When shopping for a used sailboat, one of the most important things to look for is soft or springy spots in the deck. They’re a sure sign that water has seeped into the soft wooden core and caused rot that’s difficult and expensive to repair. Water damage is also common around chain plate bolts, wooden bulkheads, and anywhere else that hardware fasteners penetrate the exterior fiberglass. There is no easy fix for water damage but preventing it in the first place is quite simple if you seal all penetrations with butyl tape.
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Butyl is a pliable, synthetic rubber compound that does not harden with age. Butyl tape is a rolled strip of thin butyl that is a convenient way to store, measure, and use butyl as a marine sealant. Bedding hardware is the process of installing the hardware in a “bed” of sealant to keep water and grime out.
Butyl tape is particularly good when compared to other marine sealants for a bucket full of reasons:
- No smearing
- No running
- No cleanup
- No waiting to cure
- No hardening in the tube
It’s inexpensive and is even reusable in some cases. Try that with 3M 4200 or 5200. Those sealants are also good and are best used in specific applications but for general ease of use and future disassembly, nothing beats butyl tape.
There are right ways and wrong ways to apply butyl tape. What follows is the procedure that I learned when I got started and it has served me well ever since.
Make your bed and sail in it too
To bed hardware with butyl tape:
1. Drill normal size holes to receive the fasteners. For straighter holes, see DIY Drill Guide for Accurate Holes.
2. Chamfer the outside of the holes with a countersink bit or a regular drill bit. The general rule of thumb is twice the diameter of the holes. If you’re using hollow finish washers like I show here, the chamfer can be minimal because the washer itself will hold plenty of butyl.
This will do two things:
- Remove microscopic cracks in the gelcoat that can spread when the fastener is under pressure.
- Make a funnel around the fastener for the butyl to squeeze into and make a more reliable seal.
3. Tear a piece of butyl tape from the roll long enough to seal the holes when rolled into a string and shaped into a ring. For most small fasteners, this is about the size of a Cheerio.
4. Knead the butyl with your fingers until it is as soft as it will get, especially in cold temperatures. It should be the consistency of soft clay. Then roll the butyl between your fingers into a string 1/8″ to 1/4″ in diameter, depending on the size of the fastener and the gap to fill. For sealing screws, bend the string into a ring shape just large enough to slide onto the fastener. Roll the ends together until they join completely. For larger or irregular shaped holes, make a shape that completely surrounds the hole.
5. Slide the butyl ring onto the fasteners tight against the washer or head. For finish washers like I show here, the butyl should easily fill the washer with excess to spare.
6. Insert the fasteners into the holes and press hard to compress the butyl and force it into the chamfer.
7. Tighten all fasteners as usual. The excess butyl should squeeze out around the fastener, a good sign that it is also squeezing into the chamfer and fastener threads.
8. Even though it seems soft enough, the butyl will continue to squeeze out for hours or even days, depending on the amount and the temperature. The next day, re-tighten any loose fasteners.
9. When the butyl has finished squeezing out, carefully trim off the excess with a utility knife.
If you want to get started bedding your hardware with butyl tape, I recommend that you begin with one 3/4″x30′ roll. It’s enough to seal practically every hole in a small sailboat but you’ll probably find other uses for it too, like RVs, home weatherproofing, etc.
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