Cultured marble is a man-made product produced from a mixture of marble dust and resins. The liquid mixture is poured into molds, which harden into countertops or shower panels. While cultured marble is a fairly durable product, it can warp under some conditions. Many counters may warp very slightly while a few may warp more severely. Understanding what may be causing the counter to warp can help you take precautions to correct it.
One of the biggest causes of warping in cultured marble is incorrect storage before installation. The vanity top must be laid perfectly flat during transport from the factory while being stored prior to installation and during installation. Standing the counter on one end and leaning it toward a wall for any length of time may cause minor warping of the top, which can be further exasperated once it occurs because the top is now out of level with the vanity. This type of minor warping can be treated by placing the vanity top on a flat surface and heating it gently with a heat gun until it relaxes.
Just as heat can relax a warped top, it can also warp the top. Extremely hot water, hot appliances left on the vanity top, hot hair dryers aimed at the top and heat sources like radiators or registers that are installed too close to the vanity can all cause the vanity top to warp over time. Check the use of the vanity for excessive heat. Examine the hot water heater to see what setting it is on, and lower it if it is in excess of 160 degrees F. Minor warping can be heated out gently with a heat gun; otherwise stopping the heat source from affecting the top will halt the problem.
Direct sunlight will warp a cultured marble vanity top. If there is a bathroom window that exposes the top to sunlight for a portion of every day, over time the vanity top will warp. Cover any windows with shades or curtains during the time of day that the vanity top is exposed to sunlight. Store any unused tops in a dark area, away from direct sunlight to prevent warping between installations or prior to installation. A top warped prior to installation can be gently heated once installed to remove any minor warping.
Cultured marble can warp due to excessive weight. If heavy items have been stored on the vanity, particularly in the sink area, which is both unsupported from below and attached to heavy metal pipes, it can cause strain on the resins, causing the vanity to warp. Do not store objects on top of the vanity or in the sink for extended periods. Verify that the vanity is supporting the top evenly from below; if there is not adequate support from the cabinet, even moderate weight from above could cause the top to warp slightly downward.