Saturday, 16 February 2019

Centre Board Case | Epoxy Dramas

The very first build activity is the centre board case. The inside of the case is lined with fibreglass cloth for strength and sealed with three coats of epoxy resin.

This was the first time I had used epoxy in over thirty years (on the first boat I built), and the first time ever with fibreglass, and I was somewhat unsure how it would go.

So the first thing I did was to lay out the 'glass on the inside faces of the case.



I found that an old wallpapering brush was excellent for smoothing out the cloth, and that an expensive dressmaker's cloth cutter worked well but was probably over the top for this purpose.

I used a disposable roller for wetting out the 'glass. The roller worked well and I found that I really enjoyed it!



The drama with the epoxy began when using the pumps supplied with the kit to dispense the right dosage. The resin is supplied by Professional Epoxy Coatings (PEC) from the same location as Fyne Boats, so I guess they are sister companies. It is mixed two parts resin to one part activator, with one plunge of each pump dispensing the right amount. Once primed the resin pump stayed primed because it is quite viscous, but the activator pump refused to stay primed. Being a thin liquid it simply drained back into the bottle after each use. This made it difficult to be sure I had dispensed the correct quantity of activator, because the pump kept spitting and running dry.

I persevered and successfully wetted out the cloth, but I was not 100% confident that I had used the right dosage, or even if it mattered!

When I thought the resin had cured I gave it a light sanding to provide a mechanical key for the next coat.



Herein lay another drama. The instructions with the resin say that it can be recoated using a chemical bond (i.e. without sanding) within twelve hours, when the surface is tack free. After twelve hours the surface has to be sanded to provide a mechanical key for the next coat. The trouble is these times are based on an ambient temperature of 25 degrees Centigrade! The temperature in the workshop was much less than that, and I had really no idea how long to wait for it to cure. So I just left it for a couple of days and then sanded it lightly with P80 grit.

This is the Festool Rotex 90 sander which I bought when decorating the house in 2017, in anticipation of the boat build.

Used in conjunction with the Festool Mini dust extractor it does a really excellent job with virtually no dust created.





It is expensive kit but it is many, many times better than any DIY grade equipment and I love it. The Rotex 90 can be switched between random orbital and geared rotary sander, and it has a delta pad for getting into awkward corners. Fabulous tool.

While waiting to be certain that the resin had fully cured (it felt a bit soft during sanding and gummed up the sander) I cut the blocking for the inside of the case.



This was when my trusty old Elu jig saw gave out on me. Well, it was over thirty years old and had built two kitchens, lots of furniture, and one boat. Snapped drive shaft and not repairable, so off to the nearest decent tool store to purchase a replacement.



It's Festool and again it is an excellent tool and cuts cleanly and effortlessly.

T
hen it was back to resin application to 'fill the weave' in the 'glass cloth and more drama and uncertainty about whether the mixture was correct and if it was curing properly or indeed at all.



The second coat went on fine and cured nicely, but the third and final coat stayed tacky for several days, despite being taken inside to cure. I still don't know what went wrong, if anything, but after a few days and a lot of sanding the intended hard, flat matt surface was achieved.

Next I glued and clamped the blocking in place on one side of the case, carefully cleaning off squeezed out resin on the inside face.




We don't want anything jamming the centre board in there!

Finally, I glued the other side of the case to the blocking, using lots of spring clamps.



I was worried about how to remove the squeeze out from inside the case when doing this. The build manual says to use a rag soaked in solvent on a stick, but the PEC resin is solvent free and the guys at Fyne Boats say not to do this, because it does not like solvents. They gave me a super-top-tip on how to clean out excess glue. You cut a piece of scrap timber to the exact thickness of the slot, and put a sharp chisel-type edge on the tip, like this.



When the case is all clamped up, you use the tool like a chisel to scrape excess resin out of the slot. You do it a few inches at a time starting nearest to you first, to minimise spreading the squeeze out around. I made three scrapers but I only needed one. I stuck a small electric torch inside the case so I could see what I was doing.

It worked brilliantly. Thanks guys!

And at the end of all that, here is the finished article.



As it says in the manual: "Congratulations, you have made a box. It won't float, yet".

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