Chips Off the Old Block -- Tooling Mortar Joints

JNX-clusives

Chips Off the Old Block

and other ruminations about masonry, by

Larry D. Jenks

Tooling Mortar Joints
Before we get too far into the topic of tooling mortar joints, let's pause for a moment to remind ourselves why we even care about mortar joints. Of course, mortar joints will affect the appearance of our masonry walls, so we obviously need to pay attention to them for that reason.

But more importantly, the mortar joints are the first line of defense against water penetration. To reduce water penetration through the wall, there is no substitute for the proper filling of the mortar joints. 


Improperly filled joints... 

• reduce masonry strength 
• result in leaky walls 
• are susceptible to freezing and thawing damage 
• contribute to disintegration and cracking
• reduce sound insulation
• contribute to corrosion of embedded steel elements 
• may contribute to disintegration and cracking due to water penetration and subsequent freezing and thawing.

Figure A: Tooling a concave mortar joint

If integral water repellent is being used, as it will be for most single-wythe walls, the water repellent will reduce the absorptivity of the block, so tooled and compressed joints become even more critical. Integral water repellents make masonry materials hydrophobic, thereby significantly decreasing their water absorption and wicking characteristics. While these admixtures can limit the amount of water that can pass through units and mortar, they have little impact on moisture entering through relatively large cracks and voids in the wall. Therefore, even with the incorporation of integral water repellents, proper detailing of control joints and quality workmanship to preclude beeholes and unfilled or inadequate mortar joints is still essential. 

More on Tooling Mortar Joints

Filling Mortar Joints

A Specification Section on Procedures for Laying Unit Masonry
As I discovered last time when I searched YouTube for videos showing the proper techniques for laying masonry, masons may have a different understanding of how various elements of the process should be carried out. The ways that they have been doing things for a generation or two may not be exactly what you are looking for in order to attain good moisture penetration resistance. A section in the masonry specifications describing the procedure for "Laying Walls and Partitions" can help. Such a specification could read: 

A. Laying Procedure: 

1. Hollow Units: In starter courses and elsewhere as noted, lay units fully bedded in mortar under both shells and webs. Other units shall be laid with fully bedded face shells, but mortar shall extend through the unit on web edges where anchors or ties occur. All head-joints, except in control joints requiring a control joint key, shall be filled solidly with mortar for a distance in from the face of the unit not less than the thickness of the longitudinal face shell. Place mortar on webs where required to contain grout in partially grouted walls. 
2. Solid Units: Spread the mortar bed full width and relatively smooth. Do not furrow. Do not fill head joints by slushing, instead butter the end of each unit with mortar and shove it into place to completely fill the head joints.

During inclement weather, tops of unfinished walls must be covered at the end of the work day. The cover should extend two feet down both sides of the masonry and be securely help in place. After completion of the walls, immediately install the wall cap to prevent excessive amounts of water from directly entering the masonry.

Bibliography

International Masonry Institute

www.imiweb.org

TECHNICAL NOTES on Brick Construction 7The Brick Industry AssociationWater Penetration Resistance - Design and Detailingwww.gobrick.com

TECHNICAL NOTES on Brick Construction 7BThe Brick Industry AssociationWater Penetration Resistance - Construction and Workmanship www.gobrick.com

Mortar Joints -- How Full is Full?

Rocky Mountain Institute

http://www.rmmi.org/ 

Rain Resistant Architectural Concrete MasonryNWCMA (Northwest Concrete Masonry Association)TEK Note November 2000http://www.nwcma.org/ 

NCMA TEK 19-2ADesign for Dry Single-Wythe-Wythe Concrete Masonry WallsNational Concrete Masonry Association 1998http://www.ncma.org/Pages/default.aspx 

NCMA TEK 3-8AConcrete Masonry ConstructionNational Concrete Masonry Association 2001http://www.ncma.org/Pages/default.aspx 

NCMA TEK 19-07Characteristics of Concrete Masonry Units with Integral Water RepellentNational Concrete Masonry Association 2008http://www.ncma.org/Pages/default.aspx 

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