Different Types of Concrete Floats and Darbies
The concrete is placed. It has been screeded and most likely gone over with the larger bull float. Now you can break out the hand tools and get close to the concrete. Hand floats and darbies are needed to touch up edges and finish the hard-to-reach areas of large jobs. They are also used for small projects. In general, hand floats and darbies are both used to smooth out concrete in the same fashion; however, darbies allow you to reach and stretch out further across the slab.
Bull floating occurs immediately after striking off, or screeding, the concrete. It is conducted for large areas and requires workers to stand upright to float the concrete. There are two types of these floats: bull and channel. The type of application and the amount of concrete will determine which one to use.
Concrete Bull and Channel Floats
Channel floats have blade lengths of 4 to 10 feet. They are used to float larger areas of concrete. Typically, channel floats have high side channels, which can push greater amounts of concrete around. Bull floats have blade lengths of 24 to 60 inches and are also used for large areas.
Both types of floats have adjustable handles and leveling head brackets. Handles are adjustable and can extend 4 to 16 feet long. They usually have extension poles that offer greater reach across the slab. Brackets allow the float to be tilted so it can reach the surface of the concrete at the correct angle.
Round edges on bull or channel floats are good for filling voids when floating. Sharp edges are good for cutting down high spots. Bull floats come in wood, resin, magnesium, or aluminum
Concrete Bull Floats
Common Hand Float Types
Hand floats and darbies come in wood, aluminum, resin (or composite), and magnesium. Each comes in a variety of sizes and lengths. Handles are often purchased separately because they also come in different materials and offer different levels of comfort. Each leaves behind a different level of smoothness, and many operators tend to have their favorite types after extended use.
Wood floats are made from hardwoods such as mahogany, redwood, or teak. They tend to rough up the surface of the concrete and leave it rough and torn open. As they are swept across the concrete, they smooth out the surface to a point; however, they still leave behind coarse aggregate on the surface of the slab. Wood floats also allow bleed water to evaporate, which is an important step in the curing process. Typically, wood floats are used to make a first pass at smoothing the surface; then workers switch to another type of float for further smoothing.
Resin or composite floats offer a finish similar to wood floats. However, resin floats are more resilient and durable than wood floats and can last longer. Resin floats last longer than wood because they do not soak up water or moisture. They draw bleed water to the surface for evaporation and push down exposed aggregate, leaving behind a smooth surface.
Magnesium and aluminum hand floats are probably the most used float types. Aluminum floats are stronger than magnesium; however, magnesium floats are a lighter option. Magnesium floats are particularly good for smoothing the surface of the concrete out. Because these floats leave behind such a smooth surface, they can trap bleed water. Therefore, they should be used after initial passes with the wood float.
Hand Floats and DarbiesAfter using the bull float to smooth out most of the concrete slab, the hand float is used to finish the floating process. The hand float gets into unfinished areas around edges and obstacles, like pipes or drains, that protrude from the slab so those areas match the rest of the slab. Hand floats create a smooth surface by pushing any exposed aggregate down. The hand float is a more precise tool than the bull float for floating harder to reach areas. It also removes imperfections left behind from the bull floating process.
Hand floats must be held as flat as possible and moved in a wide semicircular motion. The rule of thumb is to use a larger float for the first pass over the slab, then a smaller float on the final pass. This work requires kneeling, extending, and working over the concrete.
A darby is a slightly larger hand float with one or two handles (sometimes three). It is typically long and flat. Like its cousin the hand float, the darby is used for smoothing out poured concrete after screeding and bull floating. Darbies level ridges of concrete, fill voids, and push exposed aggregate down. To use, move the darby across the surface of the concrete in a sweeping arc motion. Since darbies are longer than hand floats, you can use them when you need to extend that sweeping motion further across the slab.
Both hand floats and darbies prepare the slab for troweling.
Considerations When Purchasing a Concrete Float or DarbyThe most important consideration in selecting a float or darby is application and use. If the area is small and you can kneel beside your project and reach the perimeter, you can use a hand float.
If some of the surface is out of reach, you will also need a darby float to extend out to the far sides. If the project is large, like a driveway or foundation, you will need all those tools and a bull or channel float.
If cost is a factor, wood floats are the least expensive. They are also the least durable and will degrade over time. The wood will soak up bleed water surfacing from the concrete as well as the water used to hose off equipment after use.
Aluminum and magnesium floats are more expensive than wood floats but will last longer because they will not be compromised by moisture.
Finally, resin floats tend to be the most expensive, but they are more durable and last longer than wood floats.