Paula asked me a question about shrinkage cracks affecting her new deck. She sent me three photos showing all sorts of cracks in the handrails, railing posts, and deck. The cracks were in brand new sealed lumber that was installed in April 2023. The lumber has not been sealed since the day it was installed.

Paula asked, “I wonder if this will become a problem soon.”

I would say it’s almost over. The wood now has deep cracks. Rainwater can penetrate the wood through these cracks. This water causes the wood to swell. Every time the sun comes out or the wind blows, the water leaves the wood and causes it to shrink again. These swelling/shrinking cycles cause the cracks to get bigger and bigger.

This isn’t the best comparison, but do you know the Centennial Light? It’s maintained by the Livermore-Pleasanton Fire Department in California. The bulb was first turned on in 1901 and is still burning today, after being turned off briefly a few times to move it to another location.

Imagine if the manufacturers of treated lumber put a small plastic label on every piece of treated lumber with care instructions. The label would tell you to seal the lumber as soon as possible after installation. It would also inform you that if the lumber remains sealed, it will last for many decades, much like a lightbulb.

One can speculate as to why this label is not attached to the wood. The cynic in me screams that the lumber industry is not overly upset when their lumber cracks, warps and buckles. This way, more new treated lumber could be purchased more quickly. I have no evidence whatsoever that this is their motivation, but something similar has happened in the asphalt shingle industry. I describe this in my book, Roofing Ripoff.

Water with dissolved copper is injected into the wood under pressure when it is converted from regular wood to treated wood. This causes the wood to swell. The wood will crack if the water leaves the wood too quickly. Sealers allow the water to be released slowly and evenly. Cracks are minimized or eliminated. Applying the sealer just a few weeks after the treated wood has been exposed to the sun and wind will keep it looking like new.

Shrinkage is common in many building materials. It happened to me in the last 10 days. I applied asphalt sealer to a small patch of cold asphalt. There was a small 6mm deep depression in the patch. The water-based asphalt sealer was applied too thickly in that spot. Two days later, that spot was full of shrinkage cracks.

Loss of water in concrete causes shrinkage. Shrinkage creates stresses or tensile forces in the concrete. If you don’t get the concrete to crack, you will create irregular cracks in the concrete that will release that stress.

Concrete shrinks 1/16 inch for every 10 linear feet you pour. Experienced concrete masons know how to cut expansion joints in new concrete. The depth of these cut lines should be at least 1/4 the thickness of the slab. The cut lines do the same thing as when you crease a piece of paper with your fingernail. The crease tears microscopic fibers in the paper. If you gently pull the paper apart, it will come apart at the crease line.

Cracks in walls, woodwork, kitchen backsplashes and tile joints in new homes can all be attributed to shrinkage caused by water loss. Seasonal cracks in plaster and trim are caused by water loss. Squeaky wood floors that mysteriously stop or start squeaking are also victims of water-related swelling or shrinkage.

In most cases, shrinkage cracks can be minimized or eliminated. The installation instructions for the product must be followed exactly. Pay attention to the wording regarding minimum and maximum temperature ranges.

You may be in the same situation as Paula. Your exterior wood is cracked and water is soaking into the wood as quickly as it would into a sponge. I suggest you fill the cracks with an exterior filler. Do a test and find one that is as close to the color of the wood as possible.

Seal or stain the filler once it is smooth and dry, coating all of the wood at once. Apply the sealer at least every two years or when you notice that water is not beading up on the wood.

You should spend some time on my website www.AsktheBuilder.com. Learn more about shrinkage cracks in concrete. All of my previous columns and many answered emails are summarized on my website. You can save money and time by learning about topics before you even think about hiring a contractor.

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