Waterproof cardboard - is that possible?

As a building material, cardboard is often remarkably stable and resilient, even more so if it is properly folded and shaped. There remains only one disadvantage: the low water resistance of cardboard. If and how you can waterproof cardboard, read this post.

Ways to waterproof cardboard

The following options do not only work for cardboard, but in most cases almost as well for paper:

  • seal with wax
  • treat with alum
  • waterproof with shellac

Seal with wax

Katon can either be rubbed off with a commercial household candle or coated directly with liquid wax. Rubbing with a candle is only a small protection, since only a thin layer of wax is formed on the cardboard.

For immersion, melt wax (preferably in a suitable metal container) and then immerse the parts completely to form a continuous coating.

Treatment with liquid beeswax or similar products would be another option.

Treat with alum

An alum solution (see recipe below) can help to provide cardboard and paper with a waterproof coating. After immersion in the solution, the cardboard must dry sufficiently, but then it is well waterproof.

Be used:

  • alum
  • Gum arabic
  • natural glue

as main ingredients in the ratio of 4: 1: 2 (alum: gum arabic: glue). For 240 ml of alum you usually use 2 liters of water in which the ingredients are boiled. Many recommend that you also add grated castile soap (as much as glue). Mix all ingredients in hot water and then immerse the box in it.

Waterproof with shellac

A mixture of shellac and borax (in the ratio 5: 1) and water can also be used to produce a seal. Simply apply the heated solution (150 ml shellac in about half a liter of water) to the box and allow to dry.

Tips & Tricks

Sealing with wax is certainly the easiest way. Always make sure that each of these coatings protects the carton only superficially. However, if the humidity, soil moisture or other sources of moisture (steam) are particularly high, the carton can still absorb and swell water.

Video Board: Liquid Rubber Test #2 - Making a Waterproof Cardboard Box