Components For Mortar And Grout

1) Water
2) Masonry Sand
3) Aggregates For Grout
4) Cement
5) Pozzolanic Materials
6) Lime
7) Admixtures And Colors

1. Water

Water intended for use in mixing mortar should be clean and free of deleterious amounts of acids, alkalies and organic materials. Some potable waters contain appreciable amounts of soluble salts such as sodium and potassium sulfate. These salts may later contribute to efflorescence. Also, a water containing sugar would retard the set. Thus, the water should be fit to drink but investigated if it contains alkalies, sulfates, or sugars.

2. Masonry Sand

The sources of sand can be several. Natural sand is formed by the erosive action of rivers. Such particles are somewhat rounded in shape. They are deposited on flats and on ocean fronts as beach sand. The latter, being subjected to more abrasive wave action, are more rounded. This would make for better workability but probably have a deleterious effect on the strength. Other natural sand sources occur by wind transport, such as blow sand. On the other hand, sand may be manufactured. In this case it would be a product resulting from crushing stone, gravel or blast-furnace slag. This manufactured sand is sharper and more angular and thus may require different amounts of fine cementitious particles to provide the lubrication needed for proper workability. The deleterious substances in sand may be such items as friable particles, lightweight particles, organic impurities or excess amounts of clay or loam. These materials must be removed at the plant before the sand is sent to the job site.

Unfortunately too little concern is often shown for the quality of the sand as expressed in its grading. However the properties of sand have considerable impact upon the workability as well as the strength of the mortar. To provide some sort of guide in this respect, grading limits for mortar sand are spelled out in both ASTM C144 and UBC Standard 24-21. The grading limits from the latter are listed in the tables below.

2.1 Gradation Requirements

Item	Limit
. Passing sieve no. 4	100
. Passing sieve no. 8	95-100
. Passing sieve no. 100	25 max.
. Passing sieve no. 200	10 max

2.2 Gradation for Masonry Mortar.
(UBC Standard No. 24-21)

Graduation specified, percent passing ASTM C144*
Sieve size No.	Natural sand	Manufactured sand
4	100	100
8	95 to 100	95 to 100
16	70 to 100	70 to 100
30	40 to 75	40 to 75
50	10 to 35	20 to 40
100	2 to 15	10 to 25
200	--	0 to 10
*Additional requirements: Not more than 50% shall be retained between any two sieve sizes, nor more than 25% between No. 50 and No. 100 sieve sizes. Where an aggregate fails to meet the gradation limit specified, it may be used if the masonry mortar will comply with the property specification of ASTM C270 (Table 2).

2.3. Gradation Analysis. Since the quantity of sand required to make 1 cu ft. of mortar may be as much as 0.99 cu ft, the sand has considerable influence on the mortar properties. Masonry sand for mortar should comply with the requirements of ASTM C144 (Standard Specification for Aggregate for Masonry Mortar) for masonry construction. These specifications include both natural and manufactured sands. Sand should be clean, well-graded, and meet the gradation requirements listed above.

Sands with less than 5% to 15% passing the Nos.50 and 100 sieves generally produce harsh or course mortars which possess poor workability and result in mortar joints with low resistance to moisture penetration. On the other hand, sands finer than those permitted by the above specifications yield mortars with excellent workability, but they are weak and porous.

For mortar joints that are less than the conventional 3/8-in. thickness, 100% of the sand should pass the No. 8 sieve and 95% the No. 16 sieve. For joints thicker than 3/8 in., the mortar sand selected should have a fineness modulus approaching 2.5 or a gradation within the limits of concrete sands (fine aggregate) shown in ASTM C33.

2.3.1. Limits of Allowable Sand Gradation

Percentage Retained* (natural sand)
Sieve Size	Most Coarse	Ideal	Finest
No. 8	5	2.5	0
No. 16	25	12.5	0
No. 30	30	27.5	25
No. 50	30	35.0	40
No. 100	8	14.0	20
No. 200	2	8.5	15
*Fractional percentage retained between sieves, not total percentage retained.

Established tests and experience prove that good gradation reduces separation and bleeding. It also improves water retention and workability.

2.4. Deleterious Substances. Deleterious substances such as clay and lightweight particles with a specific gravity of less than 2.0 must not be present in harmful quantities. While these materials often will not affect the plastic properties of the mortar and may even improve workability and plasticity, they usually have a detrimental effect on the mortar's strength and durability. The table below shows potentially harmful materials that may be contained in a mortar sand and includes references to ASTM tests that can be used to determine the presence of injurious amounts of such material.

2.4.1. Deleterious Substances

Material	Effect on Mortar	ASTM Test
clay	affects workability, durability, strength and may cause popouts	C-142
lightweight materials (coal, lignite,and others)	same as above	C-40
organic impurities	affects setting and hardening,may cause deterioration and discoloration	C-40
silt and powdered clay	affects workability, durability, and strength	C-117

2.4.2. Alkali-Aggregate Reactivity. There is also the possibility that the sand itself may be chemically reactive with cement or lime, a phenomenon called alkali-aggregate reaction, which may cause abnormal expansion and cracking. Experience records of the sand source usually provide the information needed for the selection of nonreactive aggregates. If a sand is suspected of being chemically unstable and there is no service record, it can be tested for suitability. The American Society of Testing and Materials has two tests and a recommended practice for identifying alkali-reactive aggregates.

The Method of Test for Potential Alkali Reactivity of Cement-Aggregate Combinations, ASTM C227, commonly called the mortar bar test, measures the expansion developed in small mortar bars during storage under prescribed moist conditions. A disadvantage of this test is that three to six months may elapse before conclusions can be drawn.

In the Method of Test for Potential Reactivity of Aggregates (Chemical Method), ASTM C289, known as the quick chemical test, the degree of reaction between a sodium hydroxide solution and a specimen of sand is determined. Conclusions can be reached in two or three days.

Another laboratory method of identifying reactive substances is the Recommended Practice for Petrographic Examination of Aggregates for Concrete, ASTM C295. This involves microscopic examination of sand particles by a qualified petrographer.

The NW Masonry Guide Table of Contents

Masonry Institute of Washington
Washington State Conference of Mason Contractors