establish corners

Mark the locations of the corners. Stretch a mason's line between the batter boards you set up before excavating for the footing, placing the line on the mark for the outside of the wall (see Preparing Sites for Walls, Related Projects). Have a helper dangle a plumb bob from the point at which the mason's lines intersect at each corner, taking care not to disturb their alignment. Mark the locations on the footings with a thick pencil.

	mark

Sweep the footings clean and snap chalk lines between the corner marks. Check the lines for square, using the 3-4-5 method described on Laying Out Sites for Slabs, Related Projects.

If your project involves just one wall, skip Steps 1 and 2. Simply determine the two end points of the wall and snap a chalk line on the footing to designate the edge of the wall. Go on to Step 3.

	bottom mortar

Make sure the footing is still clean and lay a 1-inch bed of mortar for the first course of block. Start at one corner, running the length of three or four blocks. Make the bed of mortar about 1 inch wider than the block you'll be placing.

	corner block

Carefully place a corner block in position, with the smaller holes in its cores facing up and its smooth-faced, solid end on the corner. Gently press the block into place in the mortar.

	story pole

Use a story pole to check for proper course height. To make a story pole, choose a straight 2x4 and make clear perpendicular marks every 8 inches. As you add the courses, the top of each concrete block should align with one of the marks. If the block is too high, tap it down into the mortar with the trowel handle. If it?s too low, pull the block out, place more mortar on the bed, and re-lay the block.

[Option 2: Use a folding or modular spacing rule]
If you use a conventional folding rule or tape measure, the top of the block should be 8 inches above the footing. Confirm that the mortar joint under the block is exactly 3/8 inch thick. On a modular spacing rule (see inset) the top of the block should match the line at the "2."

Before laying the second block, butter its flanges (or ears) while it is standing on end. Butter it well because this mortar forms the vertical joint between the first and second blocks. Set the block in place, making sure you have a
3/8-inch joint spacing. Repeat with subsequent blocks.

	level/plumb

Place a level along the length of the first three blocks. If they are not perfectly level or if their tops do not form a straight line, press or tap down on the high points until they are level.

Check for plumb by holding the level against the side of each block. If any block is not plumb, press with the heel of your hand or tap with the handle of your trowel to adjust it.
Every three or four blocks, check for level and plumb and make adjustments. Periodically use your level or a long straightedge to make sure the faces of the blocks align.

	build lead

Check corners for square first by holding a framing square against the outside edges of each side. Then use the 3-4-5 method as a double-check (see Laying Out Sites for Slabs, Related Projects). Apply a 1-inch-deep layer of mortar along the top edges of the blocks of the first course. As you place the second corner block, align its outside corner with the corner below it. Press the block into the mortar just enough so its weight compresses the mortar to a 3/8-inch joint. Continue laying blocks until you have built up a corner lead.

	spacers

Spacers made of cut blocks can be used to extend leads if you cannot make the number of blocks come out even by slightly enlarging the mortar lines. Cut spacer blocks and install them early, rather than trying to cut the closure block in the middle to fit.

	concrete blocks

If you need to cut blocks to fit, be sure to take into account the 3/8-inch width of mortar lines when measuring. To cut by hand, place the block on sand or loose soil and use a brick set and hammer to make a line about 1/8 inch deep on both sides of the block. Then work along the line again, hammering harder and moving the brick set each time you rap it. Continue until the block breaks along the cut line. For precision cuts, use a circular saw with a diamond or masonry cutting blade. Be sure the block is dry when you cut it.

	fill in

Once you have two corner leads in place, hook line blocks around the corners and stretch a mason's line between them. Align the mason's line with the top of the blocks in the course being worked on and hold them about 1/16 inch away from the blocks' outer edges.

With the mason's line stretched in place, begin setting the blocks between the leads. Check the line often to make sure no blocks or mortar are touching it because they might otherwise push the line out of alignment.

	closure block

Butter both ends of the closure, or final, block and lay it to complete the course. If some of the mortar falls off the flanges, lay the block anyway. Fill gaps in the joints by tucking mortar in place from the sides with your trowel.

	strike

Use a joint strike or a sled jointer to finish each joint after you have laid two courses above it. Tool the head (vertical) joints first, then the bed (horizontal) joints. Brush off loose mortar, then restrike. For blocks below grade, simply strike off excess mortar with your trowel.