Concrete is one of the cheapest most durable building materials, capable of being formed into any shape. The versatility of concrete makes it applicable to floors, standing slabs like in foundation walls columns, siding products, even counter-tops. You can mix it yourself, buy it in a self-mixing bag, site mix truck or delivered ready to pour. It can be moved in wheel barrow, chute, conveyor, line pumped or overhead pump. What-ever the intended use or method of mixing you will need to know some basic terminology.
Being such a widely used product there are many myths and the true test of quality, is time itself, done right concrete will last a lifetime or more, done wrong and it will crack and flake prematurely. The wrong is typically the result of the initial mix.
“do-it-yourself”, “do-it-with-me” or “do-it-for-me”
Often, first exposures involves a wheel barrow and bagged concrete to pour post holes or piers for a deck.
When it comes to larger pours that require a finish it is time to call in the experts. When to watch concrete cure and when to “work the concrete” takes years of experience.
There are two options to get the professional help;
- DIY “PLUS”-The DIY is you and a case of beer for friends, the “Plus” is a concrete consultant. The consultant often an experienced finisher will be there as the brains of the operation assisting you with setting forms, ordering and finishing the surface. Often consultants have access to stamps to provide a real professional look.
- DIWM- Often companies that specialize in flat work like patios and walkways have their key people and then a revolving group of laborers. If the budget is an issue or you just want to be part of the action, ask to join the crew.
- DIFM- Stand back watch the action, provide water, keep the kids and animals away and finally pay the bills.
H20 is your enemy, when it comes to concrete
The ancient building material is composed of three items, cement, gravel/sand (aggregate) and water. Typically concrete contains 10% cement, 20% water, 70% sand/Gravel. The water and cement mixture is the glue that binds the sand and gravel together.
Inexperience will have you adding water to make mixing easier but the additional water means more evaporation as the concrete cures which will mean shrinkage and ultimately cracking. The best mix is where all aggregate is wet without any standing water.
Some terms to help you out
The finish product is concrete not cement, cement is just one of the elements.
Slump- this is a term to determine the workability of the concrete, Image putting a mixture of concrete into a bucket and then turning it upside down like making a sand castle. The less the concrete runs away from the bucket shape the lower the slump, a 3” slump is typical for flat work, a 6” slump flows and is used often when pouring walls inside forms. Water (sometimes chemicals called additives) is what makes a slump higher and often weaker due to evaporation and cracking.
Air- Adding air to concrete increases the workability as millions of air bubbles let the concrete flow easier. Air is often added to outdoor concrete as the bubbles provide space permitting expansion and contraction without cracking.
Strength-MPA is a term used for the strength of concrete, typically 20 or 25mpa is in floors and slabs.
Curing- The act of water evaporation resulting in hardening. Concrete is fully cured in 28 days hitting its full strength.
Consolidation- By working the concrete with an internal or external vibration (to include tapping the forms) you are working the voids out of the concrete thereby consolidating.
Skreet- pulling a straight edge across the fresh pour to determine the finish height.
Darby- The act of using a large flat trowel on a pole soon after concrete is places pulls the water to the surface and works any large stones down away from surface.
Forms- Provide the shape of the concrete. Forms could be anything from dimensional lumber in slabs and walkways, Insulated Concrete Forms (ICF) for highly insulated foundations and exterior walls, to traditional forms stripped off after forming used in production homes or decorative forms used on concrete countertops to provide a unique edge.
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