silicone caulk + petroleum jelly = bad idea?


Well-Known Member
Okay guys, i wanted to write about this project when it's finished, but i guess i need your help to get there :lol

but here is what happened: i have a wine-bottle which is a quite good replica of the Fifa World Cup Trophy. Now i wanted to make a mold of the bottle and make a replica of it (without the bottleneck) with plaster, to give it a realistic weight. as this is my first mold-project, i decided to keep the costs low and use silicone caulk.

i wanted to make a three-piece mold, so i started by building a claywall on the vertical middle of the bottle, with registration-keys. then i applied 3 or 4 layers of silicone (of course i let each layer dry before applying the next one) with a palette knife to make sure to get a more or less uniform coat. i ended with the registration keys for the mother mold.

after that, i scraped off the claywalls and wanted to apply silicone to the other side of the bottle. as silicone sticks to silicone, i googled for cheap release agents and stuff like that, and a lot of websites advised petroleum jelly as a good cheap product to avoid the two halves sticking together. so i applied a thin layer of vaseline on the "seam" (dunno if this is the right word, but i guess you know what i mean...the thing with the registration keys on it) and started applying silicone on the other side of th bottle.
i started on friday with the first layer, always tested if it was dry, and when it was dry, i applied the next coat...and so on. i think i finished the last one on saturday evening, and i gave it time until today to get really
really dry and ready for demolding.

ok, so far, so good. i started demolding the first side (the one with that i started) and was surprised of how well the method worked out. good details, nearly no airbubbles trapped...great result!

when i removed half of the first mold, i noticed something strange: some of the silicone of the second side wasnt dry yet. it's not sticky, but neither dry. it has some kind of peanut butter consistency, but - as said - it's not sticky. very strange, never have seen this

now, my question is: can this be because of the vaseline? first i thought it was because the best-before date was expired, but it dried everywhere else, so i dont think that this is the reason. then i thought of the vaseline, perhaps i applied it too sloppy on the seam and some of it is on the glass which prevented the silicone from drying, but it dried on the seam.

as you can see, i'm a bit helpless (and that after everything started so well :cry), so if you have any idea why this happened or how to fix it, please let me know
bump and update:
i demolded the first half completely, went off quite good, some sticky spots, but who cares? it's my first try, i'm happy :lol

i think it _was_ the vaseline that prevented the silicone from curing, so i decided to cut off the seams and redo them.

now...does anyone know another cheap mold release agent?
idk if this will work for you but when i make the silicone caulk molds i mix a few drops of acrylic paint into the silicone to make it fully cure it takes drying time down significantly where you can do acouple layers in about and hr or so.. didnt time my experience with it but it dows work extremely well, just google silicone caulk and acrylic paint molds.. might help you out
Vaseline is often used as a mold release, that's not the problem. I've seen a tutorial on using silicone caulk for molding and it recommended adding acrylic paint as Nyne mentioned to aid in curing.
This thread is more than 12 years old.

Your message may be considered spam for the following reasons:

  1. This thread hasn't been active in some time. A new post in this thread might not contribute constructively to this discussion after so long.
If you wish to reply despite these issues, check the box below before replying.
Be aware that malicious compliance may result in more severe penalties.