How are "split block" split?

[Stephen Tashiro]

I've read on the web that "split block" are produced by splitting concrete block "during production". How is this process done? All I can imagine is some sort of guillotine type machinery.

[Nathan Hawkes]

Steven, I don't know that I'm going to give you an answer, but I've seen a couple things on tv lately that are along this line of questioning. There is a specialized piece of machinery used to break concrete that is much like a guillotine, but without the cutting action---a large engine repeatedly lifts and drops a rectangular weight up & down to smash concrete, kindof like a giant jackhammer. The other show I saw was quite a while ago; I'm relatively certain that the split block is perfroated and split--recess lines cast into the surface of the concrete mark lines for splitting. HTH.

[Perry Holbrook]

First of all "concrete blocks" are not made of concrete. They are a mix of cement, and a range of aggregates, usually dependant on raw materials available in the region. The mix is very low moisture and forms the "block" by metering in the mix into a mold, vibrated and pressed into the mold, and forms free standing on a steel pallet. The pallet is transported into a steam kiln where the block cures overnight and ready to use the next day.

To make a split face block, 2 blocks are made together and broken with an hydraulic guillotine that puts a knife edge where you want to break under high pressure. If the mix is designed correctly, the block will break straight and clean.

Hard work. Been there/ done that.

Perry

[Harry Hagan]

Perry’s correct. Your “Split Face” block is ½ of a block that has been split down the middle as described by Perry.

[Lee Schierer]

I agree with Perry. If you want to split your own so you have a raw edge instead of a cut face, you can "score" a line with a stone chisel by hitting the chisel with a hammer along the desired break line repeatedly. Do this on both sides of the block. Once the line is scored you can keep on hitting along the line with stronger blows until the block breaks.

[Stephen Tashiro]

I understand that concrete blocks are not made with pure cement. However, it is interesting that they are also not made from concrete. What ingredient of concrete is missing from a concrete block? - the sand?

Is the kiln necessary to make the block harden, or does it merely speed the process so the molds can be re-used quickly?

[Perry Holbrook]

I understand that concrete blocks are not made with pure cement. However, it is interesting that they are also not made from concrete. What ingredient of concrete is missing from a concrete block? - the sand?

Is the kiln necessary to make the block harden, or does it merely speed the process so the molds can be re-used quickly?

Concrete, usually has larger aggregate, sand,a larger percentage of cement and enough water to make it flow. A block mix uses a smaller aggregate, cement and maybe some other additives but a small amount of water.

There is only 1 mold in the "block machine", when the block is formed in the mold, it is immediately pushed through mold. The mix is so dry that it is able to support itself for the block to stand up (holes upward).

The kiln is actually a tunnel filled with steam. The heat and moisture speed the hydration of the cement so the block is cured in a short time.

There are several variations of this method, but that is the way my father did it as a block plant manager for over 30 years. I worked in the plant during summers and managed a plant myself for a few years.

Perry

[Stephen Tashiro]

Thank you for that information. One of my current projects is experimenting with casting a simple cap block for the top of the wall on my storage building. The concrete block wall (around the flat roof) had the top course slathered over with mortar or concrete. In order to remove old flashing, I took off the top course. Now I want to put it back and, just for the heck of it, put something neater looking on top. I tried casting Quickcrete concrete in a simple wooden mold. This works adequately, but it produces a cap with gaps in the surface and it's heavy, just like ordinary concrete. I'll have to try some sort of custom mix.