Winches, cleats, tracks and coachroof hardware are bolted to the deck, and every bolt hole is a door into the sandwich core. The quality of the bedding decides whether the deck is still dry ten years on.
Proper bedding
- Oversize the hole. The hole through the core is drilled larger than the bolt and some core cleared around it.
- Fill with epoxy. The void is filled with epoxy and, once cured, redrilled to bolt size. Water can then no longer reach the core.
- Backing plate. A plate inside spreads the load, instead of small washers.
- Sealing. A sealant suited to the hardware and the hole; bolts are not fully tightened at first, but after the sealant has set.
What the survey looks at
- Star cracks in gelcoat around hardware.
- Moisture readings rising around fittings.
- Is there a backing plate inside, or only washers?
- Rust marks around bolts and water staining on the headlining.
What we often see
- Star cracks in gelcoat: Hairline cracks radiating from a centre around cleat and winch bases.
- Wet core around deck fittings: Moisture readings rise around winch and track bases; the deck flexes underfoot.
The right method
When bedding a fitting on a sandwich deck, the bolt hole must not be in direct contact with the core. So the hole is drilled oversize, some core around it is routed out and the cavity filled with epoxy. Once cured, the bolt hole is redrilled through the filling. Then, even if the seal fails one day, water cannot reach the core. A backing plate goes under the fitting to spread the load over a wider area.
Sealant
The bedding compound is chosen for the job. Some are permanent adhesives that make later removal hard; others stay flexible and can be removed. For deck hardware a removable, flexible sealant is usually preferred. Compatibility with timber, plastics or acrylic is checked in the maker's data sheet; some compounds can damage acrylic windows.
When to rebed
Bedding does not last for ever. On loaded fittings, especially winches, cleats and tracks, the seal breaks down over the years. Rebedding at intervals is a very small job compared with the cost of a wet-core repair. When water marks show on the headlining or gelcoat cracks around a fitting, that fitting's turn has come.
On survey
Deck moisture readings concentrate around each fitting. High readings are marked on the sketch, and the report lists which fittings should be rebedded. From inside, the presence of backing plates and the condition of nuts are checked.
Order of work
Rebedding is done in dry weather with the deck fully dry; leaking and loaded fittings come first. Keeping a list of what was rebedded and when helps plan the next round.
Portlights and acrylic windows
Portlights and coachroof windows need bedding too. Acrylic expands and contracts with heat, so the sealant must stay flexible and window screws must not be over-tightened. An over-tightened screw eventually cracks the acrylic around its hole. Cracked or crazed windows are replaced before they leak.
Each rebedded fitting goes on a list with the date, the compound used and whether the hole was filled with epoxy. At the next survey, moisture readings are then read against that list, and any fitting leaking again stands out.
A repeat leak usually means the hole was not sealed from the core; the fix is to redo it properly rather than add more sealant on top.