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Brandon Whitmore

1950's slab

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Has anyone seen a concrete slab installed with concrete blocks around the perimeter.

I hardly ever see slabs in my area, and this is a first for me. At first I thought I was looking at cracks in the concrete, and then realized they were fairly uniform. Some areas appeared to be parge coated (tough to tell) while at others, there were very slight vertical cracks 16" o.c. I have pictures that I can upload, but figured I would just ask first. It seems strange to me.

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That's a stem wall. I see them all the time, mostly with attached and detached garages.

With that large horizontal joint and only minimal vertical cracks, it doesn't quite look like that's a parge coating on it.

Stem wall

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That stem wall looks about right in your diagram. Can't say I have ever see a CMU stem wall with a slab construction home. Something still doesn't strike me right about this foundation. Some areas show vertical cracks every 16" (cleaner looking concrete), while other areas don't have any vertical joints exposed. I was wishing I had a shovel to dig up an area to see what was going on. There just wasn't much concrete exposed.

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With all the hills around here, I see them all the time.

Pour a footer 25" below grade, build a CMU wall to desired height, fill it with gravel, pour the slab, build the house. They are almost always parge coated and a couple of years down the road, the parge always starts cracking and looking uglier than if they just left the CMU exposed.

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Just in case you don't know this already...

Since you don't see a lot of slab houses, you should pay special attention to termite problems. The worst termite damage I have ever seen is in slab on grade construction. Due to the fact that all of the wall framing is typically concealed, the termites are hard to find and they can be eating the framing unnoticed for many years.

Include a good CYA comment about termites.

Probe all of the baseboards and shine a flashlight on all of the walls to look for signs of termites eating the paper off of the gypsum board. Open all kitchen cabinets to see if the bottoms are eaten.

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Like Erby, I see them all the time. My home is built that way.

Another method I see is that they dig the footer trench and then form walls like for a poured concrete basement foundation, add the needed steel. They then fill the center of the "pad" with crushed rock put in the plumbing add some additional rebar and wire and then they fill the entire thing with concrete so you end up with about 3-4" of concrete in the center of the foundation.

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Has anyone seen a concrete slab installed with concrete blocks around the perimeter.

We need our footings at least 4 feet below grade here in order to get below the frost line, so foundation stem walls made of CMUs or poured concrete are common.

Would anyone recommend sealing the gaps/ cracks where exposed? Or should it just be left alone?

In our climate the biggest concern with that cracking would be with water entering the crack and the freeze/thaw cycle causing more cracking and deterioration of the wall. For that reason I would recommend the parge coating be repaired.

I'm curious. You folks on the left coast are in earthquake country. Is that the kind of damage to a CMU stem wall & slab foundation that might be caused by an earthquake?

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We did have some earthquake damage to some older buildings a while back (10 years or so). Our earthquakes have not been very serious so far. I have never even felt one (slept through them). I doubt the small gaps/ cracks are a result of the earthquakes, but could be wrong.

We don't really have problems with frost heave around here, so our footings are pretty shallow.

In one of the pic's, you can see where the concrete has started to crumble-- likely from spalling, but most of the concrete is in pretty good shape.

We don't really have many problems with subterranean termites in the area. I would say 1 in 500 houses or so have signs of termite activity, but I have never seen a home too torn up/ damaged by the little guy's--- at least not like you guys on the East side have. So I wouldn't be too concerned with termite entry at the gaps-- it goes back to the spalling issue with the concrete due to freezing.

Thanks for everyone's help

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Can anyone tell me if they have worked with a home in south florida that was build in the 1950's with a stemwall foundation.  Can you tell me if the foundation floor normally is gravel or is it a concrete slab?  

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