How to do a fiberglass layup
Composite Construction Techniques
Aluminum foil-based, "economy pre-preg method", illustrated with step by step photographs.
On this page, we will take a look at a sample layup (using a particular fiberglass hand lay-up technique) and how I have chosen to perform the work required by this step. The intention is that this page will have ample explanation, plenty of detailed illustrative photos, and background explanation so that it can be readily understood by those with very little fiberglass experience building ariplanes, doing repairs, or working on other projects.
While this example shows a specific structural reinforcement in the fuselage of the Cozy Mark IV airplane, these techniques certainly apply to many other composite construction projects using fiberglass or carbon fiber. If you are working on an airplane, boat, race car, or other project using fiberglass cloth or carbon fiber cloth then these techniques will apply. While this small instructable applies to structural and nonstructural aircraft, the techniques can be easily applied to construction or repair of many fiberglass or carbon fiber structures including fiberglass showers and hot tubs that use cloth (as opposed to mat) plus resin to form the composite.
There is a slight difference in technique used when using polyester resins and fiberglass mat such as that used in boats, fiberglass shower stalls, and other projects. When using fiberglass mat on a project, the fiberglass mat is generally ripped by hand and applied with a different type of resin system that will dissolve the binder in the fiberglass mat. Fiberglass mat materials offer significantly lower strength and, along with other properties, are not suitable for airplane structural construction. Consider the information here to apply specifically for fiberglass applications using epoxy resin.
Where or how is this layup used?
In this example layup, we are going to add a fiberglass reinforcement to the F22 bulkhead and doubler where it attaches to the fuselage sides in Chapter 6 of the Cozy Mark IV aircraft. The instructions provided in the well-written Cozy plans assume that the builder understands how to perform this task by this point and summarizes the step in four sentences with an illustration included (worth a thousand words).
Just in case you are not building an airplane, In this example, we are adding a small layup of bi-directional fiberglass cloth to reinforce and strengthen a corner that was created earlier. So, we have a fiberglass structure that we have been working on using these same techniques, and we are adding a reinforcement fiberglass hand-layup to strengthen this fiberglass corner. This instructable / tutorial is intended to be not necessairly specific to airplane building.
The quote from the plans and illustrative drawing are from the The Cozy Mark IV FEBRUARY 2002 - THIRD EDITION Copyright 2002 by Co-Z Development Corp. Chapter 6, Page 2. (Note, this quote and image 45 deg. and edges peel plied. " Your copy of the Cozy Mark IV Plans can be purchased from Aircraft Spruce and Specialty Corporation. Step 1. Prep the workpiece (In this case, the workpiece is the interior forward section of a composite canard fuselage). The first step is to fully prep the area about to receive the layup by sanding the area and then cleaning the resultant residue. For this kind of prep work, I most often use a palm sander (Porter Cable) with a fairly coarse sheet of paper (36 grit) followed by hand sanding with a sheet of sandpaper wrapped around a soft spongy sanding block. For many layups, a power tool simply will not fit in the area being worked on, so hand-sanding is a must. I always sand an area significantly larger than the area of the layup. (Whenever I see a shiny-smooth look of cured raw-epoxy area anywhere on the airplane, I sand it rough automatically while always using caution never to sand down to or past any glass fibers. I have had people ask me about white spots after sanding fiberglass. If you sand into the glass, you will see the color change to white in the surface indicating that you have weakened the structural strength of the glass fibers in that area.) Work piece (front fusealage and bulkhead) Palm Sander
45 deg. and edges peel plied. "
Your copy of the Cozy Mark IV Plans can be purchased from Aircraft Spruce and Specialty Corporation.
Step 1. Prep the workpiece
(In this case, the workpiece is the interior forward section of a composite canard fuselage).
The first step is to fully prep the area about to receive the layup by sanding the area and then cleaning the resultant residue. For this kind of prep work, I most often use a palm sander (Porter Cable) with a fairly coarse sheet of paper (36 grit) followed by hand sanding with a sheet of sandpaper wrapped around a soft spongy sanding block. For many layups, a power tool simply will not fit in the area being worked on, so hand-sanding is a must. I always sand an area significantly larger than the area of the layup.
(Whenever I see a shiny-smooth look of cured raw-epoxy area anywhere on the airplane, I sand it rough automatically while always using caution never to sand down to or past any glass fibers. I have had people ask me about white spots after sanding fiberglass. If you sand into the glass, you will see the color change to white in the surface indicating that you have weakened the structural strength of the glass fibers in that area.)
Work piece (front fusealage and bulkhead)
After sanding, wipe and dust clean with a towel and/or vacuum using a shop vac. I have read that others wipe the area clean with a solvent. This is not something I have ever done, and I do not know what solvent other builders use or what benefit it offers. (If you have a comment or can shed some light on this, please let me know.) Many recommend that shop-air should not be used for cleaning and dusting because it could contain a mist of oil.
If the layup does not have clear landmarks about where it should be placed, place markers in ink on the workpiece. In this case, a 12 inch long layup will be placed onto the structure. This layup involves an inside curve with 8 inches of the layup on the fuselage sides and 4 inches onto the F22 bulkhead at the doubler area. I have placed small red ink marks just outside 8 inch mark and the four inch mark (see below). My layup will be between the two red marks.
This is the "before" picture.
Step 2. Prep the fiberglass cloth
The plans generally specify to layup layers of glass on wax paper, and I have done many layups using wax paper. However, I have come to the conclusion that I don't like the use of wax paper and started off using 4-mil or sometimes 6-mil plastic upon which to do my layups. I went through several variations and improvements on this technique until I ended up with this technique.
Side note: Sometimes I do layups without the aluminum foil and just use plastic sheeting. When Ido, I tend to use a sheet of 6 mil plastic between the glass cloth and the table and 4-mil over the top of the glass cloth to make a sort of peel-and-stick epoxy strip. I liked the thicker plastic sheeting on the bottom to smooth out the imperfections from my work table to make the squeegee work a bit smoother. (From bottom to top- work surface, 6-mil sheet of plastic, multiple layers of glass cloth, 4-mil sheet of plastic.)
Taking the lessons from my own experience and from the suggestions of others (such as the Cozy Girrrls ), I now use my own version of the aluminum foil method.
I start with a piece of white beadfoam type styrofoam that is sold at any hardware store as insulation material. It is light, slightly spongy, and always has a nice smooth surface upon to work with. This optional step of using scrap of styrofoam serves no purpose other than to act as a smooth work surface, keep my workshop clean, and use up scrap styrofoam insulation sheets that I had lying around after insulating my shop. A plywood surface with reasonable smoothness would also work just fine.
I then roll out enough "heavy duty aluminum foil" upon which to draw out the size of the glass layup I am about to do. Work with the dull side up. I use Sharpie* markers to accurately mark out the final size the layup should be. The "heavy duty aluminum foil" is the same stuff that you buy in the supermarket for cooking.
(*Use Sharpies. I mistakenly bought some permanant markers at the discount store that looked exactly like the Sharpie brand. Only after using them did I discover the slight spelling change from Sharpie to something else. I discovered that the epoxy just makes this cheap ink dissolve into the layup, thus causing your layup lines to disappear and fade away with exposure to epoxy. Avoid the cheap Chinese knockoff Sharpie markers.)
In this case, the layup is going to be a 4" by 12" layup as illustrated on the foil with a permanant marker. I use a 2" wide yardstick and often draw a centerline to help keep things aligned. The ink may show in the final product but will do no harm. Draw large and cut small if ink in your layup becomes a cosmetic problem for your application.
Outlining my layup size and shape on aluminum foil.
Because this is a project that I work on constantly, I keep my fiberglass organized in a cloth cabinet that folds down into a cutting table. (You can learn more about the cuting table/cabinet elsewhere in my website.) Inside the cabinet, I keep an organized supply of fiberglass both on full rolls and also keep cutoff pieces and scrap that are still clean and uncontaminated. Since this layup is small enough, I am going to use up some of my scrap pieces out of my BID, or bi-directional cloth, box and save some money.
In this example, I am simply demonstrating a 4 inch by 12 inch layup on one side. If you were not trying to use up scrap material like I am, you could do a single 8 inch by 12 inch layup on the aluminum foil and complete both the left and right side of the aircraft in one layup session but cutting it in half. I had to do it twice to use the smaller pieces of fiberglass cloth from my scrap bins.
Fiberglass storage cabinet with fold-down cutting table.
Cut four pieces, or plys, of fiberglass cloth and make sure that they are slightly oversize by at least .25 to .50 inches (more if this is your first time doing this). As you can see, my BID scrap box is visible, and I have sorted through my clean/uncontaminated scrap bin to find pieces that are large enough to cut a 4 inch by 12 inch piece at the 45 degree angle required.
During the cutting step, you must be sure to cut your cloth at the angle specified in the plans. In this particular layup, the fibers must be at a 45 degree angle. My 4 inch by 12 inch cutout is cut from a piece that I have already turned at a 45 degree angle.
(I have gotten e-mails from other builders about this step and photograph. I do appreciate the e-mails. Yes, I did orient my fibers at 45 degrees for this cut and layup. The piece of cloth that you see on the cutting table has the edge of the roll at a 45 deg already and therfore cutting my recangular piece in this direction results in the 45 degree fibers.) My cutting table is premarked with 45 degree lines marked with one inch increments for convenient cutting of cloth although in this case, the layup was small enough that IВ could use cloth from my scrap box. (Only clean, epoxy free, undamaged cloth goes in my scrap boxes. Don't ever use dirty or epoxy-soiled cloth on a layup.)
Cutting the fiberglass on the cutting table.
Lay the four plies of glass cloth on the aluminum foil right over the section drawn on the foil. In this example, you can see that I have significant excess. This will end up in the trash. Notice that I like to extend my lines well past the layup. With the four plies of dry glass on the aluminum floil, the 4 inch by 12 inch layup box would no longer be visible, but by extending the lines, it is easy to visualize placement of the glass cloth. This only becomes important if you cut your glass really close in an effort to conserve materials, and the risk becomes that the layup area may not be fully covered with the specified number of plies with a weaker structure as the result.
I like to stack my glass from most oversize on the bottom to least oversize on the top.
It is very important to ensure that the cloth is all cut with the fibers aligned at the proper angles, the cloth is unwarped, and the fibers are all straight. If you ignore the 45 degree fiber angle specified, the strength and structural load distribution may not be what it should be and you may also have difficult bubble problems as the fibers try to fit into the corner. BID at 45 degrees fits into corners much easier than BID at 90 degrees. Bubbles could be a source of eventual delamination or structural failure under load.
Laying out the multiple-pieces of dry/clean glass cloth on the aluminum foil.
Prepare a piece of 4-mil plastic sufficient to cover the glass cloth.
A piece of plastic sheeting is placed over the glass cloth.
Step 3. Wet out the fiberglass cloth
Before wetting out the cloth, it is important to prepare the area with the necessary
materials before getting started. Below, you will see that I have prepared mixing sticks, epoxy cups, squeegees (rubber and hard plastic), a grooved roller (I doubt that many builders using this technique use a roller), brushes, credit cards or other plastic cards (the best squeegees around), Dritz electric sissors (mine is covered in green plastic and masking tape to protect it from epoxy), and protective nitrile gloves.
Tools and supplies used for a fiberglass layup.
I use an epoxy pump. but hand measuring is just fine also. Before any layup, I do a few test-squirts to clear the pump. To test the pump and confirm ratio calibration, I pump the resin and hardener into separate containers to prevent waste, but more importantly to ensure an accurate ratio of resin to hardener. I don't measure every single squirt of the pump, but I do ensure accuracy of the pump ratio before every single work session. In this case, I squirt several measures into separate containers for resin and hardener. I then carefully weigh each container individually (accounting for tare in the measuring cups) using an electronic balance.
*Safety note: use gloves when working with epoxy.
Delivering a shot of epoxy from the epoxy ratio pump.
Note: I recycle yogurt and other food containers for use in the shop, but note that containers of this shape are not ideal for mixing epoxy due to their tall deep shape and non-uniform bottom. A container that is wide and flat is more appropriate for mixing epoxy due to the exothermal reaction that occurs when the hardener is added to the resin. See, for example, the offering of mixing cups available at Aircraft Spruce..
After measuring the weight of the resin sample and the hardener sample, I calculate the ratio and ensure that it is close to the specified ratio of 38:100 using either a calculator or the spreadsheet that I have posted on my epoxy-warming cabinet. In this case, the ratio is as close to 38:100 as the resolution of my electronic balance allows. This makes me feel comfortable that my pump is going to deliver an accurate ratio, the outlet nozzles are clear, and there are no clogs affecting the ratio. If you can't get the ratio correct, you should not even bother even doing the layup.
(Note about ratios: Each epoxy system has a different ratio requirement. Ratio by weight and ratio by volume may not be the same if the hardener and resin densities are not the same. Consult the datasheet for the materials you are using to ensure proper ratio. I use the MGS335 system and therefore must calculate ratio by weight and ratio by volume differently.)
Calculating the epoxy to hardner ratio using weighed measurements to ensure the proper 38:100 mixture.
Use a slow-cure epoxy if you are new at working with composites or if you are doing a layup that might take you a long time. The last thing you want is for the epoxy to start to harden or thicken before you are done with the layup. A layup this small could be done with fast epoxy if you are experienced, prepared, and know what you are doing, but generally speaking, a slow epoxy is a better choice.
Mix the epoxy in a mixing cup. Flat, wide bottom cups are strongly recommended becasue the greater epoxy surface area in a flatter cup reduces the problem of an exothermic reaction. An "exotherm", as it is commonly called, occurs when a chemical reaction causes thermal runaway until your epoxy either starts to boil or burn in the cup. If your epoxy starts to heat up, take it outside, discard it, do not breathe the fumes, do not apply to your layup, and start over with a new mix. Small batches of epoxy at a time are a good way to avoid this problem. Mix thoroughly; be sure to scrape the sides of the cup to avoid any missed resin or hardener. You want to ensure a proper ratio of resin to hardener in the final mixed product. Do not whip air bubbles into the mixture by being a little over-vigorous with that stirring stick. Just mix slowly and constantly for at least 3 full minutes, periodically using the stirring stick to scrape the sides of the mixing cup. The idea is to make sure that all of the resin and the hardener that measured is completely mixed together and none is left on the sides of the cup. (If you are used to polyester resins or other systems, then this careful attention to the ratio may seem silly.
Lift the dry plastic and pour epoxy onto the stack of glass cloth. With a little experience, you will be able to judge the proper amount of epoxy. Too little will require the addition of additional epoxy. Too much will be squeegeed onto your table or floor as waste. It is better to have excess epoxy on the floor of your shop than in your airplane adding unnecessary weight. Every additional ounce of unnecessary epoxy added while building your aircraft will result in one less ounce of cargo, fuel, equipment, or people you may be able to carry when your aircraft is done.
Strength is not increased with the addition of epoxy past the point that the glass is fully wet out. Once the glass if fully wet, additional epoxy adds only two things: weight and cost.
Mixed epoxy poured onto fiberglass cloth.
Place the 4-mil plastic over the epoxy-covered glass cloth, and distribute the epoxy all over the layup area. Dont worry about the excess glass outside of the layup area being wet-out, it is going in the trash after trimming anyway. Focus on getting the glass wet in the area that you are going to use.
Plastic sheeting placed over the top of the epoxy that was just poured over the layup.
Use a rollers, credit cards, fingers, or squeegees to fully wet out the glass as you view it and work it through the plastic. The plastic credit cards used as squeegees work about the best. As the glass is being wet out, the lines drawn earlier on the aluminum foil will begin to appear through the glass. Any white areas are dry and need to be wet. Keep working the squeegee through the plastic until the glass cloth is fully wet.
Sometimes you will have a dry spot that is particularly difficult to wet out.
Dry areas in your fiberglass show up clearly as white in contrast to the wet areas.
If you have a particular bubble or dry spot that is very hard to get rid of (sometimes caused by an imperfection on the worktable), you can carefully lift up the glass from the foil watching for any disturbance in the alignment or the straightness of the fibers, and add some epoxy on the dry spot from the bottom. In this case, the glass plies were peeled off of the aluminum foil and a little bit of epoxy was added to the dry area with the stirring stick. Carefully fold back into place so that the squeegee work can be continued through the 4-mil plastic.
As you can see, the ink does transfer into the epoxy as noted earlier.
Add epoxy to the dry areas to ensure complete wet-out.
Continue to squeegee until the layup area is fully wet out. Remove as much epoxy as possible from the layup area. You do not want any dry spots in the layup area whatsoever nor do you want any excess epoxy. Once it is fully wet out, you can try and squeegee as much epoxy out of the layup as possible to reduce weight and improve the quality of the final product.
The multiple layers of glass are now fully wet out, the guide lines drawn on the aluminum foil are visible, and the plastic sheeting is still on top. This layup is ready for trimming.
Using the Dritz electric sissors, (or your wife's very best sissors) cut the aluminum-glass-plastic sandwich down to the final layup size. Cut through the plastic, glass, and aluminum foil. All excess can be discarded. If you do not have an electric sissors, other cutting tools wil have to be used instead such as a Wiss shears, pizza-razor-cutter style cloth cutter, or razor blades. (Some may not cut so well on top of a styrofoam sheet like I tend to use.)
The photo of my electric sissors looks different than you will find in the catalogs because I have it wrapped in protective plastic (green pallet wrap) because I use it constantly with epoxy-wet gloves and on epoxy-wet materials.
Cutting the epoxy-wet sandwich of materials.
This is what you are trying to create. An epoxy-impregnated (still wet) multiple-ply fiberglass layup sandwiched between a sheet of aluminum foil and and a sheet of 4-mil plastic. This stack of wet materials is cut and sized exactly to the dimensions needed for the hand-layup on your project and can be placed without any more cutting or timming of glass. It is very EZ!
We now have a "band-aid" type of home-made prepreg which can be easily handled and applied to the workpiece.
Peel away the 4-mil plastic like a Band-Aid or bumper sticker and discard.
Peel away the plastic sheeting.
Step 4. Apply to the workpiece.
Paint clean / raw mixed epoxy onto the workpiece in an area slightly larger than the layup. With the 4-mil plastic peeled away and disposed, apply the epoxy-preimpregnated glass cloth into the proper place with the aluminum foil backing still in place. Using my American Express card (actually, a sample card pulled out of some junk mail), I squeegee gently through the aluminum foil to ensure a good bond to the workpiece. Press the layup into any corners or contours well while the aluminum foil is on the layup.
Sometimes, I am able to remove additional epoxy from the layup with the American Express plastic card squeegee. With the aluminum foil still on the layup, it is easy to wipe any excess epoxy away with a cloth if you desire. Don't do this after pulling away the foil. Wiping the area with a cloth after the foil is removed is a good way to disturb the layup and mess up your work.
Apply sticky epoxy-wet glass to the workpiece with aluminum foil facing up.
Peel away the all of the aluminum foil carefully, check for bubbles, and add epoxy using a disposable brush to any dry areas. The foil should come off without causing a disruption in the glass cloth. Stipple (gentle repeating stabbing motion with a brush) any dry areas or bubble areas to distribute epoxy. Holding the credit card or finger into any corners will help avoid bubbles in that area as the foil is gently pulled off.
In this layup, there is an inside corner. This is a very likely area for bubbles to appear. After the foil is removed, a little stippling in the corners with slightly epoxy-wet brush could be helpful for difficult corners.
Peel away the aluminum foil.
Apply a layer of peel ply. (This will get removed later.)
Apply an oversize piece of peel-ply.
Squeegee further through the peel ply until the peel ply is wet and bubble-free. Use the peel ply to make sure that the corners are well attached to the workpiece, the final product looks bubble free, and that the layup looks good.
Squeegee some more (and stipple if necessary) over the top of the peel ply.
Allow to cure in a warm environment (75 degrees F or higher ideally), and remove peel ply after full cure.
The final product shows good workmanship, is bubble-free, well-textured due to the peel-ply, ready for an additional layup if t was necessary, and has a smooth transition between new glass and old glass. In this case, there is some overhang toward the lower right of the photo. This hard cured fiberglass overhang can be cut away with the Fein tool and then sanded smooth by hand or with a Dremel style rotary tool.
This is the "after" picture. Showing cured glass and peel-ply removed.
I hope that this sample tutorial on how to do a fiberglass layup was helpful.
Please e-mail me with your thoughts on this page. This is one of my most visited pages and it gets a lot of traffic. I would be pleased to hear from anyone who found this information useful.
I would like to improve this page and understand just how helpful the page is to readers just like you. Comments, corrections, and suggestions are welcome. Thank You. oxy Ratio Pump, Fiberglass Layup, Fiberglass Peel Ply Tutorial, Making fiberglass parts, White spots after sanding fiberg