Gaps form because laminated mats are independent units on moving ground; here’s what drives the failure and how to manage it day to day.
Published: March 2026 · Select Mat Editorial Team · ~6–7 min read
This is a companion piece to our parent guide, Hardwood Laminated Mats vs. Composite Mats: How to Choose the Right Access Mat for Your Project.
Key Findings
- Gaps form because hardwood laminated mats are independent units with no mechanical connection — load transfer isn’t continuous, so each mat moves with the ground beneath it.
- Soft, saturated, or fill ground settles unevenly under load (differential settlement), so one mat drops more than its neighbor and the two separate. [1]
- Repeated equipment traffic drives lateral movement. On unbound surfaces over soft soil, repeated wheel loads spread material sideways and cut ruts — the same mechanism nudges mats out of alignment and widens gaps. [2][3]
- Wet/dry cycles move the ground. Clay-rich soils swell when wet and shrink when dry, loosening compaction and increasing movement under the mats. [4][5]
- A gap is a regulated safety hazard, not a cosmetic one. OSHA defines a hole in a walking/working surface as a gap 2 inches or larger and requires workers to be protected from tripping into it. [6]
Bottom line: With board roads, gaps aren’t a possibility — they’re an expectation. The real question is whether your project can manage them every day.
Why do gaps form in board roads? It’s the system, not the mat.
Gaps form because a board road is a set of separate mats with no mechanical link between them, laid on ground that moves. Each mat is independent, there’s no continuous load transfer, and the surface is only as stable as the soil under each individual mat. When that soil shifts, mats settle, separate, and migrate — producing gaps, uneven elevations, and trip hazards.
On active sites in soft or wet ground, separation can begin fast — field crews often report gap formation within the first day or two of heavy use.
What causes the gaps to open?
Four forces do most of the work, and they compound each other.
| Cause | Mechanism | Field sign | What helps |
|---|---|---|---|
| Ground settlement | Soft, saturated, or agricultural soil compresses unevenly under load (differential settlement) [1] | One mat sits lower than the next | Ground prep, drainage, load spreading |
| Repeated traffic | Repeated wheel loads push unbound material sideways and rut the surface, nudging mats out of line [2][3] | Widening seams along the wheel path | Reposition mats; limit/contain traffic corridors |
| Dynamic equipment forces | Turning, braking, and side-loading add lateral force that shifts mats; tracked equipment is especially hard on alignment [2][3] | Mats skewed at turns and transitions | Slow turns; route planning; frequent realignment |
| Moisture cycles | Clay soils swell when wet and shrink when dry, loosening compaction beneath the mats [4][5] | Cracking, heave, or soft spots after weather swings | Drainage; moisture control; monitoring |
Ground settlement
Soft soil has high water content and high compressibility, so it consolidates unevenly under concentrated loads. [1] Two mats sitting on slightly different soil thickness or moisture settle by different amounts, and separation begins.
Repeated traffic
On unbound surfaces over weak subgrade, repeated wheel loads spread granular material sideways and thin the load-bearing layer, which is what produces ruts. [2][3] The same repeated loading walks individual mats out of position and turns small seams into wide gaps along high-traffic corridors.
Dynamic equipment forces
Turning, braking, and side-loading apply lateral forces, not just downward ones. Those horizontal forces shift mats out of alignment and create uneven transitions — and tracked equipment concentrates them.
Moisture cycles
Clay-rich soils change volume with moisture: they swell when wet and shrink when dry. [4][5] Each wet/dry cycle loosens compaction and increases movement beneath the mats, feeding more settlement and separation.
What happens after a gap opens?
A gap starts a progressive failure cycle. Water collects between mats, soil washes out beneath the exposed edges, the mats settle further, and the gap grows. The first gap isn’t the real problem — the speed at which small gaps become an unpredictable working surface is.
Why gaps matter for safety
A gap is a recognized hazard under federal safety rules. OSHA defines a hole in a walking/working surface as a gap 2 inches or larger in its smallest dimension and requires that workers be protected from tripping into or stepping through it. [6] On a board road that means three exposures: trip hazards for workers on foot, tire drop-in for vehicles, and uneven load transfer for equipment. OSHA also requires work areas and passageways to be kept clear of debris and scrap with protruding nails — relevant as boards and fasteners wear. [7]
How to manage gap formation
If hardwood laminated mats are the right call for your project, gap risk has to be actively managed every day.
- Inspect daily. Daily inspection of the surface is non-negotiable on an active board road.
- Reposition mats as gaps appear. Close seams before they widen into drop-in hazards.
- Keep seams clean. Remove mud and debris between mats so they seat properly.
- Maintain drainage. Keep water from collecting in seams, which accelerates wash-out and settlement.
- Watch high-traffic and turning zones. These fail first; monitor them most closely.
- Budget the labor. Decide up front whether you have the crew, time, and discipline to do all of the above daily — that, not the mat itself, determines whether a board road stays safe.
When to consider a continuous-surface alternative
If your project involves heavy foot traffic, mixed use (people and vehicles together), long durations, or soft or changing ground, it’s worth evaluating a continuous, interlocking surface such as composite mats — which connect into one system and remove most of the mat-to-mat movement described above. The full trade-off is covered in the parent guide: Hardwood Laminated Mats vs. Composite Mats.
FAQ
Why do gaps form in hardwood laminated mats?
Because they’re independent units on moving ground. A board road has no mechanical connection between mats and no continuous load transfer, so each mat moves with the soil beneath it. When soft or wet ground settles unevenly, or repeated traffic pushes mats sideways, the mats separate and gaps open. [1][2][3]
How quickly do gaps form on a board road?
It depends on ground and traffic, but it can be fast. On active sites in soft or wet ground, crews commonly report gaps beginning within the first 24–48 hours of heavy use. The underlying drivers — differential settlement and traffic-induced movement — start acting as soon as loads cross the surface. [1][2]
Are gaps in a board road a real safety hazard?
Yes, and a regulated one. OSHA defines a hole in a walking/working surface as a gap 2 inches or larger and requires workers to be protected from tripping into or stepping through it. [6] Beyond foot-traffic trips, gaps create tire drop-in risk for vehicles and uneven load transfer for equipment.
Can you prevent gaps in hardwood laminated mats entirely?
No — the goal is management, not elimination. Gap formation is an expectation on a board road, driven by ground settlement, traffic, and moisture cycles. [1][2][4] Daily inspection, repositioning, seam cleaning, and drainage keep gaps from compounding, but they require consistent labor and discipline.
Does wet or soft ground make gaps worse?
Significantly. Soft, saturated soil compresses unevenly under load, and clay-rich soils swell and shrink as moisture changes — both loosen support beneath the mats and accelerate separation. [1][4][5] Wet ground also lets water collect in seams, washing out soil and deepening the gaps.
When should I switch to composite mats instead?
Consider a continuous, interlocking system when you have heavy foot traffic, mixed people-and-vehicle use, long project durations, or soft and changing ground. Composite mats connect into one surface, which removes most of the mat-to-mat movement that causes board-road gaps. See the full comparison in the parent guide.
Sources
- Differential Settlement — overview — ScienceDirect Topics
- Mechanisms Governing the Performance of Unpaved Roads (lateral spreading and rutting) — Geosynthetics Magazine
- Corrugation of an Unpaved Road Surface Under Vehicle Weight — PMC (U.S. National Library of Medicine)
- Swelling and Shrinking Soils — British Geological Survey
- Expansive Soil and Rock — Colorado Geological Survey
- 29 CFR 1926.501 — Duty to Have Fall Protection (definition of a hole; protection from tripping) — OSHA
- Walking-Working Surfaces (slips, trips, falls; housekeeping) — OSHA
