How to Pour Exposed Aggregate Concrete

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A list of materials and a tutorial for pouring exposed aggregate concrete slabs, paths, or walkways
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This article is helpful to anybody who wants to pour exposed aggregate concrete at home or for commercial use. It will explain the proper procedure and list all the necessary materials. This decorative concrete is generally more expensive to have done by a company so doing it yourself can save you lots of money.

Things You Should Know

  • Build concrete forms out of 2x4s or 2x6s. Level and compact the dirt or gravel within the forms.
  • Pour the concrete into the forms then smooth and level it out with a 2x4 and a tool called a bull float.
  • Apply a surface retarder, cover the concrete with plastic, let it cure for up to 24 hours, then remove the plastic and the forms.
  • Cut the concrete into sections to prevent cracking, then seal it.
Part 1
Part 1 of 3:

Installing Concrete Forms

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  1. This box will hold the concrete in place until it is fully cured. It is important it is symmetrical and nailed together properly because your concrete pad will resemble this box.
    • Use 2x4s in order to obtain 4 inch thick concrete.
    • Use 2x6s in order to obtain 6 inch thick concrete.
    • To make a curved shape pad, you must use a more flexible kind of wood.
  2. This area must be relatively flat.
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  3. The stakes will hold the box in place.
    • It is best to put a stake at each end of the board, then fill in the middle with stakes at roughly 4 feet apart.
    • To make sure your board is strait, run a string from one end of the board to the other end.
  4. The box must be level, but if it is a large surface it is best to lower one side of the box slightly so rain will run off the edge once it is finished.
    • To make the surface of the concrete even with the ground, you must dig down 4 inches.
    • To make the concrete pad above ground, just nail it into the stakes.
  5. Now since the forms are set, make sure all of the ground within the box is at least 4 inches deep, and compact it by using a compactor or stamper.
    • To check depth, run a string across from the top of each form and measure down making sure it is 4 inches. This is also referred to as "Grade".
    • Now would also be the time to add steel mesh or re-steel, if you have it (for strengthening purposes).
  6. Call and ask for exposed aggregate concrete. They will inform you on what it is and different options they offer. As for amount, concrete is purchased by the yard. If you have trouble figuring out how much is needed, tell the concrete company your square footage and thickness.
    • One yard of concrete is the equivalent to 81 square feet per 4 inch thick concrete.
    • The equivalent for 6 inch thick concrete is 54 square feet.
    • To figure out the square footage of a rectangle or square the equation is length times width.
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Part 2
Part 2 of 3:

Pouring, Leveling, and Smoothing

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  1. [1] This step can be tricky depending on where your pad is. It is easy if a concrete truck can reach the pad with its' chute, but if not you will have to use a wheel barrow or power buggy to move the concrete from the truck to the forms. [2]
    • The concrete must be poured quickly so you have time to move it into place while it is still wet.
  2. [3] Essentially, screeding is leveling out the top of the concrete. Run a strait board on the top of your forms across the concrete, if there is a large pile-up, have someone rake back the pile so you can proceed with the screed process. [4]
    • It is best to have one person on each side of the screed board and pull back the concrete simultaneously.
    • If your pad is too large or not in a position to be screeded from the outside, one person or both people must stand inside the pad and do your best to run the board along the 2x4s.
    • If you cannot perform these two methods for screeding, it is suggested you seek help from a more advanced concrete finisher.
  3. Bull floating is the first step of smoothing out the concrete. It will knock down all of the rocks and bring the "creamy" concrete mix to the surface. Doing this correctly should leave your pad flat and smooth with no holes. The "wetter" the concrete is, the easier it will seal all the holes up; if you wait to long to bull float, it will be hard to seal the surface.
    • If some holes will not close up, you can sprinkle some water to aid in the process.
  4. Hand edging the concrete will create a nice rounded edge as opposed to a sharp rigid one. It will also seal the edge. If an error is created in the edging process, use the hand float to clean up along the edge. The hand float should be used to seal up any holes that are reachable. [5]
  5. After the first round of sealing the surface by bull floating and edging, it is generally time to do the process over again. The objective is to get the bull float lines and edger lines to go away, while the top remains smooth.
    • This may take some time depending on weather, if the sun is out it it will dry up quicker.
    • There is a video tagged in these instructions that will help you learn how to properly finish concrete.
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Part 3
Part 3 of 3:

Curing, Cutting, and Sealing

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  1. Once you have finished the top and it is smooth with no lines or air holes, it is time to spray it with a chemical retarder. The retarder chemical will keep the top layer of concrete wet while it lets the core harden. [6]
    • Try to disperse it evenly amongst the surface. Making one spot wetter than another will cause that spot to give away faster and potentially cause holes in the washing away process.
  2. The surface must be covered after the retarder is sprayed in order to lock in moisture, prevent wind from drying out the top, and to keep it out of direct sunlight.
    • Make sure your plastic is big enough to cover the whole pad with some wiggle room so you can weigh it down along the edge.
    • Gently lay the plastic down on the surface of the concrete so you do not create any smudges.
  3. [7] Now you must wait for it to harden. Depending on when you poured it and how wet the concrete was at that time, you generally need to wait roughly 10-24 hours for the core to harden. Do not wait to long to check, because the retarder and plastic cover can only keep the top from hardening for so long.
    • It is best to let it sit over night and check it in the morning unless you poured it very early, in which case you can check it later that day.
  4. Removing the plastic should be no problem. It should be safe to walk on now. Start hosing off the top evenly amongst the surface. The creamy top layer should start to wash away exposing the pea stone gravel underneath. Use a broom to help brush off the top layer if it is not washing away easily.
    • Be careful to not focus in one area for too long, doing so can create rivets.
    • Pea stone should be exposed evenly throughout the surface.
  5. Removing the forms while the concrete is still wet can cause trouble so as long as it has hardened, removing them is an easy process. Just remove the stakes and take out any nails and the 2x4 boards should pop right off.
    • Forms can be reused for future jobs.
  6. Concrete WILL crack. It is unknown when it will crack but it WILL crack. Saw cutting it essentially says to the concrete "Crack Here". So instead of an obscure crack throughout the whole surface, it will crack along the specific saw cut lines you have set out for it. Which will make it look better and last longer. [8]
    • Make the saw cuts symmetrical.
    • Square pads are cut into squares for symmetry, do not let the saw cut lines extend for more than 10' by 10'.
  7. [9] Sealing the surface with a sealant spray solution will make the surface more weather resistant and prevent erosion. It will also bring out the true colors of the pea stone and generally make a shinier surface. [10]
    • Make sure the surface is clean and free of any stains before hand.
    • Disperse the spray evenly amongst the surface for best results.
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Community Q&A

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  • Question
    Why do some people use water mixed with sugar?
    Community Answer
    Sugar water acts as a slowing agent (so does sugary soda). This is not recommended and usually done to save money. The results could be problematic, especially for the inexperienced person.
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  • Question
    Can exposed concrete be placed by a concrete pump?
    Community Answer
    Yes and no. It depends on the nature of the mix (the ratio of aggregate to cement) as pressurization is a factor in the density of the vacuum.
    Thanks! We're glad this was helpful.
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      Warnings

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      Things You'll Need

      • Bull float
      • Hand edger
      • Hand float
      • Concrete rake
      • Shovel
      • Concrete screed or strait edge (can use a piece of wood 2"x4")
      • wood forms (2"x4" or 2"x6", depending on how thick you want your concrete)
      • Nails
      • Stakes
      • Hammer
      • Concrete retarder
      • Spray can for retarder
      • Roll of nylon plastic (enough to cover the whole concrete pad)
      • Hose
      • Broom
      • Concrete saw (only needed for one time use; rent it to save money)
      • Concrete truck
      • Wheel barrow (only if the truck cannot reach the area being poured)
      • Compactor or stamper
      • Concrete color mixture (to add color)
      • Concrete chemical sealant (helps with preserving color and weather resistance)
      • Steel mesh or re-steel rods

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      References

      1. ↑ https://www.familyhandyman.com/masonry/pouring-concrete/tips-for-how-to-pour-a-concrete-slab-successfully/
      2. ↑ https://www.bhg.com/home-improvement/outdoor/walkways/exposed-aggregate-walk/
      3. ↑ https://www.familyhandyman.com/masonry/pouring-concrete/how-to-finish-concrete/
      4. ↑ https://www.concretenetwork.com/concrete/concrete_tools/screeding_the_concrete.htm
      5. ↑ https://www.concretenetwork.com/concrete/concrete_tools/bull_floats_and_darbies.htm
      6. ↑ https://www.concretenetwork.com/concrete/exposedaggregate/how_to_expose.html
      7. ↑ https://www.bobvila.com/articles/exposed-aggregate-concrete/
      8. ↑ https://www.familyhandyman.com/masonry/how-to-cut-concrete/
      9. ↑ https://extremehowto.com/pouring-and-finishing-an-exposed-aggregate-walkway/
      1. ↑ https://www.concretenetwork.com/concrete/maintaining/sealingplain.htm

      About This Article

      Article Summary X

      Before you can pour exposed aggregate concrete, you’ll need to build a wooden box to hold the concrete in place. Once you stage the box, hammer stakes into the perimeter to hold it securely in place. When your area is fully prepped, call to order your concrete from a local company. On the day you're having the concrete poured, have a strait board ready to level it. You’ll also need to bull float the concrete to make it nice and smooth. Additionally, be prepared to hand float and hand edge your concrete to give it round, sealed edges. To learn how to remove the forms once your concrete is dry, keep reading!

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