Tips and Techniques for Tuck-pointing Brick and Masonry
Masonry products and materials are by far the most durable available for construction, especially when installed by quality contractors who employ trained, skilled craft workers. Mortar joints are serviceable for 35 years or more when properly installed. The masonry units themselves, typically brick or concrete block, may have a serviceable life of 100 years or more. As with any building product continuously exposed to the elements, masonry is subject to weathering. Acids in the rain, seismic movement, building settlement, freezing and thawing cycles, impact damage, and dirt take their toll. When visual inspection reveals that the mortar joints are cracking or otherwise deteriorated, restoration is necessary to help maintain the integrity of wall systems and products. Tuck-pointing is an effective way of decreasing water entry into masonry.
Definition of Tuck-pointing
Tuck-pointing is the term most often used to describe the process of cutting out deteriorated mortar joints (Figure A)
in masonry walls to a uniform depth and filling in those joints with fresh mortar. Tuckpointing, however, is only the most common of three terms often used inter-changeably in the United States and Canada to describe the complete process of restoring older masonry joints. The other two are re pointing and pointing. In some areas, re-pointing or pointing may mean the same as tuck-pointing. But they may also mean only the placing of plastic mortar in joints without first removing damaged mortar.Tuck-pointing isn’t reserved for older buildings. New masonry walls may need to be tuck pointed when bee holes or voids appear in the finished joint, or when the joints have an incorrect or improperly tooled finish or when the color of the joints is incorrect. In this guide and in general, tuckpointing to refers to the process of removing deteriorated mortar joints and replacing them with new mortar.
Procedures for Tuck-pointing Preparation
Mason contractors who successfully bid tuck pointing jobs know that to be competitive, they have to employ craft-workers who have been trained in masonry restoration and who have relevant experience. The mason contractor must determine the scope of the work. Tuck pointing is labor-intensive. To help determine the scope of the work and prepare an accurate bid, the mason contractor needs answers to a number of questions, including:
* Are all the mortar joints on a structure to be tuck-pointed? Or only joints where the mortar has eroded to a particular depth?
* What about areas where there are hairline cracks between the masonry units and the mortar?
* Does the building need to be cleaned before the real condition of mortar joints can be observed?
*Is the mason contractor alone to determine which joints need restoration?
Once these questions are answered, the masonry contractor can accurately determine the area to be tuck pointed and see that it is clearly defined on the bid documents.
It is also important to determine the age of the building being scheduled for tuck-pointing. If it dates back to the early part of this century or is older, more care must be taken in selecting and mixing mortar. It wasn’t until after the 20th Century began that portland cement was combined with the traditional sand and lime to make mortar.
Older mortars without portland cement are far weaker than modern mortars, and have far less compressive strength. A stronger re-pointing mortar deforms less under load than weaker older mortar; which concentrates the load in the area of the stronger mortar. The stress can lead to spalling of the masonry units.
Mortar in older buildings may contain materials to give them texture or an unusual color. These additives include oyster shells, horsehair, carbon black, and others. Oyster shells, if required, can be mixed into new mortar in small quantities. If the mortar needs to be colored, use metallic oxides to match, and not organic chemicals.
The contractor must also decide whether to use power tools, such as saws and grinders, to cut out old mortar. While the mechanical tools are faster than hammers and chisels, the power tools may damage the masonry units surrounding the mortar: Additionally, if an historical building is being restored, saws, grinders and other mechanical tools may not be allowed or, if they are, only if special permits are obtained.
Keep in mind that some of the tools and materials used to tuckpoint masonry can be hazardous. Before pointing masonry, make sure you are wearing the proper protective clothing and safety gear; safety glasses, gloves, and long sleeve clothing are important for your safety. Grinders, hammers, chisels, and even the mortar used to tuck point a wall can cause hazardous conditions for the craft worker. Craft-workers should be properly trained to use the tools and materials needed to perform the task at hand.
Mortar Removal and Replacement
The craft-workers should remove old mortar to a depth of 3/8″ to 1/2″, or until sound mortar is reached. Do not remove mortar in excess of one-third the depth of masonry unit. The profile of the resulting joint should resemble Figure B,
in which the mortar has been cut back to a uniform depth.Dust and debris should be removed from the joint by brushing, rinsing with water or blowing with air. Tuck pointing mortar should be carefully selected. Use pre-hydrated mortar to reduce shrinkage. Mix in the proper additives, if any, to match the color of existing mortar. Here’s how to mix a batch of mortar for tuck pointing:
1. Place all dry ingredients in a tub or mixing box.
2. Thoroughly mix all dry ingredients.
3. Add one-half the amount of water used in new construction.
4. Mix the mortar until it will hold shape when formed into a solid ball. There should be no flow or spread of mortar.
5. Let the mix hydrate for one to two hours.
6. Add more water to make the mix workable, but still relatively stiff, which results in good workability and minimum smearing.
Joints to be tuck pointed should be dampened, but, to make sure the new mortar makes a good bond, the masonry units must absorb all the surface water. A wide variety of tool widths are available to pack mortar into the prepared joints.
Choose a tool with a width slightly smaller than the width of the joint. This keeps mason productivity high and keeps the wall as clean as possible. The craft-workers should force the new mortar into the joints in layers 1/4″ thick or less to reduce air pockets and voids, as in Figure C.
Each layer should be thumbprint hard before the next is applied.
Final joint tooling is done the same way as with new construction. The joint should be tooled to match the original profile. Mortar tags (snots) should be brushed off after the mortar is dry, to reduce smearing.See Figure D.
Commercial cleaning compounds can be used to clean the wall. Visit this guide for Cleaning Masonry Walls. When properly done, tuckpointing provides a strong, waterproof mortar joint that matches the appearance of the original mortar joints, and helps extend the commercial life of the building.
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