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.

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

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:

2. Alum Mixture

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:

3. Shellac Solution

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:

4. Fiberglass Resin Coat

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:

5. Paraffin Wax

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