Things You'll Need
White craft glue or white wood glue
Acrylic elastomeric roof coating
Weatherproofing your cardboard is a useful way of saving money and being green. Instead of buying wood or plastic signs, for example, you can make your own cardboard sign and weatherproof it. You can recycle by using leftover cardboard in moving boxes or cereal boxes, for example. The methods protect well from the Sun, temperature and friction. However, It is unlikely however that any method of weatherproofing will completely keep it safe from water. You should keep an eye on the cardboard to make sure no water has leaked in over time.
Use a paint brush to coatthe front and back of the cardboard with the glue. Wait for the glue to dry.
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Coat the cardboard with a layer of acrylic elastomeric roof coating. Wait for the paint to dry.
Apply a third coat on the cardboard, this time using a varnish. Wait for the varnish to dry. The result will be a glossy, fiberglass look that will protect your cardboard from weather damage.
Buy two low-density polyethylene films slightly larger than the dimensions of your cardboard piece. They can be found at a hardware store.
Spray or paint the cardboard with acrylic elastomeric roof coating. There are many brands available on the market.
Laminate the cardboard using the polyethylene films, one side at a time. Cut off any excess film. This will weatherproof your cardboard for the most part, but keep checking for any moisture leaks.
Do not use tape to weatherproof the cardboard because you risk altering the shape of the cardboard.