July 2019

July 5

Today I spent the whole day sanding the boat hull.  Now I can't lift my arms.  Mostly true, sanding is hard work even with the best power tools.  Worst of all, as you get tired you can't keep the tools firmly on the work and you make mistakes.  Take lots of breaks.  Your good working time between breaks will decrease as the day goes on but fixing a mistake where the belt sander digs into your glass is a lot of work.  I've managed to avoid those type of mistakes but every once in awhile I let off the pressure and the belt sander skips scuffing up a place that may or may not need attention later.  The worse places is where I have to hold the belt sander on a vertical surface.  Gravity in not your friend at that point.  This beast weighs 13 pounds (5.9 Kilograms) and after about 30 minutes feels more like 50 (pounds or Kilograms it doesn't matter).

Sanding is slow going.  Plus that belt sander weighs a ton.  Notice the mottled look to the hull.  There are still dips and undulations that I'd like to fill and can not be sanded out without cutting into the glass.

I'm experimenting with skim coats of automotive filler.  What is generally used by the industry is a glazing putty or compound.  Unfortunately, glazing putties have very short working times and in the heat of Alabama basically about 15 seconds.  Good enough to skim a small area but anything else and you'd be wasting a lot of the product and the product is typically very expensive.  I've found another product that I'm experimenting with.  I 'm not sure yet how I'm going to use it.  The above figure shows a relatively heavy consistent coat.

This image shows a thinner spread with an occasional heavier spread.  Right now, I think this works better.  I've actually skimmed the entire area but the pale yellow spots are where I've applied a bit extra usually over some visual imperfection but sometimes that is just how it applied.  It's fairly difficult to spread thin and I'm learning to start with only a small amount on my putty knife.  Naturally, my technique is improving as I learn how best to use this product on such a large surface. 

The working time on this filler is suppose to be up to 40 minutes and cure to sand time 120 minutes.  First of all, in Alabama summer heat (95 F or 35 C) this is more like 5 minutes which is actually plenty of time.  Although one section I coated over 4 hours ago is still a little tender.  Too tender to sand so I think the it needs an over night cure.  I may not have put enough harder in but if I added more that would reduce my pot life.  Life is compromise.

Keep in mind that I'm planning a few coats of epoxy with West System 422 barrier coat additive over the top of all this.  It really does not enhance the epoxy water penetration properties as it's made for polyester resin which has lousy water resistance but it also makes the epoxy coat a lot harder and should resist scratches and dings better.  It's also only a few hundred dollars and that seems cheap insurance.

That hull is going to be slick when I'm done.

July 6,

The next morning, the filler is firm and ready for sanding.  I'll just have to skim coat sections and leave them overnight in the future.  I still have a lot of primary sanding to perform before I can even apply the filler.  Not today though, my arms are still rubbery and you need strong control over the sander to avoid having it skip on the hull and dig a gouge.

The following image is similar to above but I've given it a quick sanding with the belt sander at 80 grit  followed by a quick palm sander also at 80 grit.  I really like the results:

The product went on fairly quickly.  It required a lot of working to get the thin coat I wanted.  Make sure you only put a little on the trowel or putty knife at a time.  I recommend a steal knife around 6-8 inches like used in drywall finishing.  All the light areas are areas that have been filled.  All very shallow.

This is the product.  It comes with a tube of hardener that is pictured on the left.  I purchased it from Eastwood for around $67.  But google it, you can get it cheaper but shipping may even things out.  I've ordered quite a bit of stuff from Eastwood and never been disappointed. 

I'll add this important comment here:  This stuff is pretty toxic so keep it off your hands and use a good dust mask or respirator while sanding it.  Since it will be encapsulated in another couple of layers of epoxy I'm not worried about environmental impact.  

July 7,

So, I've been mentioning the short work time for this product (despite its claims) and I guess I subconsciously have been reducing the hardener to improve the working time.  The reason I say that is the goop I've got in the photo below is what happens when you get an incomplete cure.  This happened during a few batches on one area near the keel where I had laid up the filler a bit thick.  The 'cured' product was still rubbery after 3 days.  Sanding resulted in goop filling the grit on the sand paper and smearing over the work.  I used a few old sanding belts and powered through until it was all removed.  You can see at the top left of the photo where the sanded areas start to become white again, this is where the filler is completely cured again.  It's actually difficult to meter out the hardener and I've been relying on experience but each product is a bit different.  I'll make sure I err on the side of a bit too much next time.  At least the worst that can happen is that the filler hardens up on your pallet.  Of course you can always mix too much hardener and that may also give you a bad cure but I don't plan on getting carried away.  The instructions say 3-5% hardener by volume.  The only practical way to do that is by weight.  But I think I've got the hang of it now so I'll continue mixing by eye.  Oh and there is a tint change when adding the hardener so you can go by that as well.

A goopy mess because I did not add enough hardener.  I was probably subconsciously trying to increase my working time and got carried away.  I don't really remember what was on my mind at the time but I'll pay closer attention from now on.