Clipper's Vera Cruise Build

Clipper's Vera Cruise Build

Tuesday, May 28, 2013

Encapsulation - Continued

Well I wish I had something more exciting to write about, but all I have at the moment is that I am continuing with frame encapsulation. Two frames are completed now with a third nearly there and a fourth started.

The only thing I've changed in the process is to switch to a sponge when washing the amine blush off the parts with soapy water. Before I was using a soapy paper towel but I found that it wasn't working well enough at removing the blush.

The sponge has a scotchbrite pad on the back and I will use that first, then wash with the sponge. Finally wipe down several times with warm water and a clean non-soapy paper towel. I am doing this before sanding for the next coat and after sanding (to remove the sanding dust). This seems to have yielded good results so far.

I am still having trouble getting a completely bubble free finish. The first coat is the worse since it is going over bare wood. Subsequent coats get better because of the sanding which gives a smoother surface to work with. But there are still a few bubbles in every finish regardless.

Since the parts will ultimately be painted, it is not a big concern as far as these parts go, but it doesn't bode well for the future when I am trying to protect some wood surface for a natural finish. One thing I haven't tried yet, but will be experimenting with is to sand the final coat smooth and then coat with varnish. This will be done on a scrap rather than an actual frame. Since varnish is more like paint, I am hoping that it will settle down with no bubbles. And it should cause the sanding marks in the epoxy to disappear so the final finish will be clear and shiny. At least that's the hope.

So to try and lend some interest to this post, here is a picture of one of the frames during the wash. Yeah, I know, it's not a big thrill, but it's the best I can do for now.

One final note. When I get to frames 6 and possibly 5, I am thinking of laminating a mahogany veneer over the upper gussets before encapsulation. These gussets are visible in the cabin and I want to give them a dressier appearance than plain plywood. I was originally thinking of a simple veneer but I am also considering a small decorative wood inlay as an alternative. I haven't done up any artwork yet, but it will most likely be something nautical.

That's it for now. Take care.

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.

Tuesday, May 7, 2013

Frame Assembly First Phase Completed

This afternoon I completed the first phase of the frame assembly process. This phase was about gluing everything together and cleaning up the glue lines. Technically , I have a bit more cleanup to do, but for the most part it is done. Frame 1 went together quickly. After edge gluing the parts and filler blocks for the transom (frame 0), I wanted to see if there would be any interference problems with adding the interior gussets.

After looking the plans over carefully, re-reading several books and articles on constructing the transoms, and carefully looking over photos I have of this boat and others, I determined that the interior gussets are not actually needed because the frame parts are reinforced with the plywood forming the transom wall. Additionally, these gussets can be added at a later date if desired so I elected not to add them at this time.

The research also showed that the filler blocks for the transom were not called out either and I was a little concerned that these might interfere with some other later assembly. But the research showed this not to be a problem. The filler blocks add considerable strength to the three frame parts which would only be joined on a short edge otherwise. So these will stay in place.

Here is a another shot of the two final frames.

So the next phase of frame assembly will be repairing any assembly holes from nails and then encapsulating with epoxy resin. The holes will be repaired with thickened epoxy and sanded flush.

Encapsulation is a vital part of the process as it protects the wood from moisture. It involves coating the entire frame with two (maybe three) coats of unthickened epoxy resin. Each coat is applied and allowed to cure before applying the next coat. I will also be doing a fine sanding between coats so that the frame parts that will be exposed will have smooth surfaces. All joints and possible water entry points must be coated so that there is no chance for water to seep into the structure. I will leave the outside edges of the frames uncoated for now because these will be shaped to allow the skins to lie flat. So there is no sense in coating them just yet. They will be coated before the skins are applied.

I have also started planning the next glue up project which will be the stem. This is the curved assembly that forms the shape of the bow. It is made up from three layers of 3/4 inch plywood. It will be epoxied together and also fastened with bronze wood screws. Here is a picture of that part temporarily set up with frames 5 and 6 to give some idea of how it will look.

Of course, I am also planning on starting on the building form but that will require a bit of time to save up for the lumber and hardware needed. I anticipate starting on that sometime in June. I have enough work for at least a couple of weeks and if necessary, I can purchase some lumber early and begin assembly of the building form. We'll see.

So that's it for now. Take care and enjoy the spring and summer.