While painting the kitchen block wall I started wondering what kind of block is our inner south wall made of anyway? At one point I heard this type of block called “slag block” and in Arizona where there are many block houses, I heard it called “slump block” so I was curious about the concrete bricks used for the thermal mass on the house.
Our house in Arizona was built entirely of block that was 4 x 8 x 16–actual block measurements are about 3.5 x 7.5 x 15.5. I demoed the bathtub tile and uncovered the inside of the block walls. They were framed out with 2 x 2’s and filled with a 1.5″ layer of fiberglass insulation.
I used a rented drill to create a hole in the wall for the drain pipe from the shower. That took quite a lot of drilling to get through the whole wall. For the tub drain setup there were valves that allowed the water to either run out into a soaking tank or down the drain.
The block was gray concrete color inside but it was painted on the outside.
It was an attractive home and the concrete block acted as a thermal mass holding heat on cold days and night time cool on hot days.
When we were shopping for a house in Tempe, my fellow workers and Arizona natives advised us to buy a block house not a “stick” house. They said block houses were much more comfortable in the Arizona climate and they were well built vs. some of the newer wood framed houses covered in stucco. While looking at houses to buy, I kept that advise in mind and it did appear that newer frame house had cracks in the stucco and were less sturdy. Almost all of them were two stories too.
I was trying to find out what this type of block is called when I ran across some really interesting information about why so many block homes were built in the Phoenix area. It turns out that lightweight building blocks were invented there! In the 40’s three Phoenix guys manufactured blocks originally with perlite in the concrete mix. There was a lot of demand for building materials after WWII and concrete blocks were considered too heavy and often were cast right on the building site. The manufactured concrete blocks were named “superlite” and eventually the company name was changed to Superlite. After the perlite they used an aggregate in the mix created from rapidly cooled lava. They had a mine for this volcanic scoria in northern Arizona. This lighter block trapped air which helped insulate the houses. The blocks were very successful and from the 40’s through the 80’s many many block house were built in Phoenix and the surrounding suburbs.
Notice this house has a carport. Our real estate agent told me that her husband refused to buy a house with a garage. True Phonecians knew that garages were heat sinks and trapped the very hot air from the daytime, reducing the ability of the house to lose its heat at night.
These brick/blocks are now known as CMU’s, (Concrete Masonry Units) just one variety of several types of CMU’s, they are solid like bricks but larger and can be used structurally. Bricks are mostly used as a decorative cladding for a wood framed house instead of the actual structure. These blocks became popular also because they are so much larger than bricks they can go up faster.
Slag block uses industrial waste from blast furnaces in the cement mixture. Several types of mineral wastes can be used, even the waste from making Portland cement. It is considered a recycled product because it uses waste in the mix.
Superlite also created a slump block style. They pressed on the molds to create a bulge in the sides of the blocks, but I also read that some companies take the blocks out of the molds a bit early and while still wet they sag a bit to create the bulge.
The adobe brown block planter walls around our yard were slump block and Superlite also designed this integrally colored type of block. Our kitchen wall is slump block because it has this bulge on each block. It is probably plain concrete and the original walls were painted.
There is a great explanation of concrete block materials at Cemexusa.com. According to this presentation CMU blocks have both heavy and lightweight aggregates in the concrete mix. They have various admixtures to make them stronger or more waterproof, and they are cast in molds. Once the molds are removed, they are dried in moist 140 degree ovens for 24 hours. Then they are ready to be palleted and shipped.
I can’t know where the solid block that lines our south facing concrete thermal walls was sourced or what aggregates were used. But I know it is a layer of solid concrete that increases the depth and mass of our front wall and adds a pleasant decorative brick look to the interior.