goldenshinner

hybrid RTV/Silicone mold

36 posts in this topic

any one have experience w. finepoints and tricks to get this to work? I would like to attempt using an expensive RTV grade(catalyst) silicone for a skin coat followed by a cheep "run of the mill" calking silcone(1$ grade! ha ha). i have seen some interesting threads in the past, but am still i tad unclear on exactly how this would be preformed. Q:would any cheep tube of silicone work? Q: how long do i wait after applying RTV GRade silcone before i apply the filler silicone, or does that not matter. i am allitle concerned that the filler might not adhear well to the skin layer. oh and for the sake of arguement the final goal would be a foam hardbait(lure) casting. also trying to decide the best method for addressing the hanger(eye) placemnt, should i cast some space in, or cut it out with a knife or just attempt to compression hold the thru wire eyes in place.

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any one have experience w. finepoints and tricks to get this to work? I would like to attempt using an expensive RTV grade(catalyst) silicone for a skin coat followed by a cheep "run of the mill" calking silcone(1$ grade! ha ha). i have seen some interesting threads in the past, but am still i tad unclear on exactly how this would be preformed. Q:would any cheep tube of silicone work? Q: how long do i wait after applying RTV GRade silcone before i apply the filler silicone, or does that not matter. i am allitle concerned that the filler might not adhear well to the skin layer. oh and for the sake of arguement the final goal would be a foam hardbait(lure) casting. also trying to decide the best method for addressing the hanger(eye) placemnt, should i cast some space in, or cut it out with a knife or just attempt to compression hold the thru wire eyes in place.

First, I use 100% Silicone. DAP brand is about $5 a tube, but WM ALL Purpose Silicone is $2.37.

You can cast a skim coat and lay a few beads of tube silicone (It will Adhere) after the skim cures, then fill over the cured Tube stuff OR you can lay out a bunch of beads, let them cure then lay them on the cured skim coat, as filler or dice them up and mix it in with some RTV.

Be advised, the tube stuff will float in the RTV.

In any event, the two are compatible, and using the tube stuff as a filler is a practical alternative to the very expensive RTV. The key is to make certain the skim coat totally encapsulates the model.

Instead of foam, you might want to try a Urethane Resin. You'll need micro Balloons to regulate it's buoyancy.

Here or Here.

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but WM ALL Purpose Silicone is $2.37.

You can cast a skim coat and lay a few beads of tube silicone (It will Adhere) after the skim cures, then fill over the cured Tube stuff

Thanks for the pointers. let me get this understood. filling layer of 100%silcone is added while the skim coat is not set up or after it has compleately cured, or does it realy not matter in the timing.

also my goal is a fairly large bait. as i understand the hooker baits are foam type. i just need to get say a dozen built (hopefully in the next month before fishing is done!!)

Instead of foam, you might want to try a Urethane Resin. You'll need micro Balloons to regulate it's buoyancy

is the urethane resin eaiser or stronger than the foam?? i supose at least the resin distorts a silcone mold less.

finaly while i have cast a fair amount of non-lure castings, i am somewhat concerned with joining lines from the two sides of the block.i am somewhat clumsy in my artistic abilities and am somewhat unsure if i can get the clay base sufficently flat enough(it has been a long long time since a made a mold).

by the way. thanks husky for the input.:worship:

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Thanks for the pointers. let me get this understood. filling layer of 100%silcone is added while the skim coat is not set up or after it has compleately cured, or does it realy not matter in the timing.

Completely cured for me. I don't know if it matters because I never did it the other way. You might want to experiment but I think it's worth waiting.

also my goal is a fairly large bait. as i understand the hooker baits are foam type. i just need to get say a dozen built (hopefully in the next month before fishing is done!!)

If they're floaters, it's 50/50 mb's to resin, 1/2 for suspenders and pure UR for sinkers.

is the urethane resin eaiser or stronger than the foam?? i supose at least the resin distorts a silcone mold less.

It hardens in a few minutes and doesn't expand to the degree that foam does, so distortion is minimized. Both are very strong.

finaly while i have cast a fair amount of non-lure castings, i am somewhat concerned with joining lines from the two sides of the block.i am somewhat clumsy in my artistic abilities and am somewhat unsure if i can get the clay base sufficently flat enough(it has been a long long time since a made a mold).

Read this.

by the way. thanks husky for the input.:worship:

That's why we're here.

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Hi!The hooker baits are not made of foam!They are made of urethane resin and yes it's much stronger that foam!And no distorsion in the mold!That's what i use to make my lures,work great!!Cheers,Dan

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When you make a resin body with the micro balloons, Does this method leave enough lattitude to be able to add ballast and still keep the lure afloat or is the density of the body just determined by the balloons and no further ballasting.

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i'm not sure if i understood everything right but here are "my" experiences (ps: Husky gave me a lot of info's, hints and advices on this topic :worship: ).

urethane resin baits will not float (at least the urethane i'm using) without micro balloons. i use 50% micro balloons (volume) mixed in the resin http://www.tackleunderground.com/forum/showpost.php?p=47302&postcount=7 for "floaters"

i can still put on some balast or rattles to the lure to "tune" it....

urethane foam: i use it for topwater lures or for heavy lures, because i can put on a lot more balast to the lure. (hint from Husky: spray a light coat of i.e. "acrylic paint" in to the mold and you will have an instant "prime coat")

due to the expansion of the foam i think its essential to "clamp" the mold halves thight (watch out for distorsion)

i also use the "filler method" rtv+caulk-silikone for larger molds:

- skim coat rtv: let dry

- fill the "mold" with cured-caulk and/or rtv leftovers

- fill up with rtv

its working fine for me...

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Thank's Dramone, you pretty much covered it.

Respect Husky, for sharing your extensive knowledge and experience.

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Hey dramone!The urethane resin that i use floats!It's the smooth-on feather lite resin!And it work's nice!The prize is not cheep but the product is awesome!I realy like it a lot!

Cheers,Dan

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Thank everyone! last clarifining question . according to the tutorial the dap silocone must be first cured then mixed with RTV, Why not just apply directly to the skim coat and save adding more RTV???? Also why add Water to the siliicone wont this cause the mold to shrink with time(if you ever would need to go back and cast more).

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the caulk needs a long time to cure (days...). if you you mix it with water it will cure much faster...the mold wont shrink if you use "cured" caulk as filler...

caulkrtv1ym7.th.jpg

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ok, dry the silicone(either let sit, or mix w water) out chop up, and mix w. RTV pour onto already fully dryed skim coat. is their a mix ratio for the water mixing?? im dying to pour this mold. also im thinking of trying one with the skim coat and letting the tube silicone cure on the skim.

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ok, dry the silicone(either let sit, or mix w water) out chop up, and mix w. RTV pour onto already fully dryed skim coat. is their a mix ratio for the water mixing?? im dying to pour this mold. also im thinking of trying one with the skim coat and letting the tube silicone cure on the skim.

The silicone needs 24 hours to cure and cannot be thicker than the directions on the tube say because it will not fully cure.

The silicone will only hold as much water as it needs to cure, all excess will run off. It will set in under an hour so you can pour very soon.

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The silicone will only hold as much water as it needs to cure, all excess will run off. It will set in under an hour so you can pour very soon.

thats a very bizzar process. sounds amazing. i just placed 3tubes squirted out on a plastic plate to dry. also was lucky to find a few tubes of old cured silicone. one is 100% other is 100%pure silicone ruber w anti molding stuff added(not sure if that matters).im dying to get this bait molded. picked up RTV and started skim coat drying, its been going for 4hrs and is still liquidish.

ok so to do the fast cure silicone(water added) i just pour the stuff in a container add tons of water mix it up a ton. pour off excess, and should set up quicker?? i am super nervous about adding chips of silicone to my mother mold(first time, ha ha). that whole floating deal. not sure how im going to deal with the floating portion. more than likely i will have to build the mold up in layers.

once again thanks all for the comments. i plan on posting some picts when done.

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oh so one last question. so no one has tried curing regular silicone(adhesive-rubber tube) over an RTV skin directly. that would be an ideal process if someone could figure out how to make that work!!

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thats a very bizzar process. sounds amazing. i just placed 3tubes squirted out on a plastic plate to dry. also was lucky to find a few tubes of old cured silicone. one is 100% other is 100%pure silicone ruber w anti molding stuff added(not sure if that matters).im dying to get this bait molded. picked up RTV and started skim coat drying, its been going for 4hrs and is still liquidish.

ok so to do the fast cure silicone(water added) i just pour the stuff in a container add tons of water mix it up a ton. pour off excess, and should set up quicker?? i am super nervous about adding chips of silicone to my mother mold

Don't be! As long as the model has a coat of RTV, all's well!

(first time, ha ha). that whole floating deal. not sure how im going to deal with the floating portion. more than likely i will have to build the mold up in layers.

Just put something flat with some weight over the Box.

once again thanks all for the comments. i plan on posting some picts when done.

Well, get busy!;)

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oh so one last question. so no one has tried curing regular silicone(adhesive-rubber tube) over an RTV skin directly. that would be an ideal process if someone could figure out how to make that work!!

The key with that is patience. Air cure silicone takes about 24 hrs but that can be accelerated by putting it in a super humid place.

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The key with that is patience. Air cure silicone takes about 24 hrs but that can be accelerated by putting it in a super humid place.

hmmmmm...im going to read between the lines on that ...thanks....well my aquarium hood is nearly a rain forest. it seems strange that being silicone seeps some kind of natural lubicant oil, that it will bond after curing!! my fingers are sore and beat up after an hour of chopping all sorts of old molds and dried sil caulking. ive got every finger and appendage crossed!! hope this works.

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hmmmmm...im going to read between the lines on that ...thanks....well my aquarium hood is nearly a rain forest. it seems strange that being silicone seeps some kind of natural lubicant oil, that it will bond after curing!! my fingers are sore and beat up after an hour of chopping all sorts of old molds and dried sil caulking. ive got every finger and appendage crossed!! hope this works.

It sounds like you're right on target!;)

You probably did a bit of overkill with the chopping, but it won't hurt. The key is having the model covered with a layer of RTV. All else is Filler, regardless of what it's made from.

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ok todays update. interestingly i experimented with very large blocks of silicone to very small. it seems there might be some ideal(opitmal) cut size. interestingly in the areas that i finely choped and mixed high ratio of cut(well cured) silicone in with rtv those areas are not curing at the same rate. infact they are still liquidish(24 hrs latter). i would mention that i slightly overdosed the catalyst to make extra sure that no soft uncured spots exist. also i mixed very well. i re-skim coated the lure and those areas cured compleatly, so im somewhat mystified what is causing the areas with the cut cubes to cure so much slower! i am also now running an experiment with bonding the rtv to a block of silicone, and the reverse applying liquid silicone rubber to cured block RTv. if the liquid silicone shows good adherance to the rtv then next week i will attempt to cure a block of caulk over a skin coated RTV.

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The problem is to create a stable, distortion free mould, using as little of the expensive RTV as possible.

My solution is to thick skim the pattern in the lego box, as outlined by Husky. After the RTV has set, top up the mould box with PoP. The PoP former holds the shape for the casting process. The RTV thick skin can be easily separated from the PoP former, for easy de-molding of the casting. The PoP former is sealed with 50/50 PVA and water. This will prevent dust contamination and help prevent chipping, although small chips in the former will not affect the function.

A quick, cheap and cheerful solution. Would it work?

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ok todays update. interestingly i experimented with very large blocks of silicone to very small. it seems there might be some ideal(opitmal) cut size. interestingly in the areas that i finely choped and mixed high ratio of cut(well cured) silicone in with rtv those areas are not curing at the same rate. infact they are still liquidish(24 hrs latter).

Was it 100% Silicone. I ask because the RTV will react with certain rubber. I tacked a model with rubber glue and the RTV wouldn't set near it. It remained "Liquidy", as you've described.

i would mention that i slightly overdosed the catalyst to make extra sure that no soft uncured spots exist. also i mixed very well. i re-skim coated the lure and those areas cured compleatly, so im somewhat mystified what is causing the areas with the cut cubes to cure so much slower! i am also now running an experiment with bonding the rtv to a block of silicone, and the reverse applying liquid silicone rubber to cured block RTv. if the liquid silicone shows good adherance to the rtv then next week i will attempt to cure a block of caulk over a skin coated RTV.

I'm looking forward to pictures.

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was it 100% silicone
yes it was! 100% silicone rubber caulk that is. i am now woundering if the silicone ruber caulk does infact contain sulfer in its chemistry??? it seems to be setting up slowly. so that is actualy probably a good thing as the slow cure will make for a longer lasting more durable mold.

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My solution is to thick skim the pattern in the lego box, as outlined by Husky. After the RTV has set, top up the mould box with PoP. The PoP former holds the shape for the casting process. The RTV thick skin can be easily separated from the PoP former, for easy de-molding of the casting. The PoP former is sealed with 50/50 PVA and water. This will prevent dust contamination and help prevent chipping, although small chips in the former will not affect the function.

A quick, cheap and cheerful solution. Would it work?

I am contemplating some version of this. in the past i didnt like the way rtv skins over pop molds cast. it seemed that having a super flexible skin didnt stick inside the mold well, it flaped and sloped around resulting in somewhat distorted results. but i supose like you say, if the skin is layed down thick, that might be enough. especialy for the price!(HA HA, thanks !!!)

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