Making a Fiberglass Mold

[jazz2453]

For the new silicone tail I'm currently working on, I want to use fiberglass for my fluke mold. I understand for the most part how to do this, but I just wanted to get answers for a a few questions on exactly how to go about this process.
Does it matter what type you use, or can it just be from home depot?

How durable is fiberglass? (I want to use this mold as much as possible)

I want to use gel coat since it seems to give a really nice and clean mold, but is this reasonable?

How would I use gel coat and what kind should I get?

Mostly I just want to know if gelcoat is worth it, and how to use it.

If anyone knows any other cheap, durable, lightweight materials for a fluke mold, I would be glad to know

[MerEmma]

I'm currently going to be using fiberglass to make a velociraptor head for a costume, unfortunately I can't answer these questions for you but I'm interested in the answer is well.

[Mermaid Oshun]

I used Bondo Fiberglass Resin from Lowe's, Jazz . It comes in a gallon can. The 2 small tubes of activator are under the plastic cap. I would make very small amounts at a time (like 16 ounces or less ) because it hardens SO FAST. I made 1/2 gallon and 1/2 of it hardened in the container before I could even pour it all on the surface. If you have any more questions I will be happy to help.
But I DO LIKE the fiberglass. It is thin, light weight, easy to carry, and doesn't crack or chip easily with normal delicate care. I can literally lift my scale mold with 2 fingertips and toss it around. Now if you bang it around you will need to make it thicker.

[Mizuko]

My father recommended using thinner fibreglass sheets & resin for the first few layers to capture the details- this will cost a little more than regular fibreglass. I got surfboard-grade sheets as they are some of the thinnest. Then once you've done two or three layers using those sheets move onto a thicker, cheeper sheet to build up strength/thickness. It will be heavier than other molds, but also far more resistant to cracks or breaking! I'm still in the process of doing so, so once I've got more details I can let you know

[Mermaid Oshun]

gosh there are too many details in the fiberglass I used. I can see the pores from the foam. I actually want to buff some of that away.

[jazz2453]

Thanks for all the help Do any of you have experience with gel coat?

[Mermaid Oshun]

Jazz that is fiberglass gel coat dear.

[jazz2453]

Oh lol I'm sorry, I thought you were talking about resin cause thats what your first sentence says. Oppps *im dum*


All I know is that I'm hoping to use a similar process to this.

http://www.youtube.com/watch?v=BOo8g...=TLpJ-rGjA33FM

The mold looks really clean and durable, and I thought the black stuff at the beginning was the gel coat.

[Mermaid Oshun]

Call Fiberglass Florida 800-699- GLAS
I think what you are talking about is a polyester gel coat that you can put on before the fiberglass coat. They should be able to tell you.

[Echinacea]

From my kayak making days, gel coat was usually a thin layer that was applied to the mold before starting to lay up the actual kayak. Oftentimes, that was where your color came from, and the successive layers were 'clear'. (We just used pigment and tinted the resin itself, so I have never tried using gel coat.) Like Mizuko said, use a thinner, tighter weave fabric for the first coat - we had 6 oz cloth and 10 oz cloth, plus fiberglass mat (chopped fibers bonded together, a bit like felt). The first layer would be the 6 oz cloth, then successive layers would be 10 oz cloth. The fiberglass mat was used for reinforcement, like under where the seat was going to be. For our kayaks, it was usually three layers, with some extra reinforcing in strategic locations (like under the seat). When we made the molds, it was more like 5 or 6 layers, with lots more reinforcing. We would also overlap edges once the initial layer was on. The first layer should be (as much as possible) one continuous piece, no seams, so it conforms to the shape underneath. Then successive layers would go more crosswise, with overlapping edges, to kind of make ribs. We would also do a layer of just mat on the molds. The glass cloth is fairly flexible, the mat is stiffer, and you want the mold a bit more rigid.

Hope that helps some.

[Mizuko]

Hi guys! I've been fibreglassing yesterday, and pulled my test molds apart today. It looks like the clay is melting slightly, which is taking the VERY fine imprints of the 6 oz cloth. I did put layers of a special silicone mold release beforehand, but maybe I didn't put enough layers. Does anyone recommend something else to protect the clay from melting and destroying the smooth mold? Dad said to try again with more mold release stuff, which I'm doing currently, but are there any other ideas? Thank you!

[jazz2453]

I mean I did a thin shellshock layer which worked fine. Mostly because sometimes polyester resin can inhibit the cure of silicone, so I used that since its meant to cast silicone. Did you use a gelcoat? Maybe that will work. I'm not sure.

[Mizuko]

a gelcoat still lets off lots of heat- so the clay would melt again. I think I might have to try Shell Shock if this next test doesn't work. Did you lay the fibreglass after the shell shock was cured, or while it was still curing?

[jazz2453]

after because I didn't have enough shellshock and there would be fiber pieces poking out. Idk what I really did! I just did what came natural lol. I was freaking out at first when I didn't have enough shellshock (i just used the quart order that I had handy at home) but then I just added resin and cloth after it cured and placed it. My plan was to lay the fiberglass on a second or third layer of shellshock to give strength ins tea dog wasting money on the support shell called plasti-paste.

[Mizuko]

I think that is what I will have to do too! XD Shell Shock is super expensive here, so it would be better for me to just do two or three layers with it then build up the mold with fibreglass. I tried the extra silicone-release today, and its still not working, so it looks like Shell Shock is the goer! XD Its frustrating because I got the silicone-release because the man at the molding/casting store recommended it, but its not working at all :P

[Mizuko]

Actually, Jazz, I hope you dont mind all these questions! Did the Shell Shock melt your clay a little? I read that it also heats up when curing, so I'm worried that it will blurr some of the details in my clay!

[Jessica]

Actually, Jazz, I hope you dont mind all these questions! Did the Shell Shock melt your clay a little? I read that it also heats up when curing, so I'm worried that it will blurr some of the details in my clay!

I used shell shock for my molds and it was fine with my monster makers clay. It does heat up, but honestly not as much as I thought it would. I found some on my ankle and I hadn't even realized it was there until after it dried. It captured nearly every detail of my fluke and even got the fine lines. You need to work REALLY fast or it will start curing right in the bucket though. Smooth on recommends leaving shell shock inside for as long as possible to keep it cool to help extend the cure time if you're working outside.

One more thing.....do not use shell shock if its humid!! your mold will be full of bubbles! My mold had a good amount of bubbles and it wasn't even that humid...just something to keep in mind

[Mizuko]

Thank you so much Jessica! <3 I just found a supplier for Shell Shock in my city so I want to test it tonight! My other test-mold failed and I've started to freak out that I wont have the molds done in time O_o

[Jessica]

Mizuko,

just a quick tip...measure carefully! It's important to get the ratio right. I used fiberglass cloth to back the mold up and it makes it a lot stronger. Just pour a layer of shell shock and then lay the fiberglass cloth on while its still wet. Just don't use the fiberglass cloth as your final layer...it needs to be sandwiched in between the shell shock or it will poke up out of the mold and make the mold lay funny(I learned this the hard way)

I mixed the shell shock in small batches...one cup to a 1/4 cup. It cures so fast that small batches worked best for me. The directions say to use a paintbrush for the first layer and brush it on to reduce bubbles or air pockets. This really isn't always possible depending on conditions...hot weather makes the shell shock thicken almost immediately. I mixed the shell shock quickly, dumped it all on my fluke and then grabbed a paintbrush and brushed through the shell shock. This worked well for me and my molds turned out great. Well....great except for not using enough release agent! Seriously....use a lot of release agent for your scale mold!

Good luck!

[Mizuko]

Thank you Jessica! I really appreciate the tips! I was going to use the fibreglass to strengthen the mold- especially because Shell Shock is super expensive here, so I dont want to use heaps of it, only two layers or so. I heard pouring and then speading was the best method- so its good to know you did that too! I've still got the silicone spray which creates a rubber film between the clay and the mold materials- perhaps that will be ok as a release agent? It worked as a good film between the fibreglass and the clay- the only issue was it was too thin so the heat leaked through and warped the clay. With the Shell Shock it will probably work ok! I will try a little test tonight!