Monday, September 12, 2011

Retaining Wall Blocks

Bodega and 7 cu mtrs of sand (under plastic)

We've been very busy with projects large and small. One substantial project has been figuring out how we can build retaining walls. We have many garden areas that are on fairly steep slopes.We also have some garden beds that are on pretty lousy soil. When we prepared the building site, we had to dig down well beyond the good top soil to nasty hard clay. On the sloped areas, the good soil or compost that we’ve added runs off with the rain.

On Bainbridge, we used the interlocking keystone blocks to build several small retaining wall and found them to be easy to use and attractive. They’re available at Lowes, HomeDepot, and many lumber yards. Unfortunately, we were unable to find them for sale here, although we have seen and heard about them. Since we were unable to locate them here, Norm searched online and found molds to make them and bought 14. When they came through customs here, they called them “cake molds” even though they were labeled cement brick molds.
Mario cleaning the molds
But before we could start making blocks, we needed a place to work out of the sun. So, Norm & Mario, our gardener, built a 12 x 12 shed, or bodega.

It took some experimentation, but Norm and Mario figured out the best method. Now Mario has it down; he can remove the dry blocks, clean the molds and pour 14 new bricks in about an hour.We have calculated the total cost per brick to be just about one dollar.

Freshly poured molds

The company that we bought the molds from suggested using PAM spray as a mold release. (Petroleum products will stain the concrete) They used PAM for the first batch , and it worked fine, but it took about half of a large can. Pretty expensive! For the next batch, we bought a big jug of the cheapest vegetable oil they had at PriceMart (Like Costco) and put it in a spray bottle. It takes 3-4 ounces per batch of 14 bricks. It's much less expensive,and actually works better.

Blocks curing
Another problem with the first batch, the concrete bowed the heavy plastic molds out, making the hardened blocks almost impossible to remove. Out of 14, we only have two which we didn’t have to break to get out of the molds. To get around this, Norm built 14 wood forms to support the plastic molds. That kept the bricks from bowing out. They were still a bit hard to remove, so Mario suggested cutting a slit in the back side of the mold so that it could be opened to release the brick. They settled on a u-shape that doesn’t adversely impact the shape integrity. The form ensures that the flap doesn’t bulge out and allow leakage of the cement. Now the blocks drop right out of the molds.

Norm just finished the first project, a low retaining wall along the parking area for the casita.
The first retaining wall

I am looking forward to revising the garden beds and planting in good soil. I am sure that the plants will love it and will grow and bloom more!