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Last Updated: , Created: Saturday, December 16th, 2023

Wet Styrofoam -- will it dry out?


Wayland asked: “Does wet Owens Corning Formula Styrofoam ever dry out?”

Extruded polystyrene insulation is generally considered waterproof.  In fact it was first invented by Dow Chemical for the US army in WW I to provide unsinkable floating bridges -- and has been used as the flotation element of many decks ever since.  One day they discovered it was a good insulation.  So, if it is waterproof and unsinkable, how can it become full of water?

Cold water will not penetrate the closed cells of extruded polystyrene, called Styrofoam by Dow Chemical and other things by a number of other companies.  However, hot water vapour under pressure can slowly saturate insulation panels.  This most commonly happens when foam insulation panels are placed on top of flat roofs and then covered with paving stones to make roof top patios.  If the roof is not perfectly drained, that leaves some of the insulation sitting in a water puddle for a long period of time.  If the sun is very hot, that will cause the water to turn to vapour, sometimes even steam.  Trapped under the concrete paver, that can create the pressure needed to soak into the closed cells of the foam board. 

Will this saturated foam panel ever dry out?  It took exceptional pressure to get the water in, and there is no such driving force to get it out, so it can only dry out very slowly.  It must be left exposed to the wind to carry away the water in warm weather that will promote evaporation but protected from the UV light of the sun which will degrade the plastic.  It may take all summer or more to dry out a panel depending on how thick it is and how saturated it is. 

So, Yes you can recuperate it, but not quickly.  Saturated panels are usually considered a loss.

For more information click here for Extruded Polystyrene


Keywords: Decks, Moisture, Paving, Waterproof, Foam, Water, Insulation, Steam, Roof

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