How to Harden Cardboard? Different Process With Steps

How to Care for Venus Fly Trap CareWith cardboard, you can do many manual jobs for school and home. Also, it is much cheaper than wood or metal. However, cardboard is not hard enough to support weight or serve as a foundation. The good news is that this can be fixed, as there are various techniques to strengthen and harden cardboard. Do you like to make crafts or home furnishings with recyclable materials like cardboard? Here, we tell you how to harden cardboard quickly and easily so that you can use it in all your projects and give it all possible uses. To work!

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How to harden cardboard?

There are different ways to stiffen the craft board, make it stronger, and give it a strong, long-lasting texture. In this case, the trick is to make a paste from a putty-like the ones used to patch or fix the walls, although you can also prepare a homemade paste by following the steps in our article Prepare paste at home.

how to harden cardboard

Needed materials

  • Putty to cover wall holes.
  • White glue.
  • Water.
  • Small round-tipped brush for blending.
  • Small flat tip brush for painting surfaces.
  • Small bowl or container.
  • Plastic or metal spoon.


  1. Put on gloves, so you don’t stain your hands.
  2. Take a tablespoon of the putty and put it in the bowl.
  3. Add a tablespoon of water to dissolve the putty.
  4. Add a stream of white rubber to the mixture to cover the other ingredients.
  5. Mix all the components very well with the round brush.
  6. Add another tablespoon of each ingredient and continue mixing with the round brush.
  7. When the mixture is homogeneous and well dissolved, it is ready to harden the cardboard.
  8. Clean the surface of the cardboard very well with a cloth.
  9. Take the flat brush and soak it with the prepared mixture in the bowl.
  10. Paint the cardboard until it covers the entire surface to be hardened.
  11. Wait a few hours for the mixture to dry. Ready! You will have your cardboard hardened.

How to stiffen cardboard with glue and newspaper?

For all these techniques, you must always work on a table that you can get dirty and that you place a newspaper or plastic so as not to stain the table or the floor. Next, we will show you how to apply the letterhead technique to harden the cardboard correctly:


  • Newspaper clippings.
  • Glue or white glue.
  • Water.
  • White acrylic or rubber paint.
  • Small flat tip brush.
  • Small round tip brush.
  • Small bowl or cup.


  1. Put on gloves and clean the cardboard piece well with a dry cloth.
  2. Put the glue in a small bowl and add water in equal proportion. Blend well with the round tip brush.
  3. Make small cuts of the paper by hand; that is, the cuts are not uniform.
  4. Take the round tip brush and spread it over with glue.
  5. Grease the cardboard with the glue and stick pieces of paper over the gummed area until you cover the entire surface. The idea is that the paper is superimposed on one another to give the cardboard more resistance and toughness.
  6. Let dry for a few moments and re-gum the first layer of paper, place a new layer over the entire surface. Impregnate the cardboard with at least three layers of cardboard for sturdy, hard cardboard.
  7. Let dry for 12 hours.
  8. Optionally, you can give the cardboard a cleaner finish that allows you to use it in the project you want. Brush a flat brush with white paint, paint the cardboard evenly, and let it dry. So you will know how to paint cardboard without bending.

How to harden cardboard with resin?

The reinforced resins have become an ally in the construction and repair of objects in DIY. They are perfect for stiffening cardboard but are a bit more expensive than the aforementioned methods.


  • Polyester resin.
  • Catalyst.
  • Fiberglass blankets or fabric.
  • Safety glasses and mask.
  • Scissors.
  • Cup or bowl.
  • Small flat tip brush.
  • Wooden stick to beat the mixture.


  1. Put on your goggles, mask, and gloves.
  2. Cut the mesh or fabric to the size of the cardboard.
  3. Mix the polyester resin and catalyst in the mug, following the manufacturer’s instructions.
  4. Mix very well with a wooden stick.
  5. Impregnate the brush with this mixture and pass it very well over the entire surface of the cardboard.
  6. Lay the fiberglass mesh on top of the cardboard to adhere to the cardboard.
  7. Run another coat of the mixture over the mesh to remove air bubbles.
  8. Wait for the polyester to dry.
  9. Finally, go over a coat of white paint to use hardened cardboard in any craft or project.

How to harden plasterboard?

This particular technique will give you a strong and durable surface, as it combines different elements with hardening qualities. These properties are enhanced when mixed and result in tough and strong cardboard.

how to harden cardboard

  1. Put on your gloves.
  2. Pour hot water into a bowl halfway.
  3. Remove the cardboard cylinder from the toilet paper roll.
  4. Put the toilet paper in the bowl of hot water and begin to shred it by hand. Make sure the paper is completely shredded inside the container.
  5. Squeeze the paper with your hand to remove all the water it has absorbed. You can also place it in a cloth strainer to squeeze it.
  6. Place the paper pulp in a container and add about half its weight in plaster.
  7. Add white glue until it covers these two components very well.
  8. Begin to stir this mixture with the plastic spatula until it has the consistency of pasta.
  9. Add a little hot water and white glue to decrease its density.
  10. Clean the surface of the cardboard with a microfiber or cotton cloth.
  11. Take a flat brush and brush it with this mixture.
  12. Paint the entire surface of the cardboard and wait for it to dry.
  13. Pass a second coat of this preparation with the brush and wait for it to dry. Ready! With this procedure, the cardboard will become hard.

How to harden cardboard with plaster?

This technique to harden cardboard is easy to prepare and apply, but it will take at least a day to wait for the mixture to take effect. Therefore, we recommend that you be patient and use it if you have plenty of time to prepare your project.

  1. Put on your gloves.
  2. Clean the surface of the cardboard with a microfiber or cotton cloth.
  3. Put water in a container.
  4. Cut the plaster to the size of the cardboard.
  5. Soak the plaster strip in water and place it on the cardboard.
  6. Lay more strips of plaster overlapping each other until you completely cover the surface of the cardboard. Let it dry. If you want to get fairly stiff cardboard, you should put at least three plaster layers and let it dry for at least a day.
  7. Soak the brush in white paint and paint the entire surface of the cardboard and let it dry. After this process, the cardboard will be completely hard.

How to harden cardboard with sawdust?

Sawdust is a natural product obtained in hardware stores or carpentry shops at a very low cost since they are nothing more than the wood shavings that come off the material when it is worked. In addition, it is an excellent material to give strength to other objects such as cardboard. To achieve this in a very practical way, follow these steps.

  1. Place the wood sawdust in the cup or bowl.
  2. Pour in hot water and mix with the spatula.
  3. Strain the sawdust to remove the water.
  4. Place this sawdust paste in the container and add white paint little by little, mixing with the spatula until it becomes a soft white paste.
  5. Add the white glue and start mixing with the plastic spatula.
  6. When you have a homogeneous mixture, add a little more glue to reduce this mixture’s density a bit.
  7. Clean the surface of the cardboard with a microfiber or cotton cloth.
  8. Take a flat-tipped brush and paint the piece of cardboard with this preparation. Let it dry.
  9. Brush another coat of the mixture with the flat brush. Let dry overnight to get completely hard cardboard.