Rebuilding the Mast Step

October 28, 2018

With a good portion of the coach roof cut open and the bad core material removed, I decided to begin prepping for the new balsa core installation by sanding the bottom skin of fiberglass.  While I had the small belt sander out, a tool to get into tight spaces, I went in after the repair of the coach roof structure that will be the foundation of the mast step.  

I smoothed and blended out the rough and raised areas.  The mast support beam's center pocket was filled with a resin of sorts and had contained a glassed in block of foam, which when I first cut it out was wet and mushy - losing all of its compressive strength.  I sanded surfaces of the mast support all the way across, including the outboard pockets that allowed the tops of the bulkheads to rest within the mast support.  I am still a bit confused with this technique, and will alter the design a bit to create a much stronger mast support beam.

But today my focus was on building a firm base and support for the future mast step.  I first needed to fill this cavity with  material that could not break down over time, or be compromised in any way with water ingress.  The mast step (hardware) will be secured in this location with fasteners; and of course, I will drill, fill with epoxy, and then tap for fasteners in any area that has core material.  I laid out the materials I wanted to use to fill the cavity:  1708 oz biaxial fiberglass and G-10 fiberglass board.  I had some leftover cloth and G-10 sitting around the shop, so I opted to use these materials.  After taking measurements from the coach roof, I cut the materials to size.

I first vacuumed and thoroughly wiped down the surfaces that I was about to work within, removing any debris and potential contaminates.  I then mixed a small batch of epoxy thickened with 406 colloidal silica and 407 low-density fillers.  I applied this product in order to fill in small pockets and voids, and generally to provide a good base from which to further build upon.

I then wet out a length of 1708 cloth, and laid it onto the thickened epoxy mixture.

Next, I wet out the surfaces of one of the G-10 boards, and placed it into the cavity.  With a small stir stick, I applied thickened epoxy into the small voids around the perimeter of the G-10 board, as well as a thin application across the top surface.  I then repeated theses steps with the second G-10 board.

With the remains thickened epoxy, I spread a thin layer across the top of the G-10 boards, as well as filling small voids to the outboard ends of the center cavity.

The final application was two layers of 1708 cloth, pressed firmly into place.

I applied a layer of peel ply to the repair area, which will allow me to get straight into further epoxy work without the need to water-wash the surface to remove amine blush and sanding to create a rough surface for a good mechanical bond.  The application of peel ply prevents amine blush from forming and leaves a textured surface that offers good mechanical bond characteristics.    

Total Time Today: 3 hrs