I hate CMUs (concrete blocks)

[Ivan Vegvary]

Well, I really don't hate them. I've (registered Civil Engineer) designed a lot of retaining walls and load bearing walls using CMUs (Concrete Masonry Units). I hate how they are totally abused and misused.

The following picture is a typical support under my house. 1950s construction. This crap is throughout the house. BTW, the previous owner, responsible for all of this, was successful in the lumber business. You would think that on JUST ONE support under the house he could have come up with the money for either a 4"x4" post or maybe a 6"x6". Heck, he only would have needed an 8 or 10 inch length!!

This kind of crap is throughout this part (north) of Oregon. Most of these places were improved without the benefit of permits or good advice. My neighbors are stunned that I actually fill my concrete blocks with concrete. Using rebar blows their minds.

I cringe when I see this. I cringe when I see somebody working under a car supported by CMUs.

The only allowed use for loose CMUs should be low (2 rows maximum) bookshelves in college dorms.

Sorry about the rant. BTW, I've already removed and replaced about 11 occurrences of the above.

Ivan Vegvary

[Larry Fishel]

Um... Were you employed as a civil engineer when you bought this house supported by hope and pixie dust?... Just curious...

Interesting that they not only chose to use CMUs for this, but they even turned them the wrong way... :(

[The Daring Dufas]

If I ever saw anyone who needed screw jacks, it is you my friend.

TDD

[Jon Danniken]

Ouch.

Speaking of shoring up joists, I may be doing a couple in my extra bedroom for a heavy thing I am building to put in there. Acquiring/making a slab of concrete to serve as a base isn't too terribly complicated, but how does one go about dragging a 50+ pound slab over gravel and visqueen through an 18" crawlspace to it's intended destination? Maybe a skid or something?

Jon

[JimT]

Nice insulation work too.

[David Nebenzahl]

On 7/30/2010 10:28 PM Jon Danniken spake thus:

Come-along?

[gfretwell]

As Larry pointed out, those blocks are oriented the wrong way. CMUs have little strength when the holes are horizontal.

The idea of grouting the cells and putting rebar in them is code in Florida but it is uplift protection not download.

[Jim Elbrecht]

-snip-

50 pounds? Why bother? Mine weigh 600 [assuming 150 pounds per square foot; 2x2 squares a foot thick]. I mixed mine in place-- but if I needed to put one in a crawl space I'd move it into place while still in a liquid state.

Jim

[Jon Danniken]

I was just guessing at the weight of one block, with a sack of concrete being 80 or so pounds, and me not needing to support the beam at a major load bearing location (just reinforcing it a little). I had thought of mixing it in place, but considering the short area to work in, I discounted it.

Still, I can see with the size of your blocks how that would pretty much be about the only way to get it done.

Jon

[Ivan Vegvary]

The house inspection was difficult because the crawlspace was around 4 to 6 inches in many places. The price was greatly discounted to account for the problems. I took everything into consideration except my slowly ageing body.

Ivan Vegvary

[Ivan Vegvary]

>

Using two 20 ton hydraulic jacks along with 14 house jacks (jack screws). Over the years I've been picking up jack screws at garage sales for anywhere from $ 1 to $ 3 each. The hydraulic jacks are wonderful because of their power. The down side is that they are very heavy and always bleed back slightly, so they are not to be used for final positioning.

Ivan Vegvary

[Ivan Vegvary]

Jon, The footings that I am pouring (concrete) are 18"x18"x6". This necessitates a 21"x21" form (outside dimensions). I usually screw the form together once I am down and under. As far as moving heavy things around, I've discovered that (short of a conveyor) two 3/4" PVC pipes laid parallel provide excellent skid characteristics. I've dragged up to 120 pound loads (old concrete rubble) on these two rails. Very low friction compared with dragging across the earth.

Ivan Vegvary

[Ivan Vegvary]

Regardless of orientation, you still won't get more than 2-3000 psi strength out of them. Today most home improvement stores sell only the heavy walled stuff, but there are still lots of idiots that seem to find blocks made of pumice, cinder and chimney liner applications pieces and tiles. All have good uses but not structural.

Ivan Vegvary

[JimT]

A pig in a poke. The old addage comes to mind: "You get what you....." :)

[Jon Danniken]

Ah, the Egyptian method, that sounds like the perfect soution. Thanks Ivan!

Jon

[gfretwell]

If I use your 2000 psi strength a 16" CMU in it's proper orientation will carry over 100,000 pounds. That is plenty.

[The Daring Dufas]

>>

I see the foundation screw jacks installed permanently all over this area of Alabamastan. The guys doing foundation repairs seem to be quite fond of them.

TDD

[Larry Fishel]

I don't know much about the subject or whether this has anything to do with their fondness for them, but I can see where that would allow for periodic adjustment as the grounds shifts over time...

[The Daring Dufas]

That's exactly what I thought, it makes sense. Perhaps I'll ask some of the guys at the construction supply house the next time I go by.

TDD