Method comparison · 5-min read
GPR vs chain drag. Today's delamination vs the next five years.
Chain dragging finds delamination that already exists — by sound. GPR maps the chloride-saturated, corrosion-active zones that predict where delamination comes next. For strata councils budgeting parkade repairs, the difference is one repair cycle versus three.
TL;DR
Chain drag is cheap, fast, and finds existing delamination — but only what has already debonded, and only on exposed (non-overlaid) decks. GPR maps active corrosion environments before they delaminate, works through overlays and toppings, and quantifies deterioration percentages engineers can budget against. Modern BC parkade assessments use chain drag for today's map and GPR for the five-year forecast; scoping repairs on chain drag alone routinely under-scopes by the time mobilisation happens.
Side-by-side comparison
| Feature | GPR Deck Scanning Radar condition mapping | Chain Drag / Hammer Sounding Acoustic delamination check |
|---|---|---|
Finds existing delamination | As signal-attenuation zones | The classic hollow sound |
Predicts future deterioration (chloride/corrosion zones) | ||
Works through asphalt overlays and toppings | ||
Quantified output for budgeting (% per bay) | Deterioration mapped and measured | Marked areas, surveyor-dependent |
Rebar cover depth measurement | ||
Coverage speed on large decks | Continuous scanning by lane | Slow, labour-bound |
Works in occupied parkades | Bay-by-bay cone closures | Noise + larger closures |
Cost per square metre | Higher unit cost, more data | Cheapest screening there is |
Repeatable for year-over-year trending | ||
Accepted in depreciation reports | Quantified condition appendix | Often as supporting survey |
Yes Partial / depends No
When to choose which
Choose GPR deck scanning when…
- Budgeting capital repairs — need quantities, not impressions
- Overlaid or topped decks where sounding is blind
- Depreciation report condition inputs
- Year-over-year deterioration trending
- Mapping corrosion before it becomes delamination
Choose Chain drag / sounding when…
- Quick low-budget screening of exposed decks
- Confirming bounds of known delaminated patches
- Pre-repair layout marking for the contractor
- Engineer's spot-verification of GPR findings
Choose Both together (standard practice) when…
- Chain drag maps today's delamination cheaply
- GPR maps the corrosion environment driving tomorrow's
- Engineer scopes one repair cycle instead of three
- This pairing is how serious BC parkade assessments now run
Quick answers
Frequently asked
Why does chain drag miss developing deterioration?
Chain drag detects the hollow acoustic response of concrete that has already debonded from its reinforcement. Chloride-saturated concrete with actively corroding rebar — the stage right before debonding — still sounds solid. GPR sees that stage directly: chloride and corrosion attenuate the radar signal in a measurable, mappable way.
Our engineer specified chain drag only. Is that wrong?
Not wrong — possibly just budget-fit. For a quick screening of an exposed deck, chain drag is honest value. The limitation appears when repair scopes are built from it: by the time repairs mobilise a year later, the corrosion-active zones GPR would have flagged have become new delamination, and the scope grows mid-project. We're glad to coordinate with your engineer's protocol either way.
Can GPR really scan through an asphalt overlay?
Yes — radar passes through asphalt and toppings that render sounding useless. Overlaid decks are precisely where GPR has no practical substitute, since the overlay hides visual and acoustic evidence alike.
What does a GPR deck survey deliver?
A scaled condition plan: deterioration zones mapped and quantified (square metres and percentage per bay), rebar cover-depth statistics, and ranked repair priorities — formatted as an engineering input or a depreciation-report appendix. Numbers a strata council can take to a vote.
How disruptive is each method in an operating parkade?
GPR works bay-by-bay behind cones at walking pace, quietly. Chain dragging is exactly as loud as it sounds and needs larger closed areas for the operator to hear. Neither requires closing the parkade; GPR is the gentler neighbour.
What does parkade GPR scanning cost?
Priced by deck area and access; typical strata parkades run from the low thousands for a full condition survey — usually a small fraction of one repair mobilisation. The free phone consult (604-239-9934) with your deck's approximate area produces a firm number quickly.
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The service this comparison scopes
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Concrete Scanning Guide
Not sure which option fits your situation?
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