Wet Setting CMU Block on Foundation 1

[Deker]

I've got a small one-story CMU wall building with light-framed roof where the contractor has wet set the block into plastic concrete after the foundation was poured. TMS 602 Section 3.3 B.1 requires bed joint thickness at foundations to be at least 1/4" and not more than 1-1/4", which would preclude wet setting the block. The contractor is asking if there is any way to remediate without removing the block and I'm trying to do my due diligence.

The wall is 8" CMU with #5@16 vertical, solid grouted. The walls aren't working very hard for in-plane shear, and a shear-friction check shows adequate capacity. The walls are tied to the slab on grade, so not much concern for out-of-plane shear, either.

Any thoughts or concerns?

 

[XR250]

Honestly, it is probably better than what you normally get as a first course (mortar on top of dirt covered footing). I think I would let it slide as long as there is sufficient concrete thickness below it.

 

[GC_Hopi]

That is a strange method and I have not heard of it before. I wonder if the building has some funky elevation and they were trying to avoid cutting a course of CMU or pouring a stem wall. How much did they wet set? From the photo maybe 2 inches. Check your footing design for 2 inches less. One thing I would do is ask for that course and maybe the next one to be grouted solid.

 

[hokie66]

Never seen that done. But if it doesn't affect the footing, I see no harm. But to ensure your walls are solid grouted, you will need cleanouts, which could be in the next course.

 

[MotorCity]

Better for the walls, maybe not so good for the foundation. What is the block strength f'm and concrete strength f'c? Guessing they are not the same, and I doubt the strength of the block approaches 3 ksi. I would check the portion of the affected foundation using the block strength and see if it checks out. My gut says this is probably ok for a 1 story light frame construction. That said, I'd be watching this contractor like a hawk for the rest of the project.

 

[phamENG]

Very odd method of starting a CMU wall. I've always understood the 1/4 to 1-1/4 rule to ensure that, for poorly leveled footings, you maintain sufficient mortar thickness to have a reliable bond but limit the thickness to maintain stability in what is essentially just a thin line of sand and cement paste while setting your first course level. In this case, neither of those things matter. What does matter is if what's left of the footing below is good.

I'd also wonder about moisture effects. The CMU is going to absorb water and expand slightly - hopefully it did that by sucking some water from the plastic footing and it was able to expand while the concrete remained plastic, but if not you might see some cracking.

 

[driftLimiter]

When I first looked at this I was on the same page as @XR250's initial response. But the more I look at it, the more nervous it is making me. It isn't so much structural but:
- Footing is obstructed by CMU blocks, no horiz. bar can be continuous at top. Footing needs to have sufficient thickness below and on each side of CMU.
- Cracking of the footing since it can be controlled by horizontal bars.
- Thermal and moisture expansion rates of CMU vs concrete?
- Water infiltration from cracks, the interface between CMU and Concrete has a large surface area prone to separation

I usually don't throw up my arms about small stuff like this, but this is so nonstandard I am worried that down there road there will be issues and the contractor would say, well he said it was okay!

If this was heinously different than my construction details I think it would be worth at least letting the contractor and owner know of your concerns and the issues with not following your advice.

 

[MotorCity]

If something doesn't look right, its probably not. There was no attempt even made to troweling or finishing the top of footing. Its just an unfinished blob, shoddy (no) workmanship. I find it irritating when I am asked to stick my engineering neck out to justify others' laziness.

 

[phamENG]

Another thought - if they wet set the blocks, what about the bars? I'd be surprised if they picked those blocks up and over and then pressed them in...so I suspect the order of operations went something like this:

Dig hole, dump in concrete
Set blocks, push on them because they didn't want to mess with a starter bed joint?
Oh yea...rebar...cut off the bends (if they were even there) and stick it in...nobody will notice!

So now those vertical bars probably don't have hooks in the footing. Maybe you're okay with that, maybe you're not.

 

[dylansdad]

Probably wet set the dowels also.

 

[Settingsun]

Was there meant to be a clean-out opening at the bottom?

 

[masonrygeek]

I wouldn't worry about the differential shrinkage between the concrete and CMU since they are both cementitious materials. yes, they have different water contents when installed, but it all works out in the end - they both shrink. And a lot of assumptions about the rebar, but without being able to verify, I guess it is OK to be cautious. the open end block makes me think the vertical rebar were in place when the block were set into the concrete, but who knows for sure.

 

[phamENG]

masonrygeek - good catch on the open blocks. I saw them but didn't connect that only occur at verticals. That's a good sign...

 

[Deker]

Thanks to everyone who responded. The contractor confirmed that they embedded the block 2-3" into concrete. There's a footing top bar directly under the wall that I suspect is supporting the block. The footing still works with the reduced depth, and the reduced bond on one top bar doesn't appear to be an issue. Contractor says the wall dowels were tied in place prior to the foundation pour and block installed after the pour, which I'm inclined to believe since they used open-end block. The wall will be grouted solid, but it's likely they will use low-lift grouting (4'-8" max), in which case the code doesn't require cleanouts.

I've also never seen this before, and honestly I'm a bit surprised given the generally good construction quality where I practice. Overall it doesn't appear to be a life safety issue, but there's a remote possibility it could lead to some cracking near the base of the walls. I'll present it this way to the owner, and if they're willing to accept it I'll let it go. I'm also going to reiterate that the work requires deputy inspection because I'm concerned about what other exotic construction methods this guy has up his sleeve.

 

[haynewp]

If the footing is constructed like designed then I wouldn’t sweat it.

 

[JLNJ]

I think the open blocks are just what the guy had on hand. They look like lintel blocks with the webs knocked out, but I doubt you need to run horizontal reinforcement right above the level of the foundation.

It might make for some ugly coursing at doors and windows (or maybe the guy did it to get ON coursing). If the former, it will look a little dumb at the door and window heads.

 

[dik]

That's not the way I would have done it, but one of the important things about engineering is explaining why things work, when in all reality they shouldn't. It's the most important thing about engineering, IMHO.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik