Building With Concrete Blocks

CONCRETE BLOCK has long been recognized as an outstanding structural material and, with the new developments in the field, it is being used more and more. The Besser Company, pro­ducers of Vibrapac masonry units, states that in terms of wall volume, concrete masonry accounts for more than two thirds of all masonry walls built.
There was a time when you chose between an exterior block or an interior block. While these common types of block are still extremely useful building materials, masonry units have progressed much beyond this in appearance.. Numerous textures are available, different sizes, different treatments; a masonry unit wall can resemble the most attractive stone wall. The availability of different sizes in the same style makes it possible to get away from simple, monotonous running bond assembly, and come up with intriguing ashlar patterns, basket-weave effects and so on. Pierced masonry units are so effective that they are now widely used for decorative outdoor screens, store fronts and, for that matter, entire building facades.

When planning projects for your home, consider the many orna­mental types of block available—even for fences or such prosaic projects as posts. One type of block, 4 in. thick, resembles a large brick. Some blocks are designed with ornamental recesses so that when placed together they form a design. "Split blocks" have a rough exterior face much like cracked stone. "Slump" blocks hardly resemble concrete at all, and can be used to construct a very rugged, attractive stonelike wall.

Modern masonry units can be both functional and decorative as photo op­posite shows. They are available in many shapes and sizes and solid or pierced.

Look what they've done with this material! New developments make it flexible and attractive

First course masonry units should be placed dry for exact location when you start installation. Strips of 3/8 in. plywood space the blocks exactly.

Constant checking is required to do a good job. Use the level as shown and work with the handle of your trowel to make any slight adjustments.

Check the blocks horizontally as well as verti­cally. Final appearance of wall will depend on how often and how well you check work with level.

Place first blocks very carefully—they serve as a guide for those that follow. Practice block placement before you begin. There should be enough mortar so some is squeezed out.

The first course gets a full mortar bed as in the photo above. If the footing is hot level, use the mortar bed to help compensate for the low

For standard construction (the walls of a house for example), there are specially shaped blocks to make the job easier. There are "full" and "half" headers which are shaped just right to take floor joists. "Cap" blocks finish off the top of a wall in a very professional and practical manner. For constructing a nicely rounded corner, you merely obtain blocks that have the round corner already cast for you. These are also fine for building columns and posts minus sharp edges. To do the job ordinarily done with heavy timbers over window and door openings, you simply specify lintel blocks.

Your building supply dealer should have a sufficient variety of masonry units so that you can get a good idea of what's available.

RECOMMENDED MORTAR MIX FOR CONCRETE BLOCK
Portland Cement    one part
Hydrated Lime       one part
Mortar Sand          five parts
When construction will be subject to heavy loads, violent winds, extreme frost action, earthquakes, etc., use:
Portland Cement    one part
Hydrated Lime       one-quarter part
Mortar Sand          three parts

Typical concrete block shapes are shown in the drawing below—there's a block for every need.

TYPICAL CONCRETE BLOCK SHAPES
Buttering of block ends is done as shown. Masons usually line up three-four blocks at a time, but it will be, easier if you start with a couple.

Alter the first course of block is complete, build up the comers. Note that bottom joints have been tooled—must be done as the job progresses.

The level is used frequently—even as a straight­edge as shown here. Building up the corners of a wall first gives you horizontal lines to work to.

Chances are he will also have manufac­turers' catalogs and can order blocks not in stock. Choose masonry units suitable in shape, size and texture, and plan an instal­lation that will be both luxurious and long-lasting.

Of course, appearance is not a major factor in a foundation wall or in other, similar projects. Here ease of construction, strength and economy are important. Con­crete masonry units meet these require­ments also.

Exterior block should be dense and watertight. A variety of block sizes and shapes are available which are suitable for building weatherproof walls. Aggre­gates used to produce the denseness re­quired are gravel-sand, slag, crushed rock and limestone. Interior block is constructed to provide special characteristics. Pumice, shale, cinders and natural materials are used extensively, and serve to make pos­sible many different interior wall treat­ments. Blocks made from these lightweight materials are porous and much easier to handle than the heavyweight exterior types. In addition to structural strength, they provide insulation and sound absorp­tion qualities.

Clean materials in recommended pro­portions are necessary if the mortar you use is to hold the masonry units together strongly and durably. Each masonry unit must be encased in a layer of mortar. (There is a new way to put ground ma­sonry units together without mortar de­scribed later in this chapter.)

Mix materials for the mortar carefully and very thoroughly. Do not wet the con­crete block either before or during instal­lation. Mix only as much mortar as you can use within two hours. If the batch be­comes slightly stiff during this time due to evaporation, add a little more water and remix to a workable consistency. Never add water and remix if the unused mortar has started to set. Instead, discard it. It may be a little difficult for the amateur to de­termine whether the mortar is stiff due to evaporation or whether it has actually started to set. If there is any doubt in your mind, take the safest course and mix a new batch. To avoid this kind of waste, start off with small batches of mortar. You can increase the amount as you become more proficient in block laying.

Well-prepared masonry-unit mortar will stick to the blocks. The proper mix­ture has enough water-retaining capacity so that the units will not suck out water so fast as to weaken the bond. The amateur's best bet is not to lay out a long line of mor­tar. Prepare, instead, for a few blocks— just one if you want to be really sure. You won't have to maintain this slow pace. You'll soon get the hang of putting the mortar in place and setting the blocks, and at that point you can determine your own working speed.

Positioning the Blocks

The first course of blocks should be set down dry and very accurately so that you'll end up with uniform head joints. This be­comes even more important if the footing has been prepared to accommodate a spe­cific number of whole units. (This kind of preplanning is a good idea in any case since it will avoid the necessity of cutting blocks.) There are few structures which can't be planned to go a few inches more one way or the other. One way to space the blocks accurately in the dry, layout stage, is to use small pieces of plywood between them.

These are removed after you have chalk-marked the location of each block on the footing. Once the spacing problem is solved, a taut, snapped chalk line will as­sure a straight line. Snap this right on the footing.

A special tool can be used to make the popular concave joint, but a piece of bar stock or small pipe, bent up at the end, will do the job just as well (see photograph above).

At this point you're set to place the mor­tar for the first few blocks. Spread a full bed for the first course and position the corner block very carefully. Check it both vertically and horizontally with a level and tap lightly with the handle of your trowel to set the block exactly right. The first few blocks are very important and should be placed accurately to serve as a guide for those that follow. One end of each of the following blocks is buttered with mortar and squeezed up against the preceding block to provide a 3/8-in. joint. There should be sufficient mortar on the block so that a quantity of it is squeezed out when you place the block. This is removed with a trowel and placed back on the mor­tar board. Check each block as you go to make sure of alignment and correct joint thickness. Be sure the mortar joint is full; no crack should be visible between mortar and block. If the block must be shifted or adjusted, be sure to do it while the mortar is soft and still plastic. If the block must be removed entirely, it is usually a good idea to scrape off the mortar and start all over again.

Well buttered block-ends will produce full, tight joints. If you do find a partially filled joint, fill it immediately. Don't wait until later to fill poor joints; it must be done as you place the block. Use the level frequently, checking both the vertical and horizontal alignment of each block and of two or three blocks as a unit.

After the first course, mortar is used on the horizontal face shells of the block. The vertical joints are made as before—by but­tering one end of each block. It's best, after the first course is complete, to build up each corner three or four courses high to give yourself horizontal lines to work to. You can stretch a line from corner to cor­ner to provide alignment for following courses. Just be especially careful when building up the corners. Keep joints ex­actly right and be sure the corners match. An error can mean unsightly joints and un­even walls.

The total error created by a number of small discrepancies can be enormous and it may not become apparent until you've put in considerable time and effort. Avoid problems by using the level frequently. Check each block both hori­zontally and vertically. Don't go on to the next block, or next set of blocks, until you're sure of those already positioned. With this method you can't help but get true, straight construction.

The V-joint can be done, as shown in the illus­tration, with a trowel, or you can use a diamond pointed strip of hardwood to accomplish the job.

Partition, outside walls are locked together as here. Steel bar ends are bent in opposite direc­tions, mortar locked. Note the mortar-holding mesh.

Many an amateur has helped himself considerably by practicing actual "wet" runs. To do this, mix a batch of mortar and start the job. After you've placed a dozen or so blocks, remove them and scrape off the mortar. Practice lifting and placing the block as close to correct position as possible. It doesn't matter how you lift them; it does help considerably if you can place them correctly the first time. Excessive shifting and adjusting after you've set the block on the mortar bed is not wise.

The last block to be placed in a course is called, logically enough, the closure block. The buttering procedure changes a little here. Instead of applying mortar to just one end of the block, you apply it to both ends and also to mating edges of blocks already placed. Lower it carefully into position and be sure you don't knock out clumps of mortar. The excess mortar should be squeezed out.

Concave and V-shapes are common block-joint shapes. The joints should be tooled as soon as the mortar has set suffi­ciently to permit it; this can be established only by actual testing as you proceed. The important thing is not to forget this step. After a while you will establish your own work pattern. For example, you might place two dozen blocks and then go back and tool joints on the first dozen. The "thumb test" is used by many masons. If pressing your thumb against the mortar leaves an imprint, it's ready for tooling. A concave joint can be established with a length of pipe or round bar stock. A V-joint can be made with a trowel, or a piece of square bar stock.

Decorative masonry units can be used as a handsome veneer against ordinary concrete block as in the photo above. Note tie strips imbedded in mortar joints.

Bolts for mud sills, plates or wooden caps can be imbedded in the block as shown at left. Be sure the mortar is firmly set be­fore doing any tightening of nut.

After the joint is tooled, remove mortar "burrs" with a trowel or by rubbing lightly with a piece of burlap or other rough cloth.

Masonry units can be cut with hammer and chisel —practice on a scrap block. Try to score block with light blows rather than break in one shot.

Ground masonry units must be used when bonding with Threadline Mortar (see below) due to the fact that the mortar will not correct irregularities.

GROUND UNITS WORK UP PLUMB AND SQUARE GROUND UNIT WALL UNGROUND UNIT WALL (TOP COURSE UNEVEN-IRREGULAR OR OPEN JOINTS)

Threadline Mortar

Threadline Mortar is a new and unique organic-inorganic mortar for bonding a variety of masonry products as well as standard masonry units. It has great strength, even more than ordinary concrete mortar, and is finding an impressive ac­ceptance in the concrete and masonry field.

The materials for Threadline Mortar are available in a kit which provides necessary ingredients packed in plastic bags. Com­plete instructions are included and should be very carefully followed. This method of bonding differs greatly from standard practice in that the mortar is applied with a caulking gun. Unlike ordinary cement mortar, Threadline cannot be used to com­pensate for block or footing irregularities and, therefore, only precision ground or sized masonry units should be used with it.

Footing irregularities can be adjusted in one of two ways. If the footing is off level up to 3/8 in., you can add a gallon of dry masonry sand to each unit of Threadline Mortar. After mixing, the mortar will have sufficient substance to hold a masonry unit level. If the levelness of the footing is off more than 3/8 in., use cement mortar for the footing course to establish the level-ness of the first blocks. Here too, 'the new mortar can be applied to the footing (be­fore the cement mortar is placed) and to the underside of the first-course blocks as additional reinforcement. All vertical joints are done with Threadline since there are no irregularities here.

Applying the new Threadline Mortar to the edges of ground masonry units. Small beads are forced from gun onto block; process is clean and there is little waste.

This masonry unit fence (left) was a Threadline project done by do-it-yourselfer in Connecticut. Note hanging wall experiment, the screen effect with solid units.

Strength of Threadline is demonstrated below. Gateway is unsupported within blocks—units were simply bonded with new mortar; not feasible with regular mortar.

Ground block can be purchased from any masonry unit manufacturer who is equipped with the proper grinding equip­ment. Lightweight aggregate and cinder blocks can be ground for 3 to 6 cents per unit. Cement blocks will cost more to grind. Grinding is necessary since Thread-line produces a thin joint and block ir­regularities will result in an uneven wall. Figures from the manufacturer indicate that the use of Threadline Mortar reduces the labor cost of masonry work approxi­mately 50 per cent, cutting the over-all cost of masonry construction (considering the added cost of ground units) approximately 30 per cent.

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