Didn't Coop have a complete run down link in his signature?
He did at one time then removed the link to update it.
Here you go:
Here is how you fix bad balsa.
1. Figure out how big of an area needs repaired, and draw a mark a few inches beyond it.
2. Use some sort of cutting wheel that you can set how deep you are cutting. I have used a circular saw for this, until I found better tools it works great. Set your depth at about 1/4inch or less, and cut around the area you have marked.
3. Use something to pry under the edge of the glass. The only thing holding the glass down would be the good balsa that is still there. The rotten balsa should give way quite nicely.
4. Set the piece you cut out aside to use as a pattern for new glass. Make your new pieces. Make at least one piece the same size, and the rest a few inches bigger. Use either heavy roving or biaxial cloth.
5. Use a wide wood chisel and a hammer to chip away all the balsa that is exposed. Try to get as much out as you can before you break out the grinders. Its rotten, it should come out easy.
Go to someplace like
www.fibreglast.com and order some new balsa. If you cant find any locally.
6. Use a sander or a grinder to clean up the inner skin.
7. Cut 2 pieces of 1-1/2 ounce fiberglass mat. The same size as your repair area.
8. Have your glass and balsa precut, then use your brush and wet out the repair area with resin. Then lay one of the pieces of 1-1/2 ounce mat on some cardboard and wet it down with resin, then take it and place it down in your repair area, and brush out all LARGE air bubbles. Don't worry about any small ones, as they don't matter for what you are doing.
9. Take your precut balsa and brush resin on the side that does not have the fabric holding it together, then quickly place it in the repair area over the still wet glass mat that you just placed in there. Use your hands to press it in as best as you can. After you get it in place. Take some wax paper and cover the entire repair, then cover that with cardboard. Place any kind of weight you can find on top of the card board. Books, magazines, newspapers, anything.
10. Now walk away for at least 2 hours. Have lunch, drink a wobbly pop, what ever you want, just leave it alone for at least 2 hours.
11. Now remove the weights, the cardboard, and the wax paper should have kept the cardboard from sticking, you are ready to continue.
12. Use a filler like dura-glass to fill in around the repair area, there will be some gaps between the old area and the new area. Fill these areas flush with the level of the new balsa, don't fill them to the level of the old glass layer. Let this set up. Then sand smooth if needed.
13. Brush a layer of resin onto the new balsa over lapping onto the old glass. Wet the other piece of 1-1/2 ounce mat on the cardboard again, then place the mat onto the repaired area. Brush out the LARGE air bubbles ONLY right now. Take the piece of biaxial glass or roving, that is the same size as the repair and wet it out on the cardboard. Then place it on top of the still very wet mat. Use a plastic or rubber squeegee to work all the air bubbles to the sides and out. Do this as good as you can.
14. Take the last piece of biaxial or roving and wet it out on the cardboard, the place it over the still wet glass you just laid down.
Use a squeegee to work all the air bubbles to the sides and out. Keep working at it until all the air is gone or the resin starts to set up.
15. Drink another wobbly pop, cause you just fixed your boat.
http://voices.yahoo.com/how-repair-damaged-balsa-core-old-boat-194125.html
