Review on Versatile 4 Pack Silicone Molds: Succulent Planters, Shot Glasses, Candle Holders & Small Plant Moulds for DIY Crafts by Doris Tran

The corners on these molds prevent the concrete from setting in the right direction. There will always be gaps between the corner and your concrete mix, causing bubbles to form on the final product. I've changed the mix many times, made it funnier and thicker, I've used a small concrete mixer to help the mix fill in the corners, I've tapped the shapes with my hands and on the table after I've finished them with the mixture, but always the same result: air bubbles at the corners.