How to Make Corner Stones with Flat Plastic Concrete Molds and a Wedge

You can now make custom manufactured stone for the outside corners of your do it yourself wall projects without paying the high cost for rubber corner molds. We've had hundreds of customers email and phone us for alternatives to them having to purchase ready-made cornerstones. They wanted to know how to handle or "get around", pardon the pun, the corners when they were making their own custom stone and brick for their home and garden projects. They could use inexpensive ABS plastic concrete molds to make their flat stone for pennies each, but then would have to purchase expensive corner stone pieces, or very expensive rubber molds somewhere. That would cut into the savings earned by making the stone themselves. And many times they could not get proper color or texture matches to the stone they wanted to make.

Previously, we had written a number of articles for the concrete stone casting industry and consumers offering alternatives for smaller do it yourself homeowner, craft, or home and garden projects. Rubber molds for small projects are just too cost prohibitive for the average consumer and do-it-yourselfer, or anyone but the commercial stone producer. Some alternatives we came up with were to "butt" like stones to each other at corners--- but that seldom gave the results desired. Purchase commercially manufactured cornerstones, and just make the flat stones to save money--- that worked, but usually getting color matches was difficult. Cut flat stones at forty-five degree angles and join them at corners--- worked great and saved money, but was messy, and potentially dangerous for the average homeowner or crafts person.

But now we've come up with the perfect alternative for corner stone production, without the necessity of using expensive rubber corner molds--- a Wedge! Or what we've named the Olde World Corner Stone Wedge. We now include corner wedges FREE with our stone making Kits. And you can just as easily make your own wedges with wood, for pennies each. Just cut a 2x4 or thicker piece of wood at a 45 degree angle to make a triangle. The shape should look like a pyramid when viewed head-on. There's your wedge! There's your solution to making cornerstones inexpensively!

And now we'll share with you how to use the Wedge. Just follow the instructions on using what we call the Olde World Wedge in your plastic molds below. You may save thousands of dollars on your next DIY stone or rock wall project when you compare your cost versus purchasing manufactured stone for the entire job.

The first thing you need to do is decide where you want your stone to meet on a wall corner. The flatter the face of the stone in that area, the easier it will be to insert and use the mold wedge to separate the two halves. Remember, where the Wedge is placed is where the stone will be divided into the two 45 degree angled halves. Use duct tape to hold the Wedges in place. Run the tape up the sides and insides of the Wedge, and side of the stone mold. Those seams will not be seen when the stone is installed anyway. There may be a small gap where the Wedge meets the face of the mold, but that seldom presents a problem. You will be filling the tiny seam where the two halves meet with filler cement, so the size of the seam is not critical.

This photo Illustrates what the filled mold looks like with the Wedge in place. Here is one case where a thicker concrete mix will be beneficial in keeping the two halves from running into each other. Just pour concrete into one half at a time while holding the Wedge in place. Usually, the duct tape that is holding the Wedge in place will be sufficient to hold the two halves of concrete apart anyway. Use duct tape on the inside of the Wedge to block concrete from filling the Wedge on the sides.

Once the concrete hardens, 24 hours is best, you can remove the Wedge. Note that you now have an automatic forty-five-degree angled edge on each of your stone halves---without measuring, cutting, or making a mess with a saw. These two halves will easily be joined together on the corner of your wall or project to make a perfect corner stone angle.

Turn your filled mold over while supporting the two halves of your corner stone, and de-mold them. If you can get the stones out of the mold without turning the mold over, that is even better as you'll be able to guide the separating of the two stones better. The two stones will normally break apart right at what will be the tips of the stone that will meet at the corner of your wall. Be careful with them as they will still be somewhat soft since the stone is not cured yet. That will give you an opportunity to trim off any extra edges before attempting to join the two sides.

To illustrate an installation of the corner pieces, In this photo, I've attached them to a concrete block to represent the corner of a wall. If at all possible, start installing your stone from the corners back, so the spacing works out automatically, and any cuts will be away from the corners. Install the stone from the top of your wall down, so you don't drip mortar on stones below. Fit and mortar the two corner halves as tightly together as possible against each other at the corner. The Wedge angles should make that quite easy, as is illustrated in the photo example. Whether you fill your corner seams now, or when the entire corner is complete is up to you. If the base color of the stone is the same for the entire wall, I would normally wait until the stone is completely installed, then go back and fill the seams with cement. Either way is fine, but wet the seams and corners prior to filling the seams.

To fill the seams, I use either a straight Portland cement mix with the colors of the original stone added, or colored premixed Sand Mix. The smoother the filler mix, the easier and better the seam can be filled. You can make the joint virtually disappear by blending the seam filler with the texture of the exterior of the stone or rock. You may even use grout if it is the same color as the rock or stone you made. Again, be sure that the stones are wet at the seams so the filler doesn't pull the moisture out of the stones and not stick to them as readily.

Use a putty knife or flat piece of wood to force the cement or grout into the seam, and smooth over with a wet finger or sponge. Again, the smoother the material used to fill the seam, the better you will be able to blend it into the stone, and make the seamed edge virtually disappear. Note that in this photo, the filler cement is wet, which is why the color is darker. In the next photo, the filler has dried and blended in to the seam in the stone, making it undetectable.

As you can see in the photo illustrating the finished corner, the seam is undetectable--- even when photographed from only inches away. Note that I left the seam on the top of the stones where they meet to illustrate where the seam actually was. Cover it, and you wouldn't know where the seam was located.

Rest assured that most people are not going to be looking for a tiny seam in the corner of a stone anyway. Especially when they are being overwhelmed by the beauty of the entire wall installation. And if you plan to use a topical sealer, like a matte or gloss finish sealer, that will smooth out any seam in the corner stone even further.

So--- use the "Wedge" idea to make corners--- or pay up to $70.00 per each rubber corner mold. The choice is yours .


Place Wedge where you want the split.


The Wedge will separate the concrete


Remove Wedge to see your corner angle.


Remove stones from the molds gently.


Stone installed as on a wall corner.


Mix a smooth colored filler of cement


Force filler into seam and smooth out.


Corner seam is virtually undetectable.


The photos below are actual corner stones made with expensive rubber corner molds costing $60.00 or more each.  Compare them to the corner stone made with our wedge system... for FREE!