GEL COAT -- What am i doing wrong? now i know!

[zorg]

ok, over the years i've tried making casts using an initial coat of gel coat but it always turns out bad. (silicone molds)

again i tried this week with a new mold and the layer just pulled away from the silicone and was warped with an uneven surface on the face of the casting. just a reject without a doubt.


i'm guessing
a) the gel coat should not be used on a silicone mold

b)the gel coat thickness was not even

c)im an idiot

d)all of the above

any clues or advice?

thanks

-z

 

[Nwerke]

Re: GEL COAT -- What am i doing wrong?

Are you using a mould release? Can you get good results with the gelcoat using a latex or other non-silicone mould (i.e. could the gelcoat itself be off? - also is it old/past its use-by date?)

Are you working in high temperatures? Are you certain you are using the correct amount of catalyst?

Does the piece NEED to be polyester resin? I've never had good luck using polyester resin in silicone; I guess the situation might be different these days with fifteen odd years' advance in chemistry, I dunno, but that was my experience. If the piece is being backed with glass, can you use epoxy instead?

 

[fettster]

Re: GEL COAT -- What am i doing wrong?

Hi Chris.

your gel coat is retriculating.

there can be several causes for this, one is over catalising the resin, another is moisure and another is leaving the gel to cure too much before laminating.

if you want, email me at richardmartin4 (@) hotmail.com and we can talk through a solution

 

[Nwerke]

Re: GEL COAT -- What am i doing wrong?

Er, reticulating. </smartarse> Fettster is dead right, I forgot to mention that latter point, starting a layup once the gel has kicked is best.

 

[zorg]

Re: GEL COAT -- What am i doing wrong?

even after looking it up i still don't know what that means......

e-mail sent :thumbsup


-z

 

[zorg]

Re: GEL COAT -- What am i doing wrong?

starting a layup once the gel has kicked is best.

i don't even get to that point, the gel coat just goes nuts before i get the chance........

 

[Nwerke]

Re: GEL COAT -- What am i doing wrong?

Does sound like you're over-catalysing it, gotta say. Or if the weather's hot, that can speed things up too.

If changing to a fresh tin doesn't help, you could try making up your own - mix straight fibreglass resin and car bog until you get it to a gelcoat-like consistency and see if that works. I did a lot of work with that stuff, it can be less of a pain than some gelcoats.

 

[dcc_clone]

Re: GEL COAT -- What am i doing wrong?

too much mold release. you should wipe out after spraying. causes gel to "slip" in mold

over catalyzation. too much heat causes thermocracks.

unequal thickness of gel coat. if you have crevices, which gives you more material, will cause the gel coat to pull towards the thicker area during curing. thinning out the surrounding area.

too thin gel coat plus many layers of glass will cause a warp.

moisture. sweat, humidity. messes with chemical properties and causes improper cure.

mold thickness is too thin. heat is pulled away from the layup, will cause orange peel, waviness, improper cure.

 

[fettster]

Re: GEL COAT -- What am i doing wrong?

Er, reticulating. </smartarse> Fettster is dead right, I forgot to mention that latter point, starting a layup once the gel has kicked is best.

Who's the smartarse? The guy who can't spell or the guy who feels the need to correct him? Lol

 

[ewokus]

Re: GEL COAT -- What am i doing wrong?

From the guys who taught me Fiberglassing at Icons (casting up 4 foot ID4 Attack Ships) Gel coat is intended for fiberglass molds only, not RTV. You can try to use Gel-coat, but as you can see, you run into alot of problems, but some people here have used it and got lucky with the results... All the Lost in Space Robot Body parts that were made at Icons, were made with a brushable urethane as the beauty coat, not Gel-coat. BJB and Smooth-on have this brushable urethane ready to go. You don't put it down real thick, just brush in a coat to capture all the details. As it gets tacky, you need to 'dust' the coat of resin with cotton flocking - sprinkle it all around, then use an airhose to remove the excess. (the resin will harden to glass-smooth, and the fiberglass lay-up will not stick to it without the cotton flocking) You now have a great surface for laying up fiberglass resin & cloth to make the casting strong & light. The guy who taught me at Icons has dozens of films under his belt as a model maker - using this exact technique. Hope this helps!

 

[micdavis]

Re: GEL COAT -- What am i doing wrong?

Why do you use mold release on silicone? Half the reason and expense of silicone is no release needed. Unless using some exotic casting material.

I'd say you are over catalyzing and waiting too long for the first layer.

 

[stagelife]

Re: GEL COAT -- What am i doing wrong?

i think your issue is the mold i dont know of anyone that does a gel coat on silicon molds.... try it on something thats is no silicon and i bet you wont have the issue.... if there is no way around this..... try to dust the mold first with a clear spray paint (try on the outside first to make sure no reaction with old silicon) just my 2 cents

also... you should not really be using mold release on a silicon mold... you dont need it and it could inhibit the cure a bit

 

[zorg]

Re: GEL COAT -- What am i doing wrong?

who says i'm using a mold release?

i didn't mention one. :confused

i don't use it.

well i went and tried again with less activator, 1/3 what i normally use and have been using for the last 8 yrs

and........

success!

it came out 98% good, just a couple of air bubbles on some of the corners but overall i'm very happy with the result.

-z

 

[GINO]

Re: GEL COAT -- What am i doing wrong?

In my opinion, you should never use a gel coat on a silicone mold unless you're shooting it through a high powered spray gun.
Make sure you use a scale to measure out the accurate amount of catalyst. It's critical.
After, use cabosil to fill in any sharp creases/hard to reach places while the gel coat is still tacky.
Then lastly, start your glass layup using minimal resin.


.

 

[micdavis]

Re: GEL COAT -- What am i doing wrong?

who says i'm using a mold release?

i didn't mention one. :confused

i don't use it.

well i went and tried again with less activator, 1/3 what i normally use and have been using for the last 8 yrs

and........

success!

it came out 98% good, just a couple of air bubbles on some of the corners but overall i'm very happy with the result.

-z

LOL. For years I rode a guy because he ALWAYS used too much kicker.

Finally got him to back down on it and he was amazed by the result.

Given time and temperature most stuff will kick with out kicker. A lot of them you can almost just walk it past the stuff and it will go.

Following the labeled instruction works sometimes too.

NEVER use Gel Coat with silicone??!?! Well that's just stupid.

 

[Hangar18Studios]

I use gel coats in silicone molds all the time, no problem.
Another important factor to remember is you shouldn't lay up fiberglass in freshly-made silicone molds. Let the silicone cure for a while (a week or more), or bake the silicone after it cures. Silicone emits trace amounts of alcohol upon curing and if you attempt to lay up fiberglass (polyester) in these fresh molds the alcohol will inhibit the cure of your gel coat and make it sticky.

 

[Nwerke]

Re: GEL COAT -- What am i doing wrong?

Who's the smartarse?

That was my point. </whatever> is faux-HTML for "I'm stopping doing whatever I've just done" - I was having a go at myself for being a spelling Nazi, you see.

I actually am a spelling Nazi, but also had half an idea Zorg might want to look it up. I had to look it up myself when someone first mentioned it to me.

 

[Nwerke]

Re: GEL COAT -- What am i doing wrong?

who says i'm using a mold release?

i didn't mention one. :confused

i don't use it.

I asked if you were - if you'd said 'yes' I'd have said 'don't'.

Glad you have it sorted! Now post pics.

 

[fettster]

Re: GEL COAT -- What am i doing wrong?

That was my point. </whatever> is faux-HTML for "I'm stopping doing whatever I've just done" - I was having a go at myself for being a spelling Nazi, you see.

I actually am a spelling Nazi, but also had half an idea Zorg might want to look it up. I had to look it up myself when someone first mentioned it to me.

Please note the LOL at the end of that post. Lol.

Chris, just got your email( went to my spam folder, will be replying shortly)

 

[clonesix]

Has anyone mentioned baby power the molds?

Yeah, gelcoating silicone molds (especially new ones) is tough. The gelcoat doesn't have anything to grab onto.

I have had good luck with baby powder, and spraying the gelcoat.