From old NG post of howto.



(vii) The easiest way to get a perfectly "fair" surface is to get
the shape right first before you cover the whole area, the easiest
method is to put little ridges of filler on first;
(a) In a placky putty applicator cut slots in it, say in your
case little notches 1/4" X 1/4" about 1" apart. (depends on the size of
the area, on the side of a big boat sometimes you hand build ridges 1"
high 1'- 2' apart!! & adding a little pigment is a good idea sometimes)
(b) Mix up some thick filler, catalyse & cover the are to be
faired, then scrape it off with your applicator from (a), the result is
the area is covered with little 1/4" ridges.
(c) After it's cured it's much easier to sand down (small areas
an orbital sander is OK big ones use a long board) to fair. Then you can
use a normal (no notches) applicator to apply filler between the ridges,
using the ridges as the guides.
(d) Again after cure orbital sand till you get down to your
fairing ridges & no"through" the filler even before they get to them)
(e) Just a hint on fillers, they get very hard if allowed to
completely cure & then a good finish is almost impossible to achieve. So
do a little test piece & depending on your brand, catalyst & temp you'll
roughly find;
it goes about the consistency of cheese after about 10
mins, at this stage you can remove lots quickly & easily with sweeping
smooth (fair) strokes of
a surf foam (hole punched tin file??),
at about 15 mins it starts to really go off so won't clog
open grit paper (say 36 grit) on an orbital sander but is still soft
enough to really tear off in smooth passes,
after about 20 mins it's starting to really cure & as far
as nice fair shaping is concerned it's too late!!, sorry grind it off &
start again ;-)

(f) Then you can do the normal surface finish stuff with thin
filler to get
rid of the orbital sander marks etc, prime & paint.


Karen Smith