Do you have to seal concrete planters?

I have made a few planters using mortar mix and had some problems with the planters producing dust/chalk once the soil and plants are in. I have read that this could be due to a number of factors such as temperature at cure time and the amount of water used in the mix. Will using a sealer address this after the fact? Will I need to clean the concrete with anything special before applying the sealer? Thanks!

mikeasaurus22 days ago

You could be seeing efflorescence, a powdery white substance that is an accumulation of minerals and salts. This happens on a lot of masonry structures, and usually seen on brick (since the efflorescence stands out on red). This is common for any porous inorganic structure, and caused by moisture evaporating and leaving behind the mineral deposit - likely exacerbated by the high nutrients in your soil.

To prevent this, you'll need to clean the concrete (power washer works great), and then seal the concrete. While this will prevent the efflorescence I cannot comment on how the sealer will interact with the soil, especially if these planters are used for growing food.