by Morten Olesen

Have you ever heard the saying, "A chain is only as strong as its weakest link”?  That saying very much applies to working with epoxy when building a boat.  Because epoxy is partially responsible for holding your boat together and sealing out water, if the bond isn't successfully executed, your whole boat may be at jeopardy.

Anyone who has worked with epoxy in a professional capacity will quickly tell you there are three vital steps that can make or break the success of your project.  It may surprise you to know they all deal with surface preparation and not with the actual bonding technique itself.  That's because in order for the epoxy to mechanically "key" with the surface and form a strong bond, the surface has to be prepped to receive the epoxy.

Surface Preparation

For good adhesion to occur, you must start with a surface that is:

> > > Clean - free of grease, oil, wax, mold or any other substance that might interfere with a direct bond between the epoxy and the wood.

> > > Dry - wet surfaces don't accept epoxy well and can cause bond failure or weak bonds.

> > > Sanded Properly - 80-grit sandpaper is recommended for most types of wood to produce ideal conditions for a durable bond. This includes hardwoods, teak and other oily woods as well as porous woods.

Two-Step Bonding

Before beginning this phase of the process, be sure all parts to be bonded fit properly and are dry.  Also make sure each piece has been cleaned and sanded. 

Apply the epoxy resin mixture to the area that will be bonded (called "wetting out").  For tight areas this can be accomplished with a small brush or you can use a roller for larger areas. Be prepared to move forward immediately before the resin becomes tacky.

For bonding two pieces together, stir filler into the epoxy mixture until it becomes thick enough to hold.  Apply the mixture to ONE of the bonding surfaces. Quickly fit the two surfaces together before the mixture becomes tacky-feeling to the touch and then clamp the components together with enough pressure to squeeze a small amount of epoxy from the joint. Remove the excess epoxy with a putty knife.

For fillets, apply, shape and smooth the thickened epoxy with a wooden mixing stick, a disposable plastic spoon or another round-edged tool.  A little excess bonding material will remain.  That's usual.  Simply use a putty knife to scrape evenly along the edges of your fillet, removing the excess.  This leaves a clean-looking final fillet.  After the fillet is cured, sand with 80-grit paper.

After the fillet is cured, apply the fiberglass tape. Start with wetting out the area where the tape should be and then lay up the tape in the wet epoxy. Wait a few minutes while the tape soaks up the epoxy. It is sometimes necessary to apply more epoxy to the tape if any areas remain dry. This should be done quickly before the epoxy cures. 

Once cured, you will have a strong, durable joint between the panels of your boat.

Epoxy and Hardware

Epoxy can also be used to bond metal hardware such as hinges to ensure a watertight seal.  Wet out a pilot hole and then fill it with prepared epoxy resin, using a syringe.  Insert the screw or other fastener and allow the epoxy to cure before use.

In Part 3 of this series on epoxy, we'll look at situations when working with epoxy doesn't turn out exactly as you planned… and what to do about it.

Morten Olesen is a master boat builder and Naval Architect. Visit Morten's site <a href="http://www.boatplans.dk">http://www.boatplans.dk</a> to get his exclusive line of <a href="http://www.boatplans.dk">boat plans </a> which includes 3-D computer models. You'll also get his free Boat Builder Master Course with your order.  © 2007, All Rights Reserved