Concrete is a mixture of portland cement, aggregate and water. The water and the cement combine to form a paste which binds the aggregates (gravel and sand) together to form a very hard, solid mass when set. Some concrete may also contain chemicals called admixtures. These admixtures are used to improve certain performance characteristics of the concrete. They may include bonding agents, water reducers, air entraining agents, accelerators or pigments.
Any cement, which sets and hardens when mixed with water and is capable of doing so under water, is hydraulic cement. This includes portland cement.
ASTM stands for American Society for Testing and Materials. It is an international, non-profit organization founded in 1898. ASTM provides a forum for producers, users and consumers to write standards for materials, products, systems and services.
ASTM has developed standard specifications, which define the requirements that materials such as concrete and mortar are to meet. For example, ASTM C 387 specifies the strength requirement for concrete mixes.
It means that, when mixed, placed and cured properly, the concrete can withstand 5,000 pounds of load per square inch.
In 1936, Art Avril, an engineer from Cincinnati OH, developed a process for drying and blending the ingredients necessary to make concrete and placing them in a “sack.” He named it Sakrete.
Bagged products are now the preferred method for most homeowners and many contractors. Most homeowner jobs require small quantities of material, making the use of bagged concrete the most practical choice. Many contractors prefer bagged material for variety of reasons.
Bagged products are ideal for those locations where ready mixed plants are too far away, or where physical access to the job site precludes the use of concrete mixers. The use of bagged mixes allows the contractor to place the concrete on his schedule, reducing his dependence on someone else. Factory blended bagged products offer a more consistent product than those mixed on the job site one shovel at a time.
Over-watered concrete may lead to lower strength, reduced durability, shrinkage cracking, and a variety of surface problems. It is critical that the proper amount of water be added to concrete and other cement mixes.
Yes. Impurities, salt, organic material and other substances may have a negative impact on concrete. Generally, if you would not drink it, do not use it in concrete.
Retempering concrete mix or mortar mix is the addition of extra water to the mix after the initial mixing. It promotes shrinkage and reduces strengths.
Curing is the action taken to maintain moisture and temperature conditions in freshly placed cement mixes allowing the cement to thoroughly hydrate. This can be done by misting the concrete, placing wet covers such as burlap on the concrete or by coating with Sakrete Cure n Seal.
Curing is necessary to for the concrete to achieve all of the desired properties. Additionally, the rapid loss of water from the surface of the concrete will cause the slab to cure at an uneven rate. This can happen during periods of high temperature or wind. If the top portion of the slab dries before the lower portion, the concrete will cure at different rates, causing the slab to develop cracks.
Cement based mixes can be successfully placed, finished and cured in both hot and cold weather, but it requires an understanding of the effect of weather on the material. For example, freshly mixed and newly hardened concrete can lose moisture in both hot and cold temperatures. In hot weather, cover the concrete with a wet, clean curing cloth and plastic.
Keep it continuously wet for a minimum of 3 days. In cold weather you should protect the newly placed concrete against early freezing for a minimum of 24 hours. Only a professional contractor should attempt to place concrete when the temperature is below 40 degrees.
The surface must be moisture free in order for most paints to stick. Typically paint manufacturers will allow a latex based paint after 7 days of curing. All oil-solvent based stains and epoxy materials will need to wait 28 days. Tape a piece of plastic about 8”x 8” to the concrete. If moisture droplets appear it is likely too wet to paint. Always check for paint manufacturers recommendations.
Sakrete Cement Colors can be added to almost all Sakrete products including mortars, concrete and repair products.
Most portland cement based materials will not stick to painted surfaces.