What is "Block Fill" for concrete block basement?

8 years ago

We are building a house on a basement. We wanted poured concrete like all of our previous houses, but that is not common around here and folks want big $ to do it. So we are doing a block basement. Our budget has a $4k line item for "block fill". Can someone explain what this is? I assumed they would use some form of high slump concrete to fill all the block basement walls. When they did the work, they only filled some of the blocks. Is that typical? Maybe my expectations aren't aligned with industry standards. All of my previous homes had poured concrete basements, so this is a first for me. I'm going to speak with my builder about it, but trying to get a better understanding of what "block fill" is before I start the conversation with him.

Featured Answer

User

8 years ago

last modified: 8 years ago

Depending on the height of unbalanced fill, a CMU (concrete masonry unit) foundation wall must have a certain amount of vertical reinforcing. That consists of vertical rebars in some of the cavities. These cavities are then filled with a flowable grout rather than concrete or mortar so that the entire core is completely filled without voids. The reinforcing should meet the minimum requirements of the building code or what an engineer specifies.

CMU cores that are to be grouted should be free of excessive mortar protrusions and mortar droppings at the base. Clean-out/inspection holes at the base of the reinforced cores will facilitate the removal of excessive mortar droppings, and confirm that grout has reached the bottom of the core. The holes may be waived by the designer or inspector when the contractor has demonstrated acceptable performance or where the walls are not structurally critical.

This is in addition to horizontal joint reinforcing.

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Comments (6)

PRO
GN Builders L.L.C
8 years ago
What they basically want to do is fill the block cavity.

Whatever block they already filled they did that for tone reason or another and it's probably per plan detail, like piers, first-course block, etc
Becky thanked GN Builders L.L.C
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Becky
Original Author
8 years ago
That consists of vertical rebars in some of the cavities. These cavities are then filled with a flowable grout rather than concrete or mortar so that the entire core is completely filled without voids.

So if I'm reading this correctly, not all the voids need to be filled, only certain ones. Right? The material used did look more like grout than a high sump concrete as I had envisioned.

The reinforcing should meet the minimum requirements of the building code or what an engineer specifies.

There are no building permits required in my neck of the woods; therefore no inspections by anyone other than myself, husband and GC. We (hubby and I) have no experience with CMU, so I'm trying to educate myself on the fly since I had assumed they wold be filling all voids.

Whatever block they already filled they did that for tone reason or another and it's probably per plan detail, like piers, first-course block, etc

The bock fill isn't specified on any of the plans. Building permits are not req'd here, so the plans don't show as much info as they would if we were in a larger metro area.
User
8 years ago
What will the dimension be between the basement floor slab and the exterior finished grade?

The spacing of vertical rebar (in filled cores) in the most common US residential building code varies from 16" to 72". That's every 2 cores to every 8 cores apart.

As long as the grout is thin enough to be poured into the cores from the top of the wall it should be OK. Its usually pumped through a hose from a mixing truck.
PRO
GN Builders L.L.C
8 years ago
The filled cavity with rebar acting as wall reinforcement, I guess they didn't put any piers in so instead of piers they did that to break up the wall span.
User
8 years ago
I think a buttress is used when the foundation wall thickness and reinforcement is so great the buttress will reduces the cost. The foundation wall will span from the footing to the upper floor after the floor framing is installed so the relative timing of the backfill and floor installation is a major design factor.