Fillers used with various resins, such as Epoxies, Polyesters and Vinyl Esters, give varying characteristics such as minimising shrinkage, reducing weight for a given volume, reducing cost and changing resin consistency.
Industrial Talc - is an economical filler used with Polyester & Epoxy Resins. It is an ideal 'Bog' when mixed with Epoxy, but is more difficult to sand than some other fillers. It is not recommended for use below the waterline on permanently immersed vessels. It is easy to use and very cheap!
'Q' Cells - are a lightweight, microscopic glass bubbles, used as a filler with Polyester & Epoxy Resins. Q Cells have a reasonable compression strength and are generally used to get bulk without adding too much weight. They are also ideal for fairing. Q Cells are easily sanded. Always wear dust masks & avoid breathing vapours of resins & dust residue. Not for use below the waterline on permanently immersed vessels.
Microballoons - light weight, microscopic phenelic bubbles, used as a filler with Polyester & Epoxy Resins. Generally a more flexible filler. Can be used below the waterline on permanently immersed vessels. Ideal for fairing due to ease of sanding. Always wear dust masks & avoid breathing vapours of resins & dust residue.
Aerosil - is a light weight filler added to Polyester & Epoxy Resins for 'non sag' properties. Ideal as a glue when mixed with Composite Supplies Marine Epoxy. Can also be added to Q Cells when making a fairing mix to improve non sag qualities. Always wear dust masks & avoid breathing vapours of resins & dust residue.
Milled Fibre - is a fine glass fibre powder used with Polyester, Epoxy and Vinyl Ester Resins. It adds great tensile strength and compressive strength. It can promote adhesion to foam cores.
Flake Glass - us a reinforcing material used with Polyester, Epoxy and Vinyl Ester Resins. It adds strength to castings, and helps compressive and tensile strength.
Aluminium Powder - used with Polyester and Epoxy Resins. It is traditionally added to resins to aid in high temperature applications, such as vacuum forming. Also used to create a cold cast metal effect.
None of these fillers have a particular ratio. They can be added to 'taste'. Add what you require to get the job done!
Adding the fillers
Always add fillers in a two-step process:
1. Mix the desired quantity of resin and hardener thoroughly before adding your fillers. Begin with a small batch to allow room for the filler. 2. Mix the filler into the resin in small amounts. One handful or scoop at a time untill the desired consistency is reached.
Below are some of the more common consistencies and their characteristics and uses:
Syrup - An unthickened mixture. Drips off vertical surfaces. Used for coating, wetting out prior to bonding and applying fibreglass and fabrics.
Catsup - Thickened slightly. Sags down vertical surfaces. Used for laminating/bonding flat panes with large surface areas and injecting with a syringe.
Mayonnaise - Moderately thickened. Clings to vertical surfaces, peaks fall over. Used for general bonding, filleting and hardware bonding.
Peanut Butter - Maximum thickness. Clings to vertical surfaces, peaks stand up. Used for gap filling, filleting, fairing and bonding uneven surfaces.