On a recent remodeling project, I needed to remove a window and fill the resulting hole with cinder blocks. Ordinarily, this wouldn’t be a big deal, but this wall was made with an old-fashioned type of block with wavy faces. This block is no longer available in our area, so I had to make my own.
To do so, I began by making a form out of 1x2s and 3/4-in. plywood, as shown in the drawing. The form is 8 in. by 16 in., the same size as the blocks in the wall. I nailed the 1x2s to the edge of the plywood, creating a 3/4-in. deep box. Then I filled the box with plaster of paris and covered the plaster with plastic wrap to keep it from sticking to the old block. Next, I pushed the plaster-filled form onto one of the blocks in the old wall and pulled the form away. The result was a perfect mold of one of the block faces.
To make my new/old blocks, I set a batch of smooth-face 8-in. by 16-in. blocks on their sides, and sprayed them with water to slow the curing time. Then I mounded a layer of mortar on each block and pressed the plaster form on top of each one. The result was a stack of custom blocks that perfectly matched the old ones.
Jeff Fosbre, Dunellen, NJ
