I have done many Kevlar repairs. If you want full structural stength you should make a repair where you scarf at a ratio of 1:40, i.e. for 1 mm thick material you taper over 40 mm. If you have access from both sides, you should do this from both sides to half wall thickness. If you can't get easily to the inside, make it to full thickness from the outside. In this case you have to place a backing on the inside, which allows you to laminate over any gaps, where you removed the material completely. This can be done using styrofoam covered with packing tape (the clear stuff). Use double sided tape to hold it in place for the repair. The packing tape ensures that you can get the styrofoam out easily after laminating.

In order to repair the kevlar properly, you should get rid of the fuzz. This can be done by using wet sanding paper (use it with water) in the range of 400 to 1000 grid. After wet griding and drying!! (you can use a blow dryer carefully) use 150-200 grid sandpaper to slightly roughen the surface. The wet fine grid was only to remove the fuzz. For a proper bond you should have it rougher. Don't remove any significant material at this time.

The lay-up should be of equivalent thickness. Put the largest layer down first and stack them up in decreasing size. Depending how experienced you are you should use a glass layer to cover the entire area last, which is your grinding layer to smooth everything out. If you grind into the kevlar again, repeat the fuzz grinding proceedure and put a layer of gelcoat on.

Andreas

: A friend came to me today with a 1 1/2 inch hole and 4 inch gouge in the
: front of his kayak from hitting ice chunks while paddling near tidewater
: glaciers. I have never worked with kevlar. The Kevlar seems intact but
: wrinkled, dented and leaking. The fiberglass over it (that was) is pretty
: smashed and partially gone.

: Can I dry it out, sand and taper the edges, fill in with thickened epoxy, and
: lay fiberglass patching right over it?

: Do I need to do anythig special to the Kevlar to insure a good bond?

: Thanks, Randy