GUIDE TO PAINTING A BOAT AT
Coach painting is the traditional method of applying paint to a surface using a brush. Originally developed to paint horse-drawn carriages also suitable for painting commercial vehicles like coaches and trucks as well as boats, Preparation of the surface can vary depending on the state of repair,
Synthetic products are slow air drying, Provide excellent gloss similar to cellulose, Colour will eventually fade over time unless varnished, can be sprayed brushed or even rolled on, No mask required unless sprayed. Because of the superior brush or gun finish achieved when applying synthetic substrates, polishing is not required or recommended.
Synthetic paint can be painted on any surface without worrying about solvent reaction lifting or bubbling previous paint whether it's old or new,
Terebine Driers can be added to synthetic paint or polyurethane varnish, The quantity can be varied according to the strength required to speed up drying, particularly useful late in the day to avoid a damp spell or extreme cold that would normally cause blooming. In extreme cold weather conditions a heavy bloom will turn varnish a milky white colour it may be necessary to flat and paint the areas again if they become severely bloomed.
Genuine Turpentine or pure gum turpentines are dilutents and should only be used for thinning synthetic oil paints if absolutely necessary, thinning reduces the opacity and quality of the overall product. Genuine turpentine is produced from "pine trees" so it should smell like pine. On quality work never use cheap turpentine or turpentine substitutes they smell like "paraffin oil" reduce drying time due to impurities and the finish will either dry dull or become dull very quickly. You can use lesser quality turpentines or white spirits for thinning undercoats or primers with no ill effects.
Cellulose products dry by evaporation of the solvent, are cheaper, quick drying with softer durability high gloss finish and require an ordinary spray mask. Colour will fade, lose it's gloss, and only suitable for spray application. Use a conventional suction feed spray gun for Cellulose, Lacquers and Metallic basecoats by using changeable nozzles to use with varying paint substances.
Two-Pack or two component products dry by chemical action after adding a hardener and often contain isocyanate, Two pack paints are the most expensive but do provide a very hard durable super high gloss finish, yet they require breathing apparatus to use safely. Non colour fading or loss of gloss, liable to chip easily, spray application recommended. However it is possible and in some instances favourable to brush paint two pack in well ventilated areas but a mask should still be worn. When spraying two pack substances a HVLP (High Volume Low Pressure) spray gun is better suited because of the considerable reduction in overspray and far less paint being consumed.
Before attempting to coach paint a boat the existing paintwork or gel coat must be inspected closely to see what kind of repair method may be necessary. Assessment is the first task to undertake before commencing any repair as the repairer or coach painter needs to know exactly what is involved. When the surface is prepared and ready for painting it must be free from dirt, oil, grease etc and should be "tacked off" to remove all particles of dust or other contaminants just prior to applying paint.
Applying primer is the first step when painting either bare metal, wood or fibre glass and although Red Lead (the infamous metal protector) was the favourite choice years ago it's now become difficult to obtain due to lead content paints being banned in UK manufactured paint in particular.
As an alternative to Lead based paint a Red Oxide or Zinc Phosphate primer can be used on bare metal. Or an epoxy based high build primer. Is suitable for all materials.
The primer coat will always be heavily pigmented which often leaves a rough brush-mark finish but also provides a thick protective film ready for wet flatting the following day (weather permitting). It may be necessary to apply more than one coat of primer, This will depend on the paints overall thickness after application and it should completely obliterate any bare metal or wood AFTER wet flatting, If not, reapply and wet flat again.
Primer is the single most important layer of paint as it provides the initial seal from the elements and in conjunction with a finishing gloss can do so for many years. Primers and undercoats are porous and must be protected by an additional gloss layer.
An undercoat provides build up layers and should also obliterate the primer, It's common practice to match the undercoat colour to the final gloss colour because this can have the advantage of only needing to apply one coat of gloss if the gloss is a particularly good coverer, Applying one coat of gloss is not always recommended when two coats are usually required.
Undercoat should also be wet flatted and may require several coats to completely obliterate and build up the underneath layer of colour whether it be primer or undercoat.
Unthinned undercoat can often leave heavy brush-marks just like primer does so it is customary to mix undercoat with gloss 50-50 to help with the flow out process, This leaves a smoother finish with little or no brush-marks which makes the surface easier to wet flat prior to further applications of undercoat or gloss.
It was a popular procedure in the old days to apply several layers of undercoat each one being a different colour to show imperfections and each layer was wet flatted with Pumice stone to create exceptional depth on high quality work.
Gloss is the finishing layer that takes the brunt of the weather so it has the tougher formulation so it should be durable and remain relatively colourfast.
Varnish can be added to or painted over the top of gloss to provide a glass like finish maximising durability, The gloss must first be completely wet flatted to obtain a perfectly smooth surface which will also provide sufficient key for varnish to adhere to.
Varnish should be applied over an existing newly painted surface within a week to obtain absolute maximum adhesion otherwise the finish is likely to just sit on top which would eventually lead to premature flaking through lack of adhesion.
Paint shops generally have central heating which provides the perfect environment to apply paint even in the depths of winter, for the best possible results paints and varnishes should always be applied at room temperature. Room temperature is around 68°-72° Fahrenheit 21°-23° Celsius.
1. Sand areas with an Orbital sander and remove all traces of old damaged paint using 80 grade sanding discs on stubborn parts and finishing with 120 or 150 grade. 2. Create a key for the filler on areas that require filling using 80 grade paper then fill dents with a suitable polyester filler and rub with 80 grit paper (fill and rub repeatedly if necessary) to a smooth finish just above the surface of the body, Then rub with 180 WETorDRY paper using water and a rubbing block (depending on repair) with a little Fairy Liquid (to ease lubrication and clean the paper to prevent clogging) to a level just below the panel surface feathering across the alloy as you go.
3. When the area is well prepared and ready for primer spray on Acid Etch or rub on bare areas if very small and allow to dry. Spray one light coat of primer (if using cellulose) allow to flash off then spray a heavier coat allowing to flash off and continue until at least three heavy coats of primer are applied to overall body shell remembering to apply slightly more primer to repaired areas building the level of primer slightly above the repaired body surface.
Spray a guide coat any colour except black (black has a higher density pigment than any other colour and flatting is generally harder) over the repaired areas and when dry wet flat with 800 grade WETorDRY paper again with a little Fairy liquid using a rubbing block on flat repairs. To flat the remainder of the shell use a quarter section of WETorDRY wrapped around a large wet piece of mutton cloth which is ideally suited in following the contoured shape of panels.
Use a four inch grinder with rubber backing disc and grade 80 card disc on severely corroded areas stroking the panel to avoid causing deep scratches.
4. Corrosion can be treated with various chemical anti-corrosion neutralises to help prevent further corrosion usually by sealing the metal from oxidisation. I personally use a diluted mixture of Sulphuric acid that in my opinion attacks the powdery substance adequately enough burning away most of the corrosion.