a chassis equipped with wheels for road towing. Sizesrange from 3 1/2 to 10 cubic feet and can be poweredby an electric or a gasoline motor. Mixing takes placeeither by rotation of the drum or by rotation of the bladesinside the drum. Tilt the drum to discharge plaster intoa wheelbarrow or other receptacle.When using a plaster mixer, add the water first, thenadd about half the sand. Next, add the cement and anyadmixture desired. Last, add the rest of the sand. Mixuntil the batch is uniform and has the properconsistency—3 to 4 minutes is usually sufficient. Notethat excessive agitation of mortar speeds up the settingtime. Most mixers operate at top capacity when themortar is about 2 inches, at most, above the blades.When the mixer is charged higher than this, propermixing fails to take place. Instead of blending thematerials, the mixer simply folds the material over andover, resulting in excessively dry mix on top and too wetmix underneath-a bad mix. Eliminate this situation bynot overloading the machine.Handling MaterialsPersonnel handling cement or lime bags shouldwear recommended personnel protective gear. Alwayspractice personal cleanliness. Never wear clothing thatis hard and stiff with cement. Such clothing irritates theskin and may cause serious infection. Any susceptibilityof skin to cement and lime bums should be immediatelyreported to your supervisor.Don’t pile bags of cement or lime more than 10 bagshigh on a pallet except when stored in bins or enclosuresbuilt for such purposes. Place the bags around theoutside of the pallet with the tops of the bags facing thecenter. To prevent piled bags from falling outward,crosspile the first five tiers of bags, each way from anycomer, and make a setback starting with the sixth tier.If you have to pile above the 10th tier, make anothersetback. The back tier, when not resting against a wallof sufficient strength to withstand the pressure, shouldbe set back one bag every five tiers, the same as the endtiers.During unpiling, the entire top of the pile should bekept level and the setbacks maintained for every fivetiers.Lime and cement must be stored in a dry place tohelp prevent the lime from crumbling and the cementfrom hydrating before it is used.PLASTER APPLICATION TOOLSAND TECHNIQUESLEARNING OBJECTIVE: Upon completingthis section, you should be able to state the usesof plastering tools, and describe the techniquesof plastering.A plaster layer must have uniform thickness to attaincomplete structural integrity. Also, a plane plastersurface must be flat enough to appear flat to the eye andreceive surface-applied materials, such as casings andother trim, without the appearance of noticeable spaces.Specified flatness tolerance is usually 1/8 inch in 10 feet.TOOLSPlastering requires the use of a number of tools,some specialized, including trowels, hawk, float,straight and feather edges, darby, scarifier, andplastering machines.TrowelsSteel trowels are used to apply, spread, and smoothplaster. The shape and size of the trowel blade aredetermined by the purpose for which the tool is used andthe manner of using it.The four common types of plastering trowels areshown in figure 7-12. The rectangular trowel, with ablade approximately 4 1/2 inches wide by 11 incheslong, serves as the principle conveyor and manipulatorFigure 7-12.—Plasterting trowels.7-12
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business