Top 4 Moisture Sources That Ruin Resin Castings

Top 4 Moisture Sources That Ruin Your Resin Castings

Humidity is water vapor in the air. While it can make your skin feel nice it can foam or bubble urethane castings. CO2 is formed when polyurethane resin is exposed to water or humidity resulting in bubbles or foam in your parts. Even when vacuumed and pressure casted once the resin is contaminated bubbles can keep forming.

The 4 most common sources of contamination to urethane resin are:poly purge nitrogen air blanket

1. Humidity In The Air Is Enough– Check the weather 50% relative humidity or less is best for using and storing Magikast and other polyurethane resins.

2. Opening And Sealing Containers– Humidity in the air will get trapped in your container as you seal it. The next time you use it you may think it has gone bad. It’s the moisture that was trapped when you shut the container. Use RAW Material Suppliers Dry Gas Blanket every time you close a container to greatly extend the life of your unused resin. The dry gas is heavier than air so it sits on the resin separating and protecting it from the moist air. Just a quick squirt is all that is needed.magikast fast casting resin

3. Fillers Need To Be Dry– Magikast and other resins can take a lot of filler for effects. Some fillers should be baked in an oven to drive off the moisture.

4. Paper And Wood Accessories- These can retain moisture and cause bubbles in your castings. These should be replaced with metal or plastic buckets and mixing sticks. Silicone molds are the best for urethane castings.


New Orleans, Louisiana 75.9
Jacksonville, Florida 75.8
Houston, Texas 74.7
Orlando, Florida 74.1
Tampa, Florida 74.1
San Francisco, California 73.7
Seattle, Washington 73.3
Miami, Florida 73.2
Portland, Oregon 73.2
Rochester, New York 72.6


Houston, Texas 89.7 6 am
Jacksonville, Florida 89.2 4 am
Orlando, Florida 89.0 4 am
New Orleans, Louisiana 87.6 6 am
Tampa, Florida 87.5 7 am
Portland, Oregon 84.8 4 am
Raleigh, North Carolina 84.6 7 am
Nashville, Tennessee 84.1 6 am
Birmingham, Alabama 84.1 6 am
Miami, Florida 83.9 7 am


Milwaukee, Wisconsin 62.8 3 pm
Buffalo, New York 62.4 4 pm
Seattle, Washington 61.7 4 pm
Rochester, New York 61.0 4 pm
Cleveland, Ohio 61.0 4 pm
New Orleans, Louisana 60.7 3 pm
Miami, Florida 60.5 1 pm
San Francisco, California 59.4 1 pm
Los Angeles, California 58.7 1 pm
Portland, Oregon 58.6 4 pm

Detroit gets an honorable mention because I am from there and know how humid it can be. The relative humidity typically ranges from 40% (comfortable) to 95% (very humid) over the course of the year, rarely dropping below 25% (dry) and reaching as high as 100% (very humid).

For more information contact RAW Material Suppliers technical help at 877-

RTV-MOLD (788-6653) or via e-mail at

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