What Is Gap 40 and Gap 7 Gravel? A No-Jargon Guide for Kiwi Homeowners

When it comes to landscaping or building anything outdoors in New Zealand, one term you’ll hear often is "GAP" — not the clothing brand, but a crucial type of gravel. Specifically, GAP 40 and GAP 7 gravel. If you're scratching your head wondering what these numbers mean, you’re not alone. Whether you're laying a driveway, building a patio, or prepping for a garden path, understanding what GAP gravel is — and how to use it — can make the difference between a sturdy, long-lasting result and a costly redo.

In this easy-to-follow, no-jargon guide, we’ll break down the basics, uses, and benefits of GAP 40 and GAP 7 gravel. We’ll also explore how they compare to GAP 20 and how to choose the right one for your specific project.

What Does GAP Even Mean?

Let’s start from the beginning. "GAP" stands for "Graded Aggregate for Pavement." It refers to a specific mix of stone sizes used primarily for foundations and paving. The number that follows (like 40 or 7) represents the maximum size of the stones in millimetres. So, GAP 40 means the largest stones in the mix are 40mm across, while GAP 7 has much smaller, 7mm stones.

The GAP range also includes smaller particles called "fines" that help bind the material together. This is what gives the gravel its compacting power, making it ideal for creating solid bases that won’t shift or wash away over time.

GAP 40: The Heavy Lifter of the Landscape World

GAP 40 gravel is a coarse-grade base course mix that includes a blend of stones up to 40mm in size. It’s ideal for:

  • Driveways

  • Sub-base layers for concrete slabs or patios

  • Access roads

  • Retaining wall backfill

The larger stones give it strength, while the smaller fines allow it to compact into a dense, stable base. For homeowners doing a new driveway or prepping a site for paving, GAP 40 is often the first layer to go down.

Pro Tip: Always wet and compact GAP 40 in layers (around 100mm thick) to avoid future sinking.

GAP 7: The Finishing Touch

On the other end of the spectrum is GAP 7. This fine-grade gravel mix includes stones up to 7mm and is often used as a top layer or in areas where a smoother finish is needed. Common uses include:

  • Top layer for paths and driveways

  • Under pavers for patios or footpaths

  • Asphalt and concrete base prep

Because GAP 7 is so fine, it compacts well and creates a smooth, clean surface. It's not strong enough to use on its own as a foundation, but it's perfect as the final layer over something more robust like GAP 40 or GAP 20.

How GAP 20 Fits In

Somewhere in between GAP 40 and GAP 7 is GAP 20. It offers a balance of strength and workability, making it a versatile option for medium-duty landscaping needs. It's commonly used in:

  • Residential driveways

  • Base course for garden paving

  • General fill under concrete

GAP 20 compacts more easily than GAP 40 but offers more strength than GAP 7. For most small to mid-sized landscaping jobs, it’s a solid all-rounder.

How to Choose the Right GAP for Your Project

Choosing between GAP 40, 20, or 7 comes down to what you’re building:

  • Driveway Base: Start with GAP 40 for strength, then top with GAP 20 or GAP 7 for smoothness.

  • Garden Path: Use GAP 20 for the base, then top with GAP 7 for a walkable finish.

  • Under Pavers: Start with GAP 20 or even GAP 7, depending on traffic.

Expert Insight: Never use just GAP 7 for structural work. It’s too fine to offer support. Always layer your gravel to get the best long-term performance.

Why GAP Gravel Is Better Than Random Fill

Using GAP-certified gravel ensures consistency. Random fill or ungraded stones may not compact well, leading to future issues like water pooling, cracks, or settling. GAP gravel is screened and engineered to lock together when compacted — like a well-designed puzzle.

Real-World Example: Building a Driveway in Auckland

A Kiwi homeowner in West Auckland recently took on a 20-metre gravel driveway project. They started with 150mm of GAP 40, compacted in layers, followed by 75mm of GAP 20, and finally topped with a light layer of GAP 7. The result? A driveway that looked polished, drained water efficiently, and has held up for over five years with minimal maintenance.

Cost Considerations

While prices can vary, GAP 40 tends to be the most cost-effective for bulk strength, while GAP 7 can be slightly more expensive due to finer screening. Buying from local suppliers can also cut delivery costs. Don’t forget to factor in compaction equipment rental or contractor labour if you're not going DIY.

How GAP Gravel Supports Weed Control and Drainage

GAP gravel isn’t just about strength. It also helps with water management and weed care. Properly compacted GAP layers can reduce surface water runoff and discourage weed growth. Combine with quality top soil Auckland and mulch for the best results in your garden.

Final Thoughts: Building Smart From the Ground Up

If you take one thing away from this guide, let it be this: good landscaping starts with a solid foundation. Understanding the roles of GAP 40, GAP 20, and GAP 7 helps you make smarter choices, avoid expensive mistakes, and build outdoor spaces that last.

So next time you’re planning a project, skip the guesswork. Use GAP gravel wisely and watch your landscape stand the test of time.

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