Wood is an amazing building material due to its beauty, strength and versatility, however it has a weird relationship with water. The end grain of wood is very absorbent. To properly protect against water, you may need to take special precautions with exposed end grain.
Areas of Concern
What is End Grain?
The “grain” of the wood is determined by how the wood fibers are arranged as the tree grows. These wood fibers are how trees transport water and nutrients up and down its trunk and the typical direction of the flow is vertical (up/down). You can think of a tree trunk as millions of drinking straws tightly packed together sticking out of the ground.
End grain is the grain of wood seen when it is cut across the growth rings. A common example would be the top of the tree stump that is left when a tree is cut down. You see all the growth rings forming circles radiating out from the center. End grain is cut across the growth rings; therefore, the straw-like nature of the wood fiber is still intact. Nature has designed these wood fibers to transport water efficiently and it can be extremely absorbent.
Where It Matters
The key problem areas are going to be end grain around chronic water areas. The most common problem area would be around a sink and other plumbing fixtures. Most projects deal primarily with face or edge grain and are generally, easily sealed. End grain can be quite difficult to fully seal. On many projects, the gaps are well sealed, and the end grain is usually covered when you brush the sides, however, it may not be fully sealed. On areas around sinks and the other fixtures, the hole(s) are cut through the wood exposing a lot of end grain.
Many sinks/plumbing fixtures will usually have a lip or cover that can be sealed/caulked to minimize water exposure to the surface underneath. However, if there is a weak point or minor leak/condensation, that water is essentially trapped. If that water then soaks into the end grain, it can then travel through the wood fibers and start to spread damage.
How to Finish End Grain
The key to sealing end grain for maximum protection is to fully seal it up as best you can. One of the concerns with the traditional Waterlox sealers is that they are very low in solid content and will penetrate deep into the wood. This is amplified on end grain and would take many, many coats of our ORIGINAL Sealer to saturate those end fibers. The key is to use higher solids products to plug up those straw-like fibers (like a poorly blended smoothie).
UNIVERSAL Tung Oil Sealer (UTOS) and TRUETONE Colors
The UTOS is very high in solid content, so it plugs wood fibers quickly and efficiently. The end grain will soak up more product, however it will saturate that area much quicker and allow you to put a final finish over it after just 1 or 2 applications. Rub on a healthy amount of UTOS and allow it to soak in. If it soaks in rapidly, reapply immediately. Allow it to dry overnight. If the area looks basically unfinished, repeat the application. There would be no need to sand after using the UTOS before applying the finish. This would also apply to the TRUETONE Color Infused Tung Oils, however, allow a full 24 hours before doing any reapplication and be sure to wipe off any excess.
Epoxies or Sanding Sealers
Another option would be a thin epoxy or some form of sanding sealer. These would work like the UTOS as they are typically very high (even 100%) solids and many dry very quickly. Basically, these would plug the ends of the wood fibers in the same manner, but they tend to be harder finishes and may be more difficult to apply to small vertical surfaces. There are a few things to look out for when using products like these:
- Final Color. Because end grain is more absorbent, it will usually be a little different in color compared to the face or edge grain, however, if you get either of these onto your other unfinished surfaces (like the top), it may not allow that wood to accept the Waterlox in the same way and you may see a different color. We’d recommend one coat of Waterlox product over everything to get a consistent color in the wood first and then apply your epoxy or sanding sealer.
- Sanding will most likely be required. These products dry very hard and you’ll probably need to sand them smooth and remove any from the top or bottom surfaces before continuing. This may be difficult in small areas.
If you are using our URETHANE coatings and not any of our colors or sealers. those tend to sit more on the surface and will do a better job at plugging the end grain during your regular application. Brush a little urethane onto the end grain once or twice during your application. The first applications will readily absorb into the end grain. As you achieve your final finish, you should see some film build on the end grain itself showing that you have a good seal. Watch for drips on the underside!
All of the above methods will still benefit from the final finish being applied over them. Finishing these edges as you apply finish to the top will fully seal them from water and extend your protection.
In the case of undermount sinks, or to be extra careful, apply the full finishing system (all three coats) on the top, end grain and underside in the immediate vicinity.
If you are using our penetrating finishes (PURE Tung Oil and TRUETONE Buff-In Tung Oil Finish), then you won’t really have a full film on these end grain surfaces. Just be advised that this is where the finish will most likely wear off the fastest. If those end grain fibers start to look dry or discolor, wipe in more PURE Tung Oil or Buff-In Tung Oil Finish to those spots to resaturate.