Final fairing is the inspection and refinement stage after the main low areas have been filled. The objective is a continuous fair curve, not a surface that merely feels smooth in one small area. Long tools, controlled sanding patterns, guide coats and low-angle light reveal shape more reliably than fingertips alone.
Keep this stage separate from bulk filling. If a guide coat reveals a broad low area, add fairing compound rather than sanding the surrounding surface excessively.
Quick answer
Use a contrasting guide coat, sand diagonally with the longest suitable board, read the remaining guide marks, refill true lows and stop when the surface is fair and prepared to the primer manufacturer’s required profile.
What you need to know
- Fair means a smooth continuous shape; smooth means low surface roughness. You need both before topcoat.
- A longboard bridges local highs and shows the real contour.
- Raking light and straightedges help verify shape.
- Protect structural laminate by keeping the fairing process in the fairing layer.
Tools and materials
- Longboard and firm hand blocks
- Dust-extracted sander for appropriate broad work
- Guide coat compatible with the system
- Straightedges and flexible battens
- Abrasives in planned grit stages
- Approved fairing compound for corrections
- Task lighting, dust extraction and PPE
Step-by-step method
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Allow a complete cure
Confirm the fairing compound has reached the sanding stage for the actual temperature. Soft compound clogs abrasives and tears rather than cuts cleanly.
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Establish reference shape
Use battens, straightedges and low-angle light to locate highs, lows and unfair transitions. Mark boundaries outside the sanding path.
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Apply a light guide coat
Use a thin contrasting guide that will sand away from highs and remain in lows. Avoid a heavy coating that loads paper or contaminates the next layer.
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Longboard diagonally
Sand in crossing diagonal strokes with even pressure. Let the board span the surface; do not dig into isolated marks with fingertips.
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Read the pattern
Uniform removal indicates a fair zone. Persistent guide in a broad area indicates a low; rapid breakthrough indicates a high or insufficient fairing thickness.
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Refill true lows
Remove dust, prepare within the product system and apply only enough fairing compound to restore the curve. Re-guide and sand after cure.
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Prepare for primer
Finish at the abrasive profile required by the primer, clean by the approved method and inspect under varied light. Prime soon enough to avoid contamination.
Watch the demonstration
The video is supporting material. Follow the current product instructions and safety data sheet for the products in your shop.
Common mistakes
- Judging shape with a small soft sanding pad
- Spot-sanding every dark guide mark
- Skipping cure time
- Sanding into structural fibres
- Leaving sharp transitions at repair edges
- Finishing too fine for the primer system
Safety
Read the current resin, hardener and filler labels, technical data sheets and safety data sheets before opening the containers.
Wear splash-resistant eye protection and chemical-resistant gloves selected for the product. Keep epoxy off your skin; repeated exposure can lead to sensitization.
Provide ventilation appropriate to the job and product. Sand only fully cured material, control dust at the tool and wear suitable respiratory protection where the risk assessment requires it.
Mix only the quantity you can apply within the stated working time. Epoxy cures faster and produces more heat when left in a deep mixing pot.
Frequently asked questions
What is a guide coat?
A very light contrasting layer that reveals high and low areas as it is sanded. It is a diagnostic tool, not a build coat.
Why use diagonal longboard strokes?
Crossing diagonals average the cut over a wider area and reduce grooves that follow the hull or panel direction.
When should I refill instead of keep sanding?
When the surrounding contour is correct and the remaining guide pattern identifies a genuine low. Do not sacrifice sound material to chase it.
What grit should I stop at?
Use the primer manufacturer’s required surface profile. Stopping too coarse can telegraph scratches; too fine can reduce mechanical key.
Get the right materials for the job
Tell our team what you are making and how the finished part will be used.
Shop WEST SYSTEM fairing fillers and toolsAsk our technical teamSources and further reading
This guide provides general educational information. Products, substrates and working conditions vary. Follow the current technical data sheet, package directions and safety data sheet for every material you use. Structural, code-regulated or safety-critical work may require a qualified professional.