Concrete block construction may be necessary for projects that plan to build the skatepark above ground or into a hillside.  Also, concrete block assembly may be necessary to build the back walls of free-standing obstacles such as half pipes.  A cinder block wall is the quickest and easiest in most instances.  For placing concrete block, you will need a masonry hammer, brick trowel, point trowel, joining tool, 4-feet level, tape measure, brick chisel, and mason line. 

For block construction a footing is required.  The footing prevents shifting caused by normal ground movement and distributes the weight of the wall over a greater surface area.  Footings should be made of concrete on firm ground below the frost line.  The footing should be a minimum of 12 inches in depth and at least twice as wide as the width of the wall.  The footing should be poured on a minimum of 6 inches of compacted gravel.  Consult local code before laying the footing.  The size of a standard concrete block is 7 5/8 x 7 5/8 x 15 5/8.  When working with concrete block work out your dimensions in multiples of 8 or 16 inches.  This allows for a mortar joint thickness of 3/8-inch in addition to the thickness or height of the block.  In this way, cutting of the concrete block is kept to a minimum.  Half blocks are also available for corners. 

To begin a block wall, lay a thick bedding of mortar at the corner of the footing using the masonry trowel.  This prevents the block from skidding.  Lay the corners by placing the first corner block firmly in the mortar bed at the corner.  Then butter (spread a layer of mortar) the exposed edges of the block and place the second block in the course (a layer of block is called a course).  On the opposite side of the corner, lay another thick layer of mortar on the footing and butter the edges of the block to be placed.  As you lay the block, place it firmly against the first block already positioned in order to form a right angle.  The outsides of these two blocks should be flush.  To confirm this, check with the level or a square.  Butter the exposed edges of the block and lay the second block in the course.  The mortar joint between the blocks should be 3/8 of an inch.  If the thickness of the joint exceeds 3/8 of an inch use the handle of the masonry trowel to tap the block into position. 

For the next course, butter the exposed upper edges of the positioned blocks.  Lay another corner block to overlap the joint formed by the corner blocks of the first course and continue laying (pyramiding) corner blocks in the same manner to the third or fourth course.  Use the level to check for plumb and level.  If any blocks are out of position use the handle of the masonry trowel to tap them into place.  Move to the next corner and follow the same method.  Always work from the corners to the center of the wall, keeping the corners built up higher than the rest of the wall.  Avoid spreading mortar too far ahead as it may dry out and lose its holding power before the blocks are placed within the wall.  Working two or three blocks ahead is plenty.  If the temperature is high you may have to go one block at a time.

String stretched to form a line between the corners of the wall will provide a line guide for straight courses.  By pushing gently with the level and tapping the blocks with the masonry hammer, the blocks can be moved into place.  For additional courses apply mortar to the edges of the previous course a few blocks at a time, and also apply mortar to the ends of the blocks that will be placed next.  Then place the blocks into position. The joint tool is used to strike (smooth) the mortar joint after the mortar has set for a time.  When you have layered concrete block within two courses of the top of the wall, use a piece of a sheet of wire mesh to plug the cores (the hollow center of the concrete block).  As you finish laying the final two courses fill the plugged cores with mortar.  For the greatest strength, rebar can be placed vertically through the holes in the block and the cores filled with concrete.  Consult local code for exact requirements.

RETURN TO CONTENTS