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40 Cards in this Set
- Front
- Back
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Mortar is __________
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the bonding agent that ties masonry units into a strong, well-knit, weathertight structure. It secures each of the units into a wall or other building element.
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Mortar serves four functions:
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1. It bonds the units together, sealing the spaces between them.
2. It makes up for differences in sizes of the units. 3. It provides bonding for metal ties or other reinforcing. 4. It providees esthetic (nice to look at) qualities by creating pleasing lines and color effects. |
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Mortar is generally made up of
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cementitious (cement-like) materials together with sand and water.
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cementitious materials
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These materials may include portland cement (Type I, II or III) and hydrated lime (Type S).
Mortar is mostly portland cement. It is a hydraulic material, which means that it hardens under water. |
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cementitious materials:
Specifications for portland cement, covers eight types but only 3 are recommended for use in mortar. They are: |
1. Type I - for general use when the special properties of Types II and III are not needed.
2. Type II - for use when moderate sulfate resistance or moderate heat of hydration is wanted. 3. Type III - for use when high early strength is desired. |
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Cementitious Materials
Which Types of cement are not recommended for masonry mortar unless strengths of masonry constructed with mortar containing such cements are first established by appropriate tests? |
Blended Cement - Types IS, ISA, IP, IPA, S, SA
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Hydrated Lime is _________
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quicklime which has been slaked (formed into a putty by combining with water) beforer packaging. This converts the calcium oxide. *Hydrated lime can be mixed and used immediately. For this reason, it is more convenient to use than quicklime. Quicklime, which is essentially calcium oxide, must be mixed with water and stored for as long as 2 weeks before using.
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Hydrated lime is available in two types:
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S and N.
Only Type S hydrated lime is recommended for masonry mortar because unhydrated oxides and plasticity are not controlled in Type N. |
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Aggregate used in masonry mortar is primarily ____________
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sand. Either natural or manufactured sand may be used.
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Sand that has too few fine particles generally produces ________.
Sand that has too many fine particles results in ________. |
harsh mortars.
weak mortars. |
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Manufactured sand is made by
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crushing stone, gravel or air-cooled blast furnace slag. Natural sand has rounder, smoother particles than manufactured sand. Manufactured sand, with its sharp and angular particle shapes, can produce mortars with workability properties different than mortars made with natural sand.
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Water for masonry mortar is required by ASTM C-270 to be
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clean and free of harmful amounts of alkalies or organic materials. Whether or not the water is potable is of no concern.
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Mortars have two distinct sets of properties:
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1. Plastic (wet) mortar properties:
a. Workability. b. Water retentivity. 2. Hardened mortar properties. a. Compressive strength b. Bond strength. c. Durability. |
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Plastic mortar is
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mortar that has just been mixed. It must be workable. It is uniform, cohesive, and of a consistency that makes it usable. Water content has a great deal to do with the workability of masonry mortar.
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Water retention is the
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ability of the mortar to prevent rapid loss of mixing water to an absorptive masonry unit or to the air on a hot, dry day. Water rention is also related to the ability of mortar to prevent floating of a masonry unit with low absorption. This condition is known as "bleeding." Water retentivity improves with higher lime content and the addition of fine sand. However, the mixture must be within the allowable gradation limits.
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Properties of hardened mortar
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The compressive strength of mortar increases as the cement content is increased. It decreases as lime is increased. Air entrainment also reduces compressive strength. Structural failurees due to compressive loading are rare, but bond strength is generally more critical.
Bond strength is the most significant property of hardened mortar. It is also the most difficult to predict. |
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Bond failure results from the masonry structure being subjected to:
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1. Eccentric (not exactly vertical) gravity loads.
2. Loads from earth pressure, winds, and other lateral (sideways) loads. |
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To insure good bond, mortars hould be placed in final position within
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2-1/2 hours after the original mixing. This is required by ASTM C-270.
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Movement of a masonry unit after the mortar has begun to harden will
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destroy the bond. The mortar will not be plastic enough to reestablish the bond.
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Durability of mortar is measured primarily by its ability to
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resist repeated cyles of freezing and thawing under natural weather conditions. Mortars of high compressive strength have been found to have good durability.
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________ mortar is highly resistant to freezing and thawing and has good durability. The tiny air bubbles absorb the expansive forces of freezing.
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Air-entrained mortar
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Type M Mortar
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Type M mortar has high compressive strength and somewhat greater durability than other mortar types. it is very good for unreinforced masonry below grade and in contact with earth. Structures would include foundations, retaining walls, walks, sewers and manholes.
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Type S Mortar
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Type S mortar is a medium-high-strength mortar. It is intended for use where Type M is recommended but where bond and lateral strength are more important than high compressive strength. Tests indicate that the tensile bond strength between brick and Type S mortar is near the best obtainable with cement-lime mortars. It is recommended for use in:
1. Reinforced masonry. 2. In unreinforced masonry where maximum flexural (bending) strength is required. 3. Where mortar adhesion is the sole bonding agent between facing and backing as it is with ceramic veneers. |
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Type N Mortar
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Type N mortar is a medium-strength mortar suitable for general use in exposed masonry above grade. It is best for parapet walls, chimneys and exterior walls which are subjected to severe exposure. Its principal property is weather resistance.
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Type O Mortar
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Type O mortar is a low-strength mortar. It is suitable for general interior use in non-load bearing masonry. It may be used for load-bearing walls of solid masonry where comrpessive stresses do not exceed 100 psi. In such cases, however, exposures must not be severe. In general do not use Type O mortar where it will be subjected to freezing.
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Type K mortar
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Type K mortar is a very low-strength mortar. It is best used in interior non-load-bearing partition walls where high strength is not needed.
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What type of mortar should be used on cavity walls where wind velocities will exceed 80 mph.
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Type S mortar. For locations where lesser winds are expected, use Type S or Type N mortars.
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What type of mortar should be used on facing tile?
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Any of the first 4 mortar types are acceptable (M, S, N, O). Where 1/4 in. joints are specified, all aggregate should pass through a No. 16 sieve. For white joints, use white portland cement and white sand in construction mortar. An alternate method is to rake all joints to a depth of 1/2 in. and point or grout with mortar of the desired color.
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What type of mortar should be used on tuck-pointing?
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Use only prehydrated mortars. To prehydrate mortar, all the ingredients (except water) should be mixed thoroughly, then mixed again. Use only enough water to produce a dam unworkable mix which will retain its form when pressed into a ball. After one to two hours, add enough water to bring it to the proper consistency. Prehydrated Type N mortar may be used.
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Why type of morar should be used for Dirt Resistance?
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When a dirt resistant and/or stain resistant mortar is required, add aluminum tristearate, calcium stearate or ammonium stearate to the mortar. The amount added should be 3 percent of the weight of the portland cement.
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Mortar may be colored through
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the use of aggregates or pigments. Colored aggregates are preferred. White sand, ground granite, marble or other stone usually have permanent color and do not weaken the bond or mortar.
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For white joints, use
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white sand, ground limestone or ground marble with white portland cement and lime.
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Mortar pigments must be:
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1. Capable of giving the desired color when used in permissible quantities.
2. Sufficiently find to disperse throughout the mix. 3. Non-reacting with other ingredients. These requirements are usually met by metallic oxides. Iron, manganese and chromium oxides, carbon black and ultramarine blue have been used successfully as mortar colors. Do not use organic colors, particularly those containing Prussian blue, cadmium lithopone, and zinc and lead chromates. Paint pigments may not be suitable for mortars either. |
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In discussing coloring mortar with pigments it is recommended to
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use the minimum quanityt of pigments necessary to produce the desired results. Too much may impair strength and reduce durability. Carbon black, a popular pigment will impair mortar strength when used in greater amounts than 2 or 3 percent of the cement weight.
For best results, dry mix the color with portland cement in large controlled quantities. This will ensure a more uniform color than when mixing smaller quantities at the job site. |
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The temperature of the mortar should be between __ and __ degrees F when used.
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70 and 100 degrees F - higher temperatures may cause fast hardenting which will make it more difficult for the mason to produce quality work.
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Why is antifreeze not recommended for use in mortar?
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Such large quantities would be required that it would seriously impair the mortar strength and other properties.
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What is one of the easiest methods of raising the temperature of mortar in cold weather?
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Mortar to which calcium chloride has been added will resist freezing. It should be used in a solution instead of in dry or flake form.
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Masonry should be protected from freezing for at least ___hours after being laid.
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48 hours after being laid. Unless adequate precaustions against freezing are taken, no masonry shall be built when the temperature is below 32 deg. f. on a falling temperature.
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Mortar is generally composed of _________, _______ and _________.
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cementitious (cement-like) materials together with sand and water.
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Mortars have 2 distinct sets of properties: plastic mortar properties and hardened mortar properties. The main properties of plastic mortar are ____ and _________.
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Workability
Water retentivity |
