I used a 2 parts each peat & perlite, 2 parts cement. The bee hives I added the coarse sand. I covered mine with plastic, put in shade, kept damp for a week. Finish curing about 3 more weeks. I did find hairline cracks on one I forgot to cover after unmolding. All my pots made it through the 0 degree winter days we had this year, none broke. Fully cured they are lighter weight. One key to success is make sure you follow the curing process. The darker bee hive in first pic wasn't completely dry.
Yes, more cement does make them heavier. Years ago I made some with just concrete (not cement) & peat moss, very heavy on my "retired back".
Above noted website has the recipes I used.
