JEM Watercraft

Step 4: Filleting Seams
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Author:  jem [ Thu Sep 02, 2004 12:42 pm ]
Post subject:  Step 4: Filleting Seams

Note: Our prefered way to fillet and fiberglass seams is to "tack weld" the seams first and then complete the fillet and tape after the welds have completely cured. Many builders have many views on the best way to do things. This is the way we beleive provide the best results.

We used mahagony woodflour which makes some very dark material when mixed with the resin. This was done to more clearly display the material is our pictures.

As stated earlier in the process, ensure you maintain a consistent gap. The glue/material that fills the gaps will disperse and stress loads evenly along the seam and to the fiberglass. You do NOT want a "hard spot" or wood-on-wood contact point especially below the waterline.

Mask off the opposite side of the seam from which you'll be working. Paint masking or duct tape works well.

Mix a small amount of resin. Remember: all wood surfaces, even edges must be coated with resin. Coat the wood where the fiberglass tape will be applied. Mix woodflour into the resin until reaching a peanut-butter-like consistency.

Fill the gap in the seam with just enough material to fill the void. Do not overfill the seam and have excess material flowing out of the seam. Clean up any excess material.

Fill as much of the gap between stitches as you can. Continue this process for all of you seams. The masking tape will contain the filler material.


a. The gap filling glue is strong, but can be brittle if handled roughly.
b. Filleting and taping can be a time consuming task.
c. Trying to wet out cloth with resin that is starting to cure and harden is not a fun task.

For these reason, we recommend you work with small lengths of seams rather than trying to do an entire seams at once.

Cut the lengths of fiberglass tape you'll need.

Remove the stitches from the seam area you'll be working with.

You may wish to do a light sanding of the taping area to smooth it out and remove impurities.

Mix some resin, then woodflour until reaching a peanut-butter-like consistency.

Fill in any gaps not filled before. Also apply additional material to make a smooth and tangeant surface transition. The fiberglass tape will lay on top of this radius/fillet.

Do NOT use excess material for this step. You only need enough material to form a radius. Excess material in your fillet will not make the seam stronger. Clean up any excess material.

Allow the fillet to cure until it reaches a bubble-gum like consistency. About 40 minutes using medium cure rate resin at 70 degrees F. Apply a coat of resin over the fillet and area where the fiberglass tape will lay.

Place the fiberglass tap onto the seam.

Gently work the tape into place while removing any and all air bubbles. Also press out any excess resin out of the tape. You only need just enough resin to wet out the tape.

The tape will become transparent as it fully wets out. If you encounter an area that is not wet out, apply additional resin. But use the resin sparingly. Spread any excess resin on other wood srufaces that have yet to be coated.

Let seam fully cure. Repeat this process for all your seams.

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