trowel finish
A trowel is a steel blade or blades (either handheld or motor operated) used on the surface of newly placed and floated concrete to create a dense, smooth, and hard result with good wear resistance. A trowel finish is most commonly used on interior slab and floor applications. However ‘Fresno’ trowels may be used for exterior concrete finish applications to simply help achieve a smooth, dense result after strike-off and floating.
A fresno trowel is most often attached to a pole which makes it possible for finishers to trowel the concrete without getting on the slab. Fresno trowels are not known to get the same density & wear resistance that hand troweling and machine troweling will typically achieve, but they will often improve the surface condition of the concrete.
The most common 3 types of steel used for steel trowels are blue, stainless, and high carbon steel. Blue steel trowels are lightweight and flexible while stainless steel trowels will not rust.
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Trowels commonly range between 8-24″ long by 3-6″ wide. Concrete finishers typically have an assortment of trowel sizes. On small patching jobs or tight areas like corners/steps/protrusions, something like an 8×3-inch midget trowel will come in handy. A 14 x 4-inch or 16 x 4-inch trowel can handle most smaller concrete projects. On medium sized projects, a fresno trowel might be most efficient.
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‘Broken-in’ trowels are ideal as the blades develop slight curves and the edges become beveled. Trowels can be purchased that have been “broken in” at the manufacturing plant. Trowel suppliers typically offer camel-back, straight wood, or resilient ‘comfort-grip’ handles. Camel-back handles have a slight upward curve that provides more knuckle clearance.
After the floating operation is complete, hand troweling is commonly done prior to any power troweling to get the hard to reach/finish areas: edges, joints, columns, corners, and walls. This will also address any high spots that the power trowel cannot take care of.
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Then walk behind engine powered trowels are used for larger slabs/areas and their engines range from 5-10 horsepower. Some common size ranges of power trowels are 24″ (mainly for finished building interiors, doorways, corners, etc) and 32-48″ (most common size for medium to large slabs). A power trowel machine must be consistently checked and tuned up as an out of balance blade configuration can be detrimental to the finish.
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Power troweling must be done as soon as soon as the strength of the curing concrete will allow, but not so late that the concrete has setup resisting any troweling efforts on the surface. A good rule of thumb is when the surface of the concrete leaves footprints of 1/16-1/8″.
Troweling commonly begins at the top of the slab and moves from side to side with the operator moving backwards eliminating foot traffic imperfections (also passing over the forms to promote level joints).
The first power trowel pass is considered the ‘floating pass’, is done at a slow uniform pace, and typically utilizes floating blades. On the floating pass, the trowel blades are commonly flat creating a suction between the concrete and blade. Faint circular marks are usually left on the surface and will be removed on the next pass.
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After the floating pass is complete the finish pass is usually done (after surface is dry and walking leaves no impressions) and finish blades are used on the trowel. A good rule of thumb for starting finish trowel operations is when the operator places his hand on the surface and no sand or cement is left as residue. For the finish pass the angle of the blades is increased to approximately 5-10 degrees.
Many passes with increasing blade angles may be necessary and the higher the blade angle the harder the finish.