Centerboard, Construction, Part 3: Pouring the Foam

The steel spine within the mold, just before the pour
Having finished building the new carbon steel spine and having finished building the mold, it was now time to do the pour. Before I could do this, however, I had to take quite a few steps to make sure that everything turned out just right. These steps, and the pouring of the mold itself are the subject of this third part of a nine-part article on the construction of a new centerboard for my Ericson 25.

The first thing I needed to do was to figure out a way to protect the spine in the area around the eyelet. You'll recall that this was a problem area on my original centerboard (just as it is on the boards of many other owners). It was here that water had entered the board and had caused so much rusting of the steel spine, that there was no more steel in this part of the board. To remedy that problem, in part, I had gotten my buddy to install a stainless steel pipe that would serve as a protective shaft for the housing of the centerboard pin. This would do much to prevent water intrusion. Nevertheless, I was still concerned that water would eventually creep between the outside of the stainless steel and the foam that would surround it, and it would thus eventually make its way down to the carbon steel. To help prevent this intrusion of water, my buddy suggested that I scuff the stainless steel and then wrap it many times with a piece of epoxy-soaked cloth. I thought this was a good idea, so that's what I did.

First I hit it with some 40 grit sandpaper.
Then I cleaned it up with a brush and some acetone to remove all the residue.

I didn't hold back when it came to wrapping it. I gave it as many wraps as possible, thoroughly soaking it with a chip brush loaded with epoxy as I went.

When choosing a location for doing the pour, I decided that it would be better to do it indoors rather than out. It was the middle of the summer in the South Carolina Lowcountry. It's not that I couldn't stand the heat and humidity. It's that I wanted the temperature and humidity to be consistent. U.S. Composites, the manufacturer of the pour-foam that I was using, said that the ideal temperature for doing the pour was 80 degrees Fahrenheit. We keep the thermostat set on 75 degrees in the summer, so this was pretty close to the ideal, and much better than the high-nineties that I would have been facing outdoors.
One thing I needed to do to the mold before I could fully insert the steel spine was to cut a slot in the side, in order to make room for the tang - the triangular piece of stainless steel that would one day serve as an anchor point for centerboard pendent.
I used a handheld carpenter's saw to cut my way through the side of the mold.
I then took chisels to the base of the cut-out to remove the triangular plug. I made sure to save this plug, since it would be useful for damming the flow of urethane foam during the pour.
It took quite a bit of additional chiseling to make the tang fit just right.

Another step that I took prior to the pour was to clean-up the old lead plates from the original centerboard. They still had a lot of residue on them from the original pour foam.

After about five seconds worth of grinding, I smartened up and moved the lead plates off of the saw horses on my front porch and into the grass in the yard. Better that any lead dust that might be thrown off be well-removed from the house.

It cleaned-up pretty well, with a minimum amount of grinding. That was good. Need I saw that I was fully protected with a respirator, face shield, gloves, and a long-sleeve shirt and long pants when doing this?
Having cleaned-up the lead, it was time to go back inside and secure the lead to the steel spine. Once again, the plywood blueprint was essential for knowing exactly how to put it all together. You'll recall from Part I of this article that the creation of the blueprint was only possible by the destruction of the old board. This was a re-engineering job par excellence. You'll notice in the picture below that the lead is wedge-shaped, and that I have placed the fat end of the lead on the trailing edge of the centerboard, as drawn on the plywood. This was incorrect. I should have placed the thin end of the lead on the trailing edge. I did not recognize my error until I had already screwed the lead onto the steel. Fortunately, I caught this error before I poured the foam. All of the pictures that follow (after the incorrect one shown below) show the lead in the correct position.
Having placed the lead in the correct position, with the fat end (on the right) on the leading edge of the spine and the thin end (on the left) on the trailing edge of the spine, I was ready to drill the holes and join the lead to the steel with screws. I began by drilling through the lead. Then, I placed a center-hole punch into the hole in order to score the steel beneath the lead. After I had drilled the appropriate number of holes, I removed the lead and drilled through the steel.

Note the swirls in the steel. I didn't take a picture of this, but around the same time that I ground the old residue off of the lead, I took the grinder to the steel to make sure it had a clean, yet well-abraded surface to which the pour foam could bond. If I had it to do over, I might have epoxy-coated the steel at this point, in order to seal it, but maybe not. The pour-foam itself should have provided an excellent seal, especially since I would later soak the cured pour-foam with epoxy and many layers of cloth and epoxy.
I didn't include any pictures of this, but I should have. When joining the lead plates to the steel, I did not simply use the 3/16 inch steel as the anchor point. That would have been far too shallow to hold that lead securely to the steel. Instead, I mimicked the approach taken by Ericson on the original board. They had used stainless steel screws, about three inches in length. After drilling the screws all the way through the lead and the steel (and then the lead on the other side of the steel) they took a hammer and bent the screws over. This helped to clamp all three pieces together, and it made it impossible for the screws to work themselves loose. Note the dead blow hammer sitting on the mold in the top left of the picture. I used this to hammer the lead itself to make sure that there were no gaps between the lead and the steel. When everything looked nice and snug, I started bending over the stainless steel screws, just like Ericson did it back in the 1970s. There was a buddy of mine helping me with this. If I remember correctly, one of us held the piece of lead and steel together and slid one end off of the plywood at a time so that the other one of us could bend the screws over with a hammer.
Now it was time to transfer the steel spine to the mold . . . or so we thought. Look closely, and you'll see that first we had to install some stainless steel screws from the underside of the mold.
What was the purpose of these screws, you might ask? Well, these would serve to keep the spine precisely centered within the mold. The pour-foam had to be able to envelope the steel and lead equally on both sides. If I remember correctly, we installed the screws so that they protruded one inch above the surface of the mold. You'll recall that the mold was built to a depth of 2-1/4 inches. We figured that by having one inch on the bottom and one inch on the top (you'll see this in a minute), and 3/16 inch in the center (the thickness of the steel), the steel would be centered within the mold to within 1/16 inch.
Next, we lined the mold with plastic, eliminating as many wrinkles as we could with the staple gun.
The plastic would enable us to remove the centerboard from the mold more easily, and it would allow us to reuse the mold if necessary. To further ease the removal of the centerboard from the mold, we spread a thin coat of carnauba wax over every square inch of the plastic.
The steel spine (with the lead plates on either side of it), was now heavy and unwieldy, so in order to aid us in our placement of the steel spine into the mold we used scrap pieces of 1 x 4 material to prop up the spine until we were ready to slowly lower it, one end at a time, into the mold.
With the steel spine having been placed in the mold, we began adjusting the screws from beneath the mold to ensure that the steel was perfectly level. The small line level in the picture below was useful in the tight areas. Keep in mind that, on account of the lead on the bottom side of the steel, some of the screws had to be lowered to heights less than one inch. As you can imagine, this took a good bit of fine-tuning before it was just right.
At the same time, I made sure that the mold itself was perfectly level. This also took some fine tuning (shimming the legs of the sawhorses, etc), but not much. I was a stickler about all of this, because it was absolutely imperative the steel spine be centered and level (relative to the top and bottom of the mold). Otherwise, the centerboard would not be symmetrical with regard to its weight distribution port and starboard.

Our next task was to figure out a way to seal the top of the mold after making the pour. Without some sort of seal or lid, the foam would spill over the top, instead of expanding through all the crevices of the mold. This urethane foam was a two-part product, and as soon the two parts were mixed, they would begin to react and expand. Our plan was for each of us to have our own buckets. One would start pouring on one side of the mold, one on the other. As soon as we completed our pours, we'd begin to drop the lids in place and screw them down tight.
Another issue that we needed to consider was the possibility that the expanding foam would push the steel spine off center. To prevent this, we installed battens of 1x4 southern yellow pine, and into these battens we screwed stainless steel screws.
These stainless steel screws allowed us to pin the board down so to speak. There were like adjustable clamps. We could slow tighten them down by hand until we felt that there was no wiggle room whatsoever for the steel.
We also were cognizant of the fact that the steel could be pushed from right to left off-center (rather than up and down off-center) This was why we strategically placed (screws such as those in the foreground below) that would counteract left-to-right movement.
Note, for example, how we placed screws behind the fat edge of the lead to prevent horizontal movement in that direction.

On the subject of coating all surfaces of the mold with plastic and wax, note the attention we gave to the battens.
As we neared the time to make the pour, we stationed three of the wooden lids on one side of the mold, and three on the other. Notice that by this point we have also covered the lids with plastic. Likewise we have applied a thin coat of wax to them.
We also had clamps ready to go, so we could quickly get the lids down tight before screwing them down even tighter.
We didn't want to leave anything to chance. We had two buckets, two drills (with stirrers), and two pairs of quart-sized mixing pots to get the ratios just right. We would have to work independently. We would mix the two parts together into our own buckets, stir our buckets, and then get to work pouring. By the time we finished mixing for the recommended amount of time, we would have only 30 seconds of open time before the expansion of the foam began.
I used, as I said above, U.S. Composites brand urethane foam. I ordered the 8 pound density foam, because it seemed like the best one for this project. The 16 pound density foam seemed too hard, and it would have required double the amount, which would have required double the money.
Things were really hectic during the mixing and pouring stage, so I wasn't able to take any pictures until we had finished.
Here you see all six panels or lids firmly clamped and screwed into place. We had expected to see quite a bit of foam pour forth from the pressure-relief holes that we had drilled into each lid in advance of the pour. When we didn't, we began to wonder if the foam had fully expanded throughout the mold. We tapped on the top of each lid to see if we could notice any differences in terms of the sounds that would be emitted. Some areas were solid-sounding; others sounded hollow or drum-like. Consequently, we removed all of the lids and discovered that, sure enough, the foam had not fully filled the voids in some places near the top of the mold. To remedy the problem, we mixed up another bucket of foam and poured it here and there into the voids. The instructions provided by U.S. Composites said that if we accomplished this second pour within a certain amount of time, then we would still be able to achieve a chemical bond rather than a mechanical one, so the fact that we had to do this second pour was not a cause of concern.

After the second pour, the consistency of the sounds omitted by the lids when tapped upon, and the consistency of the expansion of the foam upward into the holes in each of the lids told us that the foam had filled all of the voids. Not long afterwards we removed the lids  and saw that we had in fact achieved a good, solid pour.

Satisfied with the pour, we removed the battens and decided to crack a few cold ones to celebrate. We were curious to know what the new centerboard would look like when removed from the mold, but we thought it would be a good idea to let it sit overnight, just in case there were in areas within the board that had not fully cured.
Later that evening, with plenty of barley under the belt, our curiosity got the best of us, and we returned to the mold to see if we could extract the board from it. We began by removing all of the plastic that was visible. Then we flipped the mold over and began hitting it with the dead blow hammer. It didn't take long for the board to start slipping out.
Without much effort, the board eventually popped free. It looked pretty damn good, and we used this as pretty good excuse for popping a few more tops on a few more cold ones. It had been a good day.
This ends the third of a nine-part article on how I constructed a new centerboard for my Ericson 25. The fourth part will concern the shaping of the board.

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