Filler problems...need advice

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#1

Hi guys
I need to sand my wing plug until it becomes laminar. Therefor I have to minimise bumps in the profile curvature until they are smaller than 2/1000 of a milimeter. I know other human beeings managed it.
i use a engine head micrometer to measure the waviness.
I use a 2 meter heavy iron sanding block and 2 meter aluminium scaper to shape the profile.
My problem:
With epoxy, tixotropic and microballoon additives I got scapes and have to wait two days until cured and sandable. The paste isnt really creamy. Ok, suboptimal but managable.

With a standard automotive poliester filler a disaster. The Filler clogs my sanding block in one minute after 24 hours cure. Additionally the filler has a potlife of 2 minutes not enough to smooth out 2 meter sections with the scaper. And at this stage I would say the filler is too hard maybe. In one day I filled the whole wing and the next day I had to sand all of it off wasting half a box of mirka disks.

I have not only to correct imperfections, in some areas I need to add material.

Could someone please recommend a filler that has a decent pot life( about 10-15 min), sands nicely and is creamy for precision filling i can buy in europe and most important of all, doesnt clock my sanding block?

#2

If you can live with polyester, take a look into Ferro (Spanish, Valencia) fillers, or Nord Composites polyester putties, or ATC Chemicals polyfair F26 (Canada, but I know at least in Germany it is for sale, perhaps also in Spain)

#3

Why do you consider poliester a second choice? Will I get later on finishing problems?

thanks a lot

#4

Epoxy has a much longer potlife, can be build up thicker, can stretch a lot more before braking, and has a better adhesion. I use epoxy fillers for large work, an polyester fillers for the little imperfections which remain after a high build coating is applied and sanded flat, like scratches and pinholes.

#5

Also adhesion of polyester on epoxy leaves a lot to be desired.

#6

microballoons are not a good idea for a surface filler. when you sand them you open the sphere and now have a pinhole to fill. I prefer cabosil for a lightweight additive to thicken resin.

#7

I think microspheres work really well for the discussed need. They sand much easier than anything else and can be added in larger volumes than many fillers without increasing the viscosity much. This allows you to use less expensive resin to get the same volume. Microspheres also creates one of the creamiest concoctions. I’ve never had any pinhole problems because of them. Many auto body primers contain microspheres to ease sanding and reduce weight. These micro pores increase the bond of the paint without creating porosity. At least this is true with glass sphere in the K25 zone. Maybe the larger ones could be a problem. Many fillers like cab-o-sil can be very difficult to sand.

As a side note, fumed silica/cab-o-sil has a very low bulk density because most of it’s bulk content is air. This give the impression that it is light. In reality, it’s true density (around 1.8 g/cc) is greater than the resin (1.15 g/cc). When fumed silica is mixed with resin the resin displaces the air and the result is a mixture with a higher density than the raw resin. If you want to create a light filling compound then cab-o-sil is a poor choice. You would want to use fillers that have a lower true density than the resin. Microsphere is one of the few available fillers that actually makes the compound lighter. Even cotton is more dense. Microspheres don’t work for everything but if light is the objective then it is often the only one.

#8

I tried Alexit Blade repair and its awesome. Its a poliurethane filler.