Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Thursday, May 16, 2013

Encapsulation Of Frames

So this week has been spent learning the process for encapsulating the frames in epoxy. The encapsulation process is basically coating the frame in three (or more if needed) layers of unthickened epoxy resin. This seems easy on first glance but there are a few gotchas that I had to work through.

I want to digress just a bit to mention that I am paying more attention to personal safety now. Wearing a respirator when working with chemicals or sanding. Wearing heavier duty gloves when handling chemicals. And I have always been using ear protection when working with noisy machinery.

The first step is to sand down any filled in holes and give the frame a light sanding to smooth out any roughness remaining. The holes come from nails used during the initial manufacturing and assembly. I wanted to fill these holes for three reasons. First, they serve as potential entry points for water into the wood. Secondly, they are potential weak spots in the structure, and thirdly, I want a smooth finish on my frame parts. After this preliminary work, a final wipe down with denatured alcohol insures that the part is clean and ready for the epoxy coating.



I decided to experiment on one frame first before diving into the others. Using unthickened epoxy, I coated one side using a chip brush. covering one entire side of the frame but leaving the epoxy off the outside edges. These edges will be worked further later in the boat assembly so there is no need to coat them just yet. This first try revealed some flaws in the technique. When I mixed the resin, I used my usual approach of thoroughly mixing it with the only concern being to insure that it is mixed fully. However, this process introduces hundreds of tiny bubbles into the resin.

I then coated the frame using the chip brush and saw that the bubbles were in the finish. I tried smoothing it out using the brush but it seemed to do no good. After a lot of effort, I was able to remove most of the bubbles, but not all. I let this cure overnight and the next morning when checking it out, I saw that the finish was quite rough.



Instead of tackling the entire surface of the frame, I decided to see what could be done by experimenting on a small portion of the frame. First, I had to sand the resin down so that it was smooth which was quite an effort requiring many sandpaper changes. I realized this was not going to be an easy process using this approach and resolved to find a better way.

One thing I had forgotten about was a slightly greasy film called amine blush that forms on the surface of the epoxy as it cures. I am pretty sure this along with the epoxy dust was the main reason the sandpaper would clog up quickly. So all the other surfaces would get a good wash down with warm water and mild soap before sanding to remove this blush.

After smoothing out my experimental area and re-wiping, I tried putting the second coat on, but this time using a foam brush and doing a light wipe after coating. I also made sure to slowly mix the resin and not introduce any bubbles in the mixture. One other technique I used was to slowly pour the resin onto the surface in small batches and use the foam brush to smooth it out rather than dip the brush into the resin in the cup.

This process resulted in a much improved finish after curing. So I repeated the same process over the remaining surface. Of course, all that surface area had to be sanded first, which used up a lot of sandpaper. I believe the best way to deal with this is to insure that the surface is as smooth as I can get it in the application process.



The results for the rest of the frame mirrored what I had experienced in the experiment, with a much smoother surface. I have yet to try this approach on the initial coat on bare wood, so I am not sure if it will work as well. I will be experimenting with that when I do the other side of the frame. But I will need to do at least one more coat on the first side. Three coats reduces the likelihood that any areas remain uncovered or inadequately covered.

There are a few other issues that I will need to try and work out. The biggest is drips that accumulate on the bottom side of the frame as the top side is coated. I think that I can handle this by doing a wipe down after coating the top side. Otherwise these drips will harden and have to be sanded off. And I need to insure that the part is lying flat because this unthickened resin runs quite easily which results in ridges at the low points of the part. These will have to be sanded off as well.

So to recap the process so far.

  1. Lightly sand and clean up with alcohol
  2. Slowly mix the resin and slowly pour onto the surface in small batches
  3. Smooth out the resin with a foam brush, trying to eliminate any bubbles
  4. After curing and before applying next coat, wash the surface with warm water and soap to remove amine blush
  5. Light sanding to remove any roughness
  6. Apply next coat using previous technique
  7. After final coat, clean off amine blush with warm water and soap.
And again, to reiterate, I haven't tried this approach on bare wood since the initial attempt. However, I have confidence that it will work as expected.

That's it for now. This process will be ongoing for several weeks due to the curing times and multiple coats required.

Update 5/20/2013 - A friendly reader has noted that amine blush is actually water soluble and not affected by acetone or alcohol.  I looked this up and as the reader mentioned, the clean up requires warm water and a mild soap along with a scotchbrite pad.

This is considerably safer than acetone and I wanted to get the word out about this in my blog. I also found that it is a good idea to wash even before sanding  as the sanding process can actually drive the blush into the lower layers. Fortunately, I am not too far into the process of encapsulation and I can correct the mistakes I have already made.

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  1. Amine blush is water-soluable, so using solvents is not only unnecessary, but using solvents will not do the job. All you need is plain water and a Scotch-Brite pad. Use a spray bottle for ease of application (or any other way you like), light pressure with the pad, followed by a quick wipe with a clean, dry cloth. Easy and safe and effective, and the right way to do it. Good luck.

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    1. Well I am certainly glad you mentioned this. I had assumed that this could be cleaned by acetone. I thought that resin could only have solvent based by products and I didn't even bother to look it up. I have since done so and I appreciate it that you brought this to my attention. Fortunately, I am not too far into this process and can correct the mistakes already made.

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