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Working with concrete blocks, pavers and roofing
In home construction, concrete has long been the standard for foundations, slabs, driveways and patios. But until recent years, its heavy weight and lackluster appearance relegated it primarily to low-visibility uses. Now a variety of new technologies and products have given concrete an entirely new personality. Today, concrete materials are used for house wall construction, roofing, siding, flooring, paving and more.

Concrete basics
Composed of cement or lime, an aggregate such as sand or gravel and water, concrete dates back to Roman ruins. In fact, concrete was prevalent in many early civilizations where natural cement deposits existed. Its modern-day popularity began in the early 19th century, when portland cement--a strong, durable, artificial cement that can be manufactured almost anywhere--was invented (cement is produced when quarried calcium, silica, alumina and iron compounds are heated at very high temperatures). Concrete soon became the material of choice for dams, highways, large buildings and other structures requiring strong, massive construction.

Today, ordinary structural concrete is made from portland cement, water and sand or aggregate. The cement and water mix to form a paste that, through a chemical reaction, binds together aggregate such as sand, gravel or crushed stone. A pigment--iron oxide, for example--may be added to give the finished concrete a decorative look. As this paste cures, the mass becomes rock-hard.

The quality and strength of finished concrete rely on the makeup of the "mix." Ideally, the cement paste coats and completely fills all of the voids between every particle of aggregate, a feat accomplished through proven formulas. Concrete is "cured" to minimize shrinking and increase tensile strength, normally by keeping it damp for several days.

In most cases, concrete alone is not strong enough to withstand eventual cracking unless it is properly reinforced. A slab or patio typically has a wire mesh embedded in the surface; a foundation or wall has a skeletal core of steel reinforcement rods.

Conventional driveways, patios, slabs and foundations are cast in place; normally, temporary forms contain the semi-liquid material until it dries, then the forms are removed. The concrete is mixed on site or delivered from a central supplier by rotating-drum truck. The latter type, called "ready-mixed" concrete, is usually more consistent in quality than site-mixed concrete.

Concrete is also sold precast as foundation piers, roof tiles, pavers, building blocks and more. As discussed below, many of these precast products incorporate innovations that make them highly practical choices for home building. In general, precast concrete eliminates the variables and inconsistencies of site casting and the need for building forms.

Concrete building blocks
The utilitarian concrete block has gained new respect in recent years. Now called "concrete masonry units" or "CMUs," blocks are used increasingly as substitutes for conventional wood-framed, above-grade exterior walls. Concrete masonry construction may cost slightly more, but builders and homeowners like its durability, strength and heat-retention qualities. Insulation can be foamed or inserted into the hollow cores or applied as a rigid board to the surface to increase resistance to heat flow.

Concrete block won't burn, rot or be eaten by termites. And it produces a wall that is secure, sound-deadening and effective at reducing thermal swings. "If you want permanence, security, resistance to fire, wind and insects, you ought to consider concrete masonry," says Robb Jolly of the National Concrete Masonry Association (NCMA). He adds, "Concrete masonry has a life that extends into the hundreds of years. It is still one of the most environmentally friendly products on the marketplace."

Home Magazine's Safe and Sound Home, featured in the February, 1996, issue, is an example of how beautiful and effective concrete units can be as a primary building material. This 3200-square-foot traditional home has an exterior of stucco and concrete-lookalike limestone that gives it the feel of an adobe-and-stone farm house. Interior walls have a durable, sound-deadening finish of rigid insulation and gypsum wallboard.

The cost of concrete block construction varies from one area to the next. A concrete block house can run from 5% to 10% more than a wood-frame house where builders aren't familiar with the material. The blocks themselves cost from 60 to 90 cents each.

Architectural concrete block
For those who want blocks that can be left exposed, architectural blocks are the answer. These are essentially the same as conventional concrete blocks, except they resemble polished granite, look like hand-hewn stone or tile or have other decorative finishes.

One popular variety, "splitface architectural block," has an irregular, coarse texture that provides contrast and shadow lines. It comes in several earth tones; the color is integral to the block's makeup. "Half highs," only half the height of conventional concrete blocks (4 inches, not 8) are popular for visual contrast.

Architectural blocks are ideal for a house with a walk-out basement, where considerable foundation wall can be seen because they can eliminate the need for brick veneer, stucco or other exterior finishes. Exposed architectural blocks look good as interior walls, too. The Concrete Masonry Association promotes a basement with exposed architectural blocks as "Smart Space" because it can provide finished living space for a relatively small investment.

Prices for architectural block vary, depending upon the type of block and area. Most run from about 75 cents to $1.25 each.

Lightweight solid concrete blocks
Successfully used to build houses in Europe for many years, "precast autoclaved, aerated concrete" (PAAC) blocks are now being manufactured all over the World. This system employs an oversized, lightweight solid block that is laid-up with very strong, thinset mortar.

During manufacture, the raw material is mixed from cement, fine aggregates and a natural expansion agent. Once molded, it is given a moisture and heat treatment under pressure, called autoclaving. As a result, the material rises like bread dough, with thousands of tiny air pockets. The resulting block is durable, lightweight and a relatively good insulator. Even more impressive is the fact that it can be cut and drilled like wood, using ordinary carpentry tools, and you can nail or screw into it.

Technically, these blocks have an insulation value of about R-10, but a wall built of these effectively offers about three times that, because it blocks air infiltration and provides thermal storage mass.

The 8 by 8 by 24-inch-long blocks weigh about 28 pounds (conventional poured concrete weighs about 150 pounds per cubic foot). They're laid with a tiny, 3mm mortar joint between blocks; the latex mortar is trowelled on like a thick paint.

Cement-base stucco can be applied directly to the block surface. Or the block wall can be finished with any conventional siding on the exterior or drywall over furring strips inside. Channels for wiring are carved out with a router.

This system is currently available only in the Southeast. Finished inside and out, this system runs about $2.50 to $3.00 on the average--about 1% to 5% more than conventional wood stud or masonry construction with insulation but, as Hebel's Mike Sweeny points out, "It's like buying a good HVAC system--you get a return on your investment over time."

Foam form systems
Insulating forms are another bright idea; they're used for cast-in-place concrete construction. With these lightweight, rigid expanded polystyrene (EPS) units, a builder can quickly form house walls, insert steel reinforcing, then pour concrete in the center cavities. The rigid foam is left in place to serve as wall insulation, providing values of from R-20 to R-50.

These EPS systems are made either as panels or stackable blocks. Both are extremely easy to work with. The foam may be routed or cut to accept electrical wiring. Stucco or conventional siding may be applied over the exterior foam skin; interior walls are often drywalled.

A panel system typically has 4-foot by 8-foot foam panels that are easily cut, then joined by special plastic ties. One typical block system, from I.C.E. Block Building Systems, employs 48-inch-long by 16-inch-high blocks rimmed with tongue-and-groove edges. Once filled with concrete, hollows in the forms create a waffle-shaped concrete web with vertical columns on 12-inch centers and horizontal beams every 16 inches. Interlocking integral steel "studs" fall every 1 foot on center, holding the two sides of the foam together and offering a member for attaching finishes. Although this system can be used for basement walls, it is intended as a complete, footer-to-roof system.

For foam materials only, you'll pay $2.80 to $3.00 per square foot of wall area, delivered. The cost of building, including foam, concrete, steel and labor, varies greatly but is in the range of from $5.50 to $8 per square foot of floor area. This can vary widely depending upon the house and location. Overall, an I.C.E. Block house may cost an extra 5% to 10% to build, but it offers exceptional savings on heating and cooling, as well as the quiet, solid, pest- free benefits of concrete construction.

Concrete pavers and paving stones
Concrete has also made enormous strides right at our feet, with pavers and decorative paving systems. Precast interlocking pavers, concrete stamping, stenciling, coating and more have given concrete paving great character and visual interest at relatively affordable prices.

Mortarless interlocking pavers are available in a variety of colors, shapes and sizes. Machine-made, they offer high-strength paving solutions for driveways, walkways and patios floors. Assembled without mortar, they are typically installed in a shallow bed of sand and, to create a solid interlock, sand is vibrated between the paver joints. Material prices of pavers tend to run from about $1 to $2 per square foot.

Companies train and certify installers to stain, color, acid wash, stencil, coat, stamp and otherwise decoratively treat concrete surfaces. Their services and products are used for both existing and new concrete work. Many different colors, designs and textures are possible, simulating slate, fieldstone, brick and a world of other materials. Bomanite, for example, comes in more than 90 patterns and 25 standard colors.

Some of these treatments make the surface harder, too. Ed Garcia, National Sales Manager of Increte, says, "We more than double the surface hardness, making it more durable and easier to clean. " Cost varies widely, depending on the size of the project, the type of treatment and your location. For a stamped concrete patio that looks like brick or stone, you're likely to pay from $6 to $8 per square foot.

Concrete siding and roofing
Because cement-based roofing and siding products are durable and won't catch fire, rot or be eaten by termites, they cap and clad more and more of today's homes. Stucco is essentially a type of concrete, made from a mixture of cement, lime, sand and water. Applied in three coats over a lath base, it provides a solid, durable and seamless siding. Newer EIFS (exterior insulation and finish systems) are popular alternatives to stucco; these acrylic-polymer and aggregate coatings are applied over several kinds of approved substrates, including cement-board panels made from aggregated portland cement, reinforced with glass fibers and given polymer coatings. Cost of EIFS tends to be competitive with brick where brick is common; less expensive for intricate walls or where brick siding isn't prevalent.

What appear to be stone and brick walls on houses may actually be a lightweight concrete manufactured-stone veneer. A mixture of portland cement, natural aggregates and iron oxide pigments is poured into molds made from real stones. The result, available in a broad palette of colors and styles, looks incredibly realistic. Installed prices vary widely, depending upon the cost of labor; the national average is about $8 per square foot. Retail average per square foot for materials runs from about $2.25 to $4 per square foot.

Imitation slate and tile roofing materials are made from concrete and fiber cement. Concrete, in both flat and Spanish-style tile units, is extruded under high pressure to make a rugged, dense, durable tile. Although conventional concrete tile weighs about 10 pounds per square foot, lightweight varieties are available at about half that weight. Installed, concrete tile roofing runs in the range of from $5 to $10 per square foot. Thinner fibrous-cement tiles are manufactured using portland cement, reinforcement fibers and a lightweight mineral aggregate such as perlite; they weigh about 5 pounds per square foot. Though priced competitively with wood shakes, they are highly resistant to fire, termites, moisture damage, ultra-violet breakdown and other problems associated with wood.

When you roof with some of the heavier varieties of concrete tile, the roof's supporting structure may require strenghthening. Even so, most homeowners agree that the costs are outweighed by the benefits of a solid, durable, trouble-free roof that will last as long as the house.

 
     
 
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