In spite of the added complication of repairing the finished deck
surface, this kind of repair is usually done by removing the top skin,
then working down. That's easier. Is it possible to turn the boat
upside down so you're working downwards? You didn't identify the type
of boat, so I had to ask.
If not I'd think about vacuum bagging and sucking from the top side
through the top side.
Get the West System booklets on fiberglass boat repair and on vacuum
bagging techniques. They're very good and complete.
I'm sure that others will think of refinements , but here's my rough
outline of the 'stack" from bottom to top:
I'm assuming that the deck has some compound curvature.
- the vacuum bag itself
- a layer of peel ply
- a layer of glass cloth, saturated
- maybe 36-48 oz./yd^2 of knitted glass, saturated
(the glass plies to be tapered out over the feathered edge of
the old laminate.
3/16" is probably much thicker than the FRP needs to be.
Consider using slightly thicker foam.)
- your foam, kerfed from both sides so that it'll pass resin and vacuum
- some thickened resin, to bond the foam to the upper skin
- the old upper skin, with holes drilled at intervals to pass excess
resin and vacuum
wax the upper skin well and spray with PVA before drilling
- another sheet of peel ply
- a layer of bleeder-breather
- the upper bag, with vacuum tap(s) in it.

I'd think about laying up he whole lower stack from bag to foam on a
slightly oversize piece of plywood.
Assemble the upper stuff, lay up the stack, offer it to the opening,
tape off the bag, start the pump, fix the leaks and have a beer.
If the deck has NO compound curvature, you might think about using a
sheet of Formica (with pva & wax) instead of the lower bag and peel
ply. If you pull this off, it'll be a very neat trick.

This will take long enough to cure that there is no substitute for a
vacuum pump. It would be BAD THING if a shop vac crapped out when the
layup was at the gooey stage.

I recommend that you first do some other small jobs using vacuum bagging
for practice.
Also, do a dry run, pulling vacuum on the bag glss and foam, to make
sure that there aren't voids in the deck core which prevent pulling a
vacuum.

This is a complicated job. Don't jump into it. Ask questions. It can
be done right.



Marc wrote:

I have discovered that I have wet core in several locations on my
cabin top. My limited experience with fiber glass has been with West
System Epoxies and I am comfortable with their use. The bottom skin
has been removed, the wet core excised and the top skin abraded and
prepped for bonding. I intend to wet out the underside of the top skin
and use Baltek Contour Kore AL600/10 to replace the core. After that
cures, I need to build up a bottom skin of at least 3/16". I need a
layup schedule that will give me max strength with the fewest number
of plies. This is a winter project. I will be able to maintain 40* in
the boat and intend on using the fast hardener. All suggestions are
welcome and hints as to technique or alternate methods are
appreciated.