I know this is an aviation orientated web site and most people want to see things about airplanes, but some times you just have to work with what you've got. So with that in mind I'm going to go ahead and post a little report of a recent project I did in repairing a fiberglass faring on the top of a Winnebago Motorhome.

The project described here is a repair on the fiberglass Epoxy wind screen faring. The Motorhome was apparently damaged some time ago and had been repaired once before. The windshield and all five of the running lights up top were leaking when ever it rained. The new owner attempted to stop the leaks using silicon but that only made things worse. Every time it rained the silicon would run down the inside of the windshield. In short the vehicle was in severe need of some attention.

The fiberglass faring I'm referring to is the large piece across the front of the vehicle up over top of the windshield. This piece of fiberglass is similar in construction and uses the same type of epoxy that is currently being used in many of the composite kit airplanes. This is the main reason I felt it should be included here on an aviation web site.

Nearly all factory or production fiberglass composite construction these days is done using some type of laminate build up. If you've ever done any fiberglass work you know the process as a lay-up. What it means is simply layering a sheet of fiberglass weave material and then a layer of epoxy then more matting and so-on until the desired thickness is achieved. When you're working at home or in your own workshop, you would probably take a few days to complete something the size of this motor home faring. But production manufacturing processes don't have the luxury of taking a few days to complete things like this. Instead it has to be done in minutes.

You and I know that it takes at least 30-60 minutes for an epoxy resin to cure enough to take it out of a mold. And that is where the process changes when working with production pieces. The composite materials and the process used to construct parts in a factory environment are known as Sheet-Molded-Composites, (SMC).

These SMC materials and the process can manufacture a piece the size of the Motorhome wind faring in as little as 5-15 minutes. This is definitely not your typical home lay-up fiberglass process. The process goes something like this. A mold of made of the final piece. The mold is generally large and heavy since it has to withstand pressure and heat. A lay-up is done on a plug that resembles one side of the mold until the desired thickness is achieved, but this is not the final thickness of the finished part. Instead it is much thicker.
Then it is set aside to blend in for a few days. At this point there is no catalyst applied to the resin so the system remains liquid and does not cure, it simply saturates the fiberglass mat until every pore is completely saturated. Then the whole thing is placed in the mold and pressure is applied to squeeze it all down to the working thickness desired. The mold is opened slightly and then the catalyst is injected under pressure.
This is when things really begin to happen. The mold is again closed and both heat and pressure is applied. Depending on the piece and the design as much as 3,000psi is applied and the mold is heated to as much as 300-350 degrees.
The part is fully formed and cured in as little as 5-15 minutes.

But the heat, pressure and curing time is not the only difference from your typical back yard fiberglass project. In order to separate the finished part from the mold, just in all cases of injection molding, a mold release agent has to be introduced into the system prior to making the parts. The process of first coating the mold with a sufficient release agent can be lengthy and is prone to mistakes. Any small part of the mold that is not suffently covered with the release agent is subject to cause the part to adhere to the mold. This could cause damage not only to the part but also has the potential of damaging a very expensive mold.

With this in mind manufacturing engineers have devised a system of incorporating the mold release agent directly into the epoxy resin. This is probably the biggest and most significant difference in working with fiberglass at home or in your work shop as opposed to working with the SMC products. Since the mold release agent is integrated directly into the resin it remains there even after the part has cured and the epoxy has completely setup.

The release agent obviously does not remain in a liquid state, it cures right along with the epoxy, but nothing will stick to it. That is perhaps the single most important point to be made when working with these SMC or factory made Epoxy fiberglass products. Your standard off-the-shelf fiberglass resins such as the poly-resins will not adhere to SMC parts because of the mold release agent. That means you can not use standard poly-resin materials or even the poly-resin fabrics to repair an SMC part. This applies to Motorhomes, boats, Corvettes, or airplane parts.

If you make the mistake of repairing an SMC part using an automotive style poly-resin material, the parts will eventually separate and fall off. (This is not good if you're talking about a wing repair).

Ok, so now that we've got that part straight, what do you use to repair an SMC product? And how can I tell if the part I'm working on is an SMC part or simply a fiberglass part? There are several different materials available under the general name of Epoxy Resin. Note the difference in the name Epoxy as opposed to Poly-Resin or Polyester-Resin Epoxy. Check the list of suppliers at the bottom of this article. Several of the suppliers and manufacturers also have some very good how-to articles available on their Internet web sites so please be sure to check them before attempting any repairs on critical components.

How to tell if you're working on a fiberglass or SMC part? A fiberglass product generally has a very smooth side, (gel-coat outer surface) and a farely course or rough under side. An SMC product is smooth on both sides. The outer side will have a very smooth polished surface while the under side may not be finished but it will still have a fairly smooth feel. SMC Epoxy products do not use a gel-coat to finish the surface but rather the smooth outer surface is derived from the molding and finishing processes.

Now about that Motorhome repair job I mentioned.

When I first looked at this repair job I had no idea of any of the things mentioned above, but fortunately I was alert enough to know that I was not looking at my typical fiberglass material just by paying attention to the feel of the materials used on the front of the vehicle. As I said earlier an SMC product will be smooth on both sides. When I started to inspect the damage and made an attempt to determine what type of materials would be required to complete the repairs I noticed the smooth texture of the under side of the panels. It almost felt like the whole thing was made of a really thick plastic. My research uncovered the information noted above. So at this point I'm not sure if I should charge the customer for the long hours of research time spent in finding out how to do the job or if I should pay him for the education and knowledge gained from it all.

The first look at the vehicle was nearly enough to make me want to go home and leave it alone. The vehicle had apparently been driven under one of those gas station canopy's that the truckers usually hit. Then at some point a recreational vehicle (motorhome ) dealer made some repairs using a standard off-the-shelf poly-resin fiberglass. The surface finish and texture was accomplished like many home or back yard repair jobs using Bondo and body filler materials. All of this had cracked and was separating from the rest of the wind screen. But with all that mess the job looked like I could simply grind off the old repair work and build the thing up from what ever was left underneath it. Wrong-again, - When I got under the paint and outer surface layer of Bondo I found nothing that could be saved as a basic form or structure of the original part. The repair shop had used a poly-resin epoxy and the whole thing was separating. The fiberglass layers were not holding together and several places the fabric material was not saturated properly when the job was done. The fiberglass mat was dry and falling apart. There were holes the size of half dollars and I still don't know what was holding it up there except the paint and Bondo.

There was nothing left to do but to cut the whole repair job away and start from scratch. I found some styro-foam blocks at the local Wal-Mart and purchased some instant foam in a can and went to work rebuilding the basic structure. The foam blocks provided a backing to support the instant foam which in turn provided the necessary build-up. This instant foam stuff can be cut, sanded and shaved to form the plug which will eventually support the first few layers of fiberglass.

Cutting the corner off the wind screen required very little effort, but then the edges of the remaining material had to be featherd down to provide enough surface to lay-up the new patch and make the final surface even with the original surface. A patch will never be as strong as the original product but the more overlap you can get with the old material the better the chances are that the patch will stay in place when finished.

I used the instant foam to build the basic structure and then began to lay-up my fiberglass making sure I got plenty of overlap to the old part. I also had several places where I had to make a smooth cut edge around the windshield and up the side of the cap above the passenger door. In order to get this smooth cut edge, I simply built up the whole area to the thickness I needed and went far beyond the area where it would be cut. To prevent the overlap from sticking to the side of the Motorhome I put two layers of wax paper kitchen wrap over the area that I did not want the epoxy to stick. After the epoxy had set up I simply pulled the wax paper out, the epoxy wont stick to that either. From there it was simply a matter of building up the necessary layers until I got the thickness and surface level that I wanted.

The final surface texture was accomplished by using an Epoxy filler product (don't use Bondo) and then covering the whole thing with a thin layer of pure epoxy resin. As I said earlier epoxy and SMC products do not use a gel-coat. The epoxy filler and an epoxy primer filler is used to get the finished surface texture.

Once we had the basic repairs done we moved to Motorhome out to the airport to be painted. The final paint job is Imron.

As usual click on any of the images to see a larger view.

At first glance it didn't look like it would be that bad a job.

The surface was in bad shape but the basic contour was still intact.

That was before I got down through the paint. That crack went all the way through the panel.

The poly-resin fiberglass repair job was separating and full of holes.

There was nothing left to do but cut out the old repair work.

I used the car-port to help brace the repair while building up the structure.

That piece of plastic on the side panel had to be rebuilt and put back in place.

I put kitchen wax paper over the plastic side panel to prevent the epoxy from adhering to the wrong places.

With the wax paper in place I could extend the epoxy fiberglass layup beyond the cut off edge.

A Dremel saw worked perfect to cut off the edge and form the corner.

We moved to the airport and inside the new hanger to do the painting.

Tape and paper and more sanding. That's Randy on the spray gun.

The weather seal around the top of the windshield had to be replaced so we used B2 aircraft window sealer.

Ok, So here's the final view of this fiberglass Epoxy repair job.

Please don't ask me how many hours I spent doing this job and please don't ask me what I charged for the work.
And don't ever expect to get the same rate.

When doing a layup of epoxy and mat layers, try spreading the material out on a piece of kitchen style wax paper. Wet the area of the patch down with epoxy using a brush first and then carry the layup to the patch area on the wax paper. When you put the layup in place it will stick where you put it and then simply peel off the wax paper and smooth the layup out with a spreader. This way you can build up several layers at once.

Also make sure you have planty of rubber cloves on hand.

I used painters (auto) measuring cups to measure out precise amounts of epoxy and catalyst. The plastic cups have ingredient amount lines to get the correct mixtures plus they are transparent so you can see how much product you have in them.

Referance to suppliers;

Fiber Glast Development Corp. This is the Epoxy Resin I used. It seemed to be the best of several that I tried. The 30-minute catalyst set up to a good tacky gel in 30 minutes just like it claimed. I brushed a good layer of Epoxy on to the cured surface done the day before and then continued adding more layup when ever I had to quit for the night.
They also have some very good tutorial and work sheets available.

West Systems Epoxy This is quickly becomming one of the best known manufacturers of Epoxy resins.

Aircraft Spruce and Specialty carries the West Systems line of products. They also carry the various types of mat and fiberglass cloth you will need.

Poly Fiber Aircraft Coatings Don't let the name fool you, their SuperFil Light Weight filler is made for epoxy use. This is the filler material I used to get the final smooth surface and to finish out the contour. Unlike other filler products like Bondo this stuff does not shrink when it dries.

A good two-part plastic epoxy made specifically for repairing and bonding plastic can be obtained at the local automotive hardware store. Be sure to get Epoxy made for plastic.