How To Waterproof Cardboard: 8 Methods

If the delivery man has ever left your parcel outside in the rain you will be well aware of just how useless cardboard is at dealing with damp.

how to waterproof a cardboard box

Cardboard boxes quickly absorb moisture, once this happens the box will lose all its structural strength and often falls apart in your hands.

Thankfully there are plenty of ways that you can ensure your parcel won’t experience the same fate.

Here are 8 methods you can use to waterproof any cardboard:

1. PVA Glue

PVA glue is surprisingly water-resistant so coating your boxes in it can help them survive being left out in the rain for a few hours.

use pva glue for waterproofing cardboard

Be aware PVA isn’t fully waterproof so your box probably won’t survive for days if it’s left in a puddle however it should be able to endure a brief rainstorm or persistent shower with far more success than a non-waterproofed cardboard box.

To waterproof your cardboard using PVA follow these steps:

  1. Mix 1 part PVA with 1 part water.
  2. Use a paint brush or roller to apply the mix to your box.
  3. Leave to dry for at least 2 hours before checking if it is dry.
  4. Apply a second coat.
  5. Leave to dry for at least two more hours.
  6. Make a final mix of 2 parts PVA and 1 part water.
  7. Apply the mix to the cardboard.
  8. Let it dry for a couple of hours.
  9. Check it is dry and your cardboard box is ready.

This method is also routinely used to make paper waterproof.

2. Plastic Bags/Sheets

This is the easiest and most cost-effective method of waterproofing a cardboard box.

plastic bags can be used to waterproof a box

You simply need to find a couple of plastic bags or a plastic sheet that is big enough to fit your box inside or wrap it in.

Double bag the box to protect it in case the outer bag gets ripped.

Then seal up the bag opening using a waterproof tape such as gorilla tape or flex tape.

If you don’t have any waterproof tape to hand don’t worry, standard duct tape or packing tape should be sufficient to keep the bags closed providing you wrap tightly around the bag opening.

3. Liquid Shellac

Shellac is a natural waterproof resin that is deposited on trees by the lac bug, it has been called a ‘natural plastic’.

Shellac is harvested and sold both as dry flakes and liquid shellac.

Liquid shellac can be used to waterproof cardboard, once applied it will quickly harden into a stylish waterproof finish.

All you need to do is:

  • Buy a tin of liquid shellac.
  • Open the tin and stir it.
  • Use a paintbrush to apply it to your cardboard.
  • Give it two or three coats for greater durability.

4. Fiberglass Resin

Fiberglass is 100% waterproof (they make boats with it) so the resin used to make fiberglass will definitely help waterproof your cardboard.

fiberglass resin

To waterproof your cardboard using fiberglass resin follow these steps:

  1. Buy a jug of polyester/fiberglass resin.
  2. Find a well-ventilated place (outdoors or in a garage is ideal).
  3. Place a protective sheet down and wear gloves, goggles and a mask to prevent fume inhalation.
  4. Your resin should come with a catalyst that will activate the resin causing it to harden, mix the resin with the catalyst – pay attention to the manufacturer’s instructions and mix at the correct ratio.
  5. Paint the resin mix onto the cardboard.
  6. Leave to dry for 24 hours.
  7. Apply a second coat.
  8. Leave to dry again for 24 hours.

5. Waterproof Tape

Wrapping your entire box in waterproof tape is a simple (albeit somewhat fiddly) way of waterproofing cardboard.

Ideally you should use a fully waterproof tape such as Gorilla tape or Flex tape, however you can use standard tapes such as masking tape.

is gorilla tape waterproof

Masking tape will not fully waterproof your box as the adhesive is likely to become loose if any moisture gets to it however using masking tape will still make your box far more resistant to rain than it would be without any tape at all.

To waterproof a cardboard box using tape follow these steps:

  1. Get enough tape to cover your entire box (better to get too much than too little).
  2. Enlist the help of a friend.
  3. Stick the end of the tape in the middle of the box.
  4. One person should feed the tape to the box and prevent it from getting tangled up..
  5. ..while the other person spins the box carefully around ensuring the the tape covers every inch of cardboard.

6. Paraffin Wax

Paraffin wax is the same stuff that many candles are made from.

Coating cardboard in these type of wax will seal it up and make it completely waterproof.

We recommend you only use this method on small boxes.

To waterproof a cardboard box using paraffin wax follow these steps:

  1. Prepare an area with sheets or old newspaper.
  2. Get a double boiler and fill the bottom boiler with hot water.
  3. Place wax flakes in the top boiler.
  4. Place the boiler pot over a flame to get it hot enough to melt the wax.
  5. Stir until all the wax is melted.
  6. Use a brush to paint the cardboard with the melted wax.

7. Waterproof Paint

Oil-based paints are water repellent meaning they are perfect for keeping a box dry.

The good thing about using paint on a box is that you can decorate it with any color you like.

Make sure that the paint is oil-based not water-based as water-based paints are more vulnerable to water.

Be aware the cardboard must be completely dry before painting it as any damp on the cardboard will repel the oil-based paint meaning it won’t adhere to the cardboard.

To waterproof your cardboard using waterproof paint take these steps:

  • Find a well-ventilated area.
  • Apply the paint.
  • Leave at least 6 hours to dry.

8. Rubber Cement

Rubber cement is an adhesive made from elastic polymers.

A well known waterproof rubber cement is Plasti Dip.

It is super effective at waterproofing things and easy to apply with many rubber cement types coming as a spray:

  1. Find a well-ventilated area (the fumes can be dangerous).
  2. Lay a sheet or newspaper down to protect the floor.
  3. Spray the box generously until it is completely covered.
  4. Leave to dry for at least two hours.

Also Read:

How To Waterproof Cardboard With Duct Tape
How To Waterproof Paper Mache
Is Contact Paper Waterproof?

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