Small disc grinders are indispensable for repair contractors who do a lot of masonry repointing. These electric-powered right angle grinders allow hardened mortar to be cut out quickly and efficiently. Some people think grinders should never be used on historic masonry because of the risk of damaging the masonry units, while others contend that grinders can be used on historic structures but only in certain circumstances. The soft lime mortar used in older masonry buildings can be removed with hand chisels; in contrast, the very hard mortar used in many modern buildings may require the power of a grinder for removal.
The most popular disc grinders for masonry have 4-, 4 1/2-, or 5-inch cutting wheels. The grinder is powered by a small electric motor. Small disc grinders usually retail for less than $150, and for this reason are considered throwaway tools.
Even the modest projected 6-month life span assumes some minimal maintenance.
For repointing applications, contractors should generally use diamond cutting wheels, which can be more expensive than the grinder. Manufacturers admit that tuckpointers typically buy lower-priced blades and throw them out when they show signs of wear.
When small disc grinders are in constant use, small differences in power output, tool weight, and other features can make a big difference in productivity and safety. In addition, greater awareness of the dangers of silicosis has prompted OSHA to give special emphasis to preventing this very serious disease. When grinding out mortar joints, tuckpointers should wear a respirator or use a dust-collection system. However, many dust-collection devices affixed to small grinders impede the tool user's line of sight, thus creating a threat to safety and quality workmanship.
Features other than price should be considered as well. A tool with a higher amp rating means less effort on the user's part to do the job. Tool weight is another important consideration. A heavier model may cause the operator to become fatigued more easily. But a lighter model may actually be more difficult for some people to control, tempting the operator to apply too much pressure and force the blade into the material. Also a dust-collection device will add more than half a pound to the tool's weight-and sometimes considerably more.
Many features of a disc grinder affect the user's safety and the tool's longevity. Look for a double-insulated grinder, which will have a polarized plug that fits into a polarized outlet only one way. Double insulation eliminates the need for a three-wire grounded power cord and a grounded power supply system. Select a tool that features a "soft start," which reduces the stresses that occur from a high-torque start, and overload protection.
Small angle grinders manufactured by Metabo also come with an automatic safety clutch designed to protect both the user and the motor. The engineering of the motor is primarily what differentiates Metabo grinders from other brands, and this is reflected in the higher price.
All grinders have a cooling system to keep the motor from overheating. Metabo grinders have a fan attachment that prevents foreign matter from reaching the front of the armature.
Because repointing is inherently dirty and demanding on the tool, ease of maintenance is also a crucial aspect of choosing a grinder. Be sure to purchase a tool that can be opened and closed quickly. Consider buying a grinder that permits direct access to the motor's carbon brushes, which need to be replaced periodically.
Tuckpointers should select segmental rim rather than continuous (smooth) rim diamond blades so there is less dust.
Although price often governs the selection of a diamond blade, tuckpointers should realize that if the grinder is used several hours a day, the cost per cut may decline with the purchase of better blades.
When selecting a diamond blade, it is important to know the compressive strength of the material to be cut and the hardness of the aggregate. When purchasing a blade, be sure to check the packaging carefully for appropriate applications and specifications.
The silica dust produced by grinding out mortar joints can be extremely harmful to a worker's health. "Silicosis is a disabling, irreversible, and sometimes fatal lung disease caused by breathing respirable crystalline silica.
Consequently, when using an angle grinder for repointing, it is essential to wear a respirator or use a dust-collection system. OSHA is moving toward requiring the use of dust-collection systems, but many of the dust-collection devices available for small grinders are unwieldy and obstruct the operator's view of the cutting blade and work surface. As a result, most tuckpointers won't use them.
In addition to concerns over dust generation, many other safety issues impact the use of a disc grinder since it is an electrically powered tool with a rapidly spinning blade. The instruction manual will contain general safety guidelines for using a power tool, as well specific safety guidelines for using that particular grinder model.
Basic maintenance must be followed for the tool to last more than a few months.
Small angle grinders may be simple, relatively inexpensive tools, but they do not need to be thrown away so soon.