Silicone baking sheet for mold/casting

[Luke0312]

Having a thought about this and looking for input.

When doing open face molds, I've seen the recommendation to use waxed glass over the opening to help control moisture contamination. I'ved used that method, sometimes the cast pops right off, sometimes I have to break it off, then use a razor to scrape all the resin off the glass. Never could get consitant results.

To combat this, I poured a bit of rubber onto some glass and used it. However given how thin the sheet was, it needed support, but the biggest issue was it didn't seem to level out perfectly, one end being thicker than the other, so it had the potentional to change the cast.

I was trying to think of a simple and cheap way to make something rigid and that the resin wouldn't stick to, then thought of the silicone baking mats.

Anyone know of why this wouldn't work? The biggest issue I see is adhering it to a more rigid surface such as some plexi. If you got a good bond though, you should be able to use it for a multitude of open face molds.

Checked the bay and baking mats are only a few dollars, so it would be cheap as I'm sure I have some scrap plexi, mdf, or something laying around.

Input? Ideas on the best way to adhere it to something rigid?

 

[Geohazard]

Maybe it's my lack of experience with your process, but it stands to reason that you may not have to glue down the silicone to the plexi, given that it is already somewhat slip-resistant? On a smooth, flat surface, a silpat should have significant area in contact that it wont move/slip.

 

[robn1]

I've been doing something like that to make parts with a flat back. I made a slab of mold silicone, just made an empty mold box. I pour resin into an open faced mold, then place the slab on top.

 

[Luke0312]

Maybe it's my lack of experience with your process, but it stands to reason that you may not have to glue down the silicone to the plexi, given that it is already somewhat slip-resistant? On a smooth, flat surface, a silpat should have significant area in contact that it wont move/slip.

Right, it won't slip, but with the open face made, you're pouring in from the top, then just laying the silicone sheet over the opening. With a small opening, the sheet probably won't sag enough to make a difference, but with a large opening, it will dip into the mold cavity.

 

[Luke0312]

I've been doing something like that to make parts with a flat back. I made a slab of mold silicone, just made an empty mold box. I pour resin into an open faced mold, then place the slab on top.

Yea, also considered pouring a thicker sheet/slab, but it could also have the same sagging, depending on the opening size and the durometer of the rubber.
Also, the cost of it, pouring a bunch of rubber to make a more rigid slab vs a 5 dollar baking sheet and some free scrap material.

Just throwing out some ideas for a low cost, but versatile tool for molding/casting.

 

[msleeper]

If sagging is an issue, why not put some sort of support onto the back side of the baking sheet? The side that won't be going into the resin.

 

[robstyle]

Im trying to wrap my brain around this, are you talking about placing a flat sheet over an open face mold for sake of moisture contamination to the freshly poured casting material? If so, why? How long is this material taking to kick?

If your just after a smooth surface level the mold on a firm board, pour the material to the desired edge and spray the freshly poured material with a dusting of mold release. The dusting of mold release will combat air bubbles but it your using a cheap resin and not a quality plastic air bubbles are an inevitability.

 

[cavx]

I think I understand what he wants to do, so why not a spray on adhesive? It may or may not stick to the silicone mat, however if it does, then a win.