I used mostly Expancell (FairLite ?) as supplied by Europa. Micro and
Superfill were also used in relatively minor amounts. I used micro along the
wing spar where there was a narrow but fairly thick layer required, near 1/8
inch in some places. Micro was also used for the filler on the wing walks
with the idea that it would be less prone to denting on inadvertent contact
with shoes. Superfill was used as a spot filler in small areas after most of
the filling was complete, mostly because it was easy to mix in small amounts.
West epoxy was used along with their low temperature hardner to allow
working at low workshop temperatures of 50F or so.
Cabosil (15% by volume) was added to the micro and Expancell fillers to
improve spreading, as suggested long ago by Graham.
Some impressions of the various fillers and their characteristics:
Micro is very hard, more difficult to spread than Expancell, and takes a long
time to sand. Avoid applying more than necessary to minimize any sanding
required.
Expancell is much easier to sand than micro. By varying the amount of filler
vs epoxy the ease of spreading can be adjusted; a very thin layer with a nice
feather edge can be applied smoothly when a slightly wetter batch is mixed.
I used multiple thin layers to get to the required thickness in some areas --
this to reduce the required sanding by avoiding excess buildup.
Superfill was used to finish up some areas, especially around the
windshield, cowl, and fin joint. I found it more difficult to smoothly spread
Superfill than Expancell, probably because of the inability to adjust the mix
as was done with Expancell as well as the low workshop temperatures (around
60-65F by the time Superfill was used). The filler in the Superfill I
received seemed coarser than the fill particles from Europa, sometimes
resulting in fine lines in the surface as the filler was spread.
Overall, I preferred the Expancell filler with West epoxy for its ease of use
and sandability. However, workshop temperatures may have affected the
apparent characteristics.
John N44EU
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