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How to waterproof styrofoam to create a shelter for feral cats?


My 80-year-old mother spends a lot of her energy fretting about the feral cats she has been caring for (including medical care such as neutering and immunizations). I've been "building" a shelter for them out of a large styrofoam box, with a thick, sturdy lid, that originally was used to ship delicious barbecued ribs packed in dry ice. So far I've carved out a circular door (with optional thick plastic flap-door), 2 windows made of plastic bowls formerly used to hold fruit salads in the grocery store (held in place with duct tape and insulated with soft foam), and I've lined the inside with soft foam and moving blankets. I've concocted an A-frame roof/tent out of tarp to direct water down to the ground, rather than have it pool on the box's flat surface. It will be sitting on a tarp-covered above-ground base. BUT--if I can't find a reliable way to waterproof the styrofoam, I think I should cover the entire shelter with a close-fitting plastic surface (like tarp).

To add to my confusion, I read on another website that styrofoam is already waterproof, without a sealant.

What do you think?

Rosa Elias
hobbyist - Valencia, California, USA


Yes, styrofoam is waterproof - think vending machine coffee cups. It will, however, be damaged by sunlight. A simple covering of black plastic will stop that.

jeffrey holmes
Jeffrey Holmes, CEF
      South Carolina

June 7, 2008

We made a hot tub lid and put styrofoam inside a marine vinyl cover with only an opening inside against the hot tub, the styrofoam absorbed water to an enormous weight from inside.

Then we painted it, a new piece, it still seemed to absorb water and then cracked.

Do you have any suggestions?


Alyce Mintz
- Ontario, Canada

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