micromark silicone rubber and resin

Having spoken to a hobbyist and a commercial caster re shelf-life, consensus is to use within 6 months.... or less!

The packaging on the stuff I've seen also says use within xx months, so it's something you should buy when you want to use it, even if you keep it in the fridge with your CA.

The Commercial guy (MDC) buys it in 10-25 KG  (22-55Lbs) tubs, plans purchases based round planned production, buys from a supplier who has high turnover to keep it fresh, and then dumps unused material if/when it goes 'off' ie when it doesn't cure properly.  

MicroMark's products are re-labeled Smooth-On.     I use Smooth-On's  OOMOO RTV and it seems to remain useable in an open but tightly sealed container for several months.

Conversely Smooth-On's Smooth-Cast 305 5-minute pot-life resin seizes up the cap when the bottle is closed for just a week or two.   Takes a pair of slip-joint pliers to loosen the cap.  Wait a couple of months and you're not going to get it off.

Be sure to stir both products well before dispensing.

Go to Smooth-On.com for all kinds of info on their products.    Check their distributor list also.    There is one nearby which I've gone to pick up supplies and for help on molding and casting problems  -- their counter help is very knowledgeable.     They (Reynolds Materials) also offer seminars throughout the year on molding and casting.  They may be able to recommend a product which is better than the MicroMark relabeled products.

Please don't hate me ;

  I don't use any of that stuff .I use " DAP " silicon in the tubes to make my molds, when I need one.The kind you get at Home Depot, My resin comes from the same place.The silicon makes good molds and the resin seems to remain bubble free when casting.

I pop the part out after a week and I've never had a failure .Both can be bought in small packages too . Nice part,.low product loss because of setup or cook-off of the product in their containers .

    Sounds stupid, I know , but, I have been doing this for over fifty years and I am not going to change now .

I find the the two part RTV a lower viscosity that makes a better, more detailed mold then the DAP. in the tubes.

Also, about shelf life, I have used both rtv and urethane resin slightly over a year old okay. I wouldn't use it any older.  One important thing in using the resin.  I forget which component of the resin seperates, but one does.  Since I can't remember, I pre-mix both.  By pre-mixing I mean I agitate the bottle before pouring the resin into the mixing cup.  It is not enough to mix well AFTER pouring, the components must be agitated by inverting and turning upright several times BEFORE pouring.

thanks for the info to all

Didn't know you could get resin from home depot. Two part?

The dap silicone  sounds doable,however I don't how much temperature it will withstand as I pore more lead tin mix than resin and rtv has no problem with that

thanks I did not know home depot had resin.our closest one is an 2 hours away but it just happens I am going that way on Saturday will stop in and check it out

Raualduke

Didn't know you could get resin from home depot. Two part?

I know that Home Depot & Lowes carry Bondo catalyzed epoxy putty  (or similar product),   but I do not remember seeing a pourable resin.  Perhaps fibreglas epoxy? 

With the Bondo you mix up a batch and smoosh it into the mold.  Not too sure how good it would do for filling fine details.  The quality of your mold becomes critical

That won't work for you then .This is only for cold resin pours-sorry .

The quality of the mold is very important .If you choose to do a two part mold though you have a great stability factor here .That's my experience anyway .You do all just like you're supposed to. You just use cabinet nails for alignment pins. They might work loose , but it will be a year or more .

I cut and/or drill notches in the bottom part of the mold before pouring the top part.  That way the locating "pins" are part of the mold.  It is not easy to drill holes in RTV, hence the cutting of a hole/notch- whatever shape, just something that will help pin the orientation.

Don Stauffer

I cut and/or drill notches in the bottom part of the mold before pouring the top part.  That way the locating "pins" are part of the mold.  It is not easy to drill holes in RTV, hence the cutting of a hole/notch- whatever shape, just something that will help pin the orientation.

A tip I picked up recently was to use acorn nuts (not tree nut, rather hardware store hex nut with decorative closed end) as locating pin material.  Position on clay surface as you are setting up the first layer of the mold pour.   They become negative space in that first layer when they and the clay are  removed for pouring the second layer.

The hex-shaped locating pins make for a positive alignment.

I will also poke hokes in the clay using an Allen key or wrench (another hardware store item).

Depending on the shape of the part,you may also have to vent the mold. That is to say, give the air a way out.. Not hard to vent an rtv mold

If it is a two -part mold you ALWAYS need vent tubes- often more than one.  You need one vent tube for every local high spot in a mold. Otherwise air will get trapped in that area and either leave a void in that spot or bubbles around the high spot.  The RTV is airtight, so you MUST leave an out for all the air in the mold.  When designing molds think like an air bubble- "how in the world will I get out of this area?"