The three most common lamination, or ‘lay-up”, methods used to transform raw carbon fiber into solid composite parts are Infusion, pre-preg, and wet layups. In this post we’ll talk about the process and applications of a non-vacuum assisted wet lay-up.
Wet lay-ups are typically used to repair existing carbon fiber parts or when using a resin system that isn’t designed for infusion. The process outlined below does not use a vacuum to provide pressure, so it is not appropriate for parts that require the additional strength from compaction. Not sure where to start with resin systems? Stay tuned for a post on a basic overview of resins available at a hobbyist level and their different properties. Trying to revive an abused carbon part? Come back later to our Carbon Trauma Center Q&A currently in the works! Need better properties? Do a vacuum assisted wet lay-up, or an infusion.
A (no-pressure) wet lay-up is the simplest of the three methods – both in terms of skill level and the amount of equipment and materials required. If you’ve used a paintbrush before you’re already well on your way to mastering wet-layups.
First, prepare the surface on which you’ll be laying the carbon. In the case of a part repair this means scuffing the existing carbon with a low-grit sand paper and wiping it with acetone to ensure that the patch repair will adhere. If your goal is to create a new carbon part from an existing form (ie a flat sheet from a table or skinning an existing part) you’ll need to “release” it with a chemical or wax release agent; this ensures that the part won’t get stuck to the surface of your form. A paste wax will generally do the trick for most resin systems.
Next, measure your surface and cut all of the carbon you’ll need for the lay-up. Organization in this step is critical to avoid a sticky mess! Cut a piece of plastic to place under your workspace for easy clean up.
Cut a piece of plastic about 2.5 x the size of your largest piece of carbon. Lay the first piece of carbon on to the plastic so that half will fold on top of the carbon piece. Thoroughly mix the resin and hardener. Paint a generous layer on to the carbon – stop when 90% of the fibers look wet. Fold the remaining half of the plastic on top of the carbon, then take the squeegee and pull it across the plastic, squeezing any excess resin and distributing it across the carbon. Once it looks evenly ‘wetted out’ (you can flip over your plastic/carbon/plastic sandwich to check the back), pull the carbon out of the plastic and place it on to your lay-up surface. Repeat this process until you achieve the desired part thickness.
Thoroughly mix the resin and hardener. Paint a generous layer on to the lay-up surface to help adhere the first piece of carbon. Place carbon as desired, then paint it with resin until all fibers are evenly ‘wetted out'. Repeat this process until you achieve the desired part thickness.
The Squeegee method is best suited for smaller parts or parts that require a neat lay-up. You will need a slow curing resin system for this method. The paintbrush is typically messier but works well for large, non-cosmetic parts and for resins with a fast cure time. The paintbrush method should be used for large parts that require a singular layer of cosmetic carbon on the final part surface. In either case, it’s critical that there are no dry fibers within your lay-up – don’t be afraid to get creative with your smooshing and squishing technique to make that happen! Things like paint rollers are great for large surface areas. Any uncured resin on unwanted surfaces can be carefully removed with acetone.
Once the resin is fully cured, carefully separate and lift the part from the lay-up surface using plastic wedges and a hammer. If you’ve done a patch repair, leave the carbon as is but trim any stray fibers that impede form, fit or finish. Read our next post on Hand Trimming carbon fiber part for tips on this next step!