Helpful Information for Beginners
Working with concrete isn’t as hard as it may seem. The easiest projects include setting posts for mail boxes, putting deck supports in, and forming small pads.
There are many different brands and types of concrete and mortar. A trip to your local home center for “cement” can be a confusing process. Multiple brands and product names that seem to be for the same use .
For most projects you will either need a “Concrete Mix” or “Gravel Mix” which are used for footings, supports, or “slabs” such as a patio or walk. Generically concrete mixes are blends of coarse sand, gravel or rock, and Portland cement. You add water to get concrete like you would get from a ready mix supplier (in a large truck with a rotating barrel or compartments that deliver concrete).
There are products that say ‘Fast Setting”, “High Strength”, or “Crack Resistant”. These are all concrete mixes with chemical admixtures or synthetic fibers added to make the concrete set faster, increase strength, etc.
For repairing and setting bricks or concrete blocks (which used to be called “cinder blocks”) you will need a mortar. Most mortars are mixtures of fine sand and either “masonry cement” or Portland Cement and Masonry Lime called “hydrated lime”. These mixtures do not have stone.
When patching concrete surfaces such as walks, driveways, or floors you want a patching or “topping” mix. These products often have admixtures to help with bonding when resurfacing the damaged area. Other products such as “Sand Mix” are basically fine sand and Portland cement. For best results a liquid acrylic admixture should be added to the Sand Mix. These are often referred to as “fortifier” or ” concrete admixture”. There are also bonding adhesives which get brushed or rolled on the old surface before patching with the new material.
Nearly all concrete products have one thing in common- they contain “cement” and aggregate (sand or sand and stone). “Cement” is the powder that “glues” the mix together. Cement is made in large kilns by heating limestone and other ingredients at very high temperature. The molten material is later ground to a fine powder to form cement. Most cements are “Portland Cement”. This gets it’s name from the inventor of current day cement, as he thought the finished product resembled the native stone found in Portland, England.
With a little homework you can work with concrete and mortars to make repairs for long lasting additions to your home.
Vita-Crete® ready-mixed products differ from raw materials sold individually such as Portland cement, masonry cement, and aggregates such as mason sand ,concrete sand, crushed stone or gravel, etc. These ready mixed products can be compared to pancake mix where only water is added, as opposed to getting the individual materials: cement, sand, and stone for concrete, or with pancakes- flour, eggs, oil, etc.!
Information on Concrete Mixes
Concrete Mixes in bags have simplified field work by eliminating the need to proportion aggregates and cement on the job and where a ready mix truck is not practical. Today nearly every supply yard, lumber/building material dealer and home center carry one or more brands of packaged cement mixes.
The two most prevalent concrete mixes are “standard” strength Concrete Mix (also known as “Gravel Mix”) which contain stone, coarse sand and Portland cement. These mixes are supposed to reach 3500 psi at 28 days when used correctly. “High Early” or “High Strength” are often used for mixes that are designed to meet 5000 psi. This depends on how the manufacturer markets their product. It’s best to get the design strength of each product you use instead of going by product names.
The industry standards are found in a publication from ASTM International (The American Society of Testing & Materials) known as C-387. The strengths of concrete discussed above are all based on specific test procedures done in a materials lab under certain required conditions.
Information on Mortars
Mortar formulas are designed to be approximately the same strength as the masonry unit being built with (brick, concrete block, stone, etc.). The designations for mortar are easy to remember with the term “MaSoN wOrK”. Where every other letter represents a mortar type:
- M= Type M or high strength which has a strength rating of 2500 psi at 28 days. This is typically used for blocks laid below grade.
- S= Type S which is most common in above grade concrete block work. The strength is specified as 1800 psi at 28 days.
- N= Type N which is largely used for brick work and is specified as 750 psi at 28 days.
- O= Type O a low strength mortar with strength of 300 psi at 28 days. This kind of mortar is selectively used in historical buildings for repairing/tuckpointing old softer bricks and limestone, sandstone, etc.
The strengths of mortar to the masonry units allow for building movement that may cause cracking. The mortar joints are “sacrificial” in that they crack before the brick or block break. This allows for subsequent repairs.
All mortars can be made with masonry cement and sand or with Portland cement, hydrated lime, and sand. Most commercial work in freeze/thaw areas call for mortars made with hydrated lime and are commonly called “Portland-Lime Mortars”.
With nearly all mortars, compressive strength is not necessarily better. Mortar is primarily a spacer between masonry units where bond is as important as strength for providing a water tight building envelope.
Nearly any mortar type can be colored using synthetic pigments at the job site or in a production plant like ours. Advantages to having colors pre-blended at the factory include consistency in proportions, water content when mixed, and simplified job site production.