There have been a couple of posts to do with custom formed kayak seats so I thought I would share my experiences...

I am just in the process of making my first fiberglass seat from a mold that constructed from some wood and some mortar. It took about 3 hours to make the mold (not considering setting times) and about 2 hours forming the seat.

The mold is made from about 8 feet of wood (24" scraps of spruce 2x6 & 2x8) 3/4 of a bag of premixed mortar and covered with scraps of 6 oz fiberglass - under $10.00 of materials.

I made the frame from 3 pieces of 2x6 and 1 piece of 2x8 for the back. The width of the frame was set by width of the cockpit so the back rest and front of the seat were cut to size. The length of the seat was determined by sitting against the backrest and moving the front piece until I got the support I wanted under my legs. The front is angled back slightly and, in hind sight, I should of angled the other pieces as well. The sides are shaped to be narrower at the top. The "armrests", back and the four corners are radiused to blend together and make for easier glassing. A piece of masonite was added for a bottom.

The inside shape is formed of mortar that was mixed to a VERY stiff consistency and packed around the inside of the frame. I covered the frame with a plastic bag and sat in the mortar to form the seat. It took a couple of adjustments to get all the bumps and hollows in the right places and to smooth the thing over a bit. If you try to work the mortar too much it will start to "float" the water to the surface and the mortar will sag. Once I was happy with the basic form I put the mold aside to partially cure. After about 3 hours the mortar had cured firm enough that I could use a stiff bristle brush to sculpt the seat. It only took a couple of minutes to remove the extra mortar to make room for padding and to blend the contours nicely.

After the mold had set/dried for a week, I applied a layer of fiberglass and a coat of resin to give a smooth finish. A light sanding is required to remove the gloss from the resin to allow the mold release to adhere better. I mounted the mold on a "lazy susan" so that I can rotate it conveniently while glassing - it is quite heavy.

I applied two coats of a mold release that I cooked up from a mixture of bar soap, water and vegetable oil. The mold release is applied like old fashioned shaving cream - a foam whipped up with a soft damp brush. When the foam had dried to a hard waxy surface I covered the mold with one layer of 6 oz cloth. The next morning I popped the casting off of the mold and did a rough fitting to the kayak. I then put the casting back on the mold and build up the high stress areas (corners, armrests and front of the seat) with some scraps of glass before adding 2 more layers of glass all over.

The seat is very light in weight. The side panels are a bit thin but the main support is in the reinforced corners and the base - it is actually solid to sit in and does not flex at all.

I had intended to add some pieces of rigid foam or strips of luan inside the seat as stiffeners but the whole thing seems strong enough as is. I will have to use the seat a couple of times to see if additional reinforcing is required.

This is my first attempt at butt molded seats. I use my kayaks for fishing and flat water touring so I don't need the "press-fit" style of cockpit/seat the is required for playing in the ocean surf. I got to use the seat for a couple of hours on Sunday :-) and I am quite pleased with it - very comfortable, even without any foam covering.

Hope this is of help. As always, comments and suggestions are welcome.

Hank

Here is a picture of the mold:

http://ross.secant.com/kayak/bbsposts/hanksseat.jpg