Specs don’t fail on paper—they fail in the field. Here, we discuss the Spec vs. Reality gap: why your geomembrane isn’t performing and what to do about it. If your geomembrane isn’t performing, it’s likely a QA/QC disconnect rooted in misaligned assumptions. This guide helps you tighten your specs, align with installation realities, and avoid costly rework.
The Spec vs. Reality Gap: What’s Breaking Down
When geomembranes underperform, it’s rarely because the material itself is defective. The real issue is often a mismatch between what’s written in the spec and what’s actually achievable in the field. You may have specified the right product, but if the installation environment, crew capability, or QA/QC protocols aren’t accounted for, performance drops fast.
Here’s what typically causes the breakdown:
- Idealized assumptions in specs: Many specs assume perfect subgrade prep, flawless seams, and consistent weather. These conditions rarely exist on site.
- Lack of field-driven tolerances: Specs often omit acceptable limits for wrinkles, seam overlaps, and destructive test frequency.
- Overreliance on generic standards: Referencing ASTM standards without clarifying how they’ll be applied in the field leaves room for interpretation—and error.
- Disconnect between design and installation teams: Engineers may not be looped into field constraints, while contractors may not fully understand the design intent.
Let’s look at a scenario that could easily play out on a real jobsite. A design engineer specifies a 60-mil HDPE geomembrane with double fusion seams, referencing ASTM D6392 for seam testing. The spec includes no guidance on wrinkle height, overlap tolerances, or destructive test spacing. The contractor installs the liner during a cold snap, leading to excessive wrinkling and poor seam fusion. QA/QC tests fail, and the project stalls while the team debates whether the spec was met. The issue wasn’t the material—it was the gap between spec and reality.
To help visualize where these disconnects typically occur, here’s a breakdown:
| Spec Element | Common Assumption | Field Reality | Resulting Issue |
|---|---|---|---|
| Subgrade Preparation | Smooth, compacted, dry | Uneven, damp, rushed | Wrinkles, bridging, poor liner contact |
| Seam Welding Conditions | Controlled, consistent temperature | Variable weather, wind, crew fatigue | Weak seams, failed tests |
| QA/QC Testing Frequency | “As needed” or per ASTM | No clear schedule or criteria | Missed defects, inconsistent coverage |
| Crew Skill Level | Assumed certified and experienced | Mixed experience, subcontracted labor | Inconsistent installation quality |
Another issue is how specs treat geomembrane performance as a static property. You might specify tensile strength, elongation, and puncture resistance—but those values don’t mean much if the liner is poorly installed. Performance is a system outcome, not just a material attribute.
To make your specs more field-ready, you need to shift from idealized design language to installation-aware guidance. That means:
- Defining acceptable wrinkle height (e.g., max 25 mm before seaming)
- Specifying overlap requirements (e.g., minimum 100 mm before fusion)
- Calling out destructive test spacing (e.g., one test per 150 m of seam)
- Including weather limitations (e.g., no welding below 5°C without preheat)
Here’s a quick comparison of spec styles:
| Spec Style | Description | Field Impact |
|---|---|---|
| Feature-Based | Lists material properties only | Doesn’t guide installation or QA/QC |
| Performance-Based | Defines how the system should behave post-install | Encourages accountability and clarity |
| Field-Aware Spec | Includes tolerances, crew requirements, testing | Reduces ambiguity, improves outcomes |
If you’re writing specs that only describe the geomembrane itself, you’re leaving performance to chance. Civil and design engineers who want defensible, repeatable results need to write specs that anticipate what can go wrong—and build in safeguards that make sense on site.
Where QA/QC Fails—and Why It’s Not Just a Contractor Problem
When QA/QC issues show up in geomembrane installations, it’s easy to point fingers at the contractor. But the root cause often starts with the spec itself. If your spec doesn’t define how quality should be measured, verified, and enforced, then QA/QC becomes reactive instead of proactive.
Here’s where things typically go wrong:
- Vague testing language: Specs that say “test as needed” or “follow ASTM standards” leave too much room for interpretation. You need to define frequency, location, and acceptance criteria.
- No field verification plan: Without a clear plan for how testing will be conducted and documented, QA/QC becomes inconsistent.
- Missing crew qualifications: If your spec doesn’t require certified welders or trained QA/QC personnel, you’re risking poor execution.
- Unclear roles and responsibilities: Specs often fail to assign who’s responsible for testing, reporting, and approving results.
Let’s say a spec calls for air channel testing of fusion seams per ASTM D7177 but doesn’t specify how often or who performs the test. The contractor runs a few tests early in the day, skips the rest, and submits a generic report. Later, a leak is detected under the liner. The engineer realizes the seam wasn’t tested consistently, but the spec didn’t require it. The failure wasn’t just in execution—it was in the lack of enforceable QA/QC structure.
Here’s a breakdown of how QA/QC gaps can impact performance:
| QA/QC Element | Weak Spec Language | Field Impact |
|---|---|---|
| Seam Testing Frequency | “As needed” | Inconsistent coverage, missed defects |
| Crew Certification | “Experienced personnel” | Unqualified welders, poor seam quality |
| Documentation Requirements | “Submit results” | No format, no traceability |
| Acceptance Criteria | “Per ASTM” | No clarity on pass/fail thresholds |
You can’t control the weather or the crew’s experience level, but you can control how your spec prepares for those variables. QA/QC should be embedded into the spec—not treated as a separate process. That means defining how testing is done, how results are verified, and what happens when something fails.
How to Align Your Specs with Field Realities
Specs that work in the field are written with the field in mind. That means anticipating what can go wrong and building in safeguards that are practical, enforceable, and clear.
Start by shifting from feature-based specs to performance-based specs. Instead of just listing material properties, define how the system should behave once installed. Then go further—make your spec field-aware by including tolerances, testing protocols, and crew requirements.
Here are practical ways to align your specs:
- Define installation tolerances: Specify acceptable wrinkle height, seam overlap, and panel alignment. For example:
- Wrinkle height: Max 25 mm before seaming
- Seam overlap: Minimum 100 mm
- Panel alignment: ±50 mm deviation allowed
- Include weather limitations: Welding below 5°C or above 40°C should require preheat or cooling protocols.
- Specify crew qualifications: Require certified welders and QA/QC personnel with documented training.
- Add mock-up requirements: Before full installation, require a mock-up section to verify seam quality and crew capability.
Here’s a comparison of spec types:
| Spec Type | Key Features | Field Suitability |
|---|---|---|
| Feature-Based | Lists material specs only | Poor—doesn’t guide installation |
| Performance-Based | Defines system behavior | Better—sets expectations |
| Field-Aware Spec | Includes tolerances, testing, crew requirements | Best—anticipates real-world conditions |
You’re not just writing specs—you’re writing instructions for how your design becomes reality. The more your spec reflects field conditions, the more likely your geomembrane will perform as intended.
Case Study Snapshot: Spec Revision That Saved a Project
A design team was facing repeated seam failures on a containment project. The original spec called for a 60-mil HDPE geomembrane with fusion seams and referenced ASTM D6392 for testing. But it didn’t define wrinkle tolerances, overlap requirements, or destructive test spacing.
After multiple failed tests and delays, the team revised the spec to include:
- Wrinkle height limit: 25 mm
- Seam overlap: 100 mm minimum
- Destructive test spacing: One test per 150 m of seam
- Crew certification: Required for all welders and testers
Once the revised spec was implemented, seam failures dropped by over 70%, and the project was completed on schedule. The contractor reported fewer RFIs, and the QA/QC team had clear benchmarks to follow. While this is a hypothetical scenario, it reflects what can happen when specs are written with field realities in mind.
Spec Writing Tips That Actually Work in the Field
Specs that get followed are specs that make sense to the people doing the work. That means being clear, specific, and practical.
Use these tips to make your specs field-ready:
- Use numbers, not generalities:
- Instead of “adequate overlap,” write “minimum 100 mm overlap”
- Instead of “test as needed,” write “one destructive test per 150 m of seam”
- Avoid ambiguous language:
- Replace “as required” with “required when ambient temperature is below 5°C”
- Replace “experienced personnel” with “certified welders per GSI-07”
- Clarify how standards apply:
- Don’t just reference ASTM D7177—specify who performs the test, how results are recorded, and what constitutes a pass
Field crews don’t have time to interpret vague specs. The clearer your language, the more likely your design will be executed correctly.
How Better Specs Drive Better Results (and Repeat Business)
When your specs reflect field realities, you reduce RFIs, speed up approvals, and improve installation outcomes. Contractors trust specs that make sense—and when they trust your spec, they trust your material.
Here’s what happens when your spec is field-aware:
- Fewer delays: Clear tolerances and testing protocols reduce back-and-forth
- Better QA/QC outcomes: Defined procedures lead to consistent results
- Higher contractor confidence: Specs that match field conditions get followed
And when contractors trust your spec, they’re more likely to recommend your material on future projects. That’s how you move from one-off sales to repeat business.
3 Actionable Takeaways
- Audit your specs for field fit: Review your geomembrane specs against actual installation conditions—adjust for crew skill, site constraints, and QA/QC realities.
- Define QA/QC in detail: Don’t leave testing protocols vague. Specify exact seam test methods, frequency, and acceptance criteria.
- Make your spec the contractor’s ally: When your spec reflects field realities, contractors trust it—and your material becomes the default.
Top 5 FAQs Engineers Ask About Geomembrane Specs
1. What’s the most common reason geomembrane installations fail? Poor seam quality due to unclear specs and inconsistent field conditions. Wrinkles, misalignment, and inadequate testing are frequent culprits.
2. How often should destructive seam tests be performed? A good rule is one test per 150 m of seam, but this should be adjusted based on project size, risk level, and crew experience.
3. Can I just reference ASTM standards in my spec? You can, but it’s not enough. You need to clarify how those standards will be applied, who’s responsible, and what pass/fail criteria look like.
4. What’s a reasonable wrinkle height tolerance before seaming? 25 mm is a commonly accepted maximum. Beyond that, wrinkles can compromise seam integrity and should be trimmed or flattened.
5. Should I require certified welders in my spec? Yes. Certification ensures the crew understands proper fusion techniques and QA/QC procedures. It’s a low-cost way to improve outcomes.
Summary
Specs are more than paperwork—they’re the blueprint for performance. If your geomembrane isn’t holding up, it’s time to look beyond the product and into the assumptions baked into your design documents. Civil and design engineers have the power to define outcomes, but only if their specs reflect the realities of the field.
By writing specs that anticipate installation challenges, define QA/QC protocols, and guide contractor behavior, you build defensibility into your design. You reduce risk, improve performance, and earn trust—not just from contractors, but from clients who see results.
Geomembrane performance isn’t just about tensile strength or puncture resistance. It’s about how well the system behaves once installed. And that starts with you—your spec, your clarity, your foresight. Write it right, and your material becomes the default. Write it wrong, and you’ll be chasing failures. The choice is yours.