6 Best Wedge Shims For Leveling Heavy Stone Worth Using

Leveling heavy stone requires precision that common building materials simply cannot provide. A shift of even a sixteenth of an inch can cause a stone veneer to buckle or a garden slab to rock under foot traffic. Choosing the right shim isn’t just about height; it is about load-bearing capacity and material longevity. This guide breaks down the best wedge shims for professional-grade masonry and hardscaping projects.

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Wobble Wedges: Best for Fine-Tuning Stone

Wobble Wedges are the gold standard when a stone installation requires micro-adjustments. These tapered shims feature a patented gripping texture that prevents the stone from sliding once set in place.

They excel in scenarios where a stone slab is nearly level but requires a slight nudge to eliminate a rocking corner. Because they are made from a rigid, durable plastic, they do not compress under the immense weight of granite or slate.

The interlocking ridges allow for stacking without the shims slipping apart. Use these when working on patio furniture leveling or setting capstones where absolute stillness is the priority.

Pylex Foundation Shims: For The Heaviest Stone

When moving into heavy-duty structural applications like foundation stone or massive landscape boulders, standard plastic shims often fail. Pylex foundation shims are engineered specifically to handle high-pressure loads without deforming.

Their reinforced design ensures that the weight of the stone is distributed evenly across the shim surface. This prevents the “point-loading” that causes brittle stone to crack over time.

These are essential when the stone is the base layer of a larger structure. If the foundation is out of level, every course above it will inherit that error, leading to visible gaps or instability.

Go-Ez Shims: Top Choice for Paver & Patio Slabs

Go-Ez shims are the go-to for hardscapers dealing with uneven sand beds or sub-base settling. They are designed with a wide profile that provides a stable landing for large pavers and natural stone slabs.

The material is semi-flexible, which allows it to conform slightly to the underside of a rough-cut stone. This characteristic is critical for preventing “hollow spots” that lead to paver breakage when heavy weight is applied.

Keep these on hand for jobs where the base is slightly inconsistent. They provide the necessary support to keep slabs flush, ensuring water drains away from the structure rather than pooling on the surface.

MARSHALLTOWN Horseshoe Shims: Best for Veneer

Horseshoe shims are the professional choice for vertical stone veneer installations. Their U-shaped design allows them to be slipped over a fastener or anchor bolt, holding the stone away from the wall substrate.

This spacing is vital for air circulation and drainage behind the veneer. Without this gap, moisture can become trapped against the house wrap or sheathing, leading to premature rot in the structure.

Because they are color-coded by thickness, they make it easy to maintain a perfectly consistent mortar joint or air gap across an entire wall. They are non-corrosive and will not degrade when buried behind the masonry.

EZ-Shim Composite Shims: A Rot-Proof Workhorse

Composite shims bridge the gap between the affordability of wood and the durability of high-end polymers. Unlike traditional pine shims that swell and eventually rot when exposed to damp masonry, composite versions are impervious to moisture.

They are incredibly easy to snap, which is a major time-saver when trimming excess material flush with the stone edge. This efficiency is why contractors reach for them when working on high-volume wall cladding.

Use these in any environment where water runoff is a constant. They offer the necessary stiffness to lift heavy stone while remaining stable enough to last for decades without degrading.

Glazelock U-Shims: For Precise Course Spacing

Glazelock U-Shims are essentially the precision instrument of the masonry world. They are designed for tight-tolerance spacing, making them perfect for leveling the first course of stone veneer on a foundation.

Their high-impact plastic construction ensures they won’t crush under the weight of the wall. They are designed to stay in place, meaning they won’t wiggle loose during the mortar application process.

If you are working on a high-end project where the reveal and joint thickness must be perfect, these shims provide the necessary accuracy. They turn a tedious leveling job into a straightforward, systematic process.

Plastic vs. Wood Shims: What The Pros Use

Wood shims have long been a staple of carpentry, but in the world of heavy stone, they are rarely the correct choice. Wood is organic and susceptible to moisture, termites, and compression.

Once a wood shim absorbs water, it loses its structural integrity. In a stone installation, this can cause the entire assembly to shift or crack as the shim deteriorates.

• Plastic/Composite: Impervious to water, non-compressible, and consistent in size.
• Wood: Prone to rot, swells with humidity, and lacks uniform thickness.

Always opt for high-density plastic or composite shims for exterior stone work. The extra cost is negligible compared to the expense of repairing a failed stone installation.

How to Match Shims to Your Stone’s Weight

Selecting the right shim depends entirely on the weight per square foot of the stone. For heavy landscape boulders or structural granite, always prioritize “full-bearing” shims that cover as much surface area as possible.

Avoid using thin, narrow shims on large slabs, as they will create stress points. A large, heavy stone resting on a single, tiny point of contact is a recipe for a stress fracture.

If the stone is massive, use a wider shim that spans the load. This ensures the pressure is distributed safely across the entire base of the stone, preventing it from snapping under its own weight.

Stacking Shims: The Right Way & The Wrong Way

The wrong way to stack shims is to create a “tower” of mismatched materials. This creates an unstable pivot point that will inevitably fail as the ground settles or the masonry dries.

The right way is to ensure all shims are of the same material and, ideally, the same brand to ensure a consistent footprint. Never stack more than three shims high; if you need more height, use a piece of mortar, a concrete base, or a solid leveling pad.

Excessive stacking creates a “hinge” effect that loses rigidity. If the gap is too large to fill with a few shims, it is time to re-evaluate the substrate or the mortar bed depth.

Can You Leave Shims in Place Permanently?

In most stone masonry applications, shims are intended to be permanent, load-bearing elements. They remain encased within the mortar bed or hidden behind the stone, supporting the weight for the life of the structure.

There is no need to remove them if they are high-quality, rot-proof plastic or composite shims. Removing them after the mortar has set can actually introduce unwanted movement and potential cracking.

Ensure that the shims you select are chemically inert and will not react with your mortar or stone adhesive. When properly installed and embedded in mortar, they become an invisible, essential part of a durable, level finished project.

Mastering the art of leveling stone is as much about the hidden supports as it is about the visible finish. By selecting the right material and avoiding the pitfalls of poor stacking, you ensure your work stays level and stable for years to come.