June 27, 2014

Composites Aboard - Technical Post

I built a good portion of Ceilydh, using about 100 gallons of epoxy. So it would be fair to say I know a bit about composite boatbuilding and repairs.  Here is a sampling of what we carry aboard, and why we may use some specific items.


1 & 2 - Epoxy resin and hardener. Unless you have a very low budget or are building a new good size part, skip polyester resin. It's weaker, less waterproof, stinks, and has a limited shelf life.  I get very fidgety unless I have 4L or more aboard.  That's enough for a good sized repair job.

Brand preferences: 
  • West System is expensive so I avoid it. 
  • Epiglass is very sensitive to mix ratio errors so I don't like it either. 
  • System 3 is nice. 2:1 mix ratio.
  • www.bateau2.com sells an economical house brand called e-poxy I've used with good success. 
  • Currently I'm using Ampreg 22 with slow hardener.  Like it a lot. Dyed resin and hardener helps to make sure you mix it well. Hardener is nice and slow, even in summer temperatures (yes I know it's winter here). 

    Whatever type of epoxy you use, get the SLOW hardener if you're cruising tropical areas.
3 & 4 - G/flex - a wonderful thickened epoxy glue made by West System. Only epoxy that I know that will reliably stick to most plastics. We have a water tank fitting held in a polyethylene tank with the stuff. 1:1 mix ratio which is very forgiving, and it's often what I reach for when doing a very small batch. 

5 - Marinetex - inherited from other cruisers. Works fine, is quite hard but mix ratio is tricky with the small bottle

Not shown - little tubes of JB Weld. Useful for engine repairs because it is heat tolerant.

 6 & 7 - epoxy fairing putty. Useful for big fairing jobs (I'm building a new rudder right now). Usually I mix my own fairing compounds but the pre-prepared stuff is nicer, if more expensive.

8 - colloidal silica. Used as a thickening agent and to make a gluing compound. About 2:1 silica/epoxy resin ratio by volume with make a very stiff mixture.  You can buy a huge sack for about $80 from commercial fiberglass suppliers (about the size of 3 x 20L buckets). Compare that to the price that West charges for little carboard tubes of the same stuff...

9 - microballons. Lightweight balloons that are easy to sand. You still need to add some colloidal silica to stop the fairing mixture from slumping.

10 - milled fibers. Highest strength structural filler but use with discretion as the resulting mixture will be very lumpy. I only use this on items that have to take really big loads like a sloping winch base mount.

Mold wax - used to wax irregular shaped molds. A little can of it will go a long way. A hard car wax can be used but make sure it has no silicones (they stop stuff from sticking)


1 - Biaxial stitched cloth is my normal choice of fiberglass for all purpose repairs and construction. It's about 40% stronger than woven cloth of the same weight and drapes better if you use the +/- 45° style. 
  • I almost never use roving because stitched cloth is so much better for most applications
  • I almost never use mat unless it's for a very small part with tight contours. It sucks up resin like a sponge and is very weak.
  • I do use light woven cloth as the final layer on parts where I want a nice cosmetic appearance
 2 - I usually have some 4" wide x 6 oz (100mm x 200 gram/m2) woven tape on hand. Used for tabbing parts and joints. It's tidy to use. I wouldn't use it to rebond a main structural bulkhead but for everything else 1 - 3 layers will provide a strong bond

3 - woven braided sock - this is pretty esoteric stuff. I used it to build some new glass/carbon tillers. You slide it over a form like a sock and it will stretch to suit the diameter and take gentle bends. Not really required for most cruisers!

4 - carbon twill about 7.5 oz/250 gram/m2. This is a woven weave and it always looks nice. If I'm building a carbon part with an exposed weave I'll use this as the top layer for looks. Drapes very easily. Very costly.

5 - carbon unidirectional fiber - 9 oz/300 gm/m2. Left over of a 500' roll from when I was building the boat. I use this when I want a part to resist bending in one direction primarily. Not usually found on most cruising boats

6 - Coremat. This thin (about 2-3mm) stuff acts like a sponge and absorbs resin to form a thin core for small parts. Useful when stiffness is the main governing requirement for a part. I used this to make Dorade boxes when I wanted to keep the wall thickness thinner than a typical 6mm core would provide.

7 - Stirring sticks. Get your kids to save their popsicle sticks. Rinse them first. Then stir for 2 minutes, timed with a watch. It's longer than you think and boring too. Scrape the sides of your mixing container well.  Nothing sucks more than having your epoxy not cure. Do not use your wife's wooden spoon and try to wipe off afterward. She will notice.

8 - Mixing containers. Save those yogurt containers too. Rinse well. Nothing stops a nice epoxy from curing than a lump of fermented milk product. When the resin has hardened, pop out carefully and re-use a few more times if you are lucky

9 - protect your hands. Epoxy is a skin sensitiser and you will get allergic reactions if you keep letting it get it on your hands. Or thigh. Or in your hair. 

(White vinegar will get uncured epoxy off your skin and is much nicer than using acetone. Wash with soap and water afterward. Epoxy in hair? Let cure and reach for the scissors)

10 - Digital Scale, accurate to +/- 1 gram. Many epoxy mixing errors are caused by measurement errors in measuring volume.  Almost all epoxy suppliers will provide mix ratios by weight and volume.  The ampreg 22 resin I use is a 100:28 ratio.  For every 100 grams of resin you add 28 grams of hardener.  If you pour in 172 grams of resin you need 172 x 0.28 grams of hardener. The math is not hard!  I can reliably measure down to about 30 grams of mixed epoxy. That's about the weight of a small chocolate bar. 

I really should cover the scale with some cellophane wrap too but I pour carefully instead.  I also weigh my cloth before starting so I know about how much resin to mix.

If you're using those little mini pumps watch out for when they 'burp' and give you a little air bubble as you're mixing. Or the pump gets partly clogged at the end of its travel by the plunger mechanism. It's all too easy to get it wrong. Some people even forget to keep count of how many pumps they did.

11 - A Calculator dedicated to my sticky fingers.

12 - I almost always use plastic squeegees for spreading resin onto cloth. The only place it won't work well is on vertical surfaces. I will wet out the cloth on a horizontal piece of plastic drop cloth and then stick it the to the vertical surface. If you want a good cloth / resin ratio, squeegee hard until the cloth looks almost dry.  Brushes soak up more resin and are expensive.

You can more easily pop off dried resin from squeegees by leaving a thick layer of resin on it. Sand the working edge with fine sandpaper to you don't catch fiberglass cloth with little burrs when re-using squeegees

13 - Very well used Olfa rotary fabric cutter. Much nicer than scissors for cutting large quantities of cloth. Use on a hard backing surface.

14 - syringes are used to squirt epoxy into holes in the deck or other tight crevices

15 - packing tape - one of the best mold releases known to mankind. Really effective on flat or mildly curved parts. Use the brown stuff so you can see it better on your mold surface. Forget wax paper or cellophane. Wax paper doesn't have enough wax to reliably release, and cellophane is too flimsy.

 oops - forgot to put a number on the item above 5.  Call it 16

16 - peel ply.  Peel ply is a fancy name for a lightweight nylon fabric you apply to a wet laminate top surface. Squeegee it down firmly onto the laminate. When the glass is hard, peel it off the laminate. You will get a much nicer surface with no stray glass shards or hairs and suitable for further bonding. Once you try it you will never stop using it.

Buy your peel ply at a fabric store. Look in the discount bins where nobody wanted that neon green ripstop nylon for some reason.

NOT SHOWN - a decent supply of biaxial fabric and Corecell foam core is stored in a locker for all those projects that are just itching to ... that reminds me of one other very important item: 

BABY POWDER.  If you have to grind or sand a lot of fiberglass, very liberally dust your exposed skin with the stuff. It seems reduce the itchies significantly. That, and a cold shower immediately afterward.

Here's a recent project. This is a bracket for a swing out seat at Maia's school desk. The old bracket was a piece of bent aluminum pipe with a bloody big bolt for the seat to pivot on. It eventually bent when 2 kids sat on the seat.  The new bracket is lighter and structurally cleverer using thin carbon tubes. It supports my weight.

How you make it: Used carbon fiber windsurfing mast tubes are the base material. The tubes are roughly notched to fit, joined with epoxy putty fillets, and allowed to harden.

Thin strips of wet out carbon uni fiber is wrapped around the joints. Peel ply is used to cover the laminate. Then electrical tape (used backwards i.e. sticky side out) is used to squeeze the joint and consolidate the laminate. The outboard end of the bracket has a s.s. pin in place for the seat and this technique is being used to tape the pin in place. Note the drips of excess epoxy onto the plywood scrap below.

- Evan


She-Kon said...

Great post! I've used most of the same materials and can second your opinion on the Bateau.com ePoxy. So far I think I've used 30 gallons of it. About the only thing I have to add is a good pair of fabric sheers. The pair I have are special for cutting carbon fiber but slice through fiberglass like a hot knife through butter. I had a 3 yd sample of biaxial Basalt fabric and used it on my transom. It is absolutely amazing material and much easier to work with than fiberglass or carbon fiber. If you get a chance to get ahold of some it's really nice to have for repairs.

Keep up the great postings!



Behan said...

White vinegar instead of acetone = YES!

Can I just say... Jazz Hands on the glove box are kind of awesome.

We had tubes of JB Weld that came with the boat, and came in VERY handy recently...just when you start to wonder about what fills the bilges...

Unknown said...

Yeah, kicking myself for all the acetone I've wiped down with, can't be good. Now I know, gracias.