While going over the crown molding in your house, you might have noticed little cracks here and there along the width of the molding, especially when it’s fresh after a season transition. These cracks are caused by a variety of reasons both within and outside of your control.
In this article, we’ll learn exactly why crown moldings crack along their width and what can be done about it.
What causes cracks in crown molding?
As far as the causes of cracks in crown molding is concerned, there are 4 big culprits. They include:
- Humidity Fluctuations
- Temperature fluctuations
- Building movement
- Impact
Let’s take them one after the other to understand how they cause cracks in crown moldings.
Humidity
When we’re talking about humidity, the crown molding material that comes to mind first is wood, because of the love affair it has with humidity.
Wood is hygroscopic in nature, meaning that it tends to absorb moisture from the atmosphere where it is kept.
Wood’s hygroscopic nature is the reason why it expands and shrinks with season, because as seasons change, the level of moisture in the atmosphere changes as well, and as wood likes to maintain moisture equilibrium, it would give off moisture as well as absorb equally from the surrounding.
Now the degree of expansion or shrinkage of wood would depend on the pattern of its wood grain. Each and every sawn lumber has a specific grain pattern that it comes with, and the most popular are the flat-sawn and cross grain.
In spring through summer and all the way to fall, you have moisture levels rise, which is when wood tends to absorb moisture from the surrounding in order to maintain equilibrium.
As a result, wood expands tangentially and radially to its grain which causes distortion of varying magnitude depending on the grain type of course, and also the length and depth of the wood in question.
During winter also, you have less humidity, which causes wood to give off moisture to the atmosphere to reach equilibrium. This results in an inward distortion tangentially and radially to the wood grain.
The degree of this inward distortion has a magnitude that depends on a variety of factors such as the length of the wood in question, the thickness of the wood and of course the grain pattern.
Temperature Fluctuations
Temperature fluctuation isn’t really that big of a deal when it comes to cracking of molding.
If there ever is a crown molding material that would crack due to temperature fluctuation, it will still have to be wood as the rest of the materials are pretty stable during temperature changes, although polyurethane may expand or contract to reveal seams and gaps but never really crack.
Temperature fluctuation as a cause for crack on moldings happens when you have a quick change in temperature from hot to cold and vice versa in quick succession. This induces strain in the wood that causes it to crack along the width.
Building movement
There are a variety of ways in which building movement can happen. And by building movement, we mean the movement of the structures that make up a building from the beams, to the ceiling trusses, the walls, the flooring, the ceiling etc.
One of the very popular ways is through pressure, a.k.a extra weight. When you have pressure applied to a certain structure of the house, for instance the roofing, this pressure or additional weight will seek to be distributed for achieving balance, otherwise the structure alone would not be able to handle it.
So there would be weight distribution to other structures that are directly connected to the roof, and these too will distribute the weight to the materials that are directly connected to them in order to maintain the original balance.
Let’s see a clean sequence of how this can work in a real world situation, and possibly cause a shift or even crack in a crown molding.
So when you have pressure in the form of snow during winter applied on the rooftop, the extra weight on the roof will be distributed throughout the entire structure.
So the beams will be affected and the ceiling trusses would also be affected, then the ceiling connected to the trusses would move a little, then the moldings connected to the ceilings would move as well, and if strained in some way, would likely crack.
Let’s take the case of an expanding or contracting beam due to temperature change. The walls the beam is connected to would move as a result of the expansion or contraction of the beam which would increase the risks of cracking of the crown molding attached to the walls.
The same thing with the floor. As it is connected to the walls, when it sags, the walls too would move a bit, and then the crown on the walls would shift or possibly crack as a result.
So there are different ways that a building can move and this movement would cause the crown molding on the walls to crack or develop seams and gaps.
Impact
And then of course, the last way in which crown moldings can crack is when you actually have an impact force on them, either directly or indirectly.
Maybe when you’re trying to fix something using a hammer from the other side of the wall, or you accidentally throw a solid object directly on the molding. You can have a quick line of crack develop in that way especially if the crown molding is any other than wood.
Can you prevent crown molding from cracking?
Preventing cracks as a result of Impact
Impact can be the result of an accident, and accidents aren’t in our control, so the best advice would be to simply go carefully and be gentle whenever you’re performing repairs that involve working around the areas where crown molding is installed.
Preventing cracks as a result of temperature and humidity
It is established that a rapid change in temperature, consistently, can cause cracks to develop on crown molding, and so a way to tackle this problem is to try and maintain a consistent interior temperature all the time.
You can do this through regulatory devices and structures such as the air conditioner, the windows, the home heater etc. Always try to maintain a moderate temperature using these devices.
For humidity, when transitioning from one season to another, maintain a stable climate inside using an air conditioner or a humidifier and dehumidifier. Try to maintain a humidity between 25 – 55% year round.
Preventing cracks due to building movement
For building movement, there really isn’t anything you can do to stop it. Just make sure your crown molding is made from the best quality of wood out there ( if you’re not using polyurethane or any other type of molding material), is acclimated to the home before installation and is installed properly.
How do you fix cracking molds?
You have two options when it comes to fixing a cracking mold, the first option is to replace the mold with a new one, which, depending on your budget and the type of mold in question, might be a very expensive, or, to fill up the crack using a flexible caulk.
The latter is recommended because it is cost effective, very simple to do, and it delivers really great results that lasts.
In order to caulk properly, you need to make sure you lay your hands on the right product.
Choose a premium caulk that is flexible and can expand and contract without cracking. This way, the caulk filling won’t crack along the way when the wood experiences pressure through the many factors that cause pressure on it.
A perfect product to use is the Dap DYNAFLEX 230 Premium Elastomeric Sealant made of silicone.
The product is waterproof and weatherproof, and is also paintable in 2 hours.
To use, simply apply it to the surface of a 2 inch or less than 2 inch crack to fill it up, then remove excess caulk using a rag and allow it to sit for about 2 hours. Paint over using acrylic or latex based paint and your crown molding should be as good as new.
Can crown molding be replaced?
Absolutely, if you have a crown molding that has been damaged beyond repair, you can remove and replace it with a new one.
If it’s wood, then all you need to do is cut around the seam with a knife and then use a prying tool to gently lift the wood away from the surface of the ceiling and wall. Then replace it with a perfectly cut piece and you’re good to go.
For other types of crown molding, removing it in its entirety might not be possible, and you might have to destroy it with a hammer and then replace it with a new one.
Why does crown molding caulk crack?
Crown molding caulk would crack because there is pressure applied to it from the crown molding whoch also has pressure applied to it through temperature fluctuations, humidity, building movement as well as direct impact.
If the caulk isn’t built flexible in the first place, then the likelihood of a crack is increased, but if the sealant is built flexible like the Big Stretch or DAP Dynoflex 230, then the likelihood of a crack is reduced.