Do you need to fill every hollow core in a concrete block wall? Not always. The answer depends on whether the wall holds steel reinforcement and on what the design and the code require.
Not always. Concrete block cores are filled, or grouted, to add strength, and TEK 03-02A says this applies to both reinforced and unreinforced walls. CMHA/NCMA TEK 03-02A says partially grouted walls get grout only in spaces with steel, while solidly grouted walls have every core filled. The adopted code and engineer’s drawings decide which applies.
What Grouting a Block Core Means
Grouting means filling the hollow cores of a concrete masonry wall with grout. The sources used for this page call the material grout, so this page does too. CMHA/NCMA TEK 03-02A says grout is used to give added strength to both reinforced and unreinforced concrete masonry walls.
The question is not only whether to fill, but which cores to fill. A wall can be grouted in several ways, and each way has a different set of rules. The two TEK sheets read for this article separate those ways clearly.
If you are still choosing units, start with the block sizes and dimensions guide. Core layout follows from the unit you pick, so settle the unit first.
Solid Grouting Versus Partial Grouting
A wall is solidly grouted when all of its cores are grouted, with or without reinforcement. A wall is partially grouted when grout goes only into the wall spaces that contain steel reinforcement.
| Grouting type | Which cores get grout | Steel reinforcement |
|---|---|---|
| Solid | All cores, with or without reinforcement | May or may not be present |
| Partial | Only wall spaces containing steel reinforcement | Must be present in each grouted space |
The sketch shows the three states from the table. Gray webs are the block shell, teal cores hold grout, and the coral bar marks vertical reinforcement. The proportions are not measured, so use the sketch for the idea only.
How the Planning Estimate Works
The concrete block fill calculator estimates grout volume from wall area, a fill rate and a waste allowance. It does not decide whether a core must be filled. The tool page says fill rates vary with the block maker and the wall shell thickness, so confirm them with your blocks and specification.
Here is the tool’s default case: a solid 8 in wall, 20 ft long and 8 ft high, with no openings. The fill rate in this case is the tool’s planning rate, not a published standard.
- Wall area. 20 ft x 8 ft = 160 sq ft, with no openings to subtract.
- Grout before waste. 160 sq ft x 0.30 cu ft per sq ft = 48.0 cu ft.
- Add 10 percent waste. 48.0 cu ft x 1.10 = 52.8 cu ft.
- Convert to cubic yards. 52.8 cu ft / 27 = 1.956 cu yd, or about 1.96 cu yd when rounded.
Each step is simple arithmetic, and the result depends entirely on the planning rate in step two. A different block or a partial wall needs a different rate, so check the rate against your supplier before you order.
Grout Slump and Aggregate Rules
Grout must have a slump between 8 and 11 inches (203 to 279 mm) at the time of placement, according to TEK 03-02A. TEK 09-04A says the Specification for Masonry Structures and ASTM C476 both require that same range.
TEK 09-04A also sorts grout by aggregate. The two types differ in the size of the largest particles allowed.
- Fine grout. Sand smaller than 3/8 in (9.5 mm) is the only aggregate.
- Coarse grout. Sand plus pea gravel smaller than 1/2 in (13 mm), or other acceptable aggregate.
The sources here do not say which type your wall needs. The specification and the engineer decide that choice, so ask before the mixer arrives.
Pour Height, Cleanouts and Consolidation
TEK 03-02A says the wall is constructed to a maximum pour height of 24 ft (7,320 mm) with the required cleanouts. The diagram below shows that limit and where the cleanout sits.
Cleanouts must sit at the bottom of all cores that contain dowels or vertical reinforcement, according to TEK 03-02A. The excerpt used here does not give a reason for that rule, so this page does not add one.
Consolidation eliminates voids. TEK 03-02A says this helps ensure complete grout fill and good bond in the masonry system.
When the Code and Drawings Decide
The design and the adopted code decide whether a core must be grouted. The sources read for this page do not set that rule, so this page does not state one.
Before you order, confirm the following with the engineer or the project documents.
- Code. The adopted code and edition named in the project documents.
- Drawings. Which cores hold steel and which cores the drawings require to be grouted.
- Cleanouts. Locations at the base of every grouted core with dowels or vertical steel.
- Grout. Fine or coarse type, and the 8 to 11 inch slump range in the specification.
- Lifts. The maximum pour height and the lift plan for the wall.
- Rates. The block maker’s fill rates, checked against the calculator’s planning rate.
If the drawings and your estimate do not match, ask the engineer before ordering grout.
Use the block fill tool for a planning estimate, then confirm the fill rate with your engineer. For the block count and mortar, the concrete block calculator covers the units.
FAQs About Filling Concrete Block
Do you have to fill every hollow core in a concrete block wall?
Not always. A partially grouted wall gets grout only in spaces that contain steel reinforcement, under TEK 03-02A. Whether other cores may stay empty depends on the adopted code and the engineer’s drawings.
When is a concrete block wall considered solidly grouted?
A wall is solidly grouted when all of its cores are grouted, with or without reinforcement, according to TEK 03-02A. Solid grouting does not depend on whether steel is present.
What slump range does masonry grout need?
TEK 03-02A requires a grout slump between 8 and 11 inches (203 to 279 mm) at placement. TEK 09-04A says the Specification for Masonry Structures and ASTM C476 require the same range.
What is the difference between fine and coarse grout?
Fine grout uses sand smaller than 3/8 in as its only aggregate. Coarse grout adds pea gravel smaller than 1/2 in, or another acceptable aggregate, to the sand. TEK 09-04A gives both definitions.
What is the maximum pour height for grouted block?
TEK 03-02A gives 24 ft (7,320 mm) as the maximum pour height when the required cleanouts are provided. Check the specification and engineer’s drawings for the lift plan on your project.
Where do grout cleanouts go?
TEK 03-02A says cleanouts must be at the bottom of all cores that contain dowels or vertical reinforcement. The excerpt used here does not give a reason for the rule.
Why does consolidation matter for grouted block?
According to TEK 03-02A, consolidation eliminates voids. That helps ensure complete grout fill and good bond in the masonry system.
Sources and Further Reading
References Used in This Article
- CMHA, “Grouting Concrete Masonry Walls” (TEK 03-02A), accessed 2026-11-11.
- CMHA, “Grout for Concrete Masonry” (TEK 09-04A), accessed 2026-11-11.
Grout rules come from the design and the adopted code, and local practice decides the details. This page explains the terms and what the CMHA/NCMA sheets say. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-11-11.
Shakeel Muzaffar is the Founder and Editor-in-Chief, with over 15 years of experience in digital publishing and online tool development. He oversees editorial quality and formula verification to ensure accurate, practical, and easy-to-use calculators.