It used to be that the EkoFill was applied directly to the bare fabric but I guess there were some issues with adhesion so they now recommend using diluted EkoBond as a first coat on the bare fabric to better prepare it for the EkoFill and later coats. From section 10 of the master procedures manual:
Section 10 Sealing the Weave
Before EkoFill (E620) can be applied, the
weave of the fabric must be sealed with
EkoBond (E610G or E610L). (To simulate
the look of cotton fabric on the inside of
the aircraft use EkoBond Linen (E610L) to
seal the weave.) In the past EkoFill was
used to seal the weave of the fabric, but
we have found that using EkoBond is both
easier and provides better adhesion.
EkoBond must be used on all fabric to fill
the weave prior to application of EkoFill.
Prior to applying EkoBond to seal the
weave, the fabric should first be cleaned.
Dust should be removed with a vacuum or
compressed air. Next the fabric should be cleaned with EkoClean (E670) diluted at a
15:1 ratio applied with a spray bottle and a sponge. The fabric should then be rinsed
with clean water. Allow the fabric to dry completely. The fabric is now ready for
EkoBond application.
Dilute the EkoBond with distilled water at a ratio of exactly 3 parts EkoBond to 1 part
water by weight. Apply EkoBond to the fabric with a foam brush, being careful not to
miss any area. Only one coat is necessary but may be brushed in multiple directions to
ensure complete application. Do not wipe off excess but allow to dry. If the foam brush
begins to shed small pieces of foam, use a new one. It is not necessary to apply
EkoBond over areas that have been glued with EkoBond. Once EkoBond is applied,
allow it to completely dry for approximately 30 minutes to 1 hour. It will be susceptible
to dust and dirt because EkoBond will remain somewhat tacky even when dry. * Once
the fabric is sealed with EkoBond and dry, EkoFill should be applied as soon as
practical to prevent dirt and dust build up. It is acceptable to store parts for a long
period of time once EkoFill has been fully applied, but care should be taken to keep it
clean and dry. If the parts are to be stored it is advised to not sand the final coat of
EkoFill until ready for topcoat. When ready for topcoat, wipe with a rag lightly
dampened with Isopropyl alcohol prior to sanding. If the cleanliness of the surface is
still in doubt, you may add an additional coat of EkoFill (E620) or EkoPrime, (E75XX)
prior to top coating