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Before you buy · Guide
What fails, and when
Specialty vehicles rarely fail at a feature. They fail at a seam, a floor, a wire or a roof penetration, and they fail on a schedule that is easy to predict if you know what to look for. This page describes the five failure modes that take mobile units out of service, when each typically appears, and what causes it. It is written as education, not as an accusation; the causes are construction methods, and the methods are choices every builder makes.
1. Seam corrosion — years 2 to 5
What it looks like: rust staining below the beltline or along the skirt, bubbling paint at panel joints, then a soft spot you can push with a thumb.
What causes it: a body built from separate panels has horizontal seams — above the windows, below the windows, and at the floor line where the skirt is screwed on. Water gets behind the seam. If the steel behind it is primed on one side only, or not primed at all, rust starts inside the cavity and works outward. By the time it is visible, the frame member behind it has been rusting for a year or more.
What prevents it: a one-piece sidewall with no floor-line seam, a skirt welded to the structure rather than screwed on, and every steel member powder-coated all the way around before the wall goes on.
2. Delamination — years 3 to 6, sooner in the sun
What it looks like: bubbles or waves in the exterior panel, a hollow sound when you tap it, panels pulling away at the edges.
What causes it: the exterior skin is bonded to a substrate. If the substrate wicks water — some do — or the bond is thin or applied without pressure, the skin separates. Heat and UV accelerate it. Once the skin is loose, water travels behind it and the seam-corrosion clock starts.
What prevents it: a non-wicking inner layer (Azdel or equivalent) bonded to the exterior with hot-melt adhesive under pressure, and a thick enough exterior that it does not oil-can.
3. Soft floors — years 3 to 7
What it looks like: a spongy spot near a door, a wheel well or a sink; flooring that lifts at the cove; a musty smell.
What causes it: plywood subfloor. Plywood absorbs water from a leak you never saw — a wheel-well seam, a door threshold, a plumbing drip — and rots. On a clinic or kitchen with daily wash-down it happens faster. The floor is the single most expensive repair on a mobile unit because everything sits on it.
What prevents it: a resin-infused subfloor that sheds water instead of absorbing it, edge-encapsulated and sealed at every seam and wheel well, on cross-members that are sealed where they meet the floor.
4. Electrical faults from poor terminations — year 1 onward
What it looks like: intermittent lights, a generator that will not start, a lift that works on Monday and not on Tuesday; a technician chasing a fault for hours and finding a corroded splice under the floor.
What causes it: butt connectors and tap splices, exposed exterior connections without weather sealing, wire pulled through drilled holes with raw edges, and no documentation. Vibration loosens the splice; salt and water corrode it. This is the fault your fleet shop will hate most, because it is intermittent and it is hidden.
What prevents it: harnesses built to length in a harness shop, watertight marine-grade connectors on every exterior connection, grommeted pass-throughs, wire loom, corrosion protection on every connection, no butt connectors or tap splices anywhere, and a wiring document delivered with the unit.
5. Roof leaks at penetrations — years 1 to 4
What it looks like: a water stain around the air conditioner, the mast, an antenna or a vent; a ceiling panel that sags; insulation that is wet when it is opened up.
What causes it: a roof-mounted unit bolted through fiberglass and plywood. The fasteners compress the substrate, the seal opens, and every rain finds the hole. A thin fiberglass roof also weakens under UV and cracks under a branch or a hailstorm.
What prevents it: a composite roof that bends without cracking, a steel plate welded into the roof structure under every penetration so hardware bolts to steel, and a self-leveling sealant band across roof joints.
The timeline, together
| Failure | Typically appears | Root cause |
|---|---|---|
| Electrical faults | Year 1 onward | Splices, unsealed connections, no documentation |
| Roof leaks at penetrations | Years 1–4 | Hardware bolted through fiberglass and plywood |
| Seam corrosion | Years 2–5 | Multi-panel walls, screwed-on skirt, one-side primer |
| Delamination | Years 3–6 | Wicking substrate, thin or unpressed bond |
| Soft floors | Years 3–7 | Plywood subfloor, unsealed seams and wheel wells |
Notice that none of these is a feature. None of them appears on a spec sheet. And all of them show up after the warranty conversation has moved on.
What to do with this
Take the builder vetting questions to every proposal. Use the inspection checklist at delivery. And read how we build it to see what the alternative looks like at each station.
Request a proposal
Tell us the vehicle. We tell you what it costs and what to attach.
Pick a plan or describe the program. Say whether you need a price, a bid package, a grant kit or a formal proposal. A person at HLE reads every request; nothing goes to a queue.
Or call 574-343-2150, 7:30 to 4:30 Eastern, and ask for Tabatha.