Today is the day, y’all. It’s the day I can finally start placing my Austin faux stones on the front porch baseboard. We’re going to have a beautiful day here in central Texas (hot, but at least no rain in the forecast), and I have all the big stones ready and waiting, and about half of the small stones ready to go.
So far I only have half of the small stones because I need a lot of those two sizes, but I only have one mold of each size. While I only need three or four of each of the large stones to complete the porch plinth, I need many more of the two small stones: nine of one and ten of the other. And those small stones take just as long to pour, cure and demould as the large stones. But at least I have enough to start on the baseboard while I continue pouring the rest of the small stones I’ll need to finish the entire baseboard area.
I wanted to show you a big problem I ran into with the design of my silicone mold and the change I made to them to make the job of pouring these stones much quicker and easier.
When I originally made the molds for the textured silicone mats, I needed something to place under the silicone mats to keep the edges straight and give them support underneath. Otherwise I would end up with wavy edges on my stones…
I ended up using the type of sand you would use under pavers. I already had the sand on hand and found it easy enough to lift the edges of the silicone mat, drop some sand underneath, and then adjust the silicone mat so the edges were straight.
Once I had the mat at the correct height on all sides and fully supported underneath, I vacuumed up the excess sand and then caulked around the edges of the silicone mat where it met the PVC boards I used to make the molds.
I thought it would mostly be a one-time process. I knew that to unmold each stone, I would have to remove one side of the mold, so I figured that meant I would simply have to re-caulk one side of each mold before pouring the next stone. It turned out that that was not the case. As I removed each stone, I lifted the silicone mat slightly along with the stone. And that dislodged other areas of the mat. Once those other areas of the silicone mat were separated from the putty, sand would come out. And because I was using silicone caulk between the silicone mat and the PVC boards, which constantly remained sticky, the sand would get stuck in the caulk and create a big mess.
So I basically had to go through half the mold building process before each new pour: adding more sand, changing the sand, getting the silicone mat perfect, cleaning off the excess sand, and then re-caulking everything. That took so long!
I knew there had to be an easier way and there had to be a better solution than using sand under the silicone mats. I just needed something to fill the gaps between the silicone mat and the bottom of the mold box, but it had to be something that would dry and hold its shape instead of moving around like sand did every time I unmolded a stone.
I finally decided that the perfect product for that is Great Stuff Expanding Spray Foam. It would fill in those areas and once cured, it would hold its shape. I specifically chose this brand because, after a quick Google search to find the fastest curing spray foam available in big box stores, this was the one. It hardens in about 15 minutes and cures in an hour.
So I removed one side of each mold, poured out the sand, and cleaned each mold by removing all the remaining sticky putty with sand attached. And then I lined up the silicone mat along the straight guide I had drawn on each one, indicating where the edges of the silicone mat should be. I held it in place with one hand as best I could and then sprayed the spray foam between it and the bottom of the mold box. It did its thing, expanded and came out the open side. As it expanded, I kept pushing the silicone mat into place to make sure it stayed aligned with the mold case.
After it stopped expanding, I scraped off the excess that had come out of the side…
And then I screwed that side of the box back on and made sure the mat was still aligned with its guide. I had to push it down further in some areas and that caused the spray foam to come out between the box and the mat. But I left it and let the foam dry completely. Once it was completely dry, I cut off the excess foam, re-caulked and was ready to pour the next stone.
This made the entire process much easier and cleaner. I no longer had to deal with quicksand. I no longer had to deal with basically remaking the mold again between pours. The foam held its shape and, because it is very sticky when wet and grabbed onto the silicone mold, it also kept the silicone mat in place while I unmolded the stones.
I was able to lift the stones off the mat while the mat stayed in place on the other three sides.
The stone came out very clean and three sides of the mold were completely intact.
Then I just had to replace the side of the mold, re-seal one side and two corners, and it was ready for the next pour.
I wish I had thought to do it this way from the beginning, but of course DIY is all about trial and error. And now, if I ever do another project like this, I know the correct (and much easier) way to build a mold using a silicone textured mat. And who knows? Maybe I’ll use these molds for another project in the future. I’m definitely going to keep them in case I want to do something else to match the Austin stone in our house.
So although I haven’t finished pouring the stones, I’m ready to start placing them on the front porch baseboard area. I hope to have some progress to show you tomorrow!
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Addicted 2 Decorating is where I share my DIY and decorating journey as I remodel and decorate the 1948 upper that my husband Matt and I purchased in 2013. Matt has MS and can’t do physical work, so I do most of the house work myself. You can learn more about me here.
