Micro-Ballons for Easier Fiberglass Sanding

I have written blog entries in the past in which I have shared my experiences with new techniques and new products that are available for construction with composites.  This is another one of those.

Whenever I am building the surface of a part that is being made of chopped mat, I end up with a fairly course surface that will need a final finishing.

I have employed various means to smooth out a fiberglass surface.  Some of these finishing methods include the following:

For some applications I use veil over the final layer of chopped mat.  This method hides most of the course fibers of the chopped mat without adding an excessive amount of extra weight to the final product.  In fact, when I add a final veil covering I very rarely have to add any extra resin to the finish.  Usually I can use a small roller to press the veil onto the surface of the still uncured mat / resin underneath it forcing the resin to seep into the veil and provide adequate saturation on the surface.  The individual fibers of veil are much finer than those of chopped mat so the final surface is smoother.

For other applications I mix a putty-like consistency combination of resin and cabosil that I use to smooth over the surface.  This has been one of my favorite methods for finishing a fiberglass surface.  The cabosil / resin mixture can be made as thick or thin as your project requires.  Once this mixture is spread over the surface and cures, it can be sanded smooth and finished.

Sometimes I will simply skin the surface with bondo.  I like bondo because it sands so easily and cures so fast.  You can smooth out a surface in a hurry with bondo.  The drawbacks to using bondo are that it is easily chipped / damaged and it almost cures too fast.  I have wasted a good amount of bondo over the years by mixing more than I could use in its working period.

The other day I went to my local fiberglass supply store and asked for a ¼ pound of cabosil.  The gentleman that helped me asked if I wanted something that would sand a little easier.  I said “sure” and he suggested microballoons.  The microballoons mixed into a nice white paste and spread easily on the surface of my project.  It also sanded easily as promised.  In addition to easy sanding, it also seems durable as it passed the hammer tap test that I performed on the tip to the bow of my boat project.  It didn’t hit it full force but I hit it hard enough to crack bondo and the microballoons didn’t crack.  I was impressed.

In the beginning of this article I said that I was writing about a new product.  Microballoons are not “new”, they are simply new to me.  Once again, we tend to get comfortable with methods and materials that are known to us and close ourselves off to other products and procedures that are available.

Keep at it.


One Response

  1. JustGetToIt Says:

    Excellent Article Steve.

    I’ll have to remember about MicroBalloons.

    Nice the way you have matched you main site’s look on your blog now too.

    Take Care,

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