Mold making help. Mixing silicone.

I am at the tail end of a project and have run low on silicone. The front half is fully covered, but I only have enough rebound 25 left for a thin layer for the back half. Can I do my 2nd through final layer with a different silicone? Oomoo maybe? Even hardware store silicone? I believe it's mixing platinum cure with tin cure. Does anyone have any experience with this?

You can pour your silicone in layers and the silicone with stick to itself.
HOWEVER!
-Tin cure and Platinum cure silicones work differently, and do not play well together. In fact, they keep each other from curing (which is obviously bad).
-I'm not sure what you mean by "Hardware store" silicone; but if you mean the silicone caulking that cures by evaporation, it may not work very well.
-I have used different brands of the same type (tin or platinum) of silicone with no problems. This would be my recommendation if you can't get more of your original brand.

For whats its worth I use alot of " hardware store " silicon, mainly for rough casting of prototypes. I have though used it to correct an oops, in short i molded some parts but didnt have the sides of the mold thick enough, causing warped or distorted casts. I made small v cuts on the side of the mold, placed the original part in, and used the clear store silicon to thicken the mold sides. When I have ran low on two part silicon, I made a beauty layer mold, then after enough time for curing made a filler layer, The main issues with the clear silicon curing, a thin layer less than a 1/4 inch close to 1/8, and trying to get the air bubble to a minimum. Last but certainly not least is it will shrink and can cause the mold to warp. Basicaly put it on in thin as possible layers

If you know you are going to be low on 2 part silicone, get a thin layer over the part as a "print" layer. Then you can go back with more silicone later to thicken it up. As mentioned, it is always best to use the same type of silicone to prevent reactions. Silicone only sticks to silicone, so the other layers (assuming no major dust contamination occurs in between pours) will bond really well and should even fuse together.

I recently used caulking silicone to thicken up parts of a mold originally made from an additive silicone. It stuck to the 2 part really well and the use of a "spirit" helped speed up the curing. Basically, as the spirit evaporates, it produces condensation which the caulking silicone needs to cure. The problem is, now your (my) mold is "contaminated". I can't go back and pour more 2 part silicone as it just won't cure where it comes in contact with condensation curing silicone. If more silicon is needed, it has to be an air curing product.