Butyrate dope surfaces are fairly easy to repair as you will discover. The final topcoat of butyrate dope will allow you to blend in the color of the repair to the point that it is barely visible.
Let’s briefly review the legalities of doing repairs on your own airplane. If you own an amateur-built airplane then you may legally perform any repair—fabric damage included. If you have not done any fabric work you will want to find someone familiar with fabric techniques and have them inspect the area and recommend a repair. A good A & P mechanic with fabric experience may be in order.
If you have a production airplane you can perform a fabric repair under the supervision of a licensed airframe mechanic. The mechanic has the responsibility of ensuring that the repair is done properly and then signed off in the airframe logbook. Most fabric repairs are very simple to perform. If you are not a licensed mechanic I would recommend you contact one and then have that person inspect the damage and offer their suggestion as to how to repair the area. You can then legally accomplish the repair under their supervision. They will sign off the patch in the logbook. We are talking about minor repairs. Major damage requiring structural repair followed by replacing fabric is another matter.
REPAIRING CECONITE FABRIC
Ceconite fabric may be coated with nitrate and butyrate dope or with a polyurethane covering system. The repairs we will discuss apply to fabric covered with nitrate and butyrate. For repairs to Ceconite fabric coated with polyurethane systems you should refer to the particular covering manual for the system you are using. We will briefly discuss repair techniques for butyrate dope that has been topcoated using a polyurethane enamel.
The method of repair on an aircraft surface is dependent upon the size of the damaged area. Larger tears or rips will require sewing the fabric while smaller areas may be repaired using a doped on patch. The Ceconite manual outlines the proper method of repairing fabric. This manual also makes reference to Advisory Circular 43-13-1B (Aircraft Inspection and Repair) for repairs involving major damage. Major damage is defined as any area exceeding 16 inches in length. Any damage less than 16 inches is referred to as casual damage.
Tools and Materials Needed
What about tools and materials necessary to properly do a fabric repair? A list for repairing Ceconite fabric is presented below. You should acquire the needed materials prior to beginning the repair. You should use the same weight of fabric that was originally used on the airplane. That should be noted in the airframe logbook.
- Small piece of fabric
- Masking tape & paper
- Small glue brush
- 2 inch brush
- Pinking shears
- 3 inch curved needle
- Thermometer to calibrate iron
- Small touchup spray gun
- 280 grit sandpaper
- Super Seam cement
- Nitrate dope
- Butyrate dope (clear)
- Butyrate dope (silver)
- Butyrate topcoat (color)
Lets start with the process involved in repairing casual (less than 16 inches) damage. This type of damage may be repaired two different ways—either with a doped in patch or a sewn in patch.
This type of repair is only allowed on aircraft with a never exceed speed of less than 150 MPH. Also, the damaged area must be less than 16 inches in length.
The first step is to remove the butyrate dope down to the nitrate layers. The dope should be removed outside of the damaged area far enough to allow for either a 2-inch overlap of the patch or a 4-inch overlap. The 2-inch overlap will be used if the damaged area is less than 8 inches long. If more than 8 inches but less than 16 inches then the overlap must be 4 inches. If you are familiar with nitrate and butyrate dopes, you will recall that nitrate dope is the first chemical applied to Ceconite fabric. (Butyrate dope will not adhere to any polyester fabric). Butyrate is then applied over the nitrate to build up additional coats. Nitrate dope will not adhere to butyrate dope so all butyrate coats must be removed prior to beginning the repair process.
There are two ways to remove the butyrate dope coats—either by sanding or by soaking the area with butyrate thinner. Sanding may be the easier way depending upon the size of the area. 280 grit sandpaper may be used initially. You will have to sand almost down to bare fabric to ensure you have removed all of the butyrate dope. You will first sand through the color coats and then through the silver coats. Both of these should be pigmented butyrate dope—one with a color pigment and the other with silver pigment. You want to sand until you reach the nitrate dope layers. This will be difficult to ascertain. So keep sanding until you are just about to bare fabric. If you actually reach bare fabric so much the better.
Another method of removing the butyrate layers is to use butyrate thinner and soak the area using a clean rag. After a short period of time you will be able to remove the layers of dope using a putty knife or a dull blade. Carefully mask the area around the patch. You do not want to remove any more of the dope around the damaged area than is necessary. Using this method is risky because the fabric is easily damaged. You also need to be very cautious not to cut good fabric with the dull blade you will be using.
After removing the dope you are ready to cut a patch. Measure the area carefully and then using your pinking shears cut a patch out of new fabric that will overlap the damaged area. Again, if the area in need of repair is less than 8 inches long, make the patch large enough to overlap the old fabric by 2 inches. If the damage is more the 8 inches long (less than 16 inches) then allow for a 4-inch overlap of the patch onto the old fabric. The patch should be cut out of very smooth fabric. Any wrinkles present will be very difficult to remove.
After cutting out the patch using pinking shears, you will then glue it in place using Ceconite Super Seam fabric cement. Pinking the edges will allow for a greater gluing surface (the pinked edges) versus a straight cut. Make sure you apply glue to the entire overlap area. Let the glue thoroughly dry (at least 1 hour) and then heat tauten the patch using a calibrated iron set at 250 degrees F. Do not iron over the cemented areas. Heat will loosen the fabric cement.
You will then need to put finishing tapes over the area. If the tear was small and you were able to simply sew it together, then place the finishing tape directly over the sewn area. If you had to sew in a new piece of fabric, then apply the finishing tape (usually 2 inch width) over the sewn seams used to attach this new fabric.
Nitrate dope or Rand-O-Proof should be used to glue the tapes in place. You will probably need to thin each one of these chemicals slightly to brush them in place. Do not thin too much as you will reduce the adhesion capability.
After brushing the finishing tapes in place, you must then reapply all of the chemical coats necessary to build up the area to match the dope layers on the surrounding fabric. Brush on at least 2 coats of nitrate dope over the patches and tapes. Then brush or spray 2 coats of clear butyrate dope followed by several coats of silver butyrate dope. Apply enough silver coats to bring the repaired area up to the level of the old coatings. After the dope has dried, sand it smooth and apply the final color coats of butyrate dope. After the color coats are dry you can then polish the area to blend in with the old dope. We will discuss sewn in repairs and major repairs (larger than 16 inches) in the next article.