Are cinder, not CMU, blocks bad for a foundation?

My home built in the late 60’s has a foundation made from actual cinder, not CMU blocks. A couple of them have broken down to where a quarter inch of the actual block itself, not the parging, is missing.

Didn’t they stop using actual cinder blocks in homes before the 60s? If so, why was my house built with them!

Are cinder, again not CMU blocks, ok to have as my foundation or are they a failure waiting to happen?

What is the difference between a “cinder block” and a “concrete block”? Are there formal
definitions for these products?
Concrete masonry units are colloquially known by many names, most predominately “concrete
block”, “cinder block”, “CMU”, or simply “block”. Related concrete products, manufactured
using similar materials and production methods but used in different applications, include
products such as concrete pavers, segmental retaining wall units, and articulating concrete block.
There are many, many opinions and theories that have been proposed through the years (and
continue to circulate) that attempt to explain the difference between a “concrete block” and
“cinder block”. The reality, however, is that these masonry units are essentially the same
product produced with the same three basic constituent materials: water, cement, and aggregate.

In the early years of the 20th century as concrete masonry units were beginning to be used with
more frequency, producers were looking for ways to reduce the weight of the units to facilitate
their use in construction and increase mason productivity. To reduce the unit weight, many
producers (but not all) incorporated cinders into their block as an alternative to conventional
stone aggregate. Cinders, which include both waste by-products of coal combustion as well as
volcanic cinders, were an ideal, cost-effective, lightweight aggregate that was readily available in
many areas of the country. Soon after, the terms “cinder” and “block” were perpetually
linked. The use of waste by-products such as coal cinders effectively made concrete masonry the
first construction material to adopt green, sustainable practices; a century before it was
fashionable to do so.

The practice of incorporating coal combustion cinders (as well as other waste by-products) into
concrete masonry units continues today. Yet, using cinder aggregates as a lightweight
alternative to stone and gravel aggregate may have inadvertently led to another common
misconception regarding the term cinder block: that cinder block are lighter (have a lower
density) compared to concrete masonry units. While it is true that a concrete block manufactured
with cinders will tend to have a lower density compared to a concrete block manufactured with
stone aggregate, there are many other lightweight aggregate types (both natural and man-made)
that are commonly used in block production. As such, the density of a block is not an indication
of whether it has been manufactured with or without cinders.

For many the term cinder block is associated with older concrete masonry; presumably
manufactured during the first half of the 20th century. As previously discussed, cinders (both
volcanic and coal combustion by-products) continue to be used in block production today – as
such, there is no differentiating a concrete block from a cinder block based upon its age.

What has changed over the past 100 years is the technology used today to produce concrete
masonry results in a consistently high-quality product with uniform properties. Likewise, codes
and standards have evolved through the years to comprehensively address minimum physical
requirements for concrete masonry to ensure the long-term durability and performance of these
products. Consequently, some associate cinder block with inconsistent or poor quality units
produced in early 20th century, which has led some to believe that cinder block are not permitted "

Great post Roy!

Thanks !
I does answer the OP question.