Fiberglass Mold Making and Fabrication How To – Project Blog

Hello fiberglassers,

I maintain Steve Jone’s web sites and blogs.  Well, I sort of maintain them. I had to move this blog to a new server due to a couple of issues.

1. I did not stay up with WordPress Security Updates which resulted in the site getting hacked. (You would think hackers could find something constructive to do with their time.)
2. The older version was a pain for Steve to manage.

I am sincerely sorry and apologize to you for the time this blog was down.  Know that Steve will be posting his no fluff straight talk posts on Fiberglass Mold Making and Fiberglass Fabrication.

Thank you for your patience and understanding,

Mike Claggett

I have written blog entries in the past in which I have shared my experiences with new techniques and new products that are available for construction with composites. This is another one of those.

Whenever I am building the surface of a part that is being made of chopped mat, I end up with a fairly course surface that will need a final finishing.

I have employed various means to smooth out a fiberglass surface. Some of these finishing methods include the following:

For some applications I use veil over the final layer of chopped mat. This method hides most of the course fibers of the chopped mat without adding an excessive amount of extra weight to the final product. In fact, when I add a final veil covering I very rarely have to add any extra resin to the finish. Usually I can use a small roller to press the veil onto the surface of the still uncured mat / resin underneath it forcing the resin to seep into the veil and provide adequate saturation on the surface. The individual fibers of veil are much finer than those of chopped mat so the final surface is smoother.

For other applications I mix a putty-like consistency combination of resin and cabosil that I use to smooth over the surface. This has been one of my favorite methods for finishing a fiberglass surface. The cabosil / resin mixture can be made as thick or thin as your project requires. Once this mixture is spread over the surface and cures, it can be sanded smooth and finished.

Sometimes I will simply skin the surface with bondo. I like bondo because it sands so easily and cures so fast. You can smooth out a surface in a hurry with bondo. The drawbacks to using bondo are that it is easily chipped / damaged and it almost cures too fast. I have wasted a good amount of bondo over the years by mixing more than I could use in its working period.

The other day I went to my local fiberglass supply store and asked for a ¼ pound of cabosil. The gentleman that helped me asked if I wanted something that would sand a little easier. I said “sure” and he suggested microballoons. The microballoons mixed into a nice white paste and spread easily on the surface of my project. It also sanded easily as promised. In addition to easy sanding, it also seems durable as it passed the hammer tap test that I performed on the tip to the bow of my boat project. It didn’t hit it full force but I hit it hard enough to crack bondo and the microballoons didn’t crack. I was impressed.

In the beginning of this article I said that I was writing about a new product. Microballoons are not “new”, they are simply new to me. Once again, we tend to get comfortable with methods and materials that are known to us and close ourselves off to other products and procedures that are available.

Fiberglass Deep Vee Radio Controlled Boat

Happy Glassing

Steve

www.fiberglassmoldmanual.com

Its funny how we do things that we think are not only the right way but the only way only to find out later that there are better ways. Years ago, when I first discovered the use of dry foam as a medium for plug construction, I thought that I had found the perfect plug building material. I easily carved out complex structures in a fraction of the time that it used to take when I used plaster and wood.

Then my bubble burst. I finished carving the foam for my new plug, covered it with resin and sea glass from the hobby store and let it cure. To my surprise, when I was applying bondo and glazing putty to level the surface of my plug, the plastic putty knife that I used easily went through the surface of my plug. It was then that I realized that the outer skin of this plug was too weak and needed re-enforcement. I fixed this problem by removing the thin layer of glass that I used to cover the foam and applying a 1/8 inch layer of bondo over the entire surface of my now less than pretty plug. Since this episode, I have always used foam in my plug construction but I always took that extra step with shaving down the foam and covering it with a layer of bondo before I start the final finish.

Recently, I began to evaluate my plug building procedures. While my tried and true method described above never failed me, I wanted to try something new. I recently was building a plug that I wanted to move quickly with. After carving the foam, I went ahead and decided to cover it as it was with 1 ½ ounce chopped mat and resin. I remembered when I had my bad experience with this method I had used very light material from my hobby shop. The 1 ½ ounce mat worked perfectly. It provided a very solid surface to work with without adding excessive size to the plug that I had carved from the foam.

I basically did two things differently with the foam. The first thing that I did was thoroughly saturate the surface with resin. The second thing that I did was use a much heavier chopped mat to cover the plug.

I always read and research fiberglassing techniques. I had not really researched or evaluated my plug construction techniques for years. This “new to me method” saved me a TON of time and materials (bondo). I don’t believe that this way of plug building affected the quality of my final product at all.

I would recommend trying this method for your next project.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

In the post prior to this one I had just started to get into the benefits of using silicone for a mold for a fiberglass project like this one.

First of all, silicone doesn’t smell and it doesn’t stick to anything other than itself.  With silicone I would never have to worry about ruining the original like I did with my first effort with building a fiberglass mold.  Secondly, there is no need for parting agents like wax or PVA – pieces simply effortlessly pull right out of silicone molds.

So, let’s get started.  The process of mounting the plate to a parting plane remains the same expect for the fact that I want the silicone mold to be little deeper than the fiberglass mold so I am mounting the plate to a ¼ inch piece of MDF that I traced the plate onto and cut out with my scrolling saw.  This ¼ piece of MDF is then glued to a parting plane and the plate is secured to the MDF with wood screws.

The pieces of the parting plane with the plate.

1/4 inch mdf glued to parting plane.

Aligning the plate to the parting plane with clamps.

Plate screwed to the parting plane.

The next step is to seal the edges of the plate with clay to prevent the silicone from getting in between the plate and the MDF.

Now I use 1 X 1 pine to build a perimeter around the plate that will act as a wall that will contain the silicone.  I leave about a ¼ gap between the plate and the pine perimeter that will define the boundaries of the mold.  At this point I go around the outside of the pine with masking tape to prevent any silicone from leaking out.

Sides of the mold clamped in place and Silicon at the ready.

With the plate prepared I go ahead and mix some silicon with its curing agent and pour it over the plate.  I make sure that there is enough silicon to completely cover the plate with about a ¼ inch depth.  The next step is the easiest of all – let it stand for 24 hours.

Silicon is flowing.

The silicon is curing – will be ready in 24 hours.

More on this project soon!

Happy Glassing

Steve

www.fiberglassmoldmanual.com

To begin laying up a fender, I mix about a half a cup of gelcoat with the recommended amount of hardener.  Once this is thoroughly mixed, I use a disposable chip brush to paint the gelcoat into the mold.  I try to get a heavy layer of consistent thickness.  This gelcoat needs to cure to a tackiness before I apply the fiberglass mat and resin.  Usually this takes about 45 minutes. 

While I am waiting for the gelcoat to cure a bit, I begin to prepare for the next steps of this process by tearing 1 ½ ounce mat into small pieces that will be easy to lay into my mold.  Since this is a fender, it has compound curves – one that goes side to side and one that goes front to back.  In my experience, smaller pieces of mat are easier to work with in a mold like this.  Just FYI, my pieces of mat are approximately 4” X 4”.

Now that the gelcoat has cured to a tack, I mix an 8 ounce cup of resin and catalyst (as directed by the manufacturer) and begin to work my way around the inside of the mold with resin and mat.  I soak a chip brush with resin and use it to blot the resin onto the mat over my freshly applied gelcoat.  Since the gelcoat is still tacky to the touch, it holds the mat in place while I soak it with resin.  I work my way from one end of the fender to the other and then back again (two layers of mat and resin) being careful to make sure that the mat has no air trapped underneath and that the mat overhangs the mold by an inch or so.

Once this mat and resin cure to a gel-like state (this takes about ½ hour of 45 minutes) you can safely trim the overhanging extra mat with a razor knife.  If the resin pulls or is too sticky to cut, check back in another 15 minutes and try it again.  This is the best way to clean up your parts of excess fiberglass.

After trimming, I allow the part to sit in the mold for a day or so to let it fully cure.  Once fully cured, I pop the part from the mold using a couple of plastic putty spreaders.  I simply use my fingers to pick at the part until I get slight separation from the mold then I push the plastic spreader between the part and the mold and work my way around until the part pops out.  Since I used adequate release wax and two coats of PVA, this part easily separated from the mold.  One fender down, one to go!  

My New Beach Cruiser With Fiberglass Fenders Installed

Last summer a buddy of mine asked me if I could make him a duplicate license plate for his vintage truck.  The original California plate that he had was black with yellow lettering and he wanted to keep that plate.  Apparently you can’t purchase duplicate California plates so his only option was to make a copy.

Even though I have never attempted a project like this one I jumped at the opportunity.  The concepts of the making of a fiberglass mold don’t change so I knew that if I followed the standard protocol that it would work out fine.

This project went smoothly – just like planned.  The old plate was stripped of its registration tags and it was straightened out as good as possible.  It was then mounted to a parting plane with wood screws and the edges were sealed with clay.  The plate was then waxed heavily with mold release wax and then it was sprayed twice with PVA and set aside to dry.

When the time came to build the mold itself I started getting nervous.  While I have only once before had a plug ruined by a combination of failed release agents and tooling gel coat that failed to cure, I really didn’t want this to happen to  my buddies license plate.  That being said I did what I always do and pushed forward.

After a liberal application of tooling gel coat followed by fiberglass resin and a few layers of 1 ½ oz mat my mold was complete.  I was thrilled when I de-molded a few days later and found a perfect mold and even better – an un-marred original plate.  Whew!

With my new mold I went ahead and prepared it with mold release wax and PVA and proceeded to follow all the steps to make a part with this mold (all of these steps are covered in my series of fiberglass mold manuals).  Just like with the making of the mold, making this part went just as planned and I ended up with a near perfect duplicate of my buddy’s license plate.  The mold however did not do so well.  After pulling the part from the mold a host of flaws were revealed in the mold – most of them were air pockets / voids in the tooling gel coat.  The flaws in the mold were significant enough to make the mold not suitable for further use.

After this experience I decided to try this project again – only this time I would use silicone rubber for making the mold and simply make parts by laying gel coat, fiberglass resin and mat into the silicone mold.  There are several benefits to this process for this particular mold as compared to making a fiberglass mold.  More on this project in the next post!

Happy Glassing

Steve

www.fiberglassmoldmanual.com

With the keel and the hull sides attached, I can think about filling the hull with foam and carving out the bottom of the hull. As I study the hull bottom as it sits, I notice that the hull sides have some waves in them. Since it is much easier to fix this now, I go ahead and glue then clamp some thin pine strips along the inside of the hull sides about ½ inch below the upper edge. This strip will also help me with the construction of the hull bottom. Once these extra hull pieces are secure, I measure and cut Read the rest of this entry »

Preparing the plug is the next stage of this build. I begin by mounting the two halves of the plug to a piece of inch thick MDF board. I attach the plugs by using screws from the back side of the MDF. Some people glue or epoxy their plugs to the parting plane. I prefer to use screws because I can remove the plug from the MDF after the mold is finished with out destroying it.

Once I have the plugs securely attached to the parting plane, I need to go around the base of the plugs looking for gaps between the board and the plugs. Any gaps are filled with clay. This is just a matter of forcing the clay into the gaps in order to prevent resin from getting under the plug. When the gaps are filled and all excess clay is removed, I can apply mold release wax to the plugs and the MDF parting plane. I like both McGuire’s and Part-All mold release waxes. It is important to apply at least five coats to the plugs in order to ensure adequate coverage. The plugs should be polished to a shiny smooth finish.

PVA is now sprayed onto the plugs and the parting board. The PVA is an excellent barrier between the mold and the plug. I like to spray a coat, let it dry and then re-apply. Applying two coats of PVA can result in lost detail but that is not a concern for me with this project. An additional coat of PVA will ensure an easy release when I de-mold the plugs.

I apply the PVA with my spray gun at about 60 psi and a distance of 8 to 12 inches. PVA is cheap and valuable at the same time. This set of mirror image plugs is now ready for molding.

For the molding process I need my air compressor and dump gun along with: tooling gelcoat, fiberglass resin and chopped mat, MEKP, rubber gloves, disposable brushes and a respirator or fume mask.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

At this point, I will start to fiberglass over the foam. I have decided to hold off on forming in the turbine housing and the top of the tail section. My thoughts are that I would like to have something to place clamps on so I can check the alignment of the body halves during this next phase of the plug build.

I begin the fiberglassing process by using a brush (a cheap disposable brush is best) to cover the foam with catalyzed resin. I have decided that initially I will only do the main part of the fuselage and I will do the tail later. Once the foam has been soaked with a coat of resin, I can start applying chopped mat over the foam.

Work the mat onto the surface of the fuselage. It must lay as flat as you can get it. I have spent a bit of time forming this fuselage. I don’t want to get sloppy at this point. Laying fiberglass mat over the foam will provide a nice hard surface for the next step of this build which will be the bondo application. Once the fiberglass has been laid, the only thing to do is let it cure. It is time to put the chemicals away and clean up.

After the resin cures, the surface can be rough sanded to knock down any loose fibers.

Once the surface of the plug has been cleaned up with coarse sandpaper, I can examine the pieces and decide where to go with this plug from this point. I began this plug imagining depressions with well defined edges where the windows should be. At this point, it seems that following this course will make this plug much more difficult to complete. This being the case, I have decided that the next phase of this plug build will see the side windows smoothed flush. Flush windows will make building the mold and pulling parts from the mold much easier.

After the rough sanding is complete, I can apply bondo to smooth out the surface of the helicopter. I only mix enough bondo that I can use in a few minutes. By mixing a little less bondo than I can comfortably work with, I am able to be much more efficient from a number of perspectives. First of all, I have time to work the bondo on the surface since I am not rushed by the thought of unused bondo curing on my mixing surface. Secondly, when I mix too much bondo, I end up just piling it on only to have to remove most of it later on because of sloppy application.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

I let this mold cure on the plug for almost a week before demolding. This mold popped off its parting board with little effort. Likewise, the mold separated from the plugs with ease. The process for removing the mold from the plug is simple. I use a half dozed small plastic putty knives that I insert between the mold and the parting plane.

Once I have one putty knife between the mold and the parting plane, I simply insert another putty knife at the edge of the separation that occurred as a result of the first knife. This is repeated time and time again as I work my way around the perimeter of the mold. Once you get started, this is an easy process.

At this point the mold is inspected for any flaws, repaired and then prepped for its first part pulls.

Making parts with this mold is very similar to making the mold itself. I begin by applying five coats of mold release wax to the inside of the mold. Once the mold is waxed, I can apply a coat of PVA to the inside of the mold with my spray gun. After the PVA dries, I can do my first parts lay-up. This is part that I really enjoy – I am very close to seeing the results of my efforts and planning.

Happy Glassing

Steve

www.fiberglassmoldmanual.com