Originally written by Keith Bradley on the Keith Bradley Boat Forum (KBB) on Wednesday October 30, 2013, it was lost when the forum went down. Keith has been nice enough to give Offshore Electrics Inc OSE permission to re-post it.
The below paragraph was originally in Keith's closing thoughts, I thought it was important enough to say it first, since OSE agrees so heavily.
"It's tough to find info about this type of stuff from people who are good at it, because most of the people who have a high level of experience prefer to keep their trade secrets to themselves. I believe that if we all make an effort to contribute the knowledge we have, it will raise the level of all of our builds."
Carbon Fiber Inlay Tutorial
INTRODUCTION
After many requests, I have decided to make a tutorial on carbon fiber inlays. Our intention here at KBB is two-fold: First, we want to lead the charge into the next level of FE boating. So far I think KBB forum members have done quite well at accomplishing this, and raising the bar for everyone else. I look on other forums, and it seems that even there, 90% of the most admired builds are done by KBB members, some of which are even relatively new to the hobby!
Second, I want to share some of the high-end qualities that are unique to our boats with all of the KBB community, making it possible for everyone here to accomplish a high-level build themselves. In the spirit of this, I am sharing some of my knowledge with all of you. Please take the time to read this, and fell free to share it with others. I don't care if you post some of this somewhere else, just provide a link so viewers can know where it came from.
While many will tell you there are different ways to do an inlay, this is mine. I'm not saying my way is the best, oh wait...yes I am. :-) I do believe that this is the best method. There are other methods that definitely work well and are ok to use, some that are questionable, and some that are downright silly. I am not a proponent of using other glues, adhesives, hair spray, etc. other than a little tape and the epoxy resin meant to do the job. While the chemical reaction between resin and hardener may break down other adhesives, it does not have the capability to make them magically disappear. Anything that has the ability to leave a film or fill the scratches you put in your hull will hinder adhesion. Also, thinning your resin with things like other adhesives (either on purpose, or indirectly), alcohol, etc. will weaken your final product. If you want to thin your mixture, gently heat the resin and hardener separately (putting them in warm/hot water works well). Be advised, though, that this will greatly accelerate chemical reaction and shorten pot life, so you will have to work faster with warmer resins (conversely, cool temperatures will slow the process, or sometimes even prevent proper cure, depending on resin used and temperatures observed).
RESIN CHOICE
As I alluded to, different resin/hardener combinations will have different characteristics and may or may not be appropriate for a given temperature range. Pay attention to this. I recently read some info from a self-proclaimed expert that his product of choice produced better results and a stronger work-piece. In reality, the resin and hardener he uses is intended for lamination's that go in an oven, and will not produce an appropriate bond at room temperatures. He actually is choosing to produce a weaker product and doesn't know it.
While there are many resin choices out there, when it comes to CF or Kevlar, Epoxy resin should be used. Epoxy resin is superior in fiberglass layups as well, but more expensive than vinyl/polyester resins. In the sub-category of Epoxy resin, there are again a number of choices.
A pre-thickened epoxy that is intended to be an adhesive (six10, G-flex, PT-39, 5 minute epoxy, etc.) will not produce good results. Epoxy resin that is too thin (types intended for vacuum resin infusion) will also make your task difficult. A typical laminating resin like West systems 105, Pro set 125, System 3, etc. can be used. There are many other choices, just make sure you look into pot life and cure temps before buying. As a general rule of thumb (not an absolute), the longer a resin takes to set, the more it can bend without breaking. This means that 5 minute, 1 minute, and similar setup resins are extremely hard and brittle. Faster setup resins are typically more prone to yellowing over time as well. Being in the sun and/or water will accelerate the yellowing process.
For inlays, I recommend West systems 105 resin and 207 hardener. I like these because the pumps they sell for their bottles make mixing easy, and the 207 hardener doesn't yellow over time. This sounds like clever marketing, but if you use both in a boat and view it a year or two later, the difference is quite apparent.
FABRIC CHOICE
This part is up to you and your tastes, but I will outline a few basics that might save you some time:
- Kevlar is hard to cut! Some people who have used Kevlar assume that carbon fiber is just as difficult to work with. This is not true! Carbon fiber is much easier to cut and grinds away much more clean compared to Kevlar. Carbon Fiber also conducts electricity quite well, so be careful where you use it.
-Colored fabrics look good on the roll, not as much in the hull. Most people want to be different and use colored fabrics their first time. This is ok, but most find that in the end, black CF is unbeatable.
- 3k, 12k, 24k, etc...these are relative to the size fiber stranding groups. If you look at a carbon fiber weave as a series of carbon cables, each cable having multiple tiny strands of carbon fiber, the "k" rating would refer to the number of strands in each "cable". As many would guess, there are 1000 strands in a "k", so a 3k weave has 3000 strands in each bundle of fiber, and a 24k would have 24000 strands. It's essentially like weaving with larger diameters of rope.
- The most common types of fabric are Plain weave, twill, and Harness weave. These can be further expanded with numbers (2x2 twill, 4x4 twill, H4, H8, etc.). In a plain weave, the bundles (or cables in the former comparison) are woven over and under each other, in successive alteration (1x1). In a twill fabric, each strand bundle will cross over/under a given number of the opposing bundles before going back over or under said bundles. The first number in the weave represents the number of bundles that a will go over, and the second represents how many it will go under before coming back up. This results in a looser fabric that conforms to curves better than plain weaves. A 4x4 fabric would conform even more than a 2x2 fabric. A harness weave will conform even better than a twill.
- There are differences in fabrics. While there are a number of sources for quality weaves, sometimes places will buy "seconds" and sell them as new. Seconds are weaves that are inconsistent, loose, or otherwise not fit for top tier sales, so they are sold off to lessor retailers. I have also heard of places using black fiberglass/CF hybrid weaves and selling it as pure CF. I'm not going to tell you who does or doesn't have quality fabric (we sell fabric right here at KBB that is top of the line), I can tell you that I am 100% sure that there is a retailer out there selling plate/sheets that are comprised of CF AND black fiberglass. Please don't PM or email me asking who it is. It's pretty easy to tell. If one place is substantially cheaper than everyone else in the industry, don't expect that they are offering the same product.
Sand the hull thoroughly prior to doing any inlay work. This is done to give the resin more surface area to bond to. An un-sanded hull will not support a strong bond, so sanding the hull is critical and should not by any means be considered an "option". While sanding the hull, you can also use this as an opportunity to remove or reduce any blemishes that may be in the hull from the factory. High/low spots, resin and fabric chunks, loose fibers, etc. should be removed or minimized. Any "bumps" on the surface under your fabric will be apparent even after the inlay is completed, so a little extra work here will produce a better looking finished product. Sandpaper as course as 80 grit and as fine as 220 can be used here, depending on hull size and construction material.
The first step when doing an inlay (after the hull is sanded) is to make a pattern or patterns for the fabric that will be used. In this demonstration, I used paper that is available on a roll. First, a basic set of measurements can be taken to acquire a starting shape. Once a basic shape is attained, place the paper inside the hull as a template. Mark and cut this piece as needed, until you have the shape that you want. Allow for an additional 1/8" to be added to your piece when you transfer it to fabric. Hint: While only the main pattern is shown in this pic, I made another pattern for a piece that lays behind it to complete the inlay. This piece was done in the same manner, and was made to cover the area behind the hatch and the inside surface of the sponson transoms.
Once patterns are established, place said patterns on an unrolled sheet of fabric (this may be fiberglass, Kevlar, Carbon fiber, etc.). With the pattern lying flat on the fabric, outline the fabric with 1/4" masking tape. Once the outline is completed, remove the pattern and discard it, or save it for future use if needed.
Cut through the center of the masking tape that you laid on the fabric. The resulting fabric piece will have a 1/8" masking tape border, which helps to keep the fabric from fraying and eases cutting.
After test fitting your newly-cut fabric piece in the hull, apply a coat of resin/hardener mixture to the hull surfaces where the fabric will be placed. Be sure to cover all the areas that fabric will be placed in order to achieve proper bonding throughout the inlay.
Fold the fabric evenly in thirds, with the tape facing as shown. This will allow easy insertion of fabric into the now wetted hull. When in place, the tape around the perimeter should be face down. The tape will be left on but not visible when the inlay is completed. Slide the fabric into position, holding it ABOVE the hull until it is centered in place. Then, unfold each side and press the fabric into position. Once the fabric is where you want it, apply a light layer of resin to the top side of fabric, making sure that there are no dry spots in the layer. If you are doing multiple layers (It's best to do them all at once so that a chemical bond is created between layers), apply a generous amount of resin to the top of each layer before adding another.
Once the fabric has been wetted, a small foam roller can be used to help ensure more uniform resin coverage, and better press the fabric into place. This can also remove or redistribute small puddles of resin, but it won't work miracles. Pay attention to depressions in the hull, such as the sides of the tunnel and steps. Fabric can easily bridge over the gaps if not paid attention to, which will lower the overall integrity of the inlay and greatly diminish the aesthetic appearance of the hull.
Here are a couple pics of the inlay demonstrated in this thread before dry. Once dry, it will loose a bit of the "wetness" that you see in these pics. This was done with a honeycomb carbon fiber fabric, which is slightly heavier and more difficult to wet. This fabric is slightly more difficult to lay onto curved surfaces like a boat hull, but still one that is possible to lay with good results. If this is your first time laying carbon fiber, a 2x2 twill or 1x1 plain weave will be easier to use.
That's it!
