PROPERTIES OF SHIMS

The most important properties of shims are their ability to separate and adjust the spacing between items in construction. The thickness of a shim is chosen according to the depth of the space it is intended to maintain. The footprint is chosen according to handling and load distribution needs. A permanent shim should be sized to fit entirely within the joint, behind the finish materials and without interfering with any sealant that can be installed in the joint. Typically withstanding ten tons of compressed force, lightweight "U" shaped Bridge Fasteners are designed to fit around bolts and anchors. They are often used for aligning windows and curtain wall, for example. Their rounded shape allows greater flexibility in aligning the shim with no protruding corners. They are offered in eight sizes and four color-coded thicknesses. Supplied bulk packed in boxes.

SHAPE

• Flat Blocks are used for simple conditions where spaces will be later filled with grout or sealant, such as joints in tilt up concrete panel construction.

• U-Shapes fit around bolts and are useful for many systems of construction, including precast concrete cladding and curtain wall systems.

• Wedges are used anywhere wood is inappropriate and a gap needs filling.

SPECIFYING SHIMS

GENERAL

Shims are considered "accessories" and are appropriately specified with other parts of each building system.

PRODUCTS

Review the criteria listed above and include specification necessary to assure proper performance for project conditions. It is usually unnecessary for the specifier to require a specific shape or size of shim. When load bearing is important, specify that shims shall be solid and that hollowed profiles will not be accepted.

EXECUTION

Execution requirements for shims should also be results-oriented. Example requirements may include:

• "Shims shall not remain permanently exposed to view, sun, or weather."

• "Hold shims back from face of panel at least two times joint width." (For mortar or grout joints)

• "Shims shall not intrude into depth required for sealant and backer rod specified." (For sealant joints)

• "Remove shims progressively as sealant is installed" (For movement joints in stone flooring)

• "Install shims to shed water. Horseshoe and keyslot shim openings shall face down." (For shims in cladding, outside the weather barrier)

• "Do not shim [secondary structural members] [cladding members] more than [1/2 inch] without written acceptance by [Architect ][Engineer]."

IMPACT RESISTANCE

Impact resistance is the shims ability to withstand a sudden force, usually over a small area, without breaking or crushing. Impact resistance is often required for shims used to install glazing systems. When high impact resistance is required, high-impact polystyrene or PVC shims are often required.

RESISTANCE TO BRITTLE FAILURE

If very cold temperatures are expected during construction or the service life of the shim, brittle failure needs to be considered. The temperature at which cracking occurs should be below the expected ambient temperature. In some conditions, the shim can be retained in the joint with adhesive, making cracking less of a concern.

EASE OF USE

• Color Coding: Shims are colored by thickness, simplifying and speeding selection and inspection in the field.

• Stackability: Stackable shims can fit virtually any size joint, from 1/32" to 6", by combining standard sizes. Grove Structural Shims can be banded together. They also are readily heat-welded at the edges, forming a permanent stack custom-built for the joint required.

• Fitting: In order to fit joint requirements, shims should be available in a variety of widths and in shapes that are easily cut to size. Grove Structural Shims offers 6-inch and 8-inch wedge shims that are notched to be snapped at convenient lengths and depths.