joists could be up to 19.5”. If you’re ever unsure, it’s always best to check with your timber supplier to see what they recommend.


    In general, if you want a more rigid deck, you can shorten the spacing to include more joist beams. Keep in mind, however, this will increase the overall cost of your deck, as you require more timber and more TuffBlocks.

    The longer your joist spans, the more TuffBlocks you will need. This is because there is a limit to how long a span of joist can support a load without failing. The species of the timber also affects how well the joists handle these pressures, with hardwoods able to take higher loads in general. Speak to your timber supplier to learn more about the product’s rating before you purchase, as timber with a lower load-bearing capacity will require more TuffBlocks as supports.

    Step 5 - Protect your joists

    Protect your joists against moisture build up and rotting of the timber by applying a protective barrier. We recommend using joist tape as a simple way to keep your deck lasting longer.

    Apply joist tape on top of all the joists.

    Step 6 – laying boards

    At this stage, your deck should be square, level and protected against moisture. From here, we lay the decking boards across the length of our joists.

    Deck spacers are a great little tool for ensuring the space between each decking board is uniform. Also, remember to arrange the boards in a way so that your shorter lengths are not all grouped in one corner.

    Once all your boards are in place and screwed into the joists, treat your deck with a high-quality decking oil.

    See the finished product for yourself

    Chris used TuffBlocks to build a low-profile deck in his own backyard. We caught up with Chris 12 months after completing his deck to see how TuffBlocks, and his new deck, were holding up.

    Ready to build?

    There’s nothing stopping you getting started on your own decking project. A low-profile timber deck can quickly expand your outside space and revolutionise your home.

    If you have any questions about TuffBlock or want more deck building information, head over to our YouTube channel, or get in contact with us directly.

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