Aquasport Model Rebuilds, Mods, Updates and Refreshes > Fiberglass and Materials Corner

Re-Coring Old Coffin Box Cover

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Ulysses485:
Hello,

I am in the process of doing some repairs and refreshing up the boat to hopefully get on the water before the end of the summer. I pulled the tank to check it and found the coffin box cover dripping with brown water so its time to replace the core. I am hoping someone has done a similar repair or can guide me to a write up. I have spent hours over the past year or so learning how to lay fiberglass, types of materials etc. but im stuck on how to "glue" the coose to the underside.

My initial thought is grind off the bottom section and remove core. Prep hatch cover and lay coosa in, lay glass over bottom and done. Quite honestly, i am not sure about the specifics...how do i go about "glueing" the coosa to the underside of the hatch top?

Any help is much appreciated!!

Thank You



Ulysses

mshugg:
The big chunks of your plan are spot on.  I recommend an oscillating multi tool to cut out the old core.  It makes less dust than grinding out the core.  Once the underside is clean and prepped, you’re ready for glueing.  This is more or less the same depending on what resin you’re useing, but there are subtle differences.  For example add thickeners to epoxy after mixing A & B, but add thickeners to poly/vinylester prior to adding catalyst.

1. Hot coat your core with catalyzed but unthickened resin.  This will help insure a good bond by avoiding a resin starved joint.
2. Use silica, (AKA Cabosil, fumed silica or colloidal silica) to thicken resin for glue.  You’re after a mayonnaise consistency.  Spread with a notched trowel To get uniform application of glue.
3. Press core into place and weight to clamp.  (You can get as fancy as you want here with vacuumed bagging etc, but for a one off this is overkill.
4. Clean up any squeeze out of  resin.
5. When cured glass the underside of your core.

There are many subtleties and tips and tricks that will make things easier.  Two biggies are: 

Bevel your core, so the glass will lay better in the transition between core and lid.
When ever possible perform steps when the resin has set, but before it is fully cured To minimize sanding.  With epoxy, this usually means day 1  hot coat. Let it tack.  Glue In core.  Day two glass core.  If you can dent the resin with a thumbnail, you’re ok to add glass without sanding.

Ulysses485:

--- Quote from: mshugg on May 14, 2020, 06:04:42 AM ---The big chunks of your plan are spot on.  I recommend an oscillating multi tool to cut out the old core.  It makes less dust than grinding out the core.  Once the underside is clean and prepped, you’re ready for glueing.  This is more or less the same depending on what resin you’re useing, but there are subtle differences.  For example add thickeners to epoxy after mixing A & B, but add thickeners to poly/vinylester prior to adding catalyst.

1. Hot coat your core with catalyzed but unthickened resin.  This will help insure a good bond by avoiding a resin starved joint.
2. Use silica, (AKA Cabosil, fumed silica or colloidal silica) to thicken resin for glue.  You’re after a mayonnaise consistency.  Spread with a notched trowel To get uniform application of glue.
3. Press core into place and weight to clamp.  (You can get as fancy as you want here with vacuumed bagging etc, but for a one off this is overkill.
4. Clean up any squeeze out of  resin.
5. When cured glass the underside of your core.

There are many subtleties and tips and tricks that will make things easier.  Two biggies are: 

Bevel your core, so the glass will lay better in the transition between core and lid.
When ever possible perform steps when the resin has set, but before it is fully cured To minimize sanding.  With epoxy, this usually means day 1  hot coat. Let it tack.  Glue In core.  Day two glass core.  If you can dent the resin with a thumbnail, you’re ok to add glass without sanding.

--- End quote ---

Mshugg,

I really appreciate the response and the thorough breakdown. I kept scratching my head on how cuts are made through fiberglass to start gathering tools and my budget options led me to the grinder and rotary sander for prep. I never thought about the oscillating tool, great tip. The wood seems rotten in the core so i may be able to pry it out but we will see. I am going to have at it this weekend and see what comes of it. I am also removing everything from the center console along with the rotted back there to replace.

Thank You!!

Ulysses

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