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Picture of DIY CONCRETE:: How-To-Mix Concrete
This Instructable will cover three ways to mix regular concrete, one way to mix glass-fiber-reinforced-concrete (GFRC), and instructions on performing a Slump Test to check the consistency of the concrete mix.

The method you use will depend mostly on the size of your project, but also on what tools and equipment are available. For a larger project, like a concrete countertop, you'll have to rent a mixer. For something smaller, the concrete can be mixed in a wheelbarrow. For even smaller projects, under 30 lbs., mixing by hand in a big bucket is perfectly fine.

Supplies:
  • Sacked Concrete Mix
  • Pigment, Water Reducer, CHENG Pro-Formula or other all-in-one Admixture (optional)
  • Concrete Mixer (there is a wide range of mixers out there)
  • Buckets
  • Water
  • Particle Mask
  • Thick Rubber Gloves
  • Trowel
In General:
  • Calculate the amount of concrete you'll need using a little bit of math or online volume calculators (don't subtract for knockouts).
  • Always mix up more concrete than you think you'll need.
  • Don't use sacked concrete that has been exposed to moisture and is hard like a rock.
  • Always throw out any big clumps in the mix that won't break up when squeezed in your hand.
  • If the mix is getting too stiff, agitating it with vibration will help it become fluid again.
 
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Step 1: Mixing concrete by hand

Picture of Mixing concrete by hand
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For smaller projects, 30 lbs. or less, mixing the concrete by hand is pretty easy. It can be mixed in a 5 gallon bucket, a wash tub, or on a plastic sheet or a tarp. When you're getting your hands in the mix like this, be sure to wear thick gloves. Concrete is caustic and thinner gloves will rip too easily. It helps to have a hand trowel or a small shovel to scrape the sides and bottom of the bucket.

Supplies:
  • THICK Rubber Gloves
  • Particle Mask
  • 5 - 8 Gallon Bucket / Wash Tub / Similar
  • Trowel
  • Bucket / Clean Water
Paddle Mixer Attachment (optional):
Using a 1/2" corded or cordless drill with a paddle mixer attachment is one way to mix the dry material. After the water is added, the concrete will be more difficult to mix, unless you have a very powerful drill.

1. Weigh out all of the DRY material and add it to a bucket (Sacked Concrete Mix, Dry Pigment, Dry Water Reducer, Fiber, or any all-in-one Admixture like CHENG Pro-Formula).
2. Blend the dry material together until it's a uniform color. Always wear a dust mask when mixing dry concrete.
3. Break apart any clumps of concrete or toss them out if they won't break apart.
4. Measure out 3/4 of the recommended water and mix. If you're using liquid pigment or liquid water reducer, pre-blend it in this water.
5. Add the water to the dry material and mix. Scrape the sides and bottom of the bucket as you go, making sure you don't leave any dry material.
6. Add the remaining water gradually as needed until the mix is a workable consistency. If the mix is too stiff, you may need to add a little bit of water. There should be no dry pockets at this point. Mix thoroughly before casting.

Clean out the mixing bucket with water. Don't pour it down the drain because it contains active cement and it will clog the drain.

Step 2: Mixing concrete in a wheelbarrow

Picture of Mixing concrete in a wheelbarrow
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A wheelbarrow is ideal for mixing 60 - 80 lbs of concrete. Mixing over 80 lbs. is tedious, but it can be done. The size of the wheelbarrow doesn't matter, but you'll need a mortar hoe or a flat shovel to mix the concrete.


Supplies:
  • Rubber Gloves
  • Particle Mask
  • Wheelbarrow
  • Mortar Hoe / Flat Shovel
  • Buckets and Water

1. Add the DRY ingredients to the wheelbarrow (Sacked Concrete Mix, Dry Pigment, Dry Water Reducer, Fiber, or any all-in-one Admixtures).
2. Blend the dry ingredients until homogenous. Wear a dust mask.
3. Break up or throw out any hard clumps that can't be crushed by hand.
4. Measure out 3/4 of the recommended water (along with any liquid pigment or liquid water reducers).
5. MIX the concrete with a mortar hoe or a flat shovel.
Using a mortar hoe: Pull the concrete toward you and push it back, scraping the bottom of the wheel barrow.
Using a flat shovel: Scoop and turn the concrete over on itself.
6. Add the remaining water gradually as necessary and thoroughly mix. There should be no dry pockets at this point.
7. Scoop up wet concrete with a bucket and begin filling your form.

Spray out the wheelbarrow with a garden hose, but don't let the water run down the drain because it contains active cement.

Step 3: Using a Concrete Mixer

For larger projects, like a concrete countertop, a motorized concrete mixer is necessary. They can usually be rented from your local hardware store. Mixers come in different volumes, the most common is a 9 cubic foot mixer. 9 cubic feet is the total volume of the mixer, but the batch volume is actually 6 cubic feet, meaning you can only mix up to 6 cubic feet of concrete at a time. For larger pours you can mix up one batch, dump it in a wheel barrow, and then begin mixing the next batch.

What size mixer do you need?
12 cubic foot mixer has a batch capacity of 9.5 cubic feet (1200 lbs.)
9 cubic foot mixer has a batch capacity of 6 cubic feet (750 lbs.)
5 cubic foot mixer has a batch capacity of 2.5 cubic feet (300 lbs.)

How a concrete mixer works:
The drum of the mixer has fixed paddles attached to the inside. When the mixer is rotating, these paddles pick up the concrete, pull it to the top, and then gravity lets it fall down on itself. This churning motion mixes the concrete. If the drum of the mixer is tilted up vertically, the churning motion can't happen. Tip the mixer as horizontally as possible without spilling out the concrete.

Water:
Using cooler water will extend the working time of the mix. This will be helpful if you're in a very hot climate. Every bagged concrete mix has a range of water requirements. Play it safe by adding less water than recommended, and then gradually add the remaining water while keeping an eye on the consistency of the mix.

Supplies:
  • Rubber Gloves
  • Particle Mask
  • Concrete Mixer
  • Plastic Tarp / Garbage Bag
  • (2) Bungee Cords
  • Wheelbarrow
  • Buckets
1. Load the mixer with all DRY materials (Sacked Concrete Mix, Pigment, Fiber, Admixtures).
2. Cover the mouth of mixer with a plastic trash bag using a bungee chord to keep the dust to a minimum.
3. Blend for about 5 minutes until homogenous. Tip the mixer forward so it is horizontal. Stop the mixer and break apart any remaining clumps by hand.
4. Measure out 3/4 of the recommended water along with any liquid additives like pigment or water reducers.
5. Add the water, distributing it evenly over the mix. Tip the mixer as horizontally as possible before it spills out concrete and mix for 5-7 minutes.
6. Stop the mixer to check the consistency of the concrete.
7. Continue mixing, adding the remaining water as necessary. If the mix is still stiff and clumpy, add 8 oz. of water at a time and continue mixing.
8. Pour into a wheel barrow.
9. Cast concrete.

Clean the mixer by dumping the excess concrete in a 30 gallon trash can and rinsing out the mixer with a hose until the water runs clear. Catch everything with the trash can. The water still contains active cement, never pour it down the drain. Let it sit for 24 hours. The heavy stuff will settle to the bottom and then you can pour off the water. Dump the sludge out onto a tarp, let it dry, and then dispose of it.

Step 4: Mixing GFRC (Pre-Blended)

Picture of Mixing GFRC (Pre-Blended)
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GFRC (Glass Fiber Reinforced Concrete) differs from regular concrete because it doesn't contain rock aggregate. It is a mixture of fine sands, portland cement, fibers (Alkalai Resistant Glass, Polypropylene, PVA, or Natural Fibers), and some chemistry that accelerates the cure time (commonly a polymer curing agent). Making your own GFRC mix involves weighing out all of these ingredients yourself, but there are also pre-blended mixes available. Some pre-blended mixes require a liquid activator (unlike regular concrete that only requires water).

The main advantage of GFRC is that the pieces can be much thinner without losing strength. It can also be applied with a range of techniques, unlike regular wet-cast concrete. It can be sprayed through a texture hopper, packed into a form by hand, or wet-cast as usual. Because you're using less material, the formwork doesn't need to be as heavily reinforced. Another advantage of GFRC is that pieces can be demolded in 12 hours or less.

GFRC is mixed using a mortar mixer or a paddle mixer, instead of a traditional concrete mixer. Small batches under 30 lbs. can still be mixed by hand.

Supplies:
  • Rubber Gloves
  • Particle Mask
  • 17 gallon mixing bucket
  • Paddle Mixer
Paddle mixer:
Dual paddle, on a stand (this is a luxury). You can also use a 1/2" drill motor and a paddle, but a proper dual paddle mixer will work better, especially for something very stiff like the fibrous backing blend.

Size of bucket:
8 gallon = 50 lbs.
17 gallon = 100 lbs.
25 gallon = 150 lbs.

1. Add liquids to the bucket first. Then blend in pigment, whether it's wet or dry.
2. Add 1/2 of the total batch of the DRY components.
3. Thoroughly mix with the paddle mixer, moving the paddles around the bucket, and scraping the walls with a trowel.
4. Add 1/2 of the remaining dry mix.
5. Thoroughly mix again.
6. Add the rest of the dry material.
7. tempering the mix: the art
8. if it's too dry, add water



Step 5: Concrete Slump Test

Picture of Concrete Slump Test
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A slump test is used to determine the correct hydration of a batch of concrete. The slump is the distance the wet concrete settles after the slump cone is lifted off. The ideal mix will not be too stiff or too soft, but will have a slump of about 4". If you're working in very hot or dry conditions, or if the mold has intricate shapes, you may want a slightly wetter mix. Keep in mind that the more water in the mix, the higher the risk of cracks. A mix that is too dry is hard to pour and vibrate.

Performing a slump test will help give you an idea of what the right mix should feel like. Over time you'll develop a feel for it, but in the beginning it helps to keep track of the amount of water you add so you can reproduce the same results throughout projects.

Professional Slump Test Supplies:
  • 12" Slump Cone
  • Mixed Concrete
  • Straight Edge
  • Plywood Base Board

1. Moisten the inside of the cone and put it on a smooth, level surface such as a moist piece of plywood or a concrete slab.
2. Fill the cone one-third full with a sample of concrete. Push a rod down into the concrete (called tamping) to help the concrete fully settle and allow any air to escape.
3. Fill the cone until it's two-thirds full, and tamp this layer with the rod.
4. Add more concrete until the cone is slightly over-filled and tamp this layer.
5. Scrape off excess concrete
6. Slowly lift the cone away from the concrete.
7. Put the cone beside the concrete, but not touching it. Rest a straightedge across the cone and measure the distance down to the top of the sample as seen in the photos.


Homebrew Slump Test Supplies:
  • 15+ oz. (450+ mL) Plastic Cup
  • Pen to poke hole
  • Mixed Concrete
  • Ruler
1. Poke a 1/4" hole in the bottom of the plastic cup with the pen to allow air to escape.
2. Fill the cup with freshly mixed concrete and pack it well.
3. Place the filled cup upside-down on a flat, rigid surface.
4. With your hands, carefully vibrate the cup in a steady lifting motion without stopping.
5. Measure the distance of the slump with a ruler.

The ideal slump should be about half the height of the plastic cup. If the mix is too wet, add more bagged concrete mix by the cup.


Hopefully this Instructable has given you some tips that will help when it's time to mix the concrete for your next project. For some easy concrete project ideas, check out our other Instructables.

Feel free to ask questions or offer any tips that haven't been mentioned. Thanks for following!
JustinL44 months ago

When mixing larger jobs, how do you dry mix once the concrete mixer already mixed wet concrete?

racoontnn1 year ago
Very detailed and easy to understand about the batch of concrete. Thank you!
cjf1 year ago
Nice, thanks for this.
PeckLauros2 years ago
Really helpful. Thanks to share.
ringai2 years ago
I've read your countertop book. It's not a project I'll probably ever tackle, but it was extremely interesting, as was this instructable. Thanks for sharing more of your knowledge.
Horef2 years ago
wow thats some great instructable right there, thanks for the share!
dana-dxb2 years ago
thats a really helpful share a banch of thanx