During hot humid weather wood flooring will, Expand or Swell during summer months and Contract or Shrink during dry winter season allowing cracks to appear in the wood flooring.
This is constant and forever happening to wood flooring. The wood floor could be 100 years old and the process of gaining moisture and losing moisture continues from season to season.
Owners of wood flooring whether it be soft or hardwood floors need to understand that wood flooring will last them for years and it is an investment for them. Cracks/Gaps in wood floors will always be visible unless some form of humidification is installed during the winter. Use either a humidifier on the furnace or portable ones that you fill. Opening of windows or allowing moisture to escape from the dishwasher or laundry room during the winter months. We should also know that stained wood flooring will also play a big role in seeing cracks or gaps in wood flooring. Light wood stains, white stains, and white wash stains, taupe colored stains, even natural maple floors will show gaps and cracks more prevalent than darker colored stains applied to wood flooring.
Wood Strip Flooring say on 2″ wide can shrink (lose moisture) up to 1/32″ or more. Wider Plank Flooring can shrink up to ,1/4″. Most of these gaps/cracks will close up again once the heating season ends and the summer time begins to expand the flooring. Remember MOST gaps/cracks will close up. You are the owner of the flooring so it is up to you and how you look after this investment which will determine its overall appearance. Either do something or not, it’s your floor. This does not mean that everything will go back to its original state. We are talking about natural wood fibers, not something that is man made.
We talked about wood losing moisture during the winter months. Now let’s talk about wood gaining moisture during the summer months.
Cupping of wood boards is when the edges of the individual boards are higher than the center of the board and occurs across the width of the board. This gives a washboard effect on the flooring. The cause is high humidity readings, excessive moisture from sub-floors, improperly maintained wood flooring (washing your floor with water), plumbing leaks, drainage problems, your ice-maker, and so on. However, usually the problem comes from high humidity. When wood expands excessively each board compresses against one another causing the edges of the boards to push upwards, deforming the boards. You need to investigate the problem and resolve the moisture issue before further damage to your wood flooring is not repairable.
Excess Moisture can be removed by adding heat at 80 deg. F. Moving air across the wood flooring with fans, operating your furnace fans to circulate air, purchase a dehumidifier, opening windows during evening hours during low humidity levels. If cupping is seen and caught on time the floor just might stabilize and cure it’s self. One thing to understand is DO NOT re-sand your wood floors until the problem is identified and fixed. If flooring is sanded before the floors moisture returns to normal, it will cause what they call reverse cupping or Crowning of the wood floor.
Reverse Cupping or Crowning is when the center of the board is higher than the edges. This is Opposite to Cupping. In a cupped floor the edges are higher than the center of the board because of the compression between the boards during expansion. If the edges are sanded prematurely, the floor when sanded looks flat, but as the floor dries the edges subside back to its original position.
NOTE THIS: From the NWFA, National Wood Flooring Association. It should be noted that some slight cupping and crowning may occur naturally, and should be tolerated: The bark side of lumber shrinks and swell more than the side closet to the center of the tree. Largely seasonal in occurrence, it’s common in wider planks. Its appearance can be minimized by using beveled-edge flooring products with a satin finish, rather than square-edge flooring with a high gloss finish.