What to do when that fitting doesn’t want to let go.
What exactly is the rubbery material beneath your pulpit bases, sealing your thru-hulls, or gripping your port lights? What type of goop is holding that fitting to your deck? Maybe you know if you are the one who put it there, but if it came with the boat, or was applied by someone else, you probably don’t know. Only when faced with separating component parts will you learn the true nature of the sealant.
Why does this matter? Because some sealants permit easy separation and renewal while others turn de-bedding into a contest of will. If the sealant is a bedding compound (e.g. Dolfinite), acrylic caulk, butyl rubber, silicone, polysulfide (e.g. Life-Calk), or even the more tenacious polyether sealant, separation will normally just be a matter of prying to break the bond or stretch the sealant beyond its elongation capacity. However, if the sealant is polyurethane, particularly the ever popular 3M 5200, any attempt to separate the components by simply prying them apart is likely to end in the damage of one or both of the joined pieces.
So how do you separate parts bonded together with adhesive sealant? Start with step 1 and stop when the fitting comes free. However, if you’re trying to remove plastic fittings that you know were bonded with 5200, you’ll get less frustrated and do less damage if you skip down to step 6 right now.
Step 1: Extract Mechanical Fasteners. Even this can be a challenge when they were originally installed with a coating of polyurethane. Bolts should be unscrewed. A big screwdriver, perhaps with a wrench on the shank, can normally deliver adequate force. For more torque, try a manual impact driver.
Step 2: Try Separating The Parts By Pulling Or Prying. Continuous pressure will be more effective than hammering and carries a lower risk of damage. It gives elastic sealants time to resolve internal stresses and either elongate or release. If the sealant does neither, it is probably polyurethane. More force is not the solution. Plastic and cast parts will break and machined parts bend. The grip is even strong enough to rip away gelcoat. Time to move on to step 3.
Step 3: Cut The Bond. You’ll need a sharp blade — a razor knife, carpet knife, or single-edge razor blade. If you can reach all sides and the sealant is thick enough, slicing the perimeter weakens the bond. Pry just enough to allow your blade farther into the joint and keep slicing deeper until you cut the components apart. If whatever tool you’re using isn’t working, try a wire saw, simply a foot-long length of thin wire — leader wire, guitar string, braided fishing line, what-have-you — with rings or dowels at each end that will allow you to saw the wire back and forth between the bonded parts. Wedges or prying behind the wire can assist in sawing completely through the sealant pad.
Step 4: Try Some Stress. If you cannot cut the components apart, try putting the adhesive under moderate stress, then giving it time to elongate or release. For a piece of deck hardware, that might mean driving a couple of chisels or other wedges under one edge sufficient to deflect but not bend the base, then leaving them for a day or more. As separation allows, tap the wedges deeper.
Step 5: Heat Things Up … Carefully. Where both bonded surfaces are metal, a heat gun or torch can melt the adhesive and break its grip. However, if your boat is fiberglass, the use of heat risks permanent damage because the temperature required to soften cured polyurethane will also soften cured polyester. Only heat the blade of your knife, razor, or wire, which can help it to penetrate the cured sealant more easily.
Step 6: Chemical Reaction. The list of solvents tried by desperate boat owners is exhaustive: acetone, toluene, xylene, MEK, alcohol, gasoline, WD-40, citrus cleaners, and more. Most have no effect on cured polyurethane and none work well enough to recommend. One chemical product that does get high marks is DeBond Marine Formula. More liquid knife than solvent, it is sprayed onto the exposed sealant after the edges have been scored with a blade. Employing wedges to keep the sealant under stress exposes a fresh target to the chemical as the bonded edge moves back with release. Given time and repeat applications, it’s usually successful at breaking the bond of 3M 5200 (and other adhesive sealants as well).
Unlike some other release chemicals — there are several on the market — the DeBond product is also compatible with most plastics, except polycarbonate (Lexan). Without the use of a bond releaser, plastic parts — port light frames, for example — installed with 3M 5200 or other high-strength adhesive typically cannot be dismantled without damage. There is no downside to using a release chemical, beyond expense, so going to it first rather than last can pay dividends.
Here is a takeaway about polyurethane: The bond is permanent but the seal isn’t. That means things may still be stuck together just fine, but they will still be leaking. If you don’t want to do this again, re-bed with a less adhesive sealant.
Remove Thru-Hull Fittings
Thru-hull fittings can be jacked free with a length of threaded rod, a stiff backing plate, and three scraps of 2×4. Drill a hole through the center of the backing plate and the center of one of the wood scraps. Pass the threaded rod through the wood, up through the thru-hull fitting and, inside the boat, through the backing plate. Add a washer and thread on a nut inside, then seat the plate on the inside end of the fitting. Outside create a bridge by using the other two pieces of wood to support the ends of the speared piece on either side of the fitting. Add a washer and a nut, tightening until the bridge is clamped in place. Now turning the nut will pull the backing plate toward the hull, extracting the thru-hull in the process. Putting the sealant under stress then giving it time to stretch can avoid the common result of tearing away bits of the fiberglass laminate. If the sealant is polyurethane, a release chemical can help.