Proper mixing technique is critical when working with concrete. This post will teach you how to properly mix small batches of concrete. Save yourself time, frustration, and money by following the instructions in this short blog.
Have you never mixed concrete before? Fear not! It is actually incredibly easy to mix concrete and make your own concrete products.
Before we mix, let's talk about Mix Design
Mix Design is another term for your concrete recipe. Perfecting your concrete recipe will yield better consistency, more strength, better mix reliability, more color-stability, and more workability. The mix design below works great for small to medium concrete wares like planters, cups, dishes, tiles, book ends and other homegoods. This tutorial should be used as a guideline for you to follow, adjust your own mix accordingly.
What You'll Need
- Cold Water
- Flow Control (plasticizer)
- Cement-All fast-setting concrete mix
- Plastic Mixing Buckets
- Mixing Drill
- Rubber Gloves
- Gram Scale
Cement-All has a beige base-color and comes in a blue-white bag, you can find it at most home improvement stores (Home Depot in the USA).
I use a 5:1 concrete-to-water Ratio. So for every 500 grams of concrete, 100 grams of water are needed.
Step 1: Mix The Ingredients
Place the bucket on the scale and zero the scale. Add 200 grams of water. Don’t waste time being too precise here, plus or minus a few grams is okay.
If coloring this concrete, this is when you want to add the pigments.
Zero the scale Add 1,000 grams of Cement-All, careful to not splash it into the bucket. Shovel the scoop to the left side of your mixing bucket so that the concrete and water are on opposite sides
Using a drill mixer, mix well from right to left. Scrape all the sides and keep mixing at a moderate to high speed until smooth, about 2 minutes.
Step 2: Add Flow Control
Next add ~ 1-2g flow control. More information about flow control is available in our other videos, linked below. We keep our flow control in a bottle for easy dispensing.
Mix the flow-control into the concrete at a slow speed until smooth about 30 seconds.
Keep the mix activated by keeping it moving, swirling or jiggling the bucket. As soon as you stop moving that concrete it’s going to start firming up.
Move to your molds and pour. Try tapping your molds vigorously during pouring to help release any trapped air. Pour slowly near the top of the mold until flush, then shake the mold until the top rests flat. Wipe off any spills now.
Scrape your bucket clean, and let your concrete sit for about 20-30 minutes.
Step 3: Curing
Water temperature, water content, ambient temperature and humidity can all effect your typical curing time.
20-30 Minutes is typically long enough to wait for Cement-All to cure.
Once your concrete is cured enough to come out of the mold, it should be impervious to the fingernail test. If you can scratch the top of the concrete, give it more time. If it’s hard as stone, it’s time to de-mold.
Step 4: De-Mold
Unwrap your mold and remove the concrete vessel. Let the concrete object sit out and dry. At this time the concrete has reached approximately 70% strength. It will achieve 90% strength after a day or two, and full strength after a week.
Step 5: Dry & Seal (optional)
Wait at least 24 hours before applying a sealer to this concrete. Unsealed concrete will absorb water, get stained and may even develop cracks when watered or potted.
Wrapping up, this method for mixing Cement-All in small batches is easy to to and easy to remember. For batches larger than 4-5kg, You will most likely need to adjust your mix design to further reduce the water content.
If you want more flow from your mix, add a few drops more water or a dash more flow control.
Again, save yourself the headache! Invest in a good easy-to-read gram scale and weigh out your mixes each time. In no time this process will become second-nature and you will develop your own knowledge about how to alter the concrete to your specific casting needs.
If you’re interested in the silicone molds featured in this blog, you can find them HERE on the Bold Molds section of Boldmakerstudio.com
Lastly, this is not a comprehensive guide to all concrete mixes or applications. This tutorial a particular process I’ve developed that works well for me when casting small concrete objects. Remember to do your research and always keep experimenting.
That’s all for now, thanks for reading!