I often hear of people being afraid of drilling holes into their kayak to install various fittings and attachments. Providing that the fitting is above the waterline and decent sealant and/or adhesive is used then there is really nothing to be afraid of! So on that note lets take a quick look at some recommended sealants and adhesives for kayak rigging....
When it comes to retro-fitting accessories and equipment such as pad eyes or a cleat for an anchoring system, or a mount and transducer for a fish finder, it is down to the user to ensure the installation of a water tight fixture.
The ideal sealants and adhesives need to be flexible when cured to prevent cracking and splitting when the plastic hull of a kayak flexes, or a load bearing fixture moves under stress. For this reason, solid adhesives, such as epoxy resin, are not recommended for use on plastic hulls. There are 3 sealants that are commonly used when installing kayak fittings and equipment, and these all remain flexible to some degree once cured: General Purpose Silicon, Marine Goop and Sikaflex. They all do the desired job of sealing a fixing but each have their advantages and disadvantages so lets take a closer look at each in turn....
General Purpose Silicon
General Purpose Clear Sealant is both cheap and easy to source at practically any hardware store for a few pounds a tube. It works well to seal fixtures when using trifold rivets, bolts/washers/nuts and well nuts. Liberal amounts can be applied as any excess can easily be wiped off with a cloth.
The downside to silicon is that it does not really stick to the polyethylene hull of a plastic kayak or the gel coat of a composite kayak. This causes any beading around the edge of a fixture, such as a cleat or rod holder, to lift over time and eventually peel away. I have also found that the clear stuff does discolour over time in sunlight and saltwater too. Still... it does the job of sealing a fixing and its cheap!
Marine Goop is fantastic stuff! It is not only a marine grade sealant, it is also an adhesive that will stick to polyethylene and gel coat. In fact the label will tell you not to use it on polyethylene but i have never had an issue, neither have the hundreds of others using this product on their kayaks. It is clear and UV resistant so shouldn't discolour in sunlight. It is also slightly flexible so will not crack or split with flex in the hull of a plastic kayak, or the movement of a load bearing fixture. It is great for sealing fixtures such as trifold rivets, bolts/washers/nuts and well nuts as well as providing additional strength to fittings such as cleats, accessory mounts (e.g. Ram Balls, StarPorts) and flush mount rods holders etc. Liberal amounts can be applied as any excess can be wiped off with a cloth without to much mess.
Marine Goop is also commonly used for the installation of a fish finder transducer inside the hull of a kayak. Simply make a foam well to contain the Goop, fill the well around 1/2 way with Goop ensuring there are no air bubbles introduced, and push the transducer into it against the hull. It takes a day or so to set solid but the transducer will then be held in a solid block stuck to the hull. This allows the transducer to shoot through the hull and read the return signal with very little, if any, loss of resolution.
Marine Goop is a bit more pricey than silicon but is a far better product and can be brought in 10.2 fl.oz tubes from Cornwall Canoes for £10.95 (at the time of writing). It is my number 1 choice for use on my kayaks!
Sikaflex is widely used in the plumbing trade as a sealant, adhesive and filler. It comes in several grades and colours. I have used the weatherproof Sikaflex-EBT+ and the marine grade Sikaflex-291i, both in black. Both seem to work well on a kayak. As with Goop, Sikaflex is also slightly flexible so will not crack or split with flex in the hull of a plastic kayak, or or the movement of a load bearing fixture.
This stuff is really really sticky and really really messy!! Keep your hands/fingers wet when using this to keep it from sticking and staining everything! The trick is to use just enough and not too much so that you don't have to wipe much or any away. Any excess can be wiped away with a damp cloth but can be a tricky job to get a neat finish. As with Silicon and Goop you can run a wet finger over the excess bead that emerges as you tighten a fixture down. This will leave a smoother and neater finish.
Whilst i prefer Marine Goop to work with, Black Sikaflex looks really good on black surfaces, such as the hull of my Tempo, or the centre hatch of my Rytmo. Its tricky to work with on light coloured material as its hard to achieve a neat finish but with patience and persistence it can work well.
Sikaflex-291i can be brought from several online websites for around £10 a tube.