How To Waterproof Cardboard

Cardboard is one of the most durable and versatile materials out there. It is lightweight, recyclable and reusable, which makes it the ideal material for a plethora of purposes.

Cardboard boxes (corrugated fiberboard) are best suited for shipping and transportation, and project construction. They’re available in a variety of thicknesses, and are pliable, yet have a high strength to weight ratio.

Paperboard, single ply cardboard, can be easily cut and formed, and is fairly strong, so it’s used a lot in packaging materials like cereal boxes, and also to make paper tubes. It is also used in high-quality graphic printing, such as magazine covers and postcards.

Our recommendations for waterproof coatings are suited to either type of cardboard.

How To Waterproof Cardboard

Why Should You Waterproof Your Cardboard?

Perhaps the biggest reason to waterproof cardboard is so that you can reuse it multiple times. While wet cardboard does dry out, it is never the same as before. Water weakens the paper fiber, which makes the cardboard brittle and crumbly. Waterproofing makes your cardboard long-lasting and sturdy.

Another reason to waterproof cardboard is to reduce the chances of mold growing. Wet cardboard, especially, is prone to mold growth, which not only poses severe health hazards, but also makes the cardboard unfit for recycling.

Since cardboard is mostly used for shipping and packaging, waterproofing it ensures that any harsh weather conditions will not harm the items inside. Waterproofing cardboard used in crafts and DIY’s is also essential to keep away the moisture.

How Should You Waterproof Cardboard?

The basic procedure for waterproofing cardboard is the same, regardless of the waterproofing medium used. It’s pretty easy and straightforward — at least 2 layers of waterproof coating are needed, and they must cover every corner and edge of the cardboard.

Remember: waterproofing doesn’t make the cardboard itself waterproof; it’s the coating applied which is waterproof. That’s why nothing should be left uncoated, otherwise the tiniest amount of water can ruin the entire cardboard.

There’s a wide variety of waterproof resins, paints, adhesives etc. available for your needs. But before we get into that, let’s see what precautions you must take before starting the waterproofing process.

Getting Ready for Waterproofing Cardboard

Make sure you’re following the proper safety precautions. Using gloves and goggles is an absolute must. Your workspace should be set-up properly as well: work in an isolated, well-ventilated space, and spread out some plastic or old newspapers to keep your cardboard on while working. Definitely read the instructions given on the waterproofing medium thoroughly, and proceed accordingly.

Now that that’s out of the way, let’s jump right into the many coatings available and start waterproofing!

1. Water-resistant Coatings

Krylon Acrylic Spray Paint


  • Moisture-resistant and smudge-proof.
  • Improves artwork and photo contrast.
  • Dries to the touch in 10 to 15 minutes. Dry to handle in 2 hours.

Polyurethane coating, transparent acrylic spray paints and lacquer sealer sprays are good choices to waterproof cardboard with. They’re widely available and easy to use. The Krylon Acrylic Spray Paint is a popular choice. It is a permanent, protective coating that is moisture-resistant, smudge-proof, and doesn’t yellow with age. Using it is fairly straightforward:

  • Shake the contents of the can well before using to mix the pigments. Remember to shake it periodically in-between the application process too.
  • Keep the can at a distance of at least 12 inches from the cardboard and parallel to it, and spray a thin layer all over the cardboard. Spray in a back and forth motion. Make sure to not miss any spots.
  • Once the first layer has dried off, apply another layer in the same way as before. Let this layer dry too before using.

2. Alum Mixture

 Anthony's Premium Alum Powder


  • Premium Granulated Alum Powder - Also known as Granulated Pickle Powder.
  • Ammonium Aluminum Sulfate - fruit and vegetable firming agent.
  • Granulated powder, perfect for adding to pickle brines to crispen, firm and keep the cucumbers fresh.

Homemade alum mixtures are quite convenient when it comes to waterproofing cardboard. You can paint the final mixture on with a brush or use a spray-gun for application:

  • Warm up a pot of water to start the mixture preparation. Pour 8 ounces of alum, 3 ounces of grated castile soap, and 4 ounces of natural glue and stir the solution until homogeneous. Make sure the water doesn’t start boiling. The mixture does take a while to get ready, so remain patient and keep stirring.
  • Once the mixture is ready, pour it into another container. Then spray or paint it onto the cardboard. A single, fine layer of this mixture is enough.

3. Shellac Solution

LKS Shellac Solution


  • Classical natural resin primer.
  • Decreases the absorbency of painting surfaces.
  • Composition: Leaf shellac, ethanol.

Shellac is a resinous product obtained from the female lac bug. While shellac solution is mostly used as lacquer for coating musical instruments, it can be used for waterproofing cardboard too:

  • Bring a pot of water to boil. In a different container, mix 5 ounces Shellac and 1 ounce borax. Pour the mixture in the boiling water and stir till the mixture is all even. Once it has cooled down, drain out the solution in a separate container via mesh/ cheesecloth/ muslin.
  • Brush the mixture directly onto the cardboard, or let it bathe in the mixture instead. Hang the board on a wire for drying.

4. Fiberglass Resin Coat

TRUE COMPOSITES Polyester Fiberglass Resin Coat


  • Reach cured quickly-4 hours minimum to 24 hours maximum, based on temperature!!
  • This DCPD-type resin dries tack free without the need for wax!!
  • Compatible with all types of fiberglass and coring materials, this polyester laminating resin is perfect for low-cost repairs, new construction parts, and vertical surfaces.

In addition to being water-resistant, many fiberglass resin coats are friendly with other gels and coats. Not only that, but they can also be applied on just about anything:

  • You’ll be needing an additional silicon mat for the cardboard to sit on, along with everything else. This is because the resin hardens after applying, and will not stick to silicon as much as other surfaces.
  • Mix the resin and catalyst (12 drops of catalyst per ounce of resin). Because this mixture takes approximately 15 minutes to set, it is recommended to start off with a smaller batch.
  • Apply the first layer properly and let it dry for 24 hours. Then brush on the second layer, and again let it dry for a day before touching the cardboard.

5. Paraffin Wax

Performa Paraffin Wax


  • Medical grade paraffin wax of the highest quality, evident in its extreme clarity in liquid form.
  • Bulk case of 6, 1 pound blocks of pure paraffin wax designed for use in heat therapy paraffin wax heat units.
  • Submerge hands, feet, and other joints in paraffin wax heater and remove, then wait for wax to solidify over skin.

While not as effective as the methods discussed above, laying paraffin wax on cardboard is one of the most popular waterproofing techniques:

  • In a double-boiler, pour out some water in the lower pot. In the top pot, place 8 ounces paraffin wax.
  • The double boiler pot should be set on a low heat setting. Keep stirring the wax all along until it is melted all the way through.
  • Using a brush or sponge, put a very thin layer of the melted wax on the cardboard. Let it dry. Once it’s dried, apply the second layer, and wait for that to dry before taking the cardboard for use.