Lime and Cement Mortars, Stuccos and Plasters
( Originally Published 1937 )
The countryman often needs to touch up stone-work, brickwork, or plaster walls. He may also build a kiln, forge or furnace or lay a stone terrace. For any of this work he should know how to mix lime, cement and sand. While in the past, bricks in chimneys were laid with clay inside the house and lime mortar outside, today most masonry is laid with cement mortar. If you wish to repair old brickwork, use lime mortar. You can buy slaked or quicklime in 50 lb. paper bags. Cement comes in 94 lb. bags with a volume of I cubic foot—a useful hint for calculating concrete batches.
To prepare lime mortar; make a box out of wood. Put into it about twice as much water as the lime, shovel the quick lime into it and stir well during the early stage of the slaking.
Instead of using all coarse sharp sand, you may use up to 1/3 of fine soft sand. The small grains of soft sand fill in the voids between the grains of coarse sand. The soft sand is shovelled into the creamy mixture of lime and water and mixed in with the hoe.
This should be still slushy in texture. Cover from the air with soft sand and leave it at least 24 hours. As you need it take the paste out with a shovel and mix with it the right amount of sharp sand (about 1 part lime to 2 1/2 parts total sand).
Slake the lime a day or more ahead. Mix dry 1 part of cement and 2 1/2 parts of clean, sharp sand, and form the mass into a crater with plenty of room in the middle. Pour water into it, dragging the sides down as you mix until it is plastic. Then work in 1/2 to 1 part lime paste. This mortar must be used at once because the initial setting of the cement takes place in 30 or 35 minutes and if this is broken the cement will never develop its full strength.
STUCCOS AND PLASTERS
Stuccos and Plasters are made according to either of the methods for mortars. Decorative stuccos for exteriors are cement mortars, often with pure white sand, or colored sands and marble dusts added to give color and texture. Interior plasters usually have little cement except for special purposes. Ready-mixed fibre-plasters are popular with builders be-cause they save time in preparation, but are more costly to use.
Interior plasters are applied in two or three coats. The first coats are made of 1 part lime to 2 1/2 parts sand with sufficient hair to bind it. The hair, obtained from the building supplies dealer as it comes from the oxhides in the lime pits, is matted into lumps filled with dry, dusty lime and dirt. These lumps should be set out on a board in a windy place and well beaten with a stick, keeping to windward so as not to breathe the dust. When the hair is light and fluffy it may be worked into the plaster. A small quantity goes a long way.
The finishing coat for white plaster is made of well-slaked white lime mixed up as required with about equal parts of gauging plaster (plaster of paris), and sometimes a small quantity of clean sand. This must be used soon after mixing. The white "putty" is spread on the wall and wet with water from a brush while burnishing it with the steel float.