HOW TO VARNISH
DUST CONTROL
Ideally, prepare the work in one place, clean it thoroughly, then move it into another (clean) place to apply the varnish. If the piece of work is a whole boat, then clean the boat and its surroundings in situ. Towards the end of the job, a simple polyethene tent over the boat keeps airborne dust at bay. You need a good workshop vacuum with a small brush head to remove most of the dust then a tack cloth to really deal with the fine deposits before applying any coating.
THE VARNISH
Golden rule number one: never to dip you brush into that can. NEVER. The material in that can leaves the manufacturers completely clean, so let’s keep it that way. You always decant the varnish into a clean graduated mixing pot. With a known quantity of varnish you can accurately add the correct amount of thinner using a small graduated measuring pot. On the side of the manufacturer’s can it will probably tell you the thinning ratios. Always use the manufacturer’s thinner rather than ordinary white spirit which slows the drying time. If your workshop is stone cold, say below 10 degrees C, then you can add an accelerator, such as Epifanes TDA, and this needs to be very carefully measured.
THE TOOLS
There are two application methods that suit this type of varnish. Firstly, a 4in (10cm) roller with a foam brush for tipping off is ideal for large areas. Secondly, a brush, not a throwaway item but something you keep and cherish for years. The roller sleeve can be a cheap foam variety or a small-er diameter mohair sleeve such as an Anza Elite that does not shed fine hairs. The foam brush has a chisel point that leaves a track as you lightly stroke it through the varnish bursting the bubbles and removing the dimpled surface left by the roller. The plastic roller tray attracts dust electrostatically, so always line it with kitchen tin foil. Apart from the tray itself, the roller sleeve, the foam brush and the tin foil are single use and thrown away, so you may take a view on this practice. The second golden rule, for long-term brush care, is never leave it with the tip resting on the bottom of a pot of dirty thinners. Drill a hole through the handle of the brush so it can be hung in a pot with the bristle tip off the bottom by about ½ inch (12mm) and pour in about 1 inch (25mm) of white spirit (see photo). Spin out the brush in a bin and it’s clean and ready to go. Once you have finished varnishing, pour any leftover varnish into a another pot (never back into your precious stock of clean varnish!), clean out the brush in the graduated mixing pot with white spirit, cleaning both at the same time, then spin out the brush and hang it back in the storage pot. Place the cleaned graduated mixing pot upside down on a polyethene covered surface for use another day.
HOW TO APPLY THE VARNISH
The key to success is a very logical approach, a brushing or rolling pattern that spreads the material evenly over the whole area and finishes with a fine tipping off in one direction. The usual starting point is well in from and edge and take the varnish out to the edges. On anything other than a flat surface, avoid putting a loaded brush or roller into a corner where a dollop will squeeze out and run, or, brushing onto an edge or over a hole will also squeeze out varnish that will not be able to resist gravity. Before moving onto the next area or piece, check back for any runs, curtains, missed areas, and the odd drowning bluebottle; if you are quick, these can be dealt with before the varnish shows the first signs of curing.
PREPARATION BETWEEN COATS
This is the part of the job where some loose heart, but it is not that bad if you know a simple technique that is quick and efficient. The first thing to understand is that these varnishes (and paints) need a mechanical key, they do not stick well to a shiny surface and the classic “peeling paint” image is because of poor preparation between coats. The prep must also remove any dust pimples and any other lumps. Between the build-up coats the technique is to lightly “de-nib” the surface with P240 or P320 grade paper, this can be in your hand or on a cork block and it is very quick but you must be
thorough. The surface will still have more shiny bits than dull/scratched bits, so, using a soft abrasive pad such as maroon 3M ScotchBrite or Norton Beartex, dull off the whole area. The target is to do just enough work and not too much, you are trying to build-up the varnish layers not remove them. Be wary of using a machine at this stage as it is very easy to take too much off. The spongy ScotchBrite is very useful in the inside of a clinker dinghy where it will efficiently abrade around the roves and ribs.
PREPARATION FOR THE FINAL COATS
The idea is for the build-up coats to fill the grain of the timber and arrive at a well covered and deep gloss surface. If the surface in question is horizontal, then about six coats will suffice. On a more vertical surface it will be more like eight coats. At this point, to achieve that mirrored gloss finish the surface will need a more rigorous preparation. If you are lucky enough to own a finishing sander that links to a vacuum then this tool is ideal for larger areas, otherwise use a cork block and sand dry or a rubber block for sanding with water. The grade to use is P400. You are aiming for a smooth, even, completely abraded surface. The danger is inadvertently rubbing back to the wood, particularly easy to do while wet sanding, as you cannot see what you are doing, so the trick is to regularly scrape the gunk away with a squeegee. With everything perfectly prepared, clean up thoroughly with the vacuum followed by the tack cloth. I always apply two “final” coats as the first flat-down removes a significant thickness from the build-up coats, the second preparation is very light as the surface should now be flat but you still aim for a completely abraded surface. For those last two coasts, the ambient temperature should ideally be around 18 degC, the pieces you are going to coat and the varnish all need to be at the same temperature, and this temperature needs to be maintained so there is no chance of condensation and the materials cures properly. Lastly, you need to be as dust free as possible. The woolly jumper you have been wearing all winter while you build this boat needs to be discarded and replaced with one of those hooded white coveralls favoured by murder scene investigators. I always carry a new tack cloth with me and re-clean every item as I varnish.