In my lazyass attempt to avoid having to empty and refill the birdbath when we get freezing temps overnight, to also avoid a broken tub, I add a piece of bamboo the night before. (I keep it out of the water when it stays warm enough.)
My hypothesis is that the bamboo will create a weak part in the ice to prevent the tub from cracking when the ice expands.
Any water or materials science peeps have an opinion?
@CJLavoie
MANY years ago, swimming pools were made from poured cement. Draining/refilling a swimming pool in New England was not a loved experience; not cheap either. In order to keep such a pool filled with water in sub-freezing temperatures, one dropped the water level by a few feet, then threw fire wood into the water. The expanding ice crushed the wood, instead of cracking the cement. I hope this helps.
@The_Breeze Thanks, Breeze, sounds like the same principle!