Getting started with composite parts in Indoor

In Uncategorized on October 4, 2019 by nicholasandrewray

Getting started with composite parts in Indoor

By Mike Kirda

As I get asked this quite a bit, I thought I should just write up what it takes to get started making composites for indoor models.

Here is a list of supplies needed.

Vacuum pump – Gast pumps are often found on ebay rather cheaply. You can find inexpensive vacuum pumps at Harbor Freight as well. I used a FoodSaver in the beginning. It works. Use a food saver at first if you have one. If you decide you really want to do this, a used Gast pump is, I believe, a better option than the Harbor Freight ones. Your mileage may vary.

Acid brushes – Harbor Freight

Nitrile gloves – Harbor Freight

3.5-4 mil plastic sheet – Harbor Freight

Old credit cards, stiff plastic from mailers, etc. Use for spreading epoxy or evening it out on flat laminates. Composite stores also sell purpose-made spreaders.

Caulk gun – Home Depot/Lowes/Harbor Freight

Inexpensive caulk – Any local hardware store

popsicle/craft sticks. See your local dollar store or craft store.

1 oz medicine cups for mixing epoxy – CST/ACP should carry them.

Wax – Recommend Part-all #2. Any composites store.

Laminating Resin – I highly recommend MGS resin. Nothing I have tried wets out carbon as well as MGS. I would recommend getting both the 285 and 287 hardeners so you can vary the amount of time before the resin gels. Wicks carries this. Other composite stores do too.

Fiberglass – You can get away with just two sizes of fiberglass. You want 0.5oz cloth as it is just about exactly 0.001” thick when wetted out. 3.6 oz cloth is just about 0.006” wetted out. 0.75 oz cloth comes out thicker than 0.001”, so may end up sanding a lot of it away.

Sharp scissors can cut up to roughly 7 layers of 3.5oz cloth. Offset tin snips are a better choice though, especially on thicker laminates. JoAnn and local hardware stores.

Carbon – ACP/CST have lots available. carries the hard to find Toray M60J in small spools. Mike Woodhouse carries light Russian Unidirectional cloth that can be a source of very light tow.

For a hot box, I use a simple temperature controller that turns on a lightbulb inside a plastic cooler. For very large laminates, I have used a carboard box with a bunch of blankets on top. Use of a computer fan inside the box or cooler would likely result in more even temperatures inside.

Nice to have:

A cutting mat and rotary cutter for cutting fiberglass to size. Makes things a heck of a lot easier. JoAnn Fabrics. Like Bed Bath and Beyond, they ALWAYS have 20% off coupons.

A valve between your pump and the bag. This way, once you pull a vacuum you don’t need to keep running your pump. Put the vacuum gauge between the bag and the valve though.

An interlocking bag connector.  Most of the leaks seem to occur around the hose. This can eliminate that source of leaks. Composite stores.

Glass sheet – You can wax it and place laminates on top of it to get them perfectly flat. Just make sure the glass is really really clean and wax it and wax it and wax it again before you start.  Drive around alleys to find when folks throw our furniture and grab any glass panels you find.

Mylar sheet. This also needs to be cleaned and waxed several times. Should be at least 0.010” thick, with 0.014” maybe better. Useful to sandwich laminate/core/laminate, like carbon/balsa/carbon. Composite stores.

Nylon bagging material with easy-close clamps. With the bag connector above, you have a solution without caulk that potentially holds the seal better. Alternative is bagging tape, which is even better, but this makes the setup single-use. Composite stores.

Please note that nylon bagging material does not generally last more than one or two uses. However small leaks can be stopped with caulk.

Paper towels work really well for soaking up the small amounts of resin that we will generally use. Mostly I use a good quality paper towel like Bounty. Polyester felt is sold at the composites stores and it works really well for larger jobs. Some jobs might benefit from a perforated release film with the felt on top to really soak out the resin. It depends a lot upon the job size.



Part two: A few hints

Measuring out epoxy: depending on the specificity of the work, there are a couple of ways to measure it out.

  1. Visually via gradations on the 1 oz medicine cups. Works great for non-critical work.
  2. Disposable syringes (eBay)- You can get very precise volumes with syringes.
  3. Milligram scale: You can get very precise weights with a milligram scale.

Note that by weight and volume will have different mixing ratios!

Mixing epoxy:

Get a mixing stick and get to work. It takes a good several minutes. I do a minimum of three minutes, but five is better. You can whip it into a froth, the bubbles will come out quickly.

DO NOT THIN YOUR EPOXY with alcohol. It works better to heat it, but only if necessary. Heating it will decrease pot life/working time.


Do everything with a plastic sheet over your table top. When done, put waste in center, wrap it all up and toss it out. Much faster cleanup this way.

Always wear nitrile gloves. You do not want to develop an epoxy allergy.

Sanding should only be done outdoors or within the intake range of a HEPA filter. Protect your lungs.

Always wash up afterwards, hands up to elbows.


One Response to “Getting started with composite parts in Indoor”

  1. The Harbor Freight and similar vacuum pumps that are designed for working on A/C systems have one major drawback. They use oil for lubrication, and they end up emitting oil vapor when running. This isn’t a major problem if you have a perfect seal and the pump only runs for a minute or two. If you have any leak at all and the pump is cycling on, it can fill a room with oil vapor in a hurry. I learned this after borrowing a pump from a friend. I’ve since purchased a Gast pump off of eBay for less than $75, and it uses an oilless diaphragm design which completely eliminates this problem. Go with a Gast if at all possible.

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