Mold (final shape) I used a Home Depot mixing container from the paint section
Item to keep the gift card safe, used a gift card holder from Home Depot
1+ box of PermaStone
Few items to weigh down gift card holder, used a few nuts and bolts
To bring while "opening" gift:
Step 1: Mixture
Determine how much of the mixture you'll need to build your mold and completely cover the gift card. If your mold is larger, you will need more than one box of PermaStone. I bought mine from Hobby Lobby with a 40% off (internet) coupon, costing me around $5 for the box.
The directions from the box said to mix 1.5 parts PermaStone to 1 part water or like a pancake mix consistency. I utilized the entire box and had to add a little more water than the directions suggested, keeping it like pancake mix.
Step 2: Pouring the Mold
I learned an important lesson on this step. I tried to hold the gift card holder down as I poured the mixture over it in the container. The holder floated to the top and I had to scramble to take it out, clean it off, add items to weigh it down (I used a few nuts and bolts) and re-submerge.
I've included a picture of what it looked like after the batter was poured with the submerged gift card and holder.
Step 3: Final Steps
The mold will need to set for at least 30 minutes. When I checked mine at 30 it wasn't ready. You can tell because the mold will be at room temperature once cured (it gets nice and warm while it's hardening). I can't say how long it took exactly, as I let mine set overnight. The next morning I squeezed the container all the way around and very lightly used several small taps with a hammer to loosen the mold.
It came out looking really nice. Quite an impressive product, with a marble like quality.
You'll want to write something on your mold so your recipient understands. I was short on time and used a standard Sharpie instruction, "Break Me!"
I wrapped the...what do I call this thing... Gift card Vessel??? in styrofoam and threw in a pair of safety goggles (you WILL want these, as little chips will fly). Finally I wrapped this gift in a plain box, used painters tape (for color) and taped his new hammer to the outside of the box.
Step 4: Oh What Fun!
I hope you enjoyed. Please take this idea and run with it. You could use a fun mold, paints, or an item besides a gift card.