Last fall and into the spring this year, I refinished the bottom of my 33 by myself. It was a big job to say the least. My previous anti fouling was Micron CSC but over the years it was detaching and dropping off in sections which told me that the bond between the first layer and the underlying material was failing. At these locations, I could see either white gelcoat or a salmon pink colour which I later learned was a factory applied epoxy barrier coat. As I am the second owner of the boat, I have the bill of sale from Hinterhoeller to the first owner which lists the epoxy barrier coat as an option paid by the first owner. I decided to refinish the bottom and went about researching the methods of stripping including sand blasting, chemical peel, sanding etc. These options were either unavailable locally or too messy and did not appeal to me. I wanted to preserve the existing epoxy barrier coat and so settled on hand scraping the bottom with a butt chisel and a carbide scraper made by Bahco from Lee Valley tools. While this method was laborious, it gave me better control as I progressed and generated moderate dust, mostly chips of the Micron ablative anti fouling. Beside the boat, I clamped a disc sander in a portable work bench using this to keep the chisel sharp. Surprising how quickly a chisel dulls chipping ablative antifouling.
With the anti fouling off, I was faced with an unknown coating and so consulted with a surveyor. He concluded that the unknown was a product popular in the late 80’s early 90’s known as VC Tar which can no longer be had in Canada. This was an additional layer of osmosis protection but he observed to me that over time, the tar goes brittle so that the bond between the tar and first layer of ablative anti fouling fails leading to the condition I mentioned above. I wanted to apply Interprotect so I went about experimenting with different solvents to remove the tar. I first sanded down the hard tar with 120 grit in a random orbital sander to knock off most of it and thin the tar layer without sanding the barrier coat. I then used lacquer thinner to remove the remaining tar; it worked very well and did not affect the underlying epoxy barrier coat. Lacquer thinner evaporates very quickly, so rather than apply it directly to the hull and wipe which simply spreads the tar around, I decanted it into spray bottles and then used the two rag method described by Interlux in their literature, spray soaking the rag then rotating the rag to wipe clean, working small sections at a time. I wiped down the entire bottom, keel and rudder included, which removed all the tar even from the sanding etchings in the original epoxy barrier coat. I went through a lot of rags. I then sanded the barrier coat with 80 grit using a random orbital sander and repaired several places where there were voids between the gelcoat and underlying fibreglass layup. Most of these voids were shallow and on the fibreglass section of the keel. When I mentioned them to the surveyor, he replied simply that he was not surprised. I then left the bottom for the winter.
In the spring, following the Interprotect application recommendations, I wiped down the sanded barrier coat with Interlux 202 to remove the sanding dust and any other residuals, using the same spray bottle and two rag technique. Despite sitting all winter in the wind etc, I was surprised at the amount of remaining dust which Interlux indicates must be thoroughly removed to get the best bond between the Interprotect and underlying sanded substrate. I then applied 4 coats of Interprotect alternating white and gray layers, lowering and removing the cradle pads etc while supporting the boat with jack stands. I let the Interprotect cure as per the Interlux recommendations, then sanded a third time with 220 grit and applied two coats of VC 17.
Overall, the task required a month, of which two weeks was required to strip the old antifouling and 3 to 4 days for each of the 3 rounds of sanding. The presence of the tar added considerably to the job but it had to be removed. Some might ask why not simply grind down the hull to the gelcoat and apply the Interprotect. I preferred to go about it step by step, preserve the epoxy barrier coat and ensure complete removal of the tar. As they say, for a task like this, preparation is everything; I am satisfied with my prep work. When the boat was hauled this past fall for winter storage, the bottom was flawless, smooth and sound.
Ken Dakin
NS 33 # 7
Sashay
Kingston ON