Welcome to Getting Started With Concrete!

Concrete is everywhere. But, did you know that there's a secret life of concrete beyond your parking garage slab and rectilinear high-rises. Concrete can also be small, rounded, and have a beautiful shiny finish. In this class we'll uncover why concrete is so versatile through making smaller-scale projects that demonstrate why this ancient building material has stood the test of time.

This beginner class aims to demystify how and why concrete works (the science is actually really neat!), and familiarize you with core skills about working with concrete that will set the stage for more advanced projects further down the line. You'll learn how to work with with concrete safely, using different molds to make shapes, and techniques to finish your concrete project and really make it stand out. All projects in this class use very basic tools and require no special knowledge.

Concrete doesn't need a lot of equipment to be mixed or poured, but the right tools will make the job much easier.

Here's a list of the tools and supplies I'm using in this class:

Project Supplies

Personal Protective Equipment

Sealed eye protection
Cartridge dust mask
Heavy latex gloves
White vinegar (to neutralize the base of cement)

Step 1: Tools

The mighty bucket and trowel are the cornerstone of mixing concrete. For larger jobs most people use a wheelbarrow and a shovel, which is just a scaled up version of a bucket and trowel. You'll want a sturdy plastic bucket which has enough height to prevent spillage while mixing. Plastic buckets like this are very inexpensive, so pick up a few different sizes so you have choice when working with different sized projects.

The trowel is a flattened shovel used to float on top of concrete after pouring to help smooth it out. It's also the concrete multi-tool which you can scoop, mix, and use as a spatula. It's your go-to tool in the world of concrete.

Variable Speed Grinder

To grind and polish concrete you'll need special diamond polishing pads, and a tool to mount them on. Typically professionals use a special grinder that can drip water on the work while grinding, which will suppress the dust. However, wet grinders are very expensive.

A more economical option is to use a variable speed angle grinder and a large fan to remove the dust while grinding (along with the proper personal protective equipment, of course).

A variable speed grinder will have a dial somewhere on the tool that can change the speed of the angled wheel, allowing slow rotations which will create less dust and give a more even finish.

Grinding / Polishing Discs

Since concrete is very hard we'll need an even harder material to grind and polish. Like sandpaper, diamond polishing pads come in different levels coarseness, from rough to smooth. This kit has doubles of the coarse grades of polishing discs, then steps up to very fine grade for a mirror finish.

These pads are interchangeable, so moving up a grade is really simple. Just like sanding wood, start with the coarsest grit and work your way up to the finer grits.

Orbital Sander

For most grinding and smoothing in concrete you will need the grinder mentioned above. However, you can also use a variable speed random orbital sander to knock off any flashing and sharp edges.

Since concrete is so tough and this tool really isn't designed for stone work, I'd only use 60-80 grit sandpaper.

Step 2: What Is Concrete?

In it's simplest form concrete is aggregate mixed with fluid cement. Cement is a gypsum or lime-based binder that hardens over time in the presence of water. This type of cement is called hydraulic cement, as it sets due to a chemical reaction between the dry ingredients and water.

Cement has been used by humans for thousands of years as a building material and has helped shape civilization, as seen in the mortar used to build the Pyramids, aqueducts and structures during the Roman Empire, and castles and canals during the Middle Ages. Over time cement has been refined from ash and burnt limestone to modern day cement which is universally Portland Cement, a dried mix of limestone and small amount of other minerals like calcium, aluminium, and iron which enhance the natural characteristics of cement and regulate the setting time when mixed.

Adding coarse and fine aggregate like gravel and sand add strength to the cement, and allows the mixture to be called concrete.

What's Happening?

The chemical process when water and air are added to concrete is called hydration, which produces crystals that interlock and bind the aggregate together. It's important to know that concrete doesn't dry, it cures. The minerals in the cement hydrate in the presence of water and require proper moisture while hydrating to cure effectively, if hydraulic cement dries out while curing the result can be a very weak product.

So, Concrete Is The Perfect Building Material?

Almost. While concrete is very strong in compression, some mixes supporting 12,000 psi, concrete is weak in tensile strength (more on that in Lesson 3). A common material that's added to concrete that has a high tensile strength is steel, this is commonly called rebar (reinforcing bar). Combined, concrete and steel are a very strong building material and can be seen in many construction sites today.

While concrete is very strong and versatile, it's not perfect.

Step 3: Personal Safety

The two largest concerns when working with concrete are dust and the alkalinity of Portland cement. First we'll look at dust and the protective equipment you can wear to limit your exposure.

PPE

Personal protective equipment (PPE) for working with concrete are rubber gloves, cartridge dust mask, sealed eye protection, and a face shield for good measure. This is totally overboard for most applications. However, if you consider that Portland cement contains crystalline silica dust which when inhaled can cause silicosis, a serious and incurable respiratory disease, then the safety measures included here make sense.

Make sure your cartridge mask has dust cartridges that are NIOSH (National Institute of Occupational Safety and Health) approved, and is snugly fitted to your face.

Concrete Alkalinity

Aside from the usual (PPE) there's an added caution to working with concrete, it can cause burns. Most people are familiar with what acid is, and that it can cause burns. On the other end of the scale from acid is base, and just like acid can damage your skin so can basic chemicals.

Portland Cement is very basic (or, alkaline - the opposite of acidic), meaning it's caustic and can burn your skin. If tap water is neutral at a pH of 7, Portland Cement has a pH of 12 to 13. In addition to high alkalinity, the hydration reaction that cement goes under as it cures is aiming to draw out moisture - in this case, your skin.

In most cases you're likely to have concrete on your hands. If left untreated it will feel like the worst dry skin sensation you've ever had. Even brief exposure to concrete can have effects hours later, so wear gloves and be sure to treat any areas by neutralizing the concrete.

How To Neutralize Concrete

To neutralize a base you need to add anything more acidic. Before you go dumping battery acid all over your hands there's a much easier way to combat an alkaline substance: vinegar.

It's a good idea to wash any affected area with water first, as this will begin to bring the pH levels down (pH 7 is more neutral than pH 12), this can be easily done with a hose or a bucket of water.

Flush area with plenty of water to remove all traces of cement as soon as possible - the longer you wait to remove alkaline from the skin the worse the impact to your skin. When you're sure all cement has been removed from your hands and anywhere else you can move on to raising the acidity even more to neutralize any lingering alkalinity.

Pour common white vinegar over the area to bring the pH up even more (vinegar pH is around 2.5-3) and fully neutralize any lingering alkalinity. Make sure yo rub your hands together to really get good coverage.

After, unless you want to smell all vinegary for the rest of the day, it's a good idea to rinse your hands once again with water to neutralize the vinegar acid and bring the pH back to neutral.

Step 4: Quiz Time!

Put your knowledge to the test, try the quiz below and see how you do!

{
    "id": "quiz-1",
    "question": "Cement and concrete are different names for the same thing",
    "answers": [
        {
            "title": "Yes, they are the same",
            "correct": false
        },
        {
            "title": "No, they are different",
            "correct": true
       }
    ],
    "correctNotice": "Correct! Cement is a binder, concrete is cement mixed with aggregate.",
    "incorrectNotice": "That's incorrect."
}

{
    "id": "quiz-2",
    "question": "What's happening when concrete cures?",
    "answers": [
        {
            "title": "It's hardens by being exposed to air",
            "correct": false
        },
{
            "title": "A chemical process called hydration",
            "correct": true
        },
        {
            "title": "Concrete only cures when it's heated to 50°C",
            "correct": false
        }
    ],
    "correctNotice": "Correct! Cement hydration is a chemical process that produces interlocking crystals that bind together.",
    "incorrectNotice": "That's incorrect."
}

{
    "id": "quiz-3",
    "question": "Concrete is stronger in tension than compression.",
    "answers": [
        {
            "title": "True",
            "correct": false
        },
        {
            "title": "False",
            "correct": true
        }
    ],
    "correctNotice": "Correct! Concrete needs reinforcement in order to be strong in tension.",
    "incorrectNotice": "That's incorrect."
}

{
    "id": "quiz-4",
    "question": "How long can concrete last for?",
    "answers": [
        {
            "title": "10 years",
            "correct": false
        },
        {
            "title": "50 Years",
            "correct": false
        },

        {
            "title": "Thousands of years",
            "correct": true
        }
    ],
    "correctNotice": "Correct! Man made concrete from 6500 BC has been discovered by archaeologists.",
    "incorrectNotice": "That's incorrect."
}

{
    "id": "quiz-5",
    "question": "Select the components of concrete",
    "answers": [
        {
            "title": "Water, cement, Portland cement",
            "correct": false
        },
        {
            "title": "Water, sand, eggs, Portland cement",
            "correct": false
       },

        {
            "title": "Water, aggregate, Portland cement",
            "correct": true
       },
        {
            "title": "Sand, rebar, Portland cement",
            "correct": false
       }
    ],
    "correctNotice": "Correct!",
    "incorrectNotice": "That's incorrect."
}