Before starting your project, it is wise to understand how concrete works so you can use it properly. The mixture percentages and timing are important. Contrary to popular belief, concrete does not dry when it is poured. Instead, it cures through a chemical reaction among its components.
Concrete is just a dry mixture of cement and some type of aggregate, usually sand and gravel. Cement, when it is mixed with water, becomes the adhesive that holds the aggregate particles together. The chemical reaction of the cement with the water creates solid spiny crystals that interlock and bind everything together.
The relative mixture percentages of the cement and the aggregate, along with the type of aggregate, determine the strength and surface characteristics of the cured concrete. For most repair and landscaping projects around your house, almost any standard mixture of concrete will be adequately strong.
Since you are new to working with concrete, purchasing bags of premixed concrete eliminates your need to determine the proper percentage mixtures. The bag of premixed concrete should indicate the type of aggregate used and its recommended uses. Following their recommendation, purchase different types for different projects as needed.
A word of warning: Even small bags of premixed concrete are very heavy and awkward to handle. The salesperson at your home center store will likely load them into your car trunk for you. It is very easy to strain a back leaning over the trunk to remove them. Have someone help you with the lifting.
For larger jobs, such as replacing a patio section, purchase the wet concrete from a concrete supplier. You will have limited time to get it from the truck to the patio, so have several helpers with wheelbarrows ready. The concrete company will charge extra if they have to wait longer than normal, and concrete may begin to cure before you have it installed and the surface smoothed.
When working with concrete, wear rubber gloves because it is caustic to the skin. It also gets very dusty when you pour dry cement into a mixing container, so it would be wise to wear a breathing mask and goggles.
Two keys to a successful concrete job are to make stable forms and work fast. When doing a patio or any flat surface near your house, install the wood forms so there is a slight slope away from your house. Drive strong wooden stakes deep into the ground to support the weight against the forms.
Wet the forms before pouring the concrete. Use a tamper to compress the concrete, and then smooth the surface by running a long board over the top of the forms. Never add more water to the surface to get more working time. This weakens the cured surface considerably. Once it is solid, keep it slightly moist for several days.
