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=BOo8gxp3K3w&list=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!

[Firemaid]

Why are you concerned with the fiberglass melting the sculpt?
Do you want to keep the sculpt or am I missing something?

[Mizuko]

The fibreglass and resin take about 3 hours to harden (depending on how much catalyst is added to the resin)- and they heat up alot during that time, which can melt the clay and therefore ruin the mold as the fibreglass will take the shape of the clay beneath. :)

[Firemaid]

In my experience so far (I've only done it twice) the fiberglass does melt the sculpt, but not before grabbing the image.

I am glad you posted about this as I am doing a new fin mold this wednesday and would be so sad if I lost all those hours of sculpting!

[Mermaid Oshun]

It depends on the type of clay you use. I've used fiberglass for many molds and the clay has never melted at all. For monster clay which has wax in it or with very soft playdoe type clays, this can be the case. But for other sulfur free modeling clay it is not a problem at all. For monster clay I would not use fiberglass in the first place because you would have two hard, brittle materials and releasing would be very problematic unless you use a heat gun to get the wax clay out of the fiberglass at the end. Otherwise one of them would crack. I personally would not enjoy melting monster clay with a heat gun to get it out of fiberglass because of the mess. So I use other types of molding materials if I use monster clay. I have never used very soft clays at all.

[Firemaid]

It must depend on the type of clay you use. I've used fiberglass for many molds and the clay has never melted at all.
You are right Golden Pearl!
For example water based clay wouldn't melt at all.

[Mermaid Melanie]

Hey guys Im struggling a bit to find this info - if i open my shell shock to do my scale sheet, and then close it again to wait for my mono fin to arrive - what would be the shelf life of the shell shock? like can i do that or should I wait till the monofin is here and ive done the sculpt already and do the scale sheet at the same time ?

[Mermaid Oshun]

Sorry Jazz, I have not read this in a while. To prevent any silicone curing inhibition at all, a simple coat of clear acrylic lacquer in the mold is all you need. Shell shock in addition to fiberglass is nice but unnecessary imo. It is just a matter of personal preference. Personally I only find inhibition if I use the fiberglass mold too quickly before the chemicals in the fiberglass are inert. I just leave the fiberglass mold to cure for about a week then wipe it down with alcohol before use. So for me, just leaving molds for more than 48 hours to cure is sufficient to prevent any inhibition whatsoever even without lacquer.

[Jessica]

Hey guys Im struggling a bit to find this info - if i open my shell shock to do my scale sheet, and then close it again to wait for my mono fin to arrive - what would be the shelf life of the shell shock? like can i do that or should I wait till the monofin is here and ive done the sculpt already and do the scale sheet at the same time ?


Hi melanie!

I would recommend waiting until you are ready to do both the same day. Shell shock has a really limited shelf life once it's opened. This is from the technical info for shell shock:

IMPORTANT: Shelf life of product is reduced after opening. Remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT® Dry Gas Blanket (available from Smooth-On) will significantly prolong the shelf life of unused liquid urethane products.

i don't know exactly how long shell shock will last after it's been opened. I've always poured my molds the same day just to be safe. It would be awful to pour a mold and have it not harden properly.....it could ruin your sculpture or scale sheet.

Its so exciting that you're making a silicone tail! Good luck! :)

I posted some tips for working with shell shock in my thread(post #7) I hope it helps a little! : http://mernetwork.com/index/showthread.php?6373-Jessica-s-Second-Dragonskin-Tail

[Mermaid Melanie]

Hi Jessica ! thanks very much its so great to be able to ask you lovelies for help ! thanks im very excited too ! Once the monofin arrives ill post a progress thread ! i cant wait to get the molds started :D xx

[jazz2453]

Pearl, thanks much! I thought that I would have to buy this expensive Inhibit X stuff from smooth-on. I had extra shell shock anyways and needed a way to use it xD And btw after opening my shellshock and closing it again, in about 1-2 weeks the bottom got thick and lumpy.

[Aziara]

After reading up on fiberglass around the internet, it seems it is suggested to use a respirator of some kind when pouring it. I'm wondering if just a little dust mask like this would work: http://www.lowes.com/pd_212039-98-8511HB1-A_0__?storeNumber=3015&Ntt=respirator&selectedLocalStoreBeanArray=%5Bcom.lowes.commerce. storelocator.beans.LocatorStoreBean%4058065806%5D&pl=1&productId=3090711&ipTrail=107.206.90.99&currentURL=%3FNtt%3Drespirator Or would something a bit more protective be necessary? Also, what sort of release agent would I use on oil-based plastilina clay? I thought about just giving it a spritz of Pam cooking spray, but since that's oil based too I'm worried about it softening the clay too much. I think I need to do some small-scale testing...

[jazz2453]

Make sure you do it outside and wear a respirator! Fiberglass had heavy fumes. You can seal it for a few layers with Acrylic Spray and the use PVA as the release. Smoothon also sells some nice epoxy materials that will make a great mold! It is a little expensive, but are high quality materials.
An EpoxyAcoat Gelcoat- http://www.smooth-on.com/index.php?cPath=1366

And then you can laminate it with this - http://www.smooth-on.com/index.php?cPath=1336

You can also use free form air in between the layers to build strength. A lot of people on SPFX forums recommended this for a lightweight, durable, hard mold. But the cheaper route is probably just easier xD

[LaNyah]

Hello Jazz,

You wrote: "You can also use free form air in between the layers to build strength."

What does this mean?

[jazz2453]

http://www.smooth-on.com/index.php?cPath=1384 this is a great product! It's so lightweight but has great strength.


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[LaNyah]

OK, I had some trouble with fiberglass and hoping y'all might know what I did wrong.

I used bondo brand fiberglass resin and fiberglass strips to make a mold of a fluke. I poured it in the evening. After a few hours I turned it over. When I went out in the morning it was warped. It rounded like a bowl.

What did I do wrong that would cause it to warp like that?

[Mermaid Oshun]

u rushed it. 2 hours is WAY too fast to move it. I leave it to harden for a day. also maybe not enough hardening agent also. but leave it alone for 24hrs. then don't put silicone in it for at LEAST 2 more days after you scrub all the clay out or that wont cure either. I always wait one week after I scrub the clay out to use a mold to avoid silicone inhibition. I also wipe the mold out with alcohol also before I use it just to be safe. So just have some patience

[LaNyah]

Ah. I didn't realize it was fragile that long. On the can it says to wait 2 hours.

:(

[Mermaid Aglaia]

Hi Paisely,

i hope i can helb you, i work very often with fibreglas. I use a Epoxy resin with 45min pot life time and i must wait 48hours befor i can demold it. and i must wait one week befor i can work with it. With more heat than 20° the resin cures faster and with a lower heat than 20° the resin cures slower. And a flat mold cures also slower.

[LaNyah]

Thank you guys. Now that I think about it, I bet the manufacture's "2 hour" instructions are for very thin layers, not the kind of thing we're doing.

Do you guys use the fiberglass sheets/strips?
I think is was PearlieMae that said she uses polyester batting instead. (?)

[Mermaid Clara]

1. how much fiberglass resin would I need for 2 1/2ft by 3 1/2ft scale sheet, a 5 1/2ft by 3ft scale sheet, and three 5ft by 3ft fluke?
2. what is the best temperture to make the fiberglass molds in?
3. if I used Vaseline as a mold release for my foam scales would the fiberglass resin mold all the details?

[LaNyah]

I believe can answer that last one. The resin will pick up really fine detail, so if you have a big glob of vasoline - it'll mold that too. (I had this happen to me). But a thin layer over the detail allowed the resin to still 'see' and capture the fine details. I was using clay instead of foam though.

As for #1 & #2. I would also like to hear what others have to say. I did find this and maybe it is accurate (?):
http://www.epoxysystems.com/214.htm#Material_Calculator

[Elle]

I attempted fibreglass resin molds today for extra fins. I used a basic air dry clay. however, because I didn't put a thick enough first layer of resin and give it a small amount of time to dry I ended up with air bubbles.

So I'm having a second attempt (have to re-do all my sculpts as I had to soak the fibreglass to get them out)

So in the second run what I'll be doing is, once the sculpted fins are completed. lay down a layer of resin (about 1cm thick) give it 20-30 minutes to semi set, then add more resin and start sticking the matting down and go from there.
My only fault was that I got air bubbles on the fins.
as far as getting the clay out I soaked the molds in a tub of water for about an hour once they had dried (it only took 2 hrs because of the heat today) and then used a scrub brush and the garden hose to shot the clay out. I did a scale test while I was at it, with the resin I'm using I put a layer of furniture polish over my foam scales (which had a pvc glue coat on them) and it popped out really well. asides from the air bubbles, which I'm pretty sure I have sorted now so I won't have to worry about when I get to my scale sheet.