There are hundreds of reasons why a boat moulding will not dry. Some causes may be as simple as wet bilges, damp trim linings, water filled closed spaces and damp foam filled spaces.
It’s always important that these are thoroughly inspected for before drying programmes start. The gel ‘flow coat’ applied to the interior may also be as saturated as the old exterior gelcoat. When boats are laid up they commonly suffer from condensation on the interior and also, they often have salty bilges. In these cases, the interior flow coat can never be dried and the moisture will continue to contaminate the structural laminate. Another cause of slow drying is likely to be damp or water filled stiffening frames. These may be hollow or foam filled and should be identified and drained when the boat is first presented for repair.
When the above possibilities have been eliminated, it is likely that the moulding is affected by residues from the deteriorating materials of the moulding. These may be present in friable hydrolysed laminate, between laminations of fibre, or in tiny capillary like cavities caused by erosion. When slow drying is caused by the presence of degraded GRP, the moisture indicated by the meter will be associated with organic acids, styrene and various glycols. These residues can only be removed by either cutting off the damaged laminate, burning off the damaged laminate, or by evaporation under the controlled conditions of the HotVac process.