Is CMU wall fully grouted?

[vmirat]

I'm working a project on an existing cmu building. The as-builts say,

#4 reinforcing steel (fill continuous cells w/ grout) 40" o.c.

There is also a cross section of the wall with a note that says,

8" cmu wall (fill continuous gaps w/ grout)

I'm trying to figure out if the wall is fully grouted or if they only grouted where the rebar is located. Based on the notes above, I could read it either way.

Is there a simple way to determine if the wall is fully grouted without having to do a bunch of drilling? I was thinking of using a hammer to see if the sound would be different, like locating studs in a wall.

 

[fegenbush]

If the wall is still bare (no studs, drywall, etc.) you should only have to drill a maximum of two holes.

1. Drill hole into where a cell would be in the CMU. If you hit air, you are done. If there is grout, continue to step 2.

2. Drill into the adjacent cell. If you hit air here, you know that they only grouted the cells with the rebar. If you hit grout, it is very likely they grouted all the cells.

My money is on grouting only where there is rebar. If it can be interpreted one way, and that way is cheaper, that is what the contractor will do, in my experience.

 

[concretemasonry]

You have to explore a bit. Sound may give some assistance, but a few holes (easily patched) are a more positive indication.

Obviously, the specs say the "continuous cells" must be filled with grout to insure structural integrity and load transfer with the steel.

The note is obviously very vague since it refers to "continuous gaps with grout". Since grout is used to fill voids band not lay masonry units, many block walls could be fully grouted since many block designs do not permit perfect containment of the grout within a "cell" (horizontally or vertically), so there can be many areas with partial filling since the random gaps are not always large enough to guarantee full grouting. In some of the market areas where masonry is used in a progressive manner, there are units used that insure that the units are either 0% or 100% grouted and actually look like the what the designer expects. - Because of the vagueness of grouting, I would definitely make a number of drill inspections and be prepared for a wide range of results.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[vmirat]

Thanks for the responses. Another question. There is no indication of the grade of rebar used in the existing walls. This is a carwash built in 1984. I was going to use 40 as worst case for evaluating the capacity of the wall unless 60 was just so common that 40 isn't used anymore.

 

[SteveGregory]

I would bet on 60ksi.

 

[JD2]

I was told this once but never tried it - If the CMU is exposed on the outside and you have access to a hose, spray water on it. The grouted cells will turn darker than the ungrouted.

 

[Brad805]

I also think you will have solid at the rebar only. The hammer test helps for sure. Regardless how perfect the drawings may seem, it is hit or miss if the trades wanted to follow the drawings or not. I would complete some tests to be sure.

Brad

 

[hawkaz]

1n 1984 most #4 bars were 40 ksi

 

[Ron]

You can use a hammer to detect sound differences. You can also use infrared thermography to check filled cells or magnetic means to locate rebar.

 

[msquared48]

I've used the hammer for years. For me it's been a very good and reliable indicator. I also use a small handheld rebar detector as a supplement for location. It won't tell you the size of the bar or the grade though.

If there are any doors that were cut in after the fact, you can always check the jamb and header for an indication of the bar size.

As for the grade, I would bet on Grade 40 in 1984. If you want to, you could confirm this with George Orwell.

Mike McCann
MMC Engineering

 

[vmirat]

I'll try the hammer thing and see how that goes. I'm also going to use grade 40 as worst-case.

Mike, not sure if George would be of any help at this point!

Thanks for everyone's help. Merry Christmas and Happy New Year, one and all!