Estimating materials

[galleywench]

Hi all,
I am going down to Merton's in Springfield later this week to pick up re-coring supplies and I'm having trouble trying to figure what and how much additives to buy. Here are my assumptions
- For the initial installation, bedding, and filling of the new balsa core I will need to use a structural filler (wood flour/cabosil).
- Once the cloth is in place I will need a fairing filler (microballoons/Qcell).

So if my assumptions are correct (please tell me if I'm wrong);
-Should I use wood flour and or cabosil?
-Cabosil is very expensive, is there an advantage of using that over wood flour?
-Given that I will be recoring the decks of an alberg 35 and my initial epoxy purchase will be 10.5 gallons, roughly how much will I need? Mertons sells wood flour in 40 lb bags, Cabosil in 2lb and 10lb bags, and microballons in 5 gallon pails.

Thanks for the help.

[Zach]

Cabosil is thixotropic, which means when you mix it up it will get thicker and thicker until you have a spreadable paste that will stick to the ceiling. This also means it'll stay balled up under something and not want to ooze out and give an air pocket. Some guys use wood flour for everything (They don't buy it... they dump the dust out of their belt sander into a bucket and use it.) Some guys use cabosil for most everything... I fall in the later camp.

A 10 pound bag of cabosil is the size of a 50 pound potato sack. You will be able to mix around 10 gallons or so of epoxy into really thick paste...
Retail is around a hundred dollars for a bag, which will be enough to do pretty much everything you'd want to do on a boat that size, and have some left over. 65 is the lowest I've hammered down the pricing, wholesale.

As far as the recore goes, the strips of balsa come in 2x4 foot sections, held on cloth scrim backed stuff... I would consider using divinycell PVC foam if I were to do my side decks again... though it takes a little more resin. 23-26 dollars a piece of balsa... wholesale is 15-18.

As far as the gluing down... It's about a quart of epoxy mixed with cabosil to fill the voids around the edge of the deck on a 2x4 foot section, as left by the riding a skill saw down the edge. Then you'll use about a quart of epoxy with no filler to wet out the balsawood between the grooves bent over a pvc pipe (Or the side of the boat) so that every block is glued together. I am a big fan of breaking up the panels with glue joints a 1/4 inch or so apart... just so it will be harder for the boat to ever rot out entirely from one leak at the stem. You'll then mix up some runny-ish cabosil and trowel it out evenly to plop the balsa core in.

The choice is yours if you pull polyethylene and weight down the core... or kick it off with fast hardener and hold down the places that want to lift. My preferred method is to fill the gap under the lip around the edge, let that set up and grind the bevel with a flap disc on a 4.5 inch grinder. Grind the inner skin with 60, prop it up if its very thin so it doesn't sag anywhere... then cut the balsawood so it has a gap around the edges, and lays naturally on the inner skin. I then use fast hardener, wet out the core, mix a batch of runny cabosil and trowel the inner skin, blob enough around the gap aroud the edge will be filled... then plop the core in place moving it around until all the air is out from under it and the vacuum of the glue keeps it stuck. From there I watch it my resin cup starts to go kick off... hold down any spots that may want to lift with hand pressure. 10 minutes or so of watching, the resin is starting to gel... Now I lay a roll of my pre-cut cloth on the core, and wet out the top of the roll, the top of the core and the cloth, as I unroll. You'll see dry spots on the top of the balsa core, where it has soaked up a lot of resin. There is a point where the resin has gelled up enough that no more will follow it into the balsa so keep looking down the boat and brush on more resin. There is also a point where in direct sunlight, dry spots in the balsa burp air into your cloth.

I have a squeedgee in my hand that is sloping down hill to catch the resin thats running across the top of the glass, to push it back towards dry spots. The other has a 2 inch chip brush... I pour the resin onto the cloth, squeedgee around, and work it into dry spots with the chip brush.

Once your first piece is unrolled and wet out, go back to brushing resin with one hand and rolling air with the other. After you see all the air is gone, unroll the next layer of cloth before the first one starts to gel up and get sticky. I put the first layer on resin rich, allowing the second to be a little drier. Repeat, the air rolling. You should see the grain and weave of the glass... Squeedgee off excess resin, back into your mixing pot. Air roll it one more time, and start mixing microballoons. I like glass microballoons... mix them up as thick as you can. Now go and lightly butter up the top of the cloth. Try to keep it so you can still see the weave of the glass.

You just skipped 2 days of waiting, instead of weighting down the balsa and coming back the next morning to glass... and instead of cleaning off the blush, grinding the top of the balsa, then glassing... then coming back the next day to fair... went from no deck core, to something you can start long boarding and doing the final fairing in the morning.

For glass I'd use 2 or 3 layers of 1708 biax cloth. You can figure out the resin needed for the glass, by cutting out the glass before you start gluing and weighing it. It's almost not worth your time to try and calculate the surface area of the deck to do the math. Biax is 17 ounces to the yard, and .8 ounces to the square foot. 50/50 resin to fiberglass is the standard for hand layup.

Buy a stack of mixing buckets, learn to pour by volume... Don't even try to clean them, just crack out the leftover goo tomorrow. Pre-fill 2 or 3 with resin 2 or 3 with hardener for whatever batch size you are doing. Wear 2 pair of latex gloves, and shoot them off at your friends when they get to slimey to use. Keep a bucket of white vinegar or acetone handy to put your squeedgees and air rollers in. This is a lot of acetone, so buy a bucket big enough to put a lid on. Buy a pair of real nice scissors that never touch anything but dry fiberglass. I like Wiss industrial ones... but real sharp pinking shears will work too. Trying to do glass work with crappy scissors sucks. Cut the cloth before you cut the deck. Plan out your sections. Easiest way to cut the glass is to lay strips on the 4 foot width up to the cabin top, weight it down, and sharpie the edge of the cabin and toe rail side. Then you have a stack of stuff, and have to stagger the joints. Easiest way to do the glass work yourself, is to split the cloth in two pieces 2 feet wide and however long (8, 9, 10 feet...) roll them up, unroll them on the boat, scribe the line... lay them on the next piece, and cut both layers at one time. Then just cut off a foot or so of the top one, mark it as such... and you've got your overlap for the seams.

If you have to do this in direct sunlight, rig up a tarp overhead. If its in the summer, keep your resin pot, and resin drums in the shade. Don't mix out of a chrome paint roller tray... Direct sunlight on balsa will make it bubble out air. Leave it where its going to be long enough that its the same temp as the skin of the boat.

Cheers,

Zach

[galleywench]

Wow, thanks Zach... that is a ton of information. Your an animal (I mean that in the best sense of the word). I have to read your techniques in more detail to fully digest, but I like the idea of doing it all at once. I had planned on doing it one step at a time but if I can keep from epoxying myself to the ladder during this I think I can make it work. I am taking the last week of April off to focus entirely on this and will have another person there to do the side work (mixing, etc...).

Since the weather in NH is a bit tough to predict this time of year is there a best time of day to do this? I have seen bubbles form when the temp is rising (from smaller jobs that I have done in the past). Should I plan on waiting till the afternoon peak temp? I am fully enclosed in a stimson shed so temps could be warm but not unbearable (hopefully).