Fiberglass "Structural Peanut Butter" Recipe

As you have read through my posts you have heard me make mention of Fiberglass Structural Peanut Butter. Well here is the recipe:

This stuff is great for filling in crevices where panels join together leaving small voids, just fill in the voids with this mixture prior to installing fiberglass cloth tape.  Also, great for filling in a hole, various types of repairs, creating reinforced areas for bolt through and so on.  Not only does this mixture fill in but it is actually structural in its composition when cured.  Thus, leaving you with a very strong, high load, high tensile strength region when cured.

You will need the following materials which are readily available at fiberglass supply stores online.  I purchase all of my stuff from USComposites in West Palm Beach, Florida because of their high quality resins and cloth, quick shipping, great packaging of items shipped and you can speak with a Fiberglass Technical Representative anytime by simply making a phone call.  Very knowledgeable tech reps by the way.

This is all you need to make the mixture:

1. Aerosil - resin thickening agent (AKA Cabosil)
   
2. Glass Bubbles
3. Glass Reinforcer material:  (choose only one of these)
• 1/32" Milled Fibers for very small cracks and voids
• 1/4" Fiberglass strands for cracks 1/4" wide and wider
• 1/2" Fiberglass strands for cracks 1/2" wide and wider or for filling large areas where greater strength is needed such as reinforcements for bolt through and larger voids
4. Polyester Resin
5. Catalyst
6. A couple of hard plastic (2 cup) measuring cups for mixing mixture in.  The type that are sold at most Dollar Stores work really well.

As far as the mixture reinforcers are concerned, simply choose one dependent upon type of repair at hand.  

showing three parts used to make runnier type mixture for small voids

showing three parts used to make mixture for 1/4" cracks and larger

Glass Reinforcer Agent Choices (the pictures below are close up views of #3 ingredients above)

These agents really give the mixture its strength, without which the polyester resin would simply become too brittle and crack.  These agents not only bind mixture together through a chemical matrix but provide structural strength that yields high tensile strengths. 

• 1/32" Milled Fibers for very small cracks and voids
• 1/4" Fiberglass strands for cracks 1/4" wide and wider
• 1/2" Fiberglass strands for cracks 1/2" wide and wider or for filling large areas where greater strength is needed such as reinforcements for bolt throughs and for larger voids

 

To make the mixture I would suggest starting out with 4 ounces of resin.  This amount works good for providing you with ample amounts of work time so you do not have to worry about your resin pot life.  You can take your time and work the repair properly by filling in with this compound, not having to worry about your mixture starting to set while you are in the middle of a job.  So this is a good amount to start with.

1. Pour 4 ounces of polyester resin into measuring cup
2. Add appropriate catalyst 
3. Stir thoroughly 
4. then add your Aerosil, glass bubbles and choice of glass reinforcement material using the small medicinal cup that is provided with materials at purchase

Stir all the agents thoroughly with small tongue depressor until it is obvious that all elements have mixed well. 

You can tweak the mixture by adding more fiberglass fibers, fiberglass strands or if you need a little thicker mixture - add some more aerosil to the mixture.  Aersosil (Cabosil) will change the consistency of the mixture making it thicker.  It takes quite a bit to change the consistency of mixture so when ordering Aerosil, order twice as much as the other ingredients.  

You can make it to any consistency that your repair needs. - Need to inject the mixture into a tight crevice with the use of syringe, just mix loosely.  Need to repair larger void mix more Aersosil and make to consistency of peanut butter.  Hence, Fiberglass Structural Peanut Butter.

 

 

 

Now this mixture is a little loose.  I wanted this mixture to be a little loose because I am using it for filleting inside corners and need the capillary action of the mixture to be drawn into some 1/16"-1/8" cracks.  It contains 1/32" Milled Fibers for structural strength and bonding.

However, if you were to add the 1/4" or 1/2" fiberglass strands to the mixture along with more aerosil (cabosil)  it would indeed begin to be comparable to Peanut Butter in consistency, whereas this particular mix is not because I've made it looser on purpose.

By the way, wear a good respirator which possesses dual filtering capability:
 - fine particulate matter filtration
- and organic vapor filtrations
We certainly don't want to be glass spheres or milled fibers.  I like to wear a combination particulate matter filter/organic vapor filter in my respirator. Has both filters made into one cartridge, breathing in the styrene vapors from polyester resin is extremely hazardous to our central nervous system.