April 2013

Micro-balloons filling and sanding the seams

April-Mei 2013

After insulating our shed we made ourselves a large, flat work table. This 3m x 4m table is large enough to clad three or four foam panels with fibre-glass at a time. We will eventually cut components such as frames and internal doors from these large vacuum infused panels.

Vacuum infusion table to make flat pannels

Filling the Seams with Epoxy and Micro-balloons.

In March, we started heating our newly insulated shed with electric heaters. It is not only more comfortable to work in, but also necessary for working with a Epoxy and Micro-balloon mix. The hull has to be made air tight before cladding with fibre-glass using vacuum infusion. CoreCell is inherently air tight, but not the seams, these have to be filled and sanded first.

Jolanda spent a good half an hour sawing up off-cuts of MDF into mixing sticks. We had already accumulated a stockpile of old yoghurt and sauce pots for mixing up the epoxy, we had cut up the lids to make nice, flexible scrapers that are perfect for getting deep down into the seams. Once mixed, the epoxy is only good for approximately half an hour, so to avoid wastage, we made lots of small batches.

In the next two to three years we expect to use hundreds of plastic pots (see below). If you have any laying around, they will always be welcome here. You can take the opportunity to nose-around our project as well.

Mixing sticks from waste MDF  We use a lot of empty buckets for mixing epoxy

To make the epoxy/micro-ballon mix, first mix the epoxy and hardener, a little bit of Aerosil will improve its gluing properties. Then add in the micro-balloons. Micro-Balloons keep the paste light whilst adding volume. The final mix resembles a large pot of Chocolate Paste. According to the Micro-Balloon instructions, the red powder is better for sanding than the white, so we took the manufacturers advice and didn’t do any tests first.

Mixing table to measure out hars and hardner  Mixed micro balloons looks like pasta

Mixing Micro-balloons


 

Just like using any other kind of filler, there is always a risk of getting air bubbles in the seam. Air bubbles can provide a path for false air when a vacuum is being generated, so to prevent this, we filled in three layers.

First layer of Micro balloons in the seems. Scrape away the overflowing before hardend  Filling the seems with Micro balloons for an airtight surface  Grinded micro balloons seam

To fill the seams, push the first layer deep into the seam, remove any over-spill on the panels straight away. Apply the second layer within twenty-four hours, but do not fill the seam completely, once again, remove over-spill from the panels immediately. The final layer should be applied royally, once hardened, the excess can be sanded down using an orbital sander and will leave a perfectly smooth finish.
Bringing on the following layer within twenty-four hours of the previous one means it will have a good surface to bond to without having to key the previous layer first. We planned our work in such a way that we were able to fill for three days in a row without having to sand or rub-down.

We are glad we initially only installed the slats on the outside of the mould leaving the inside free accessible. We have full access to the surface of the hull without damaging the foam.

The Inner Hull walls

Once the outer walls of the hulls were foamed, filled and sanded, we were able to start on the inner walls.

Again a reference batten. This time at the transition to the chamfer  Making the mold with extra attention for the curves  Only battens till the chamfer so we can thermoform corecell from both sides

The chamfer panel forms a 45 degree joint between the hull and the bridge deck. The chamfer panel has a complex shape, so we allowed for this by leaving material protruding out. This excess will be removed at a later date once the chamfer has been shaped properly.

Temporary chamfer frame to create right curves  A bigger temporary frame to make a good panel on bulkhead 7

Working in the bow area was not easy, there is a limited amount of space to work in and the panels have to bend in two directions. To make shaping easier we used 20cm panels instead of the 40cm used on the rest of the hull.
To prevent damage to the foam when walking back and forth to the work area, we removed our shoes and worked in socks only.

Thermoforming corecell with curves in 2 directions  Thermoforming corecell under tension

The stern extends 20cm past the last frame. So to ensure the slats were aligned properly we made and fitted a temporary tail-board, then fitted supports to secure them in place. These supports are fixed to the ground. Once happy with the shape, we were able to continue with filling and sanding.

Mold at the stern to create right curves for the hull

Preparing the 10.5m long chamfer panels made a nice change. We temporarily fixed the panels edge to edge and marked the joint. These reference marks will come in handy later when we lay the panel into the mould. To aid shaping of the chamfer panel, Paul divided the template drawing into 1m sections and printed them out on the plotter at a scale of 1:1, joined them up and laid them on top of the panels. He was then able to quickly and accurately transfer the shape to the panel. A piece of cake!

Corecell temporary connection and marks the prefit of the chamfer  Chamfer print out to draw the right shape  Preview chamfer in corecell now we can fit the temporary overlap at the bow

Material for the frames and vacuum infusion have already been ordered. It looks like we will be able to lay-up the first glass-fibre mats in the last week of June. We will use these frames as tests to perfect vacuum infusion before moving onto the hulls.