How should grout be specified?
As it relates to specifying grout for masonry, the MIM recommends the following:
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Grout shall be specified in conformance with ASTM C476. Conventional grout should be
specified by proportions instead of by strength requirements.
The minimum specified compressive strength of grout (f’g) shall be 2,000 psi (13.79
MPa), unless the structural design assumptions require a higher specified compressive
strength of clay masonry or concrete masonry (f’m). In that case, the grout compressive
strength shall equal or exceed f’m. Compressive strength shall be tested in accordance
with ASTM C1019, when required.
Fine or coarse grout are permitted, though the MIM recommends specifying coarse
unless there is a known issue with grout space or clear cover due to reinforcement
congestion or unit size. Coarse grout is the most common in the Michigan market and is
generally less expensive on a unit basis.
If conventional grout is specified by proportions, which the MIM recommends, then
compressive strength testing of grout specimens is not required during construction
unless the design requires an f’m of greater than 2,000 psi (13.79 MPa). TMS 602 Table
4, Minimum Special Inspections, requires periodic verification of the proportions of siteprepared grout for Level 2 and Level 3 Quality Assurance.
TMS 402 (2016) Requirements
TMS 402 Section 6.1.3.5 states that, “Reinforcement embedded in grout shall have a thickness
of grout shall have thickness of grout between the reinforcement and masonry units of not less
than 1/4 in. (6.4 mm) for fine grout of 1/2 in. (12.7 mm) for coarse grout.”
For Strength Design of Masonry, TMS 402 Section 9.1.9.1.2 Grout compressive strength states,
“For concrete masonry, the specified compressive strength of grout, f’g, shall equal or exceed
the specified compressive strength of masonry, f’m, but shall not exceed 5,000 psi (34.47MPa).
For clay masonry the specified compressive strength of grout, f’g, shall not exceed 6,000 psi
(41.37 MPa).”
In the 2022 edition of TMS 402, the grout compressive strength requirements were moved to
Section 4.3, and thus apply to masonry designed under both the Allowable Stress Design and
Strength Design methodologies. The grout compressive strength requirements are located in
Table 4.3.1 of the TMS 402 (2022).
TMS 602 (2016) Requirements
TMS 602 Article 1.5 B states that the following must be submitted for each grout mix:
1) Mix designs indicating type and proportions of the ingredients according to the proportion
requirements of ASTM C476, or
2) Mix designs and grout strength test performed in accordance with ASTM C476, or
3) Compressive strength tests performed in accordance with ASTM C1019, and slump flow and
Visual Stability Index (VSI) as determined by ASTM C1611/C1611M.
TMS 602 Article 1.6A Testing Agency’s services and duties and Table 4 – Minimum Special
Inspection Requirements require that, as masonry construction begins, periodic verification of
the proportions of site-prepared grout is required for Level 2 and Level 3 Quality Assurance.
TMS 602 Article 2.2 Grout Materials states,
2.2 A. Unless otherwise required, provide grout that conforms to the requirements of ASTM
C476.
2.2 B. When f’m exceeds 2,000 psi (13.79 MPa), provide grout compressive strength that equals
or exceeds f’m. Determine compressive strength of grout in accordance with ASTM C1019.
2.2 C. Do not use admixtures unless acceptable. Field addition of admixtures is not permitted in
self-consolidating grout.
TMS 602 Article 3.5 C Grout pour height states, “Do not exceed the maximum grout pour height
given in Table 6.”
Table 6 – Grout space requirements
Grout Type1
Maximum Grout
Pour Height, ft (m)
Fine
Fine
Fine
Fine
Coarse
Coarse
Coarse
Coarse
1 (0.30)
5.33 (1.63)
12.67 (3.86)
24 (7.32)
1 (0.30)
5.33 (1.63)
12.67 (3.86)
24 (7.32)
Minimum Clear
Width of Grout
Space2,3, in. (mm)
3/4 (19.1)
2 (50.8)
2 1/2 (63.5)
3 (76.2)
1 1/2 (38.1)
2 (50.8)
2 1/2 (63.5)
3 (76.2)
Minimum Clear Grout Space
Dimensions for Grouting Cells of
Hollow Units3,4, in. x in. (mm x mm)
1 1/2 x 2 (38.1 x 50.8)
2 x 3 (50.8 x 76.2)
2 1/2 x 3 (63.5 x 76.2)
3 x 3 (76.2 x 76.2)
1 1/2 x 3 (38.1 x 76.2)
2 1/2 x 3 (63.5 x 76.2)
3 x 3 (76.2 x 76.2)
3 x 4 (76.2 x 102)
1 Fine and coarse grouts are defined in ASTM C476
2 For grouting between masonry wythes
3 Minimum clear width of grout space and minimum clear grout space dimensions are the net dimension of the space
determined by subtracting masonry protrusions and the diameters of horizontal bars from the as-built cross section of the
grout space. Select the grout type and maximum grout pour height based on the minimum clear space.
4 Minimum grout space dimension for AAC masonry units shall be 3 in. (76.2 mm) x 3 in. (76.2 mm) or a 3 in. (76.2 mm)
diameter cell.
As noted in Footnotes 2 and 3, the minimum width of grout space is used when the grout is
placed in collar joints, where the minimum cell dimensions are used when grouting cells of
hollow masonry units, including consideration of vertical alignment of the cells. The grout space
dimensions are smallest clear dimensions, considering projections or obstructions into the
grout space and the diameter of horizontal reinforcement. This is illustrated in TMS 402 (2016)
Figure CC-3.2.1, which has been copied below for reference:
ASTM C476 Requirements
ASTM C476 covers two types of grout, fine and coarse grout, for use in the construction of
masonry structures. Conventional grout is specified by (1) proportions or (2) strength
requirements.
Section 4 Grout Type and Proportions states:
4.1 Type – Grout type shall be specified as fine or coarse.
4.1.1 Fine grout shall be manufactured with fine aggregates.
4.1.2 Coarse grout shall be manufactured with a combination of coarse and fine
aggregates.
Note: Building code provisions and grout space dimensions should be reviewed when selecting grout type
or types.
4.2 Proportions of Ingredients – Proportions shall be determined as follows:
4.2.1 Conventional Grout – Proportions shall be determined by one of the following
methods:
4.2.1.1 Requirements of Table 1.
4.2.1.2 Specified Compressive Strength – Proportions established by 28-day
compressive strength tests in accordance with Test Method C1019 that equal or
exceed the specified compressive strength. The grout shall be mixed to a slump
of 8 to 11 in. (200 to 280 mm) as determined by Test Method C143/C143M and
shall have a minimum compressive strength of 2000 psi (14 MPa) at 28 days.
Table 1 Conventional Grout Proportions by Volume
Type
Parts by
Volume of
Cement
Parts by Volume
of Hydrated Lime
or Lime Putty
Fine Grout
1
0 – 1/10
Coarse Grout
1
0 – 1/10
Aggregate, Measured in a Damp, Loose Condition
Fine
2 1/4 to 3 times the sum
of the volumes of the
cementitious materials
2 1/4 to 3 times the sum
of the volumes of the
cementitious materials
Coarse
1 to 2 times the sum of
the volumes of the
cementitious materials
Resources:
Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for
Masonry Structures, 2016. The Masonry Society.
ASTM Standard C476, “Standard Specification for Grout for Masonry,” ASTM International,
West Conshohocken, PA, 2020.