Motor and Motor Bracket, Part 6, Epoxy Work

Two of the plywood backing plates epoxy-coated and sanded
You'll recall from my previous postings that I did a fair amount of woodwork in pursuit of this overall motor bracket project. First, I constructed a plywood backing plate for the cockpit side of the transom. Then I constructed a small plywood backing plate to fill the cutout space between the aluminum transom plate and the plywood backing plate for the cockpit. Then I constructed a plywood backing plate for the lazarette. Finally, I constructed a motor mounting pad out of mahogany. All of these pieces of wood I left untreated at the time I constructed them. Now it was time to epoxy-coat them and, in the case of two of them, join them together. How I accomplished all of this work for Oystercatcher, my Ericson 25, is the subject of this posting.
I began by setting out the three pieces of plywood that I had constructed for the cockpit and the lazarette. Below we see the cockpit piece.
Here's the piece that would fill the cutout in the transom.
And here's the piece that would go against the transom in the lazarette.
For this epoxy-coating I used RAKA 127 Low Viscosity Resin and 350 Non-Blush Hardener. I've spoken many times about the virtues of RAKA brand epoxy.
I carried out this epoxy-coating at the same time that I epoxy-coated the shelves for the lazarette. I have discussed this lazarette project in multiple postings.

The plywood always quickly absorbs the first coat of epoxy.
This is especially evident when the light conditions are right.
The wood is hazy, not glossy. That's a sure sign of just a single coat.
Later in the day, after the first coat had cured somewhat, I came back and applied a second coat.
The glossy evidence of a second coat.

The next day I came back and applied two coats of epoxy on the other side of each of these pieces of plywood.

Two or three days later, after the epoxy had fully cured, I set up a table in my yard and started sanding each of these pieces with 40 grit paper.
In my experience, without 40 grit paper you're wasting your time.
Fully cured epoxy is almost as hard as a rock when it comes to sanding it.
Now that I had fully sanded these three pieces of plywood, it was time for me to join two of them together. Specifically, I needed to join the cockpit backing plate and the cutout backing plate. This would make them one solid piece that I could sandwich between the two aluminum plates.
To make them even more solid, my plan was to apply 12 ounce biaxial cloth to each side.
This stuff is some serious cloth. It greedily drinks down just about every bit of epoxy that you offer it.
Here's the first side of the first piece with the first coat of thickened epoxy on it.
Here's the second coat of thickened epoxy. I used colloidal silica to thicken this RAKA epoxy to the consistency of ketchup. The thickened epoxy helps to fill the weave of the biaxial cloth.
A couple of days later I sanded away the rough pieces of cloth from the edges of the plywood.
Then I sanded the surface to a smooth finish.
Afterwards, I prepared the next side for the application of the biaxial cloth. I would wet out the plywood and then apply the cloth to it. Then I would wet out the cloth. I would then thicken the epoxy and work it into the weave of the cloth.
In the picture below you can see well how the weave of the cloth is still visible after the first coat of thickened epoxy.
After the second coat the weave is much less visible.
Two or three days later I sanded the cured epoxy.

Now that I had prepared the first piece, I could work on the second. I began by drilling holes in the two pieces and installing flathead wood screws to join them together.
Then I temporarily installed these two pieces in the boat to see how they fit.
As I had suspected, the small piece of 1/2 inch plywood was not quite thick enough to fill the gap in the cutout completely.
To correct this problem, I decided to apply some biaxial cloth to the outside of it.

In preparation for gluing the small piece to the large one, I wiped both pieces down with acetone.
Then, after I wet-out the pieces with neat epoxy, I applied thickened epoxy to the large piece.
The flathead screws helped to pull all this together.
Then I wet out the plywood and applied the biaxial cloth.
In the picture below you see the cloth with two coats of thickened epoxy.
A couple of days later I broke out the sander and cleaned all this up.
The Dremel with a 50 grit sanding drum was a big help along the edges.
Then I broke out the Rockwell Sonicrafter oscillating tool for cleaning up all the edges.
By the time I was finished, these two pieces of plywood were essentially one, solid, custom-cut piece of material.
Then I carried this piece out to the boat.
It fit just right.
Now I just needed to re-drill the existing holes that I had covered with biaxial cloth.
Next I focused on the motor mounting pad. I began by roughing up the aluminum in preparation for gluing it to the mahogany.
I used acetone to remove all of the sanding dust and any remnants of oil from all of the cutting and drilling I had done on these pieces.
Then I cleaned up the mahogany with acetone.
I wet out the aluminum plates and the mahogany.

Then I clamped all three pieces together.
While I was at it, I filled the bottom two holes with thickened epoxy. These were holes through which I had planned to install bolts for securing the Yamaha motor to the pad. These particular holes were a mistake on my part, and now it was time for me to do away with them.
A couple of days later after the epoxy had fully cured I broke out several of my sanders.
The plastic that had been on the bottom of the pad during the glue-up was firmly stuck on the aluminum.
Eventually I was able to chisel much of it free.
The quarter-sheet sander made it all look nice and neat.

I used the countersink bit to clean out the epoxy from the countersunk holes.

Then I re-drilled the four holes that I would use to mount the pad to the bracket.
Now that I had completed all of this epoxy-work, I could paint all of these pieces with two-part paint. That is the subject of my next posting. This concludes this posting on how I accomplished this epoxy-work for Oystercatcher, my Ericson 25.

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