Adding Silicone Rubber to Cured Sillicone?

[Skaught]

I made a mold last night but I'm concerned that I didn't quite get it thick enough on what will be the bottom of the mold. I used Mold Max 30, which should be pretty sturdy stuff. But I'd hate to tear it after using an entire gallon of the stuff.

If I added more silicone to the top of the pour (making the bottom thicker), will this adhere strongly to the already cured silicone? It's my understanding that silicone will stick to silicone, but before I put our more bucks on the material I wanted to make sure.

Scott

 

[RelicMaker]

As long as the surface is clean with no sealing agents, it should adhere to it just fine.

 

[pandatrooper]

Yes, it worked for me. I was creating a silicone mold for a model car body. I poured the silicone but i ran out before the last top quarter of the car / roof line could be covered.

I let it cure for a day, then simply mixed some more silicone and poured it on top. After it cured, there was no line or anything where the new silicone met the previous layer. Casts turned out great!

 

[exoray]

If I added more silicone to the top of the pour (making the bottom thicker), will this adhere strongly to the already cured silicone?

Best answer MAYBE...

Depends on the silicone, many will stick to each other and become one, some won't stick at all!

My go to silicone won't stick to itself once cured beyond say masking tape adhesion a simple pull and it comes off clean...

But I have used others that bond like hell and become one... I also find that adding cure accelerator increases the bond, but not only to itself it actually will start to stick to the object you are molding as well...

 

[Skaught]

The item I'm molding is completely covered, so the new pour would only be touching the silicone. It's only 1/8" thick on the bottom at the closest point, which looks too thin to me. I'll have it sitting on wood, so maybe it's okay, but I'd hate for it to tear when I get the cast piece out of it. I don't know yet how much bending I'll have to put on the mold to release the cast.

Scott

 

[modelnutz]

Mold Max 30 will bond to it's self very well.
(As long as the bonding surface is clean )

 

[Skaught]

Thanks, guys. I've ordered another batch.

Scott

 

[weaponx82]

From my limited experience, fresh silicone bonds very well to cured silicone. As long as you give it enough time.

I've only worked with rebound 25 (smooth-on) when it comes to adding more silicone later but what I found out was if, even if your additional silicone looks cured, you want to wait another day or so.

I back filled some cured silicone with a fresh batch. The following day I checked it out thinking it was fully cured. The old and new pulled apart pretty cleanly. I just tossed it to the side thinking it was junk. I came back to it a few days later to find out, even though it separated after the initial curing, the new and the old still fused. Just not as well as I intended. If I left it alone for another day or so, it probably would have been fine.

Hopefully this makes sense. Let me know if it doesn't.

 

[Skaught]

Would it help if I carved out a few anchor points in the cured silicone? I guess it couldn't hurt as long as I stayed away from the original piece.

Scott

 

[Garthok]

I wouldn't weaken the original piece in any way if it was me. If it's going to stick, it will stick well enough on it's own.

 

[WebChief]

I've added new silicone to old...sometimes days later and never had an issue with it bonding.

 

[Vaderman]

I have added silicone to an old mold and it sticks, unless there is dust or anything in between.
Try it, if it doesn't stick, try to plaster bandages to reinforce the silicone while it is still on the piece. Or just pour plaster of paris over it in a thick layer.

 

[Skaught]

I've poured on the new layer, so we'll see how it goes tomorrow night. There would tiny bubble holes in the top of the old layer, so if the new layer sinks into those, I think it'll bond pretty well. It only needs to add strength to the bottom of the mold, so I think it'll be fine.

Scott

 

[weaponx82]

Let us know how it does.

 

[Skaught]

It wasn't quite 16 hours yet, but since the new silicone was only on the "bottom" I figured enough time has past. I pulled off the foam core walls to check the bonding and it looks like it's fine. Only a slight color variation shows me where the two pours are. I can't feel a seam and it flexes fine with the whole piece. So I think I'm good! Thanks guys.

Scott