One question we get asked quite often on DIY forums is whether MDF and water mix. While MDF is not water resistant, it is highly pliable, and can be painted. A waterproof MDF finish can be achieved by sealing the wood with a moisture-resistant sealant or varnish. While water-based polyurethanes are not a good choice for MDF, they can be used in certain circumstances. Make sure to choose paint that is 100% waterproof. While waterproofing protects your MDF surface from water, it does not provide protection against prolonged immersion in water.
Water does not damage standard MDF. While it does absorb liquid, sitting it in water will cause it to swell and warp. The good news is that you can still repair a wet MDF finish. The best way to do this is to remove the MDF from the water source as soon as possible. Depending on the weather, you can use the sun to dry the MDF. If it rains, move it indoors.
After you’ve dried your MDF, you can apply a waterproof paint. This can be a lacquer, varnish, or a stain. Make sure to apply the paint to the MDF surface from one side. Apply it to all four edges of the surface. Once dry, paint the MDF. The finish is not waterproof if it doesn’t have a sealant. This sealant will not help with water absorption.