Graphite Bottom (spring 2002)
I applied three coats of an epoxy-graphite-silica mixture to my canoe from the waterline down. This page documents why, my experiences applying it, and reviews performance after one and three seasons.
Graphite 'black bottom'
The reason for applying graphite was to provide better protection against scrapes and gouges from submerged rocks, as well as moving the canoe around on land (Canadian Shield country). After one year of use, I found even adjusting the canoeís position an inch or two while on land would leave scratches in the varnish from the rocky beaches and landscape. The varnish is necessary to protect against breakdown of the epoxy from UV light. But it just isnít in my character to be ever gentle with my canoe. More importantly, I built the canoe with the intention of using it in up to Class II whitewater and long wilderness tripping. It is definately not a day paddler! Even though the canoe did not see whitewater in its first season, the bottom was still getting scratched up. All it took was to run over a few shallow submerged rocks to put some serious scratches in the varnish. I even had a deep gouge that went right into the cloth.
The theory behind an epoxy-graphite-silica mix is the graphite powder acts mainly as a lubricant. The lubricant effect makes it "slide" over rocks with less resistance and friction. The usual varnish finish for this type of canoe construction tends to "scrape", "grab", or "bite" into rocks. Racing boats use graphite to decrease the resistance of water flowing around the hull but this benefit is so small there would be no noticeable effect on a recreational canoe - at least not with my relaxed paddling style. Colodial Silica is tiny glass particles (a powder) which, when mixed with epoxy, provides increased hardness compared to straight epoxy. The Silica weighs next to nothing. The graphite is a black powder and turns the epoxy mixture black. After applying graphite it is not necessary to apply varnish to protect the epoxy from UV light: no light passes through the black surface. I expected the additional epoxy to slightly increase the weight of my canoe, but it wouldnít be by much. First, the extra epoxy would only be on the bottom of the hull, below the waterline. Second, the varnish in this area was removed and there would be no need to reapply over the black graphite coating. One way to effectively negate any weight gain would be to apply graphite during canoe construction, in the second (filling the weave) and third coats of epoxy.
Jon invited me to use the metal-shop at his place of employment. It is not necessary to apply the mixture indoors but the timing demanded it in this case. At the end of the 2001 canoeing season I scraped the varnish off the bottom of the boat and sanded the surface lightly with 120 grit sandpaper. Then I put the boat away with the intent of applying graphite in the Spring, before any trips. However, I was invited to go on an early Spring canoe trip and it was still too cold out to be working with epoxy outdoors. I didnít want to risk applying epoxy in the cold because I had heard there could be some problems with it setting. A week or two later and there wouldnít have been any problem.
I used sponge rollers to apply two coats of epoxy-graphite-silica mixture on consecutive days. Expect to use at least one roller per coat as the rollers become useless once the epoxy begins to set-up. Indeed, it would flow on smoother and thinner using 2 rollers per coat and making at least two smaller batches of epoxy-graphite-silica. I used a sponge brush to smooth ridges created from the edge of the roller.
MAS slow cure epoxy was mixed with West graphite and West Colodial Silica. I marked the waterline with masking tape to maintain a clean finish and straight lines. The floors were covered with cardboard to protect the floor from epoxy spills. It is a good idea to wear at minimum a particle mask when mixing to protect against inhaling the graphite powder, and even worse, the very light and fluffy silica "dust" which becomes airborne with even gentle agitation.
West System recommends 10% graphite to 90% epoxy. Gilpatrick uses a thicker mixture of 40% graphite to 60% epoxy. Ted Moores, in the 1997 edition of Canoecraft, suggested 25% graphite, 5% silica, and 70% epoxy (for "a rock-hard finish." p.137). I went for a very thick mixture with the consistency of tar. The following ratios are approximate:
First coat: 25% graphite, 15% silica, 60% epoxy.
Second coat: 30% graphite, 10% silica, 60% epoxy.
Third coat: 40% graphite, 60% epoxy.
Applying the mixture was straightforward, like painting. After the first layer set, I noticed an "orange peel" effect and spent additional time sanding the finish smooth using fine steel wool. The second coat had the same effect. I think it is because the epoxy-graphite-silica mix was thicker than a simple epoxy finish. Having sanded both layers, I no longer had the thickness of application that I had intended. So after the Spring canoe trip I applied, outdoors, a third coat of epoxy-graphite without the silica powder. I assumed there was enough silica in the previous two mixes giving enough hardness to protect the underlying fibreglass cloth. Also, without silica in the mix, I was able to increase the graphite to epoxy ratio - improving the lubricating effect on the outermost coating.
When the graphite mix dries, the finish is shiny. A light hand sanding with steel wool after set-up results in a flat finish. Esthetically, scratches show up more on the shiny than the flat finish.
The "black-bottom" performed very well. The lubricating effect against rocks was even more impressive than I had expected. On my first outing, the Spring canoe trip mentioned above, I gave it a good test by dragging the canoe across 10 metres of boulders - not something even I subject my canoe to under normal circumstances. On close inspection there were minor scratches but nothing all the way through the graphite layer and nothing deep. The most noticeable thing was how the canoe slid freely across the rocks without digging in, as varnish does. Definitely less resistance on dry rocks than the usual varnish finish. Scratches do not show up as much in the flat black surface.
The same lubrication effect was noticed going over submerged or wet rocks. It feels and sounds different. I spent two weeks on Georgian Bay this past summer. There were many shallow submerged rocks in this body of water. Sometimes, especially when paddling at speed or in wavy water, these submerged rocks had a way of sneaking up under you. I also ran all the rapids from Hartley Bay on the French River to Georgian Bay, (except Devils Door).
Every night the canoe was brought up on the bare rock islands of the Bay. I prefer to leave the canoe upright, resting on its graphite bottom. The rocky landscape scuffs and dents the softwood (Sitka Spruce) trim if I do like most people and store the canoe over-turned. After two weeks on Georgian Bay there were only minor scratches with none going right through to the cloth. When I got home and inspected the surface more carefully, I discovered a small delamination (5 centimetres square) on the inside and outside of the hull. I must have impacted a rock at some point. The cloth was slightly torn on the inside but not on the outside. Because of the black surface, delaminations are more difficult to see than in clear epoxy. On close examination, they appear as a bubble in the surface, and flex in with finger pressure.
Aside from other short trips, I also spent two weeks with the canoe in Temagami in late summer. This included a trip down the Obabika and Sturgeon Rivers, running most rapids. On one set of rapids I bumped one rock hard and suffered another small delamination on the inside of the hull at the bow, behind the stem. At the impact area on the outside of the hull there was no visible damage, no dent, tear, or delamination, not even any scratches that looked worse than anywhere else.
Some people have mentioned that a black bottom would heat up in sunlight and therefore have a detrimental effect on the epoxy. Excessive heat build-up was not a problem. While car-topping the canoe for 3-8 hour drives on hot sunny days, I noticed no heat build up of the black bottom (I checked many times). As long as your vehicle is moving, the air flowing over the surface keeps it cool. For example, the surface of black cars does not get hot except when the car is stationary. Heat build up might be a problem if you store your canoe outside in the sun or leave it on top of your parked car for long periods of time.
After one seasonís (over 4 weeks on the water) relatively hard use there were no scratches penetrating through the graphite-silica layer into the underlying epoxy and cloth. The canoe saw much more abuse this season than it did last year without the graphite. Indeed, I felt more confident knowing I had the extra protection. Near the ends, just behind the stems, I could see the graphite had worn thin compared to the rest of the hull. I could just barely see through to the underlying clear layer of epoxy. This was not a scratch but an area the size of my palm where the surface has worn thin. This will require an epoxy-graphite re-application in that area. Eventually a full coat or two will have to be applied but I donít think it will be necessary for next season. The graphite will wear off eventually but I think that is part of its lubrication properties (does the graphite powder "move" in its medium?). Also, I feel I get a better idea of the amount of wear on the bottom.
All in all, I feel that without the graphite lubrication and silica hardness the hull would have major gouges and tears into and through the cloth. On the other hand, I would probably also have been more careful with the canoe (but whereís the fun in that?).
I can think of three negative points about a graphite application - all minor. First, I found I was getting black marks on my pants or thighs when lifting the canoe for portage. It washes off but it is still a nuisance. If you run your hand along the graphite bottom, it will stain much like when handling a newspaper. Second, there is a slight increase in the weight of the canoe (perhaps a pound or two). This could be minimized by applying graphite during the initial construction of the canoe. I now have six coats of epoxy below the waterline (this in itself will increase the strength of the hull). If I applied the graphite during construction I would have only three coats of epoxy (I would add a fourth for my purposes). The problem with this approach is it would be, without clear fibreglass underneath, more difficult to judge wear. I have not weighed the canoe as yet so I canít provide an accurate estimate of weight. In my case, any weight gain may have been offset when I removed the bow seat while converting to a solo-only setup. Third, the canoe is definitely not as pretty as it was before I applied graphite. Before, when the canoe was placed upside-down (car-topping for example), the beautiful wood grain and careful colour-matching and pattern of cedar strips was visible for all to appreciate. Now the outside bottom is black! Having said that, I only see the outside bottom of the canoe when I tie it to the top of the car. When I am driving it is not I who gets to look at it. When I am paddling, I can still see the wood grain and strip patterns on the inside of the hull - when not covered in gear! Since the graphite was applied below the waterline, other paddlers only occasionally see a bit of black pop out of the water (I donít). Aesthetically, other people have lost more than I have.