Allowable mortar in grouted solid cells. 1

[CBlaker114]

So... I got a question from the building department that I've never encountered in response to our plan submittals. One of the comments on our structural plans read as follows, "How much mortar droppings from laying cmu will be allowed at the bottom of the cmu cell to be grouted?" Anyone ever seen this comment or make a point of addressing this in their plans? Is this actually addressed in the ACI 530 or FBC? (Project is in Florida)... another reason why I don't know if this is a legit comment... Florida... don't even get me started....

 

[mike20793]

I didn't see any specific requirement in the masonry code specifications. I would think that unless this is a propped cantilever or cantilevered wall or highly axially loaded wall, it's not really an issue since flexural stresses are almost zero at the base a wall.

 

[JoshPlumSE]

I have never gotten this comment before. But, I know this is one of the thing the DSA (division of state architect) looks for here in California whenever you're getting a plan check done on school work. I believe they even require the bottom rows of block to have the face cut off so that they can inspect it. The idea is that the mortar trimmings will accumulate and may not allow the grout to flow and fully grout all cells.

Not really my area of expertise though.... Hopefully you've got some folks with DSA experience that can respond in greater detail.

 

[hokie66]

Where I am, it is standard practice to require cleanout of the loose mortar at the bottom. But even then, sometimes "standard practice" is not followed unless the engineer insists.

 

[BUGGAR]

We use cleanouts in all grouted cells in SoCal. Usually this is inspected masonry and inspectors look for it; they carry truck mirrors to look into each cell. You have to break off the mortar fins inside the cells to be grouted also. I think there is a height limitation for this requirement?

 

[UcfSE]

Respond with "zero".

 

[Ingenuity]

These cleanout/grout inspection 'windows' are common in my area:

 

[Ron]

UcfSE is correct!

 

[darthsoilsguy2]

low-lift grouting (under 5 ft) does not require cleanouts per code and above does. i've never found any explicit description of WHY 5 ft is the magic number. i ended up assuming that there will be some mortar droppings which occur during laying or hardened mortar knocked in during rebar placement.... and 5' feet was agreed upon by Masonry Standards Joint Committee as a height where cells should be clean enough at the base to get quality work without killing production and at that height you can still see the base with a flashlight for judgment calls on making a cleanout.

i would want to understand why the building dept is asking this specific question. also, what will the AHJ's role be during construction with regards to inspections? will there be 3rd party special inspections? or is the AHJ more involved in field inspections?... most bldg officials will not climb scaffolding. saying "none" might encourage them to demand cleanouts for low-lift grouting to confirm that your criteria is met if there is no 3rd party SI. it just seems like an odd question to ask if there is no field involvement...

caveat emptor it has been 4 years since i've dealt with masonry and codes change every 3 so i'm 2 cycles back....

 

[concretemasonry]

Since proper grout is a very wet material (8"-11"), there is ample moisture to create a good bond with the masonry materials (block, brick and mortar). This is supported with the requirement for the rate of grouting height for high lift grout where there is timing for full height grouting where there is opportunity top "top off" the grout after it has had time to consolidate after the excess water has been absorbed to create a uniform masonry structure (block, mortar and grout).

The 5' dimension is intentionally not a modular dimension for masonry because of the varieties (heights) of masonry units used internationally.

Some advance masonry areas use properly shaped units that allow maximum wall strength for both fully reinforced and partially reinforced construction. - The units are configured so there are uninterrupted grout cores for reinforcement and gout placement. - No obsolete 2 core units with flush ends.

I have seen 20 story buildings built with 6x8x16 CMUs that were partially reinforced (reinforcement at modules of 8", 16", 24" or 32". There was no routine inspection during construction, but random inspection using TV cameras that were dropped into the cores and if there was excessive debris, the wall was replaced.

These codes requirements were written by engineers that work for the owner/developer/contractor that had to prove construction quality to the governmental authority. - This was in a different part of the world where they use the ACI 530 as the standard for masonry design.

Dick

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