West System makes a widely known and well-liked “epoxy system.” In high-power rocketry, West System products are used more than any other epoxy system (although not more than basic “hobby shop” epoxy.) Everyone who tries this system loves it for the convenience and range it provides. The major disadvantages to the system are high price and difficulty in mixing small batches.
Questions and Answers
Q: Why is West System better than standard epoxy?
A: Standard epoxy (also called “hobby shop” epoxy) comes pre-thickened and mixes in a 1:1 ratio (one part resin to one part hardner). This means that the hardner part has fillers added to get the 1:1 ratio, making it easier to mix. Unfortunately, the fillers reduce strength and make the epoxy too thick for some purposes. By starting out with unthickened epoxy and using various fillers, you can get the exact qualities needed for different jobs. Also, the West System resin and hardner are typically dispensed from pumps which regulate the ratio, removing the “equal blobs” guesswork.
If you only use epoxy every once in a while and never plan to fiberglass, it’s probably not worth investing in a whole system.
Q: Why is West System so expensive?
A: It’s actually not that much more expensive than hobby shop epoxy, but you do have a higher initial investment. The investment necessary for general bonding requires you to purchase a larger amount than you might think you need, plus you have to pay for some parts which you will re-use for a long time. If you use a lot of epoxy, you will save money by buying in the larger quantities.
Q: OK, I’m sold. What should I get to start out?
A: First of all, you need to get resin (105) and pumps. Buy the “A” size initially since one pump will dispense about an ounce of epoxy, more than enough for small bonding jobs.
For general bonding, you will also need filler. The best all-purpose filler for high-power rocketry is 404 (high-density). If you want to minimize weight and are boding porous surfaces, you might also want to get 403 (microfibers). 404 is stronger than any other filler for general purpose bonding. The best hardner for general bonding is 205 (fast) which is about the same as 30 minute hobby shop epoxy.
For fiberglassing, you should probably buy 206 hardner (slow) which is about the same as 2 hour hobby shop epoxy. 206 makes a slightly thinner epoxy and gives you extra working time to get all your layers down before they cure fully.
For filling imperfections and building up fin fillets, 407 filler makes a good choice since it sands easily and feathers out nicely. Other fillers are good for different purposes, see the section on fillers below for more info.
What To Buy Initially
|Part #||Description||Need For|
|301A||mini-pumps||accurate measurement of 5:1 ratio|
|205A||“fast” hardner||bonding and filling|
|404||high-density filler||high-strength bonding, doesn’t sand well|
|403||microfibers filler||light-weight bonding of porous materials (optional)|
|407||low-density filler||general filling and filletting, sands easily|
† Buy the “A” size resin, hardner and pumps to start out.
Q: Where should I buy my epoxy?
A: You can purchase everything from Gougeon Bros. (makers of West System), but you can generally get a better price from distributors. Also check the yellow pages for marine supply stores as West System is heavily used by the boat-building industry. Check out the dealers list.
Q: I seem to waste a lot of epoxy, even with the “A” size pumps. How can I reduce this?
A: The pumps do waste a lot since you get about an ounce from one pump of resin plus hardner. You can mix the parts by hand if you want to, but this removes one of the main benefits of the system (easy and accurate mixing). Try to “batch up” little jobs so as to get several bonds out of a single mix.
Q: West System sells fiberglass cloth, but it’s thicker than I want. Where can I get finer cloth?
A: You can buy finer cloth at your local hobby shop. (SIG makes several sizes.) Also, the dealer you buy your West System products through will generally also sell different sizes of cloth. The cloth is generally not specific to the system, but make sure the cloth you buy will work with epoxy resin (not just polyester resin). Marine supply stores will generally not carry the finer sizes.
Q: I’m scared to start fiberglassing. It looks so hard!
A: Fiberglassing isn’t hard, but it is harrowing the first couple of times. You need to plan ahead, cut out all your cloth before mixing any epoxy and pick a time when you will not be disturbed. Don’t rush and you will end up with a fantastic result. Be sure to read the article on Reinforcing Tubes.
Q: Where can I find out more about epoxy and West System?
A: When you buy your epoxy products, make sure you get a West System catalog. It has great introductory material on epoxy in general and their system in particularly. Read the beginning pages and you will have a good background in epoxy use. They have a detailed user manual on their website. (Even if you don’t buy into the system, get the manual and read it. Really.)
Also see the Epoxy Tips article.
West System makes several fillers which work with their system. The most useful for high-power rocketry are 404 (high-density) and 407 (low-density).
- 403: MICROFIBERS adhesive filler
HPR Use: light-weight porous bonding
- 404: HIGH-DENSITY adhesive filler
HPR Use: general bonding (best strength)
- 405: FILLETING BLEND adhesive filler
- 406: COLLOIDAL SILICA adhesive filler
- 407: LOW-DENSITY fairing filler
HPR Use: filling, building up shapes
- 410: MICROLIGHT fairing filler
Fillers by Use
|Bonding with Fillets||**||**||***||**||***|
See West System’s Filler Selection Guide for more information.
Submitted by: John Coker