6 Best Protective Tarps for Shim Material Storage

Storing shims, whether cedar, plastic, or composite, requires a careful balance of moisture protection and ventilation. When left unprotected on a job site, shims quickly lose their structural integrity, warp, or begin to harbor mold. Choosing the right tarp is an essential step in maintaining the material quality necessary for precise leveling and shimming tasks. Proper storage prevents unnecessary waste and keeps projects running on schedule and within budget.

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Tarpestry 16 Mil Poly Tarp: The All-Around Best

The 16 mil poly tarp hits the “sweet spot” for most general construction applications. It provides enough thickness to handle the abrasion of a busy job site without becoming overly stiff or difficult to fold.

When protecting pallets of shims during a residential roof renovation, this weight prevents the premature tearing often seen with cheaper 6 mil alternatives. It offers a reliable defense against sudden downpours while remaining light enough for one person to maneuver over a stack of materials.

The bottom line is balance. If there is a need for a versatile, cost-effective solution that survives multiple projects, the 16 mil poly is the industry workhorse.

Iron Horse Canvas Tarp: For Breathable Coverage

Canvas stands apart from synthetics because it breathes, which is critical when storing natural wood shims that might still contain residual moisture. Synthetic tarps can create a greenhouse effect, trapping condensation inside and accelerating rot.

In climates with extreme humidity or frequent temperature swings, an Iron Horse canvas tarp allows trapped vapor to escape through the weave. While the fabric will get wet on the exterior, the interior remains dry and, more importantly, airflow is maintained.

This is the preferred choice for high-end wood shims where keeping the material dry is as important as keeping it ventilated. Avoid using canvas in standing water, as it will wick moisture inward over time.

18 oz Vinyl Tarp: Ultimate Weather Protection

When a project stretches over weeks or involves high-exposure environments, 18 oz vinyl is the standard for long-term protection. It is essentially heavy-duty truck tarp material, designed to resist UV degradation and high winds.

If shims are being stored in an open-lot commercial site, this weight ensures the cover stays put and resists puncture from dropped tools or debris. It is waterproof, rot-proof, and far more durable than any standard polyethylene tarp on the market.

While the cost is higher, the investment pays off in saved material costs. Use this for your “long-haul” storage where material will sit exposed to the elements for the duration of a major renovation.

Husky Super Heavy Duty Tarp: Best Value Option

The Husky Super Heavy Duty line represents a pragmatic middle ground for contractors who need immediate, local availability. These tarps are widely stocked and offer reinforced corners and grommets that actually hold up under tension.

These are ideal for short-term protection on smaller residential jobs where the material won’t be sitting for months. They offer sufficient protection against light to moderate rain and are inexpensive enough to be treated as a consumable item.

Do not expect the same UV longevity as a professional-grade vinyl, but for protecting a few bundles of shims during a weekend install, this is the most efficient choice.

Reef Industries Griffolyn: The Premium Choice

Griffolyn is not just a tarp; it is a reinforced, high-strength vapor barrier used in industrial and large-scale commercial settings. Its multi-layered construction features high-density cord reinforcement, making it nearly impossible to rip.

When the stakes are high—such as protecting expensive specialized shims for a structural leveling project—Griffolyn provides a peace of mind that standard tarps cannot match. It remains flexible in sub-zero temperatures and resists chemical contact, making it a favorite for demanding field conditions.

This is the premium selection for those who need a “set it and forget it” solution. It is the most robust barrier available for materials that simply cannot afford to get wet.

Clear Reinforced Tarp: For Quick ID of Shims

Clear reinforced tarps are invaluable on crowded job sites where efficiency is paramount. By allowing visual confirmation of inventory without removing the cover, time is saved and the risk of exposing materials to sudden weather is minimized.

The internal reinforcement grid provides the necessary strength to prevent tearing, while the translucent film allows sunlight to pass through. This can be beneficial in preventing dark, damp pockets that attract pests.

Ensure the tarp is UV-stabilized, or the material will turn brittle and yellow after just a few weeks in the sun. This is the go-to for job sites where multiple types of shims are stacked and frequent access is required.

Tarp Mil Thickness: What Do You Actually Need?

Mil thickness refers to the gauge of the material—1 mil equals 1/1000th of an inch. While many equate thicker with better, the job site reality is about the ratio of durability to manageability.

• 6-8 Mil: Light duty; good for temporary coverage, but punctures easily.
• 10-12 Mil: Medium duty; standard for most residential framing lumber and shim storage.
• 16+ Mil: Heavy duty; required for long-term storage or high-wind, high-traffic areas.

Going thicker than 16 mil is often overkill for simple shim storage. Excess weight only makes it harder to secure the cover properly, leading to “flapping” in the wind that can actually damage the materials underneath.

Securing Your Tarp to Protect Your Materials

Even the most expensive tarp will fail if it isn’t secured to account for wind uplift. If wind gets under a tarp, it can act like a sail, potentially tossing a heavy stack of shims or ripping the grommets right out of the material.

Always use a combination of tie-downs and physical weights. Bungee cords are insufficient for long-term use because they lose elasticity; opt for ratcheting tie-downs or specialized rubber tie-down straps.

If storing on a roof or flat surface, place weights (such as bricks or sandbags) on the perimeter, but ensure they aren’t so heavy that they indent the shims underneath. Remember that the goal is to create a taut surface that sheds water rather than pools it.

Poly vs. Canvas vs. Vinyl: Which Is Best?

Choosing the right material requires an honest assessment of the climate and the duration of storage. There is no single “best” material, only the right tool for the job scope.

• Polyethylene (Poly): Cheap, waterproof, and widely available, but susceptible to UV rot.
• Canvas: Breathable and ideal for wood, but heavy and prone to moisture saturation if not treated.
• Vinyl: The most durable and waterproof, but significantly heavier and more expensive than poly.

For most residential applications, a high-quality 12-16 mil poly tarp is sufficient. If the shims are being stored in an area where they will remain for an entire winter, prioritize vinyl. If dealing with cedar shims in a humid environment, consider canvas to allow for natural breathability.

Preventing Mold & Rot Under Your Shim Tarp

The biggest enemy of shim storage is not just rain, but trapped moisture. If a tarp is installed perfectly waterproof, it will still fail if it doesn’t allow the materials to breathe.

Always elevate your shim stack off the ground using pallets or pressure-treated sleepers. This prevents ground moisture from wicking up into the bottom layer of shims, which is the most common cause of mold.

Finally, try to provide a slight pitch to the tarp’s surface. Water pooling in the center will eventually penetrate even the best tarps or cause the material to stretch and weaken. Proper drainage is the foundation of long-term storage success.

Effective material management is the hallmark of a professional project. By selecting the appropriate tarp and maintaining proper storage habits, your shims will remain as stable and reliable as they were the day they left the supply house.