Below are methods that people have used to make cardboard solar cookers waterproof :
Wax applied during cardboard manufacturing
Cardboard manufacturers can foil one side of the cardboard and treat the other side with a wax-like waterproof coating during fabrication.
Tape any open edges with a waterproof tape. Then paint the cooker on the outside using latex paint.
Wheatpaste and beeswax
A cardboard cooker can be made water-proof using glue and wax (beeswax or candle wax):
- Cover the outside of the cooker with pieces of cloth that have been dipped in white glue or wheatpaste. Make sure the cloth adheres everywhere, applying extra glue to the loose spots. Allow to dry completely.
- For an alternative method that is much less messy and results in a smoother, better appearance, coat the relevant cooker surface with a thick but not dripping layer of white glue (a sponge brush works very well for this). Lay the fabric on the glue and smooth with a pad of paper towel. When fabric is lined up and smoothed out satisfactorily, use the sponge brush to completely cover the fabric with a generous amount of glue, making sure that the fabric is completely saturated with glue. Another layer of glue can be added once the first layer is dry, if it seems to need it.
- Rub a generous amount of wax over the entire cloth surface paying special attention to the seams.
- Heat the cooker near a fire or inside a larger solar cooker or other oven until the wax melts into the cloth. If the weather is warm and sunny, a parked car can also be used to melt the wax into the cloth.
- Repeat steps two and three until you are sure that beeswax has saturated the cloth completely. This process also strengthens a cardboard cooker to a significant degree. Testing is needed to see how these materials hold up over time.