Great advice Graham.
We learned the hard way here at the shop. Consistency is the key. I
mix the expand cell until the stick practically or does break when
mixing then allow it to sit for 20 minutes to gas off and apply with a
plastic spatula. If you leave it thin enough to roll it on, it will be
heavy. So make it thick enough not to sag but not dry enough that you
can't spread it without it rolling off. I'm not at the shop but I
believe we use a 4 to one ratio for thin and 6 to one for thick.
Cleanliness of the surface is next to Godliness and a careful scuffing
with 80 grit is all that is required for bond. If your cured filler is
gooey and doesn't seem to sand without clogging, check your epoxy mix
ratio and your expand cell amount added and the all important cure temp.
I use Aeropoxy because it cures at 75 degrees or higher in low humidity
in 8 hours and cures pretty rock solid. Ampreg 21 likes to be warm and
dry, closer to 100 to 130 F and cures slow. Alas, even the Superfil has
a slightly gooey top coat when cured.. Using the cheese grater type
wood rasp or plane is good for us amateurs to knock off that skim layer,
then give it a day and go to sandpaper. Where we usually screw up is we
put too little filler on. The pros put on more filler and leave 90% of
it on the floor. My body shop uses Superfil because of its consistency
and cures it in the paint booth in dry and warm conditions. A thicker
layer cures quite well. If it is applied in a thin film, by the time
you get the goo layer off, you have no filler left. Allow the Superfil
or Expandcell to set after mixing for 20 minutes (at 75 F) then spread
to a 1/8 inch coat. The pros can do a smooth application but they and I
leave the ridges and drag lines alone. Like a scab, don't pick at it.
Superfil cures fully overnight at about 80 degrees, but runs on vertical
surfaces like the fuselage side so be prepared. After cure, they cut it
with the mud hog (large random orbital sander with 55 or 60 grit) and
they throw sand paper away as soon as it clogs. For finishing, they use
a random orbital sander with a 2 foot by 9 inch plate as the sanding
platform, giving superb results. Johnny can fill an XS in a week, but
cure time has to be perfect as well as the workload in his shop. I find
for quick jobs, I use expand cell mixed thick and sprinkle a bit of
plastic micro or Cabosil on top to make it sandable quicker. The
micro/cabosil sprinkle just reduces the gummy top coat as it absorbs
some of the goo. A friend of mine with a scratch built Long EZ filled
his weave with wet epoxy and sprinkled on 3M glass sphere micro (rather
than Expandcel which are an expanded plastic sphere very compatible with
epoxy resins) in large quantities and allowed it to cure. It is a bit
heavy. He vacuumed off the dust (he has a bagged Shop Vac) and then
lightly sanded the surface to get it smooth but with irritating glass
bubbles everywhere. Now that the weave was filled, he then applied
Superfil over the now smoother but roughened surface. If your Classic
wing is very rough, like mine was, you can use thick fishing line or
string trimmer line, hung every couple feet to judge the thickness of
your filler as others have written about. Then backfill the line holes.
Sand until you start seeing the color of the glass coming through on the
high spots. Sand with 80 grit then finish to 150 or 220. Coat with
primer such as Dupont 2K or with the finishing system of your choice.
Sand again down to 320 grit and prime again. Be sure to use a good UV
protection polyurethane paint for your final finish. It will be
gorgeous.
Superfil is my preferred filler. I believe you get what you pay for.
However, I still use Expandcel quite a lot. Support your piece well as
some components tend to sag a bit and I have built in a bent flap by
sanding without center support and made the upper surface flat but the
flap bent under my sanding pressure... Oh well, sand it off and redo it
is the cure.
Please use caution and a good mask when using fillers. 3 M Micro glass
spheres will kill your eyes and lungs, Cabosil isn't a lot safer as it
is silica, and Expandcel uses an expanded plastic sphere or cell and
Superfil supposedly uses the same (it is not talc per se) but that isn't
completely safe either though it has a pretty clean MSDS sheet. So wear
protection. Get good shoes and a block sander and "git-er-done".
Regards,
Bud Yerly
Tech support.
----- Original Message -----
From: GRAHAM SINGLETON<mailto:grahamsingleton@btinternet.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Friday, December 28, 2012 8:06 PM
Subject: Re: Europa-List: Filling/Painting Classic wings & Tail.
SUPERFIL? SP106?
Dave
I use a 1/6 by volume addition of Cabosil (colloidal silica) mixed
with the expancell. It enables about 50% more expancell to be added to
the same amount of resin.
It is best to be consistent as possible with the amount of resin and
expancell you mix to avoid variations in the filler
Superfil is an easier solution but expensive. For rough sanding I use
a very sharp small wood plane, (Russ Lefevre gave me that tip) it cuts
through the incompletely
cured resin: the heat of sanding softens the resin unless it is fully
cured, (which takes days,) and that clogs the paper.
Graham
-------------------------------------------------------------------------
-----
From: G-ODTW <dave@robotas.co.uk>
To: europa-list@matronics.com
Sent: Friday, 28 December 2012, 20:40
Subject: Europa-List: Filling/Painting Classic wings & Tail. SUPERFIL?
SP106?
<dave@robotas.co.uk<mailto:dave@robotas.co.uk>>
I thought it a good idea to get my tailplanes balanced before I put my
top on. They needed filling (I used Ampreg21/Expancel as per Europa
manual) & then will need painting. But I am now finding it a heck of a
job to sand the filler. After 2 days of it, I have had enough. The
sandpaper constantly clogs, and it is bl**** hard work - And my Classic
wings are much bigger than the tail!
Some people seem instead to use Superfil. But I am also told that
SP106 is the resin many people use for the surface filling job, which
sands without problems, presumably with the supplied Expancel.
Many folk have trodden this path before me, using many methods. 20
years on, is there now a "best practice" for filling / sanding /
painting?
All advice greatfully received. Thanks. Dave Walters.
--------
David Walters
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