Frequently Asked Questions
Below is a list of our most commonly asked questions about the HotVac. If you have a question that is not answered below, please Contact Us.
Q: How is the process better than heat lamps?
Moisture combined with the residues from the breakdown of polyester resin may only be evaporated at very high temperatures. These are at least 140°C higher than can be safely achieved with heat lamps. However, the extremely low pressures of a HotVac enclosure allows evaporation at temperatures that are safe, closely controlled and also beneficial for ‘post curing’.
A second aspect is that the heat pattern generated by lamps is highly non-uniform, there are hot and cold spots and hence treatment will be irregular. HotVac manages to control the temperature of the hull being treated to ± 1°C in a very uniform manner across the heater area.
If you are cost conscious, then take a look at your electricity charges for operating heat lamps continuously for three or four weeks. HotVac’s intimate application of heat can show up to a ten fold reduction in energy consumed; and that’s good for the environment too!
Q: Where's the nearest place I can have my boat treated?
Like all good ideas, HotVac centres are spreading rapidly across the world. Visit the Supplying Boatyards page on this site.
Q: Does my boat need special treatment after HotVac?
A hull moulding does not need special treatment after a HotVac process. However, it must be noted that all effectively permanent ‘osmosis’ repairs have to address the problem of erosion damage and the existence of the open pathways of the displaced moisture residues.
The primary barrier coat should be of low viscosity, and well worked it so as to penetrate the capillaries and provide a strong bond with the laminate.
Q: Will HotVac damage my boat?
No! HotVac has never been known to have damaged a boat. The slight colour change during treatment has occasionally revealed defects that were previously hidden. These include whitening of fibres through strain damage, impact crazing, areas of de-lamination through the stress reversals of normal service, or stress cracks at bulkheads. Discovery of these defects allows effective repairs to be made. Polyester resins, even when of poor quality, should not be adversely affected at temperatures below 130°C. Good quality resin should be safe at temperatures far higher than this.
When taken beyond the glass transition temperature (the temperature after which the resin becomes increasingly plastic) the laminate will become less stiff. With moisture absorption into the hull over the years, this transition temperature at which the material changes from its hard glassy phase into the softer plastic phase, may have actually reduced by as much as 20°C.
When the laminate cools down again, it is typical for the laminate to have become stiffer than when newly moulded, and recovered its structural strength. In the process the glass transition temperature will have increased back to near its original value. This is why some boat manufacturers are now curing their hull mouldings in ovens.
Q: What if I can’t get a low enough vacuum?
Poor vacuum during start up or process is usually due to one of the following causes:
Faults causing leaks into the equipment. At the extremely low HotVac pressures a tiny amount of air leaking into a joint or seal will expand many hundreds of times and may exceed the pump’s ability to scavenge effectively.
Poor condition of the laminate. Thin laminate with serious erosion through hydrolysis or ‘dry’ laminate through poor wetting out during manufacture, may be unacceptably permeable. However, this is quite rare and only occurs on mouldings that are quite obviously seriously damaged to the point of being almost beyond repair.
Q: Where does the moisture go to?
In so called ‘saturated’ laminates, the moisture is only present in vapour quantities. This would be no more than a few millilitres per square metre; perhaps a thimble full.
During the few hours normally taken by a HotVac process, these tiny quantities are noticeable only as occasional drips from the vacuum pump exhaust or a slight sticky residue in the hoses.
Q: I've used hotvac and my boat still will not dry
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.
5 Sawmill Yard
Tel: +44 (0) 1796 482104
Fax: +44 (0) 1796 482111
Boat Services Inc.
1866 Ottawa Beach Road
Holland, MI 49424