Poly Fiber Fabric Overlap Seam

Has anyone effected this type of fabric repair and can share your results/thoughts?

I have read the Poly Fiber Manual regarding overlap seam repairs on leading/trailing edges and unsupported areas such as fuselage sides (my application). I know the recommended procedures mentioned there for E-AB and in AC 43.13 for certified aircraft. However, I can not locate any youTube or builder videos actually detailing the procedure and showing end results.

So, some additional questions come to mind:

• I am particularly interested in repair procedure/tips with 2k poly topcoats (vs. PolyTone) and paint blending techniques.
• After sanding off the 2k topcoat, does removing silver down to pink w/ M.E.K. result in the original fabric 'tautening' being reversed?
• Should one or both (old or new) fabric layers being joined be tautened prior to gluing and at what heat setting?
• Should fabric reinforcing or cover tapes be fully or partially pre-shrunk prior to application?

Again, any insight is appreciated. I have already decided my next project will be PolyTone...

Doug,

I see you haven't received any answers yet.....thought I'd give it a whirl for the things I am aware of.

1) Not real sure what is meant by 2K poly topcoats, however if that is the two part urethane it's a bit different to deal with compared to polytone. The catalyzed urethane cannot be dissolved from the top down like polytone can. The nice deal with polytone is that it is a solvent carried paint, like lacquer, so a person can essentially dissolve one layer at a time (poly tone, polyspray, and some of the polubrush) before making a repair. When taking the layers off - a person can start with a large patch for the topcoat - smaller patch for the gray and smaller yet for the pink to expose where the patch will be glued down - essentially a person can reverse feather the layers with the MEK to make it easier to blend the replacement undercoats and polytone. With the catalyzed urethane, ideally a person would do an entire panel; but, it is possible to remove the topcoat and undercoats by applying a rag with MEK to the backside of the fabric - it does not leave a nice edge like you can get by "disassembling" poly tone layer by layer from the top, but you can get down to the fabric to stick the new fabric to the old. At any rate, the catalyzed urethane isn't as easy to deal with as polytone on repairs. Don't really know what kind of repair you are dealing with. I'd sure stick with the Polyfiber recommendations and procedures from their book in any case - buy the book if you don't have it - it's good and easy to understand.

2) Removing the gray (polyspray) and pink (polybrush) needs to go all the way to the fabric where new fabric is to be overlapped. Removing the gray (polyspray) and pink (polybrush) does not untighten the fabric underneath.

3) Shrinking should be done after the patch is glued in - otherwise you could end up with some loose fabric flapping in the breeze. How much shrinking is a bit artsy - Pretty much have to see how the fabric behaves as you go - probably don't know how much the old fabric was heated/shrunk to.

good luck

Thanks Dave.

I have the PolyFiber book but they don't add much in the way of detail beyond min fabric and finishing tape overlap requirements. I know an A&P who applies tape to the backside of a slit-like tear or rip, then tauntens to pull the edges tight before ironing finishing tape on the front, but that is not what I am doing. I am replacing ~36" of side fuse fabric panel from the door aft. There is structure for 3 of the 4 replacement panel edges but the vertical seam from lower to upper longeron will require a fabric overlap seam.

Yes, 2k paint just means a two component catalyzed product, in my case Imron 5000 polyurethane enamel. I have found that just sanding the paint down to fabric is preferable to the solvent from behind trick. While the solvent certainly is easier and quicker, it creates an added level of difficulty when trying to feather edge the paint carefully right next to bare fabric. Hard not to damage the fabric or sand thru it, I've found holding a stiff piece of Lexan behind helps sand more evenly.

No matter how you approach it, it's a lot more work than PolyTone. But recovering and reprinting the entire aircraft would be a ton more time and expense so I'm going to give this a try. I may be looking for paint scheme suggestions to cover the seam with a vinyl graphic if I can't get a satisfactory paint match and blend line. :rolleyes:

I did a small repair with Aerothane and found that the edge meeting the old paint is impossible to blend very well; I even tried using an airbrush-no joy. I believe the only way is to do a complete panel where the old/new paint lines up with a structural edge and is then not noticeable. That's what Polyfiber tells you to do and I think they are right.

Don't preshrink the patch; you will want to shrink it after the glue dries. However, I do think that a preshrink or partial (at 250 degrees) is a good idea on finish tapes or gussets going over fabric patches. Don't do it on longer straight tapes though because preshrinking causes the pinked edges to get all wavy and snakey. Maybe there is a way to do it with much care.

For small punctures and holes from hangar rash I put a silver dollar size patch on the inside if accessible. Pre shrink an oversize piece of fabric and iron flat. Then cut out the patch with pinked edges. Attach with poly brush and smooth out. Let dry then fill and finish the outside as usual.

For small holes that are only accessible from the outside the procedure is almost the same, just dissolve layers of finish or sand them down. Attach your preshrunk patch and let dry. Iron down any pinking points, then finish as usual.

Whether to pre-shrink or not depends on the shape of the area being patched. Flat or simple curves get preshrunk. Compound curves do not get a pre-shrink.

The above works for small holes or rips only. Anything larger than about 2 inches you should recover a larger area out to a stringer or rib using new fabric. It's less work in the long run as you will avoid a lot of sanding and it is easier to hide the transition between new and old.

In your case, the Imron 2 part poly is resistive to almost all solvents known to man. It is also resistive to sandpaper meaning you are in for some tedious work. So I would recommend cutting out a larger panel and recovering the area with new fabric. Imron has a great wet look finish with deep gloss but you pay the piper when it comes to repairs.

Hope it goes well for you.
John P

Yes the sanding is tedious and a real P.I.T.A. to feather properly, but it is quite doable with a bit of patience. I find that starting with a mechanical advantage, ie. my Fein oscillating tool, then moving to hand sanding saves your arm. If you get aggressive when sanding it is very easy to overdue it as you cut through the harder topcoats and near the underlying fabric. It is, I find, somewhat of an art to get correct.

My nearly 10 y.o. Imron topcoat looks like new, which is one reason I am reluctant to recover the entire plane. The big problem with replacing a whole fabric panel on the side of a fuselage is that the only structure is the side stringer which, of course, can not be used as a glue point. Simply no vertical support structure to glue to at all the entire way. Again, short of redoing all fabric from the cowl back, it appears this vertical overlap seam is my only option.

Unfortunately, I have never heard of an invisible repair with the 2k topcoats so, if the fabric seam looks decent, I may not even try to feather blend and buff the new paint to old. Instead, I may just paint to a tape line and cover that with some type of narrow vinyl graphic stripe or something. Not sure if that would look goofy, but the seam runs from the rear corners of the turtle deck opening straight down to the lower longerons, so that might be better than if it went around the entire fuselage. Hey, if anyone has ideas for a design that might help camouflage that paint line please feel free to chime in.

dholly,
Send us a jpg of your plane and we'll start working some graphics for ideas...

Not the best pics but found some online showing the current vinyl graphic scheme.

Thanks dholly....we'll get to work and deliver some thoughts shortly.

Thanks Chris - here's a line drawing as well.