Concrete Strawberry Risers- 3. The first batch.

Armed with our molds, we decided to try several things this first run:

1. Addition of Perlite to make the risers lighter.
2. Paste wax along all surfaces in contact with concrete as release.
3. Murphy Oil soap along all surfaces in contact with concrete as release.

We used Sakrete High-Strength Concrete mix, which came in a 60lbs bag. We mixed up the concrete using the instructions for the product.

I won’t go into a lot of detail for this first batch, because it was a disaster. The perlite was a mess, we used a couple of handfuls for each basin, but it did not adhere in any way to the concrete mix. This was made more problematic by the fact that the gravel in the concrete mix were really large, and did not fill in the more narrow areas of the mold well. We tried to demold after 24, 48, and about 72 hours, and while the 72 hours was more structurally sound compared to the 24 and 48 hours, it was still very difficult to remove the concrete from the molds, regardless of release agent. We did this in early February, during which the daily low temperature was around low 30s (F). After pouring the concrete we would try to keep the concrete surface wet after the concrete set up after a couple of hours by watering with a small watering can (the blue one in the image below).

From this first batch we learned a couple of things.

• Perlite not useful addition: the decrease in weight not appreciable, especially given the decrease in structural integrity. Also a mess to work with. We might have been able to make this work with more troubleshooting, but we decided not to.
• Murphy oil soap not useful as a release; the best release is when the concrete has set up enough to come out of the mold. This would require 72hours minimum set up before demold, under our conditions. We were hoping on a shorter turn around time.
• The most problematic area for release is the inner concrete tube. This makes sense, as the concrete contracts during curing- this helps the form release from the plastic basin, but it also traps the tube inside.
• The forms made with Sakrete, while very durable (and the big gravel is not a problem if you vibrate the concrete in the mold), is very heavy. A single riser, when fully cured and dried, is 20.2lbs. This isn’t such a big deal until you consider that I’d like to pour 3-4 each time, and mixing and lifting and pouring 60-80 lbs of mix carefully is difficult for me.
• On the plus size, we really like the shape and size of the finished product, so we decided to continue to troubleshoot the release and weight issue.

Series Navigation