when we speak of concrete and masonry repairs, we are referring to those parts of the house which are constructed of brick, stone, cement block, tile and all cementatious products. As a rule, basement and celler floors will be made of concrete. The walls will be made of cement block, brick or poured concrete, and very often the steps and terraces are made of masonry materials.
Masonry does not have the ability to expand and contract to any great degree without cracking, or fracturing, and you will often see brick steps which are badly broken up and loosened, because water has gotten beneath them, frozen, and forced the bricks apart. You will also see cracks in a basement floor which are caused by slight settling of the walls or by the washing-out of the fill underneath the floor. We will take all of the concrete and masonry portions of the house, one at a time, and try to explain exactly how they should be kept in repair and how the repair can be most easily done by the homeowner.
The basement floor of a house is usually made by laying several inches of cinders or crushed stone and rolling them down hard. A coat of concrete, from 2 to 3 inches thick, is then spread over the bed and troweled to a finish. Cracks in a basement floor which admit water into the basement, are usually found where the floor meets the basement walls. One of the best remedies for this condition is to mix a small amount of cement and sand in proportion of two of sand to one of cement, making the mix about the consistency of pea soup; wet the cracks very thoroughly; allow them to dry so that there is no free water standing in the crack; then brush in the mixture. The crack should be cemented to the very top and then smoothed off.
The joint where basement floor meets foundation walls is liable to leak. This can be cured by filling it with a cement paste.
Frequently we see cracks running right across the basement floor. This may be caused by expansion and contraction or it may be caused by a slight settlement of the foundation walls. The best remedy for this condition is to brush out the crack so that all loose particles are removed, wet the crack thoroughly, and trowel in a mixture of prepared concrete patching material which can be found in almost any hardware or building supply store.
On some occasions a section of the floor will break up into several pieces and sink below a level of the rest of the surface. This is always caused by the settling or washing out of the fill under the floor and there is only one remedy for it. With a heavy sledge or maul, the floor should be broken up and the pieces of concrete flooring removed. The breaking-up should continue until you can see that the edge of the hole is over solid fill. Damp sand should be thrown in and tamped down solidly until the fill is even with the surrounding edge. Then fresh concrete, composed of a mixture of one of cement, two of sand, and three of crushed stone, should be thrown in, tamped and floated to a finish corresponding with the firm edges.
The above operation, however, does not quite finish this job. The fresh concrete should be covered with old burlap bags or an old blanket, and this should be kept dampened for at least five days before it is removed. At the end of that time the patch will have set up hard and be ready to walk on without any danger of fracture.
Cracks in brick basement or cellar walls should be treated in exactly the same manner as recommended for the treatment of exterior brick walls. In other words, all loose mortar cracks should be cut out, the brick well dampened and fresh mortar trowelled in.
If one brick is permitted to remain loose, the bricks on either side will follow suit rapidly. All bricks must be kept solidly in place if you want to avoid complete disintegration.
Cracks in cement blocks should be treated in exactly the same way, taking great care that the dry area around the new joint has been well wetted before forcing in the new mixture.
Repairs to brick steps or terraces must necessarily be done with great care, because when you are making a repair to a wall it is simply standing there and is not subject to contusions as are brick steps or platforms. Practically everyone who has lived in a house has seen heavy trunks or crates dumped on the brick steps with very bad effect. When a brick has been loosened there is only one proper way in which to treat it and that is to lift it out entirely. Take a very sharp cold chisel and a hammer and chip off all of the old bonding material. This should not only be taken off the brick that has been removed, but it must also be taken off the edges of the adjacent bricks and out of the space from which the brick has been removed. All surrounding surfaces must then be wet, a fresh bed of cement laid and the brick reset in place so that edges and surface match up with the adjoining area. Then the joint should be trowelled to correspond with the other work and the repair kept covered with damp cloths for five days. It should be noted, that to step on a freshly set brick before that length of time, will loosen it and make the job worthless. It should also be noted that in repairing steps, platforms, or terraces, that cement and sand mix should be used instead of mortar.
All amateur masons should remember the necessity of trying to "key-in" mortar or cement joints. It should be perfectly obvious to anyone that if you have a crack in a wall or floor, and the exposed space is wider than the inside portion of the crack, that providing the bond is not very good, the fill is liable to fall out of, or be forced out of the crack. On the other hand, if you manage to make a key by having the inside portion larger than the wide surface, nothing can ever force the fill out of that crack. It will have to be chiselled out.