| Property, Units | ASTM Test Method | Polypropylene | Hi-Impact Polystyrene | ABS |
|---|---|---|---|---|
| Tensile Strength at Break, psi | D638 | 4500-6000 | 5200-7500 | 3,500-8,000 |
| Elongation at Break, percent | D638 | 100-600 | 1.2-2.5 | 1.5-2.5 |
| Tensile Yield Strength, psi | D638 | 4,500-5,400 | 3,100-4,400 | 5,700 |
| Compressive Strength (Rupture or Yield) psi | D695 | 5,500-8,000 | 6,000-8,000 | 6,500-7,500 |
| Flexural Strength (Rupture or Yield), psi | D790 | 6,000-8,000 | 10,000-14,600 | 10,500 |
| Tensile Modulus, 103, psi | D638 | 165-225 | 330-475 | 375 |
| Compressive Modulus, 103, psi | D695 | 150-300 | 480-490 | 130-310 |
| Flexural Modulus, 103, psi | D790 at 73ºF D790 at 200ºF D790 at 250ºF | 170-250 50 35 | 380-490 | 380 |
| Izod Impact, ft-lb/in of notch (1/8-in specimen) | D256A | 0.4-1.2 | 0.35-0.45 | 2.00 |
| Hardness: Rockwell | D785 | R80-102 | M60-75 | 112 |
| Hardness: Shore/Barcol | D2240/D2583 |
For a mobile-friendly plastic shim material properties table, please download our material properties PDF.
Understanding the role of the shim in the system it serves allows the design professional to choose the best product. Temporary shims need to meet basic requirements for size, strength, and ease of use. Permanent ones are subject to more extensive requirements to ensure the continued performance of materials they support and separate.
Traditionally, shims have been made of wood and metal because these materials are easily shaped and often found as scrap on job sites. Wood is often used in wood-framed construction and cabinetry, but it is subject to crushing and rot. Steel is the material of choice in much structural steelwork, but can cause rust damage in other systems where moisture may run across it.
Purpose-made plastic shims have made a place for themselves in faster-paced construction. Requiring little or no shaping, and available in consistent thicknesses and material properties, plastic shims save labor time. Since plastic shim materials can be made stronger than wood, more dimensionally stable than steel, and resistant to moisture and microbes, it can be the material of choice for many building systems.
Find more information on comparing different shim materials.
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.
Choose compressive strength that can withstand the expected dead loads, construction loads, and live loads that the shim will carry. Shims carry large loads over their small footprints during construction, before the final fastening is complete, so including a factor of safety is a good idea.
See the shim Material Properties Chart above for compressive strengths available with different materials. Compression test reports are also available.
Shims with compressive strength adequate to the task at hand won’t deform under the expected loads. By contrast, materials like wood suffer from “creep” (deformation overtime), forcing installers to guess at the final compressed thickness when selecting shims.
When choosing shims based on compressive strength and creep prevention, plastic solid shims offer advantages over hollow shims or wood shims. It is worth noting that creep can be a problem with high-density polyethylene when used as permanent support.
Resilience is the ability of a shim to compress under load, then return to its previous shape when the load is released. It is expressed in Rockwell Hardness and Shore D Hardness. Resilience is often required in glazing systems and other panelized cladding systems. When materials being separated are brittle, like glass or stone, the shim’s job is to absorb some of the load imposed by movement of the system. Consult Glass Association of North America (GANA) standards for glazing systems and manufacturer’s recommendations for other materials.
Impact resistance is the shim’s 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.
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 solid shim can be retained in the joint with adhesive, making cracking less of a concern.
Shims that will remain permanently within an assembly may be required to be fire-resistant. In these cases, the following criteria may apply:
A compatible plastic shim material does not react with or chemically affect the materials it touches. It will not transfer color or oils, produce stains, nor corrode the item being shimmed. It will also be unaffected by the adjacent materials. Polypropylene and polystyrene both excel in this feature, being unaffected by most construction materials. In fact, inert plastics are often used to separate dissimilar materials that would otherwise react with each other: separating aluminum from concrete, for instance, or aluminum from steel.
Inert plastic shims can remain in place indefinitely, without contributing nutrients to unwanted organisms like mold or insects. Unlike wood and wood products, plastic solid shims do not rot or degrade.
Shims can act as a thermal break between conductive materials. Measured in BTU (British Thermal Units) per hour or in Watts, the thermal conductance of plastic shim materials is lower than that of aluminum or steel. For example, shims can help reduce thermal transfer from cladding materials such as precast concrete into structural elements.
In general, shims are used as alignment aids to hold objects in place until they are permanently attached with fasteners, welds, grout, adhesive, or another method.
For additional information on the common uses of plastic shims, take a look at our article Common Types of Construction Work Using Shims.
It is important to know how to accurately specify the shim properties necessary during the ordering process based on your application. Learn more how to best specifying shims.
When selecting a plastic solid shim, your manufacturer choice is equally important. If you are looking for a plastic shim expert, look no further. Grove Shims is here to help you level objects easily and efficiently with our high-quality color-coded plastic shims.
Please contact us for more information about our solid plastic shims. Our in-house experts are available to assist you.
