If you want to make square or rectangular stones I suggest:
Use four 1x2 or 1x3 boards about eighteen inches long. Stand them on edge and screw them together to form a square the size desired for the stepping stone. With the same four boards you can make stones from a few inches to the full eighteen inches on a side. When assembled to make a stone smaller than the eighteen inches, they will resemble a swastika with the unneeded portion extending beyond the square. One picture would explain all of this, but I don't have one right now. This wood frame can be set on a bench on a piece of plastic for molding.

I like the round stones, but it's simply what I prefer. This isn't mosaic, but again it's what I like. I just picked up a mold at Michaels. There are square molds available also.
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This is one my 8 year old grandson did:
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Leslie

I saw the plastic molds at Hobby Lobby like that, but figured that they wouldn't hold up long. How many stepping stones do you normally get out of one?

I may try making one out of wood....hmmmm....

leslie,
I love the stones! May I ask where you got the number stamps? or If they aren't stamps, how you did the lettering?
Thanks
Marcia

Ellie,

I absolutely LOVE your stepping stone!

I like it much better than the packaged kits you can buy at craft stores.

This is something that can have a special place in your family's gardens for generations to come, because it was
made with love.

Lisa

What I do is go to the local Goodwill or Salvation Arm & buy a plastic container in the appropriate shape. The other thing I've done is those plastic food containers that cake comes in etc. All these things make great cheap forms.

Aud

Ellie,
All of the above suggestion should work great, I found the large deli plastic containers works well, although I did have one that bulged in the bottom as the concrete swelled and dried so I would suggest if you use this type cut the bottom out and lay on a smooth surface with a piece of plastic wrap or similar underneath for easy removal.
Your little girl pics. above are worth a thousand words...
Wendy

My grandkids and I have made about 30 stones now and I have 5 molds. They're still as good as the first time I used them. There aren't any marks in the molds or cracks, I keep them clean and take care when removing the stone not to stress the mold. This is something I have set up and do in the house on a cardtable with trashbags. I can have 4 stones going at a time and then in a couple of days move one to the counter and do the 5th. The molds don't look so, but they're pretty sturdy. I am not using kits, I am making my own stones switching off with either mortar or vinyl cement patch.

I got the letters, a bag of capitals and a bag of lower case letters at Michaels. If you intend to make a bunch of stones it's worth the cost.

I have used some small plastic containers to press in single leaves just for fun and they do work just fine also.

Your daughter is darling, that's such a cute age. I wasn't criticizing, just offering up how I have been doing mine.
Leslie

Ellie's Mom,
Was this concrete (sand, portland cement and gravel) or mortar (sand and portland cement)?
Go to the home improvement store and buy a piece of ridgid insulation board. It comes in different thicknesses and you can cut it with a razor knife or any sharp knife. If you buy the thickest ones you can cut off a piece and cut your design out of the center. Make sure you leave a 2 inch border around the edge so the sides don't bulge. Or buy the thinner board and cut into 2 inch by 1 1/2 inch strips. Butt the corners together and push long nails into each corner. Wrap around the outside with duct tape. These will be bottomless molds just place on a piece of plastic wrap on top of a flat surface. The insulation boards are 8 feet long and about 2 feet wide so you can make quite a few molds. If you treat the molds nice you can reuse them quite a few times. If these are just decoration and no one will walk on them you can make them 1 to 1 1/2 inches thick. If you're going to walk on them go for 2".
Your husband is so encouraging! Tell him he is wrong. The mixture would be too hard to push in your mosaics.
You can use cardboard boxes that you wrap the outside with duct tape. BUT make sure you have something available to butt up against the sides so the cement doesn't bulge the sides.
You can place contact paper in the bottom of your mold with the sticky side up and place your mosaics on the sticky paper. Just remember that you are working in reverse. After you're done placing the mosaics pour or place your mix on top of the mosaics. If this is a ridgid mold, tap the sides to help release air bubbles. After 24 hours gently turn the mold over to remove the stepping stone. Peel off the contact paper and clean up (GENTLY!!) your mosaics.
Have fun and don't let your daughter touch these like she's doing in the pictures above. When these are fresh the lime in the portland cement can burn skin. Billie

Thanks for all the great advice.

I am using 2 parts sand and 1 part portland cement mix.

I don't think that they will be walking on them, but I do like the thicker stones just in case. I also used drywall tape.

How long should they cure before she can touch them? She helped place the glass marbles, but she didn't touch the wet cement. She really doesn't like getting her hands dirty. (I made a casting of an elephant ear this summer and didn't wear gloves...I learned my lesson about the need for rubber gloves!)

Hi, I would wait until the concrete SS is completely hard then water sprayed and dried before you allow your DD to touch. The decorative stones need to be pressed in while the concrete is still wet but slightly firm. After a few days give her a soft rag so she can do 'her part' by polishing the stones then she too would still be in the giving of something she helped hand-craft for your Christmas!
Also if you still have rough edges on your stones above they could be smoothed by using a file or a broken piece of concrete (my favorite method)to smooth; you will need to use some type of dust mask while preforming this task, maybe your DH could do this. Happy Holidays Wendy

Ellie's Mom, Until the lime is completely flushed out, every time the stepping stone gets wet can cause a burn. Use a water bath to flush out the lime or don't let your daughter touch them for quite a long time. The water bath takes about 3 days and changing the water every day to flush out the lime. Wear rubber gloves when taking the pieces out of the water. The water is full of lime. Billie

Thanks for the info about the lime burning her skin. Grandma and DH wanted to do hand print stepping stones. We won't be doing that.

She LOVES the little glass marbles, so we are going to have to soak these stones.

I did let her put in the glass marbles on one of them. She stood over the stone and threw them into the cement. I'm sure there are several that will never be seen again.

As for DH, he thinks that everything has to be perfect. Sides must be smooth and even. The marbles must be placed in a neat fashion...etc.... Poor guy just doesn't understand why I would want a leaf casting in my front yard. I just hope he doesn't squash Ellie's desire to be creative.