Duplicate a Production Seat

The fiberglass seat from my Dagger Sitka was so comfortable, I decided to take a mold from it to make an identical seat for my strip boats.  This turned out to be a simple project with fantastic results.  This process should work on any seat that has a shiny, smooth surface.  Here's how to do it....

Start by removing the existing model seat from your production boat.   Although it might be possible to take a mold from a seat still attached, it really would really be messy.

Clean the seat, cover any bolt holes on the seat with tape, and  apply a generous 2 coats of PVA mold release to the entire inside surface of the seat.    I could have used paste wax, but I didn't want to take the chance of ruining my seat.   You can get a small bottle of PVA mold release from West Marine for about $7.

The mold itself is formed by laying multiple layers of cloth on the seat and coating them with epoxy.  Start with a single full layer of cloth right next to the seat, followed by scrap pieces  left over from sheathing the kayak.   You'll want to apply enough layers of cloth to make a semi-rigid form, but not so rigid that you can't flex it to separate it from the seat.  I used 3 or 4 layers.    When the mold is partially cured, trim off whatever extends past the edges of the seat.

Allow the mold to cure and then remove it from the seat by slowly working around the edges flexing both seat and mold.  You'll know that the mold is detaching from the seat when the mold turns white and doesn't show through the color of the seat.  Don't worry if this doesn't make any sense now, you'll recognize it when you see it.  Work slowly, circling the perimeter, flexing as you go.  It will finally all detach.

To form the new seat, repeat the entire process, except now you apply the fiberglass to the outside of the mold.  The outside (where it was against the seat) should be smooth and shiny.  Clean off the old mold release from the mold, and recoat with 2 fresh coats and allow to dry.  Again, start with a piece of glass (I used 6 oz.) that covers the entire surface of the mold and begin coating with epoxy.   To make the new seat black, I used graphite powder mixed at its maximum recommended concentration; 10% by volume.  Since graphite doesn't mix easily, I mixed it into the resin first, and when that was blended, I added the hardener.

In retrospect, I should have allowed this first layer partially cure before adding subsequent layers.  This would have prevented the glass from pulling away from the mold because of the extra weight hanging over the edge (see the lower right picture along the edge of the seat).  Allow this layer to cure to green state, and then trim it (being careful not to pull up the edge), mix up some more graphite goo, and start adding overlapping scraps, moving over the entire surface evenly.  I used one layer of woven roving as one of the middle layers, but I wouldn't do it again.  It was like working with woven linguine; just too unwieldy.  On my next seat, I used all scrap 6 oz. plain cloth.  I used probably 7-8 layers with the final one covering the entire surface.  This keeps the bottom smooth without any sharp points from the edges of the scraps. 

Let these layers partially cure and then trim off the excess.  When fully cured, work the mold out of the seat (the mold will be more flexible than the seat, so it's easiest to flex).  Work slowly, circling the perimeter.  Once the seat is removed, admire your work, but don't sit on it yet.  Place it on your workbench and press down in the center, noting where it flexes the most.  Add some additional reinforcement to the underside in those areas if you think it's flexing too much.   Once the glassing is done, file the edges (I used a small Surform tool) to round-over any sharp areas.  Glue a small piece of thin (1/4") minicell foam to the bottom to help conform to your hull shape.  Congratulations, you've got a new, production quality fiberglass seat!

-Ross