CONCRETE FINISHING

[Music] [Music] la [Applause] [Music] modern construction methods employ extensive use of concrete building materials to provide a good finish we must realize that concrete may work differently from dayto day dependent on the weather conditions on a humid day it may require a long time for concrete to set up and on a hot dry day it may take a flash set a good Concrete Finisher has the proper tools on hand is ready when the concrete arrives and gets it down as soon as possible The Finisher may have to wait for the concrete to set but the concrete will never wait for the finisher the term finishing usually applies to slab concrete such as sidewalks driveways and Floors the concrete may be placed onto previously prepared and formed beds by shooting directly from the mixer by the use of wheelbarrows or by power-driven buggies to avoid overworking the concrete loads should be dumped adjacent to the work area the more the concrete is handled the more it tends to seg gate the concrete is rough leveled with a ho likee tool called a calong precautions should be taken not to overwork the concrete while it is plastic because an excess of water and fine materials will be brought to the surface next the surface is struck off by moving a straight edge back and forth with a saw-like motion across the forms or scre a small amount of concrete should always be kept ahead of the straight edge to fill all the low spots and maintain a level surface or a controlled pitch try to use the Straight Edge only once over a given area to save time and to avoid overworking the concrete The Straight Edge leaves a surface with a fairly coarse finish the Magnesium Bull Float follows immediately while the concrete is still plastic to work the aggregate down and bring up enough mortar to produce the desired finish The Bull Float is one of the most important operations if the concrete is not level at this time it probably never will be where possible The Bull Float should be used perpendicular to the straight edge pouring concrete can be hard work but a good crew working together with a power buggy come along straight edge and Bull Float can make a hard job fairly easy if desired a walking TR can be used to further smooth the surface after The Bull Float water on the surface will give the concrete a definite Sheen no finishing operation should be performed until the water has evaporated a radius at the edge of the slab can be formed with an edging tool this improves the appearance and reduces is the risk of damage to the edge a jointer is used to cut a joint partly through the fresh concrete these Impressions referred to as contractions or control joints are used to predetermine the location of any possible cracks it's good practice to use a straight edge as a guide and Tool the joints perpendicular to the edge of the slab when the concrete starts to stiffen the water Sheen disappears it's now time for the finishing operation the concrete is ready for finishing when it is firm to the pressure of the fingers or Knuckles or when the knee board under the weight of the finisher does not sink noticeably into the surface the initial finishing operation is performed with an aluminum or magnesium float this embeds the aggregate below the surface removes small imperfections and consolidates the mortar at the surface the metal float slides readily over the concrete with a good Floating Action a wood float tends to tear the surface immediately after floating the concrete should be steel Tred to produce a smooth hard surface most finishers will float and then TR an area before moving their knee boards for the first traveling the blade should be held as flat as possible too great an angle May produce a washboard effect an even harder surface may be produced by a second tring additional tring should be delayed until the concrete is hardened enough to emit a ringing sound under the TR for this operation the TR is tilted at a greater angle and pressed hard to compact the surface a trout surface leaves the concrete very smooth and quite Slippery When Wet a rougher non-slip finish can be obtained by drawing a soft bristled broom over the surface large slabs may be continuously poured without the requirement of screeds or forms if a form were used the adjacent concrete might set up too fast causing a cold joint and a possible crack at this point an alternate to the wooden form is the wet bench made up of fresh concrete placed at intervals approximately the length of the straight edge a scale placed on a known elevation is used as a reference point a reading is taken with the transit or level the wet bench is leveled off to the required elevation using the scale and the level place the scale on a metal trout to ensure an accurate reading next use the Straight Edge to level a section of concrete between the wet bench and a known elevation this forms a wet bed The Finisher must be careful not to dig into the soft concrete with a straight edge thus losing the proper grade The Straight Edge can now be used to strike off the concrete between the newly established wet bed and the previously poured slab again taking care not to dig into the soft concrete after the concrete has been struck off to the proper grade The Bull Float is used to work the aggregate down and bring enough mortar to the top to form a smooth uniform surface the wire mesh must be picked up and worked into the concrete if it lays on the bottom it will not reinforce the concrete and will serve no purpose when the concrete is stiff enough to support the weight of a man the power float can be used to embed the Aggregate and consolidate the mortar at the surface the power float machine performs the same operation as the hand float but covers larger areas in less time after the power float operation a power TRL is used to smooth smooth and compact the surface on large slabs control joints are cut with a concrete saw after the surface has hardened sufficiently the cement finisher will normally go over the entire area with a hand TRL after the power TRL has been used this is called the final Wipeout and Smooths out any imperfections left by the power equipment a membrane curing compound may be applied after the final Wipeout to prevent the rapid loss of moisture during the early stages of hardening proper curing of the slab is an important part of concrete finishing cleaning the equipment is another important step in concrete finishing tools that are coated with hardened concrete will tend to stick and tear the surface making it impossible to produce a smooth hard finish if water is not available at the job site it can usually be obtained from the truck that delivers the concrete the construction industry has thousands of square fet of concrete to finish with the proper instruction and training a new Concrete Finisher can make a big contribution to this industry [Music] Tre