Gary Martin on Boat Paints
Gary has been involved in the paint industry since 1975 when he helped his father and grandfather with boat painting at South of Perth Yacht Club. He was apprenticed to his grandfather at the time and spent his first five years in the automotive painting industry. Here he was working with what he called ‘old technology’ but when he then moved on to painting boats he took with him some of the techniques used only in the auto industry at that time. He introduced the use of random orbit sanders to the boat painting scene and was the first professional to use spraying equipment to paint boats.
In his closing introductory remarks, Gary indicated that he has always been interested in the technical side of painting and this has now become his passion in the boating context. His background is as a tradesman, having painted some 7000 vessels over his career – aluminium, timber, fibreglass and carbon fibre ranging in size from canoes to ocean going luxury motor yachts – and he emphasized that he was not a salesman. During his time in the trade, he spent six to seven years with the Eagle Americas Cup syndicate which later resulted in his being sought out to paint the Whitbread/Volvo around the world racers. Subsequently, he painted all the boats in this fleet.
Gary commenced his technical presentation by identifying key areas essential to a top class paint finish – something that at the end of the job, we would all be proud of. These were right environment, proper preparation, correct paint, correct equipment.
The atmosphere needs to be at less than 80% relative humidity. Above this value, hardeners draw in the moisture and evidences as paint blisters when it is later released. The paint itself must be kept cool in storage and contaminant free. Gary particularly made the point that rags used for wipe down or for solvent can contaminate the whole solvent container, the paint and then the job. He cited contaminants as the painter’s biggest enemy and critical to achieving the best paint job.
All substrates oxidise – aluminium the quickest followed by steel, timber and fibreglass being the slowest. In addition, previous paint coats themselves oxidise and need appropriate preparation before application of fresh paint coats. This includes anti fouling paints which need the hydrolysed layer wet blasted off but then require wet sanding to get the best adhesion and longer term performance from the new paint coat. In general terms, best adhesion is gained by surface preparation of 80 microns. As a reference, sandblasted metal has a surface of between 80 and 120 microns.
Both single pack and two pack paints are suitable for boating applications. Single pack is not as hard but is more flexible whilst two pack lasts longer in the sun – by a factor of up to ten fold. Single pack is either alkyd or polyurethane technology and hardeners can be added to improve this aspect of performance whereas two pack requires more attention to safe handling practice as it contains isocyanurate which is carcinogenic.
For single pack paints, a thinned down mix of the appropriate primer can perform well as a sealer. For two pack, application of an epoxy resin sealer such as International Everdure is recommended even though these products do not now contain the rot proofing agents that they once did. Following rubdown with 320 grit paper, the paint build up recommended is a primer plus undercoat plus topcoat for single pack and a primer/undercoat plus topcoat for two pack. Top coats should be rolled on and then tipped off with a brush. Care needs to be taken to achieve the correct thickness – too thick a coating will lead to cracking and too thin oxidises quickly and does not provide the required finish and protection.
Gary pointed out that in broad terms, boat paint materials and techniques have developed from the automotive industry and noted that the use of polymer wax three months after completing a paint topcoat or after seven to ten coats of varnish would greatly improve the life of the job. In addition, some paints can be cut and polished following application (acrylic urethanes) whilst others (linear polyurethanes) acquire their final finish from the quality of the application and cannot be cut and polished afterwards.
Anti Fouling Paints
There are some examples around where fouling has not occurred over a long period of time without application of a specific anti fouling product. Gary cited the supports on the Tower Bridge in London which have been in place for over 100 years and have apparently not fouled with marine growth. However, this in generally not the case in the boating arena and some form of anti fouling protection is required below the waterline. Cuprous oxide paints or copper thisanate (for aluminium vessels) have now completely replaced the now outlawed tributal tin based paints used until about twenty years ago and which have serious negative impacts on our environment. Interestingly, Gary noted here that families of sea horses had returned to the waters of Fremantle Sailing Club marina since the phase out of these paints.
Other ad hoc approaches such as the use of Indian Ink or white of egg on props and shafts have prevented growth build up in some marine circumstances. Only the round the world Volvo/Whitbread boats that constantly do over 30 knots are not subject to fouling and do not use anti fouling paint.
For metal surfaces such as aluminium, products such as zinc chromates were used in the past to prevent corrosion. These paints were carcinogenic and are no longer available. Corrosion is now prevented by achieving a satisfactory film thickness via the painting process. Zinc rich coatings need to be 75 microns film thickness, otherwise they separate. Two pack top coats at 10-12 m2 per litre will result in a film thickness of 100-125 microns and high build epoxies need to be up to 290 microns thick. As a comparison, a human hair is 60 microns thick.
Teak decks are best cleaned by use of saltwater and a Scotchbright pad working across the grain. The majority of commercial cleaners and brighteners contain oxalic acid that attacks the sealers in the seams. Any residue remaining falls to the bottom of the seams and each time the area is wet, the sealer break down process advances.
The question was asked as to how older paint stock, probably with a hard crust above the liquid, can be expected to perform. Gary pointed out that some of the key paint ingredients are contained within the hard crust and therefore no longer in the paint mix so the paint will not perform 100%. As a general rule, manufacturers recommend a two year life. However, if the paint is entirely liquid after a longer time, it is likely it will perform satisfactorily.
In closing, Gary indicated that he specialised in Norglass and Hempel products and is also very familiar with International products. He is passionate about boat paints and their application and is happy to share his knowledge with members who may require his specialist advice.
We thank Gary for sparing his time to share so much of his thirty years of experience and knowledge in this industry with ABBA members in this technical presentation.