By Tony Morgan
Homeowners and commercial real estate developers love wood’s long-lasting beauty. Wood blends in with most types of décor and is easy to clean and maintain. It’s environmentally safe, does not trap dust mites that can affect your indoor air quality, and it is comparable in price to other types of flooring such as stone, tile and quality carpet.
However, the natural structure of wood – which looks appealing on the outside – is also what can cause problems from the inside. It all has to do with the relationship between wood and moisture. This is why water popping is such a vital, yet risky task when installing wood flooring.
What is Water Popping?
Also called “grain popping” or “raising the grain”, water popping is a process that opens the grain in wood flooring; it involves adding water to the wood before you stain and finish it.
The Science Underlying Wood and Moisture
Wood is a hygroscopic material; it contains numerous cells that absorb water. In the tree, these cells fit together in groups of thin vertical passages like pipes. The cell wall contains a small amount of moisture, whereas the “hollow” part of the inner cell has room to hold and release moisture. The purpose of these cells and pipes is to collect and transfer water and nutrients from the roots of the tree to other parts.
After a tree is cut down, the green lumber is very moist, so the lumber must be kiln-dried to remove the excess moisture and make it ready for manufacturing.
However, the structure of the cells in the wood remains the same as before the tree was cut. Even long after cutting the tree, the cells in the wood absorb and release moisture from the environment. This moisture can be from relative humidity in the air, groundwater or water leaking from faulty plumbing.
As the humidity in a room goes up or down, the wood absorbs or releases moisture. This is a continuous exchange, even after you finish your flooring project.
Wood Moisture and Why You Need Water Popping
A wood flooring manufacturer buys kiln-dried lumber and cuts it down to size. Then, the lumber must be sanded down – often through several passes. During this process, the hardwood goes from being coarse to becoming fine and extremely smooth.
The sanding process closes the natural grain of the wood so the wood is no longer porous enough to accept stain. That’s because the tiny wood particles and sawdust get stuck inside some of the pores.
The sanding process begins with a coarse, low grit paper to flatten and clean the wood, then progressively finer grit sandpaper is applied to smooth the surface even more. Finer grits tighten the grain fibers, making the wood denser and less porous and penetrable.
The result is that the stain is not absorbed deeply into the wood, and most of the stain will be removed when wiped with a cloth.
Benefits of Water Popping
When water is added to the wood before staining it re-opens the pores in the grain. It makes hardwood floors porous again so that hardwood flooring can be properly stained and finished.
This process has many benefits.
- It allows the satin to be applied more evenly across the floor
- It raises the wood fibers so the stain goes deep in the wood for a nice finish
- It helps create a professional look and feel without any sanding marks
- It makes the color stand out
It is important to use a precise quantity of water. Too much water can oversaturate the wood. This can cause the wood to swell in the short term. In the long term – as humidity decreases – the wood will release the excess moisture.
In addition, care must be taken to spread the water evenly across the surface of the floor. Uneven water distribution can cause your floor to show blotchy areas under the stain. If this happens, the only remedy is to re-sand the surface of the wood, which costs time and money.
To reduce this risk, many flooring professionals use a “T” bar. A “T” bar is shaped like a broom with a long handle that meets the end piece at a 90 degree angle. The end piece contains a straight edged piece of rubber, like a window squeegee, that touches the floor and helps you distribute the water evenly.
Some use chemical sprayers to mist the floor with water. Some use a buffer with a soaked carpet pad. Still others run a wet mop over the floor. Perhaps the most effective way, though time-consuming, is with a bucket, a rag and getting down on your hands and knees.
No matter which method, it is fairly easy to do. This is especially true if you have experience with applying water-based finishes. The difference is that water popping employs clean water without chemicals, whereas finishes often contain substances that can hurt the wood.
It’s best to use purified or sterile water, not tap water. Tap water can contain excess chlorine and other chemicals that can react with the wood or the stain.
A standard plant watering can may be used. Pour a 2-inch line of water, with the direction of the flooring grain. Then use the T-bar to even out the water.
After coating the whole floor, no matter which method you choose, let it stand and dry on its own for between two to four hours. At that point, the floor should be somewhat gritty, with it no longer having a smooth touch to it. This is the effect of the grain in the wood reopening.
Perhaps the most important step in the process is the close examination of the whole floor. You need to make sure the surface of the floor feels the same throughout. An area that is rougher or smoother than other areas may indicate that you did not apply the water uniformly.
Two Choices for One Outcome
If the surface of the floor is consistent, then the process was successful and stain can be applied.
However, if the floor surface feels different in spots, then it is necessary to repeat the process, or more likely re-sand the floor. Remember, if re-sanding is required, the water popping process is necessary afterwards.
A Deeper Look at the Benefits
Stain More Evenly Across the Floor
Due to the application of various grits when sanding, the grain throughout the floor may not be uniform. When water popping is done correctly, the pores are opened throughout the flooring, allowing the stain to be more evenly applied.
Raises Wood Fibers Promoting Stain Penetration
Water popping causes the fiber in the wood to stand up, providing greater surface area for the stain to absorb and penetrate deep into the wood. Applying two coats of stain can give you an even nicer look.
Sustain a Professional Look and Feel without Any Sanding Marks
Even the best professionals can make a mistake. Sanding wood flooring can leave marks, however small, that are noticeable until after the wood is stained. When the grain is raised from water popping, any sanding marks blend in with the wood fibers, and when stained the marks won’t stand out.
The Stain Appears Darker and Richer
Perhaps the thing that stands out the most on a wood floor is the deep rich color. Water popping enables you to make your stain appear darker and richer. Darker and richer floors are noticeable, which many people admire. Be sure to ask to see the color you select on a sample of water-popped wood. Otherwise, the color you are shown you may not be what ends up on your floor.
If you pour uneven amounts of water on different sections of the floor, you increase your risk of the wood absorbing various quantities of moisture. This can cause your floors to break down in the near or distant future, and your stain will look blotchy afterwards.
Staining before the Floor is Dry
If you do not allow enough time for the floor to dry before staining the wood, you run the risk of the stain appearing blotchy. Drying time can differ by temperature, humidity and air circulation in the room. The lower the temperature, higher the humidity, or less air circulating, the greater amount of time you need for drying.
Sensitivity to Scuff Marks
Once the wood has absorbed water it becomes soft and more susceptible to scuff marks. For this reason, you should not walk on the floor with any type of hard shoe or boot between the time of water popping and completing the staining process. Instead, wear only socks or slippers with very soft bottoms.
The Outcome Varies by Wood Type
The outcome from water popping can be incredible. You can have a professional floor that will last for a lifetime. Visitors will commend you for a good job.
Nonetheless, your outcome can differ not only by the actual process, but also by the type of wood. Each type of wood can differ in the amount of water needed for popping and the length of time to dry. Different types of wood also vary in how the color of the stain appears. These are the reasons why you ought to sample a piece of wood to “water pop” before committing to buying and installing the whole floor.
What You Need Now – Moisture Measurement
Anyone can do it, but not everyone will do it right. To avoid the risks and maximize the benefits from water popping, it’s best to hire professionals who know how to measure moisture in the wood.
By looking at relative humidity at various places throughout the floor, you can get an accurate glimpse of how the moisture levels in the environment – now and later on – will affect the wood.
When the wood contains a low level of moisture that is at equilibrium with the environment and uniform throughout the floor, you can then seal it and apply the stain. An accurate wood moisture meter can help you lower or prevent the risks from water popping.
Tony Morgan is a senior technician for Wagner Meters, where he serves on a team for product testing, development, and also customer service and training for moisture measurement products. Along with 19 years field experience for a number of electronics companies, Tony holds a B.A. in Management and his AAS in Electronics Technology.