How to Add Straw to Your Concrete Mix for Better Insulation
There are different ways to insulate and strengthen concrete walls. Forms of Polystyrene, for example, serve two purposes: creating a mold for concrete pouring and acting as an air barrier to better insulate your home. Natural materials, such as straw, also can improve the performance of concrete walls. Adding straw to the concrete mix before pouring helps reinforce the bonds between the aggregate and cement, and it creates air pockets that improve insulating properties like an air-entraining agent. The mixture also retains moisture, which slows the curing process and improves the final strength of the wall.
Things You Will Need
- Safety goggles
- Breathing mask
- Long sleeves
- Long pants
- Strung bale of straw
- Water hose
- Heavy-duty scissors
- Concrete powder
- Concrete mixer or wheel barrel
Put on the safety goggles, a breathing mask, thick gloves, a long-sleeved shirt, pants and shoes with reinforced toes.
Place the bale on a tarp or concrete surface.
Saw the bale into thirds with the chainsaw. Set aside two-thirds of the bale.
Cut through the remaining third of the bale with the chainsaw to divide the pieces into 4- to 6-inch lengths.
Transfer the bale pieces to a wheel barrow by hand. Cut the straw as you transfer it to ensure every piece is 4- to 6-inches long.
Mist the straw lightly with a hose to keep the pieces from flying away.
Pour concrete powder into a concrete mixer or wheel barrel.
Add straw gradually to the mix as you make concrete. Stir and incorporate one-third of the bale of chopped straw in to the mixture for every cubic yard of concrete mix.
Use a cup or bucket to add water in small amounts. Add just enough water to keep the concrete mixture pourable; too much water can weaken the concrete mixture.
Mix the concrete and add the straw right before using the concrete. Do not store the straw in the dry concrete mix because this will add moisture and ruin the concrete. If you don't have much experience with mixing concrete, don't attempt to complete projects larger than a decorative garden wall. You can learn about working with concrete by attending informational workshops at a local home improvement store or by working with an experienced mason. Straw makes a handy moisture barrier while curing concrete. Mist the straw and then place a 6-inch layer of the moist material on top of the curing concrete. Cover the straw with a tarp. Mist and rotate the straw twice a day for optimal protection. You can add straw to clay when making bricks to improve the strength and performance of the building material. A slab that's 10 square feet and 4 inches thick is 33 cubic feet or 1.22 cubic yards in volume. That means that the slab requires five 80-lb. bags of concrete and a little more than one-third of a bale of chopped straw. One cubic foot equals 0.037 cubic yards with a repeating decimal value of "037."
Stored straw can combust spontaneously if the bundle is allowed to dry and sit for long periods of time because of biological activity within the organic material. The conditions for combustion can vary, but generally combustion occurs once the internal temperature exceeds 200 degrees F. and the moisture content of the straw becomes 26 to 46 percent. Keep your stored straw in small piles, under 7 feet tall, and moisten the material as needed to keep the moisture content near 55 percent.
Whenever you add moist organic material to your concrete, you're inviting biological activity. Take precautions to keep the wall dry and protected from weather such as rain and snow -- i.e., prolonged contact with moisture. Your approach to this issue may vary depending on the location, size and purpose of the wall. For example, you can seal concrete with a waterproof sealer, install a water-shedding barrier behind the wall, and protect concrete from contamination during curing by ensuring it is properly covered and not pooling water. To determine the best way to approach this problem, discuss your moisture concerns with a mason or architect during a consultation; you can bring it up while discussing grading or appropriate material.
- "Ultimate Guide to Masonry and Concrete: Design, Build, Maintain"; Creative Homeowner Press; 2006
- National Ready Mixed Concrete Association; What is Curing; 2000
- "Serious Straw Bale: a Home Construction Guide for All Climates"; Paul Lacinski, et al. ; 2000
- "Better Houses, Better Living: What to Look for When Buying, Building Or Remodeling"; Myron E. Ferguson; 2004
- U.S. Department of Transportation; Air-Entraining; 2011
- "Reinforced Concrete and the Modernization of American Building, 1900-1930"; Amy E. Slaton; 2001