A Simple Spar Repair with West System Epoxy
Learn how to extend a wooden spar using a proper 20:1 scarf joint and West System 105/205 epoxy. In this step-by-step boatbuilding and woodworking tutorial, Mark from Nomad Boatbuilding shows how to laminate, prep, clamp, and glue a long structural scarf for a mast, yard, or boom extension.
Perfect for wooden boat repair, spar restoration, or anyone wanting cleaner, stronger epoxy joints.
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00:00 – Intro & Project Overview
Mark introduces the spar extension project and explains why this small job offers a valuable woodworking lesson.
00:37 – Why This Spar Needs Extending
Discussion of the customer’s boat, new sails, and the need for a longer yard.
01:07 – Scarf Ratios Explained (12:1 vs 20:1 for Spars)
Why spars need a longer 20:1 scarf for strength.
01:54 – Examining the Original Spar Construction
Laminations, voids, and why a solid extension piece is acceptable.
02:33 – Choosing and Preparing Stock for the Extension
Selecting Douglas fir, adjusting thickness, and prepping veneer strips.
03:40 – Cutting a 12:1 Scarf on the Veneer Strips
Scarfing veneers to increase thickness as needed.
04:20 – Surface Prep Before Epoxy
Sanding, marking orientation, and preparing pieces for glue-up.
05:02 – Mixing West System 105/205 Epoxy
How much epoxy is needed and Mark’s “1 pump per square foot” method.
06:25 – Proper Epoxy Mixing Technique
Mixing times, pump priming, and avoiding bad ratios.
07:30 – Wetting Out Porous Douglas Fir
Why you pre-coat both surfaces and allow time for absorption.
08:55 – Letting Epoxy Soak & Preventing Glue Starvation
Managing resin absorption in tight-grained Douglas fir.
09:45 – Veneer Glue-Up & Clamping Strategy
Using the bench as a caul, managing squeeze-out, and clamp spacing.
11:40 – Tips for Controlling Slippery Epoxy Laminations
Clamp pressure, avoiding shifts, and selecting proper clamps.
12:40 – Cleaning Up Epoxy Squeeze-Out
Table saw trick using a temporary fence to remove cured excess.
13:28 – Building a 20:1 Scarfing Sled
Constructing a simple, accurate sled for long tapers on a tablesaw.
15:42 – Dialing in Scarf Accuracy
Shimming, recutting, and using sharp blades for clean results.
16:55 – Cutting the 20:1 Scarf on the Extension Piece
Using the sled for a consistent feather edge.
17:40 – Preparing for Final Spar Glue-Up
Aligning the new stock, marking ends, and ensuring proper overhang.
18:55 – Wetting Out the Joint (Two-Part Bonding)
Applying unthickened epoxy and allowing it to tack.
20:10 – Thickening Epoxy with Colloidal Silica
Creating a structural glue mixture with the right consistency.
21:00 – Applying Epoxy & Final Glue Spread
Using a toothed spreader to ensure full contact and no trapped air.
21:48 – Setting the Joint & Preventing Slippage
Anchoring ends, sighting alignment, and using cauls properly.
23:10 – Clamp-Up & Evaluating Squeeze-Out
Ensuring a full bond without starving the joint.
24:20 – Epoxy Cleanup & Curing Advice
Wiping excess, avoiding disturbing the glue line, and cure times.
25:50 – Choosing the Right Hardener (205, 206, 207, 209)
Temperature considerations and Mark’s preferred setups.
27:02 – Why Repair Instead of Building a New Spar?
Cost, materials, labor efficiency, and customer expectations.
28:40 – Alternatives to Long Scarfs (Bird’s Mouth & Finger Joints)
How to shorten scarf length without reducing structural ratio.
30:10 – When to Use a Nib Scarf
Why nibs work on rub rails but not spars.
31:00 – Final Results & Finished Scarf
Inspecting the feather edge and the clean glue line.
31:40 – Closing Thoughts & Tips
Recap of the method, benefits of simple jigs, and using quality epoxy.