MAS Epoxies Colloidal Silica, 1 Qt, 25-001

  • $19.00
  • Save $5.95

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Product Overview:

MAS Colloidal Silica (aka Cabosil) acts as a thickening agent to reduce sagging and enhances strength when mixed with epoxy. 

Colloidal Silica makes excellent glues for structural bonding, filling and filleting. Use when high strength and low density are required.

Features & Benefits:

  • Thickening epoxy to reduce sagging and slumping
  • Provides enhanced strength
  • Makes excellent glues for structural bonding, filling and filleting
  • Available in quarts and half gallons

How To Make Professional Fillets and Fairings:

Starting Formula:


  • 1 Part MAS Resin/Hardener mix using "Medium" hardener (or 50/50 MAS "Slow/Fast" Hardener)
  • 1 Part Colloidal Silica 
  • 2-3 Parts Wood Flour


It is important to mix epoxy and hardener thoroughly before adding thickener.

Often two fillers used in conjunction are more effective than any single filler used alone; this can be attributed to the synergistic effects found when two different particle sizes are blended together.

When filling gaps or making a fillet (pronounced "fill-its") add sufficient wood flour to make a peanut butter consistency. 

Colloidal Silica (aka Cab-O-Sil) and other white fillers may be added to make the wood flour paste match the color of the plywood exactly. Adding some Phenolic Micro Balloons or Colloidal Silica (no more than 30 percent by volume) has the added benefit of making wood flour fillets smoother and easier to spread.

When using epoxy as an adhesive (i.e., bonding wood to wood), add enough silica powder or Cell-O-Fill to the resin-hardener mix to bring it to the consistency of mayonnaise or jam.

When simply coating, sealing or saturating wood with epoxy, do not add thickening powders.