Best Epoxy Filler

Just tried to smooth out my first two epoxy/fiberglass patches using an epoxy/sawdust mix. Wow was it bad. It looked like vomit with chunks. :eek: The surface was way rougher than anything on the patches. After wiping it off with a paper towel, I am left with one question.

What makes the best filler for epoxy:confused:

Here are all of the fillers I have heard about.

  • Flour
  • Sawdust ( Maybe I had too large of particles)
  • Microspheres
  • other comercial products.

I would really like a paste type substance. I would have tried flour next but I could not find any on our shelf. We do not really bake very often.

Just send me to an FAQ somewhere if this is an old question.

BrainCorrel
________
GS550L
 
:eek:Yikes:eek:

You may want to read up on resins and resin mixing from a first hand source.

http://www.tapplastics.com
http://www.westsystem.com
http://www.uscomposites.com

Summary of common resin fillers from the above sources –

Milled Glass Fibers (Short) Add to polyester or epoxy resin to increase strength and dimensional stability for extremely high resistance to cracking.

Chopped Glass Fibers (Long) Strands of cut fiber glass approximately 1/4" in length. Adds structural strength to resist cracking.

Microspheres • Glass Spheres A light weight, white filler of hollow glass spheres that add particles of air to solid materials. Can displace 4 to 6 times the weight of resin. Improves fabrication and sanding characteristics of resin. Non-structural.

Colloidal Silica. Thickening additive used to control the viscosity of resins to prevent runoff in vertical and overhead joints. Results in an extremely hard solid with high density for structural bonding, filling and filleting. Can be used alone for a very smooth finish or in conjunction with chopped fiberglass for improved structural strength.

Wood Flour For use in glue joints and fillets on wood. Mix with epoxy to create smooth fillets that need little sanding.

Wheat Flour Used in bread and other baked goods.:rolleyes:
 
I've read that microballoons will result in easier working and sanding but will leave a porous surface that will adsorb water so it should not be used below the waterline. (Sailboat Hull & Deck Repair, by Don Casey, Published by International Marine, Camden, Maine 1996)

I agree with Dan - find a first hand source.
 
I talked to the people at US composites and they recommeded 3m glass bubbles for use below the water line and for small cracks. It was less than five bucks for 4 oz.

So much for the off the household shelf solution.

Braincorrel.
________
herbalaire
 
I gather then USC informed you microbeads are for whipping air into resin to make cosmetic fill easier to sand. Did you also discuss with them which layers might not get a filler and what other filler or fillers to mix in to the structural layers of the repair? I'm curious to hear their recommendation.
 
That video confirms what I have read. Epoxy and glass filler sands like concrete. The micro ballons sand nicely because they are hollow and result in a porous surface that you should not use below the waterline. If I were covering a patch on my boat for a cosmetic smooth finish I would use no filler or glass filler and spend the time sanding it. I would not want the finish surface of my boat to be porous. I can only imagine the type of stuff that might start growing there and you would be in huge trouble if you ever started using it in salt water. I learned in my engineering courses in college what salt does in porous concrete. As salt water dries and leave salt crystals in cavities it will blow it apart and say goodby to your patch.
 

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