All About Concrete
Always read all safety precautions and warnings before using any product.
Portland cement the base product in concrete will dry out and burn your skin wherever it comes in contact. It causes a chemical burn that you will not feel happening until perhaps hours later and they can be severe. If concrete or mortars come in contact with your bare skin rinse it off right away to prevent burns.
Most concrete mixes also contain silica powder which can harm your lungs so wear a proper mask when working with dry products.
Concrete also contains lime which can be harmful to your health. Mixing dangerous ingredients with water can cause splashes and sloping that has high potential of getting into your eyes so wear proper safety goggles when mixing or working with wet products.
Don’t let it ruin your day, it’s quite harmless with the proper protection. Just wear safety glasses a quality dust mask, rubber gloves and some long sleeves and be sure to rinse right away if it comes in contact with your skin.
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What Is Concrete
Concrete in the minds of most of us is the often grey colored hard stuff used for all sorts of useful and decorative purposes. Some call it cement which technically (I'm not a technical person) it is not. Cement is an ingredient in the mix used to create concrete.
Concrete is made up of varying ingredients depending on the intended application.
For the basics, it is water, sand, aggregate, and cement.
The water is obviously the part that allows the dry mix to become liquid in order to be able to work with it while it also begins the chemical reaction in the ingredients to eventually turn it into its solid or cured state.
The less water you use the stronger the finished product will be so always use the least amount of water possible to effectively mix the ingredients to the needed workability of your intended application.
Cement is a combination of ingredients such as lime, calcium, shell, chalk, marble, clay, slate, silica, and iron ore. The ingredients are super heated into solids and then ground into the fine powder we know as cement. Cement on it’s own even when turned solid by mixing with water has very little strength. The strength of concrete comes from sand and gravel added to it and by steel structures or armatures embedded in it while in its semi solid or liquid state.
The sand in concrete reduces the cost while actually giving it some strength if used in proper ratios similar to but less effectively than aggregate. One part sand to one part cement being the strongest with more sand gradually reducing the strength yet creating more product for less cost.
Sand comes in different qualities and sizes at varying costs. Washed sand and sharp sand create a stronger concrete, finer sands create a better finish and white sand is best for coloring or staining.
Aggregate or gravel is similar to sand as an ingredient but it adds more strength because of it’s larger size. However for optimal strength, sand and gravel are used together in combination. It then creates large grains of solids (gravel) and then fills between the larger grains with small grains of solids (sand). Sand and gravel can be purchased in bulk and already mixed for this purpose in the form of 60-40 mix. 60% gravel with 40% sand.
Lime gives concrete its stick and makes it more workable with the tradeoff of more lime = less strength. It can be added to your concrete mix or if you purchase (ready to mix) mortar by the bag it will already be in the ingredients (except type M mortar) at varying degrees depending on the mix.
Polymers can be added to concrete mixes in powder or liquid form. There are many kinds of polymers and the science behind which to use for what can get quite complex. I have successfully used two different kinds ( Acrylic Ad-mix and Thin Set Mortar Admix) which are readily available at big box stores. They both come in liquid form and serve the same purpose. They are both added as a water replacement or in combination with water depending on your desired results. They increase bonding strength, water resistance, flexibility, workability and resistance to freeze thaw cycles. They reduce permeability, shrinkage and cracking and improve curing qualities. which is a useful characteristic when applying texture coats over base coats.
However it must be noted the reduced permeability will have an effect on some coloring techniques that require absorption into cured the concrete such as acid stains.
Concrete recipes are called designs and they vary according to the application. A sack mix (5 sack, 6 sack etc.) refers to the number of 94 pound bags or sacks of plain cement per yard of sand and gravel. The more sacks the stronger the product.
There are also many purpose designed mixes in just add water form available at a higher cost but for small jobs or complex designs it can be money well spent.
Quick crete for example, is a basic sand gravel cement mix with not so much cement in it. To purchase enough of these pre-mix bags for say a small shed slab would not only be ridiculously expensive but it would be an inferior finished product. However if you just need to set some fence posts, it would be the way to go as opposed to taking your truck and buying a small bit of 60-40 mix and a couple bags of plain cement.
An good example of a complex pre-mixed product would be a mortar designed for laying tile. It might have additives to reduce shrinkage, increase flexibility, resist water, prevent mold, create better grab or stick and come in the right color to not bleed through your particular tile.
MY SECRET DECORATIVE CONCRETE DESIGN
I have personally experimented with many ingredients and mixes. I have even paid a premium $20.00 for a 60lbs. bag of specialty blended ingredients that were supposed to blow my artsy mind. It didn't perform as well as my secret design.
The results of my labors? my trial and errors? the secret ingredients?
Well, I’m not exactly sure of the exact mixture.
It's due to the fact taht concrete is not a consumable food, folks are not required to list all of the ingredients on their product.
But I can tell you exactly how to make up your own amazing batch.
1) Buy a bag of “Type S Spec Mix”
2) Add water
Technically type S spec mix is a mortar officially tested to acquire the stamp “type S”
It’s relatively inexpensive and whatever is in it, it works well!
It does lists the main ingredients, Portland Cement, Lime & Sand.
Although if you look on the warnings, (as you should before you use it) you will clearly see it contains Silica which is why you should always wear a quality mask.
Judging by how well it works, I don’t doubt it has fly ash and polymers and who knows what else.
I use it for all of my textures over concrete base coats and I use it alone for small projects and sculptures.
Concrete can be ordered pre mixed via a concrete truck for larger products and the concrete plant can help you decide on the best mix for your project when you call to order. For small projects a concrete mixer or even a hoe and wheelbarrow can be used. Concrete mixers are readily available and can often be borrowed rented or even purchased for around $300.
If you are mixing mortar, which includes lime, and no aggregate, you will have to use a purpose made mortar mixer. Mortar mixers can be difficult to come by even for rent and are a costly piece of equipment. A mortar mixer is more complex than a simple spinning drum of a concrete mixer. A Mortar mixers drum remains stationary while interior paddles rotate scraping the sides to keep it from gumming up and clogging the machine. It also entraps air within the mortar as it mixes. The entrapped air makes the mortar light and fluffy making it much easier to work with. This is why if you ever watched a stonemason at work you would see him scraping up a trowel of mud and throwing it back into the pile several times every so often.
USING A MIXER
When using a concrete mixer a good general mix is 5 to 1 meaning 5 shovels or parts 60/40 (sand/gravel) mix to 1 shovel or part plain portland cement.
First use a knife or a shovel to cut a slit in one end of the top of the bag. Now you can stick your fingers in the ends of the slit and carefully rip the bag down the length. This effectively contains the cement while you take scoops out.
Try to consistently get the same size scoops every time both of the cement and the 60/40 mix..
Next, spray some water in the mixer. Then whack the shovel on the edge of the running mixer launching the scoop to the back of it. Be careful not to get the shovel caught on the interior fins or it will give you a serious woopin!
You can keep adding 5 to 1 until the particular mixer you're using has a good load.
Just keep giving it little blasts of water trying to rinse it from wherever it may stick. Let it mix a bit between water blasts and be careful because it's a fine line between enough and too much water.
All that’s left to do is dump it into the wheelbarrow. Keep it running while you dump and give it a good rinse between loads
To add bagged ready-mix products to a mixer, cut the center of the bag open across the middle then fold the bag upward in the center so you can tear or cut the other side wherby creating two half bags standing upright and open on top. This makes the bags easier to handle, lift and pour into the mixer.