Getting a Nice Finish on Wood Kayaks
When I get calls or meet you in person at shows I am often asked the question – How difficult is it to get a nice finish on wood kayaks? As with so many questions the answer is – it depends. You need to ask yourself if you want to paddle furniture or if you want have a functional finish that looks good but might have some imperfections. We have built a lot of boats, so here are our tips for getting a good finish. The finish work begins when you put the boat together from the outset. Key things to consider are:
Make sure that the panels are aligned well before you epoxy the kayak. This is not difficult, it just takes a moment to run your hands across all of the joints to make sure they are flush. Panels that are out of line will be difficult to sand flush later without eating past the top layer of the plywood.
– If you want very fair lines on each joint, use a hand wood planer to plane the joints. It is not necessary, but makes for a very nice smooth joint line.
– Use 220 grit sand paper if you are sanding the joints, you will be less likely to eat into the plywood to any great depth. The 4mm marine plywood has a 1mm veneer on it surface, you certainly don’t want to eat into it. Eating past the top layer can happen at the bow and the stern where there are narrow panels and a bit of a concave surface.
– When sanding the plywood anything rougher than 220 grit sand paper leaves groove marks in the wood that are very difficult to remove. The same is true in the fiberglass layer on top of the wood.
– Finish with a 320 grit sand paper if you want to make the surface very smooth. I would caution going with any finer sand paper. You might run into adhesion problems if the surface is too smooth. The surface needs to be rough enough for epoxy to bond well to.
– Keep the sander flat. It is tempting to tip the palm sander on its side to get into those deeper spots to sand out, however, this creates a wavy surface.
– Change the sand paper often. Most people use sand paper much longer than they should. You can easily go through 30+ sanding disks during the build process. We recommend using a palm sander that uses sticky back sand paper. The velcro pads on the sander tend not to last very long. Remove the sticky back sand paper as soon as you turn off the sander and the paper is still warm – the glue is not as sticky then and the pad comes off clean.
– How long do you keep working on sanding – until you are happy or tired of sanding. Are you building furniture or a kayak that will get scratched up on the beach, knocked around in the garage, hit by rocks driving down the freeway….you get my drift. (The most cosmetic damage to our kayaks are from moving them around and transporting them.)
When laying the fiberglass down on the kayak, make sure not to have an wrinkles in the fiberglass or areas where the weave bunches up. You are better off to cut a little “V” slit in areas where the fiberglass does not lay down well. Make sure to use only enough epoxy so that the fiberglass turns clear. Don’t use so much epoxy that drips start or that the epoxy starts to get under the cloth and lifts the cloth up “floating” the cloth higher in certain areas.
The epoxy that comes with our kits can be “hot coated” which means when the epoxy is drying, but still sticky, you can put on a second coat to fill the weave in the fiberglass. You will need at least 2-3 fill coats to get the weave to disappear. Use as many fill coats as you need to ensure the epoxy covers the fabric weave. (Too many coats cause extra weight or extra sanding, so use as much as prudent.) Sand the fill coats holding the palm sander flat – this is very important for a smooth surface. This is your last chance to get a smooth surface. If it is not how you like it, do another fill coat and sand again.
Most epoxy resins need some sort of UV inhibitor regardless if the epoxy already has a UV inhibitor in the formulation. We chose to use a marine grade spar varnish. There are pros and cons to any finish, but marine varnish tends to be the easiest to work with. There are a few tips for a good varnish coat:
– Thin the varnish. Although you don’t technically have to thin the varnish on top of fiberglass (because the varnish does not need to penetrate the wood) you will get the varnish to flow better and any brush strokes disappear more readily. We thin the varnish between 30-50% depending on how warm it is. The warmer it is, the less it needs to be thinned. Drips/sags on fully thickened varnish tend to take a long time to develop. I have worked on a boat for an hour and had no sags then come back the next day and find a few formed. Thinning the varnish gets the drips to happen quicker so that you can catch them as you are applying the varnish.
– How many coats? Four is what we do. I have seen some people do as many as 40.
– Don’t use sand paper between coats – use a Scotch-brite pad which you clean dishes with instead (make sure to have a new one with no soap added to the pad). Sand paper takes off the varnish quite quickly. A Scotrch-brite pad scuffs the surface without removing much of the varnish.
– Have a dust free environment – you just built a beautiful boat, wood dust all over the place – how are you supposed to get the dust off of every surface? – It is a great time to clean up the shop. Wipe down every surface with a wet cloth and wet mop the floor. We have an air filter we run in the shop for a day or two before we varnish. Dust will show up on your final coat – a little. You will feel it with your hands and see it at a certain angle. You will not see the dust marks most of the time however. Getting no dust in your finish is very difficult outside a clean room.
– Brush or Spray? – If you are good at spraying and have the facility to do so, spray the varnish on. If you get an orange peel finish, the varnish was not thin enough and will have to be sanded flat. Brushes – well, here we go into a great debate. A nice $12+ brush or a $1.50 foam brush. In the end they will be the same cost – the foam brushes break apart and you will need several of them. However, I prefer the foam brush (there will be those who disagree with me) but I find that the foam brush is more forgiving with brush strokes. This is particularly true if the varnish is not thinned enough.
– Drips & Sags – you will most likely get them. Sand them out with 220 grit sand paper and varnish over them. The key is to blend in the edges of the drip or sag with the rest of the finish. Do this by hand. Varnish is very soft and can be taken off quite easily.
For the amateur builder, you should be happy with the three foot rule – if it looks good from three feet away, your boat is just fine. So, what happens if you really mess something up (with all the boats we have built – we have been there) – the answer – paint. The wood kayaks do look really good with a two tone paint job and a black pin stripe between the two as you can see in the picture. In any regard, building a kayak is fun and rewarding. The level of perfection you attain is up to you!