How to Stop Sap From Coming Out of Wood? (A Simple Trick)

Sap coming out of wood is every woodworker’s nightmare, especially if it happens on a piece of freshly finished furniture. Aside from the disappointment that comes with thinking that you have done something wrong, getting all that sap off the wood is no easy task either.

Fortunately, it’s possible to stop sap from coming out of the wood with a very straightforward trick.

Grab your heat gun, and aim it at the areas where sap is leaking. Keep the heat gun moving to ensure that you don’t damage the wood, but don’t divert your focus from the sap either. When wood eventually reaches the temperature of 160 – 170 degrees Fahrenheit, the sap will crystallize and stop leaking.

After cleaning the crystallized sap off the surface, you can re-stain the wood or bin-seal the knots and paint again.

While this trick will save the day, it’s possible to avoid having to deal with sap coming out of wood again by doing the correct preparation beforehand.

As there are a few different factors that determine whether sap will cause you problems, the preparation process involves multiple stages, starting at the wood selection.

How to Prevent Sap From Coming Out of Wood?

If you are starting a new project where you don’t want to deal with the possibility of sap leaking out of the wood, here are some steps you can follow.

  1. Choose a type of wood that doesn’t have a high sap content if it’s suitable for you. While softwoods are more suitable for furniture, hardwoods can save you from having sap-related problems when it comes to flooring. That being said, you must keep in mind that hardwoods are more expensive than softwoods on average.
  2. Ensure that the wood you buy is kiln-dried. The primary cause for sap coming out of wood is due to wood not being dried properly. When wood is properly dried, sap leakage stops being a problem regardless of the type of wood used, meaning that it’s possible to avoid sap-related issues even with woods that contain a high amount of sap. Between air-drying and kiln-drying, kiln-drying is considered to produce better results when it comes to stopping sap leakage, as the high temperature of the kiln-drying process crystallizes, or in other words, “sets” the sap.
  3. If there are any leaky knots, dry them with a heat gun. While properly dried wood won’t have any leaky knots, you can dry the knots yourself if the wood you bought hasn’t been dried properly. As you will require to apply heat to the knots to crystallize the sap, a heat gun will come extremely handy for this process. By heating the knots with a heat gun, you will observe the melting of the sap first, followed by crystallization when the required temperature is reached. When crystallization occurs, don’t forget to scrape the hardened sap that resides on the surface before moving on to sealing the knots.
  4. Seal the knots before painting or staining. After hardening the sap in the knots, it’s time to seal the knots. You should either use shellac or a shellac-based primer (also known as BIN shellac or BIN primer) for this process, as a latex primer doesn’t do anything when it comes to sealing knots. While the number of coats you should go for is situational, applying a minimum of two coats is a good starting point, and to be on the safe side, you can keep applying coats until the knot is invisible. After sealing the knots, you can coat your entire project with a latex primer afterward to get it ready for painting, just as usual.
  5. Seal the wood after painting or staining. While deemed unnecessary at times, sealing the wood after the painting process is good practice that you should follow to keep your project healthy. Even though sealing doesn’t directly prevent sap leakage, it protects your project from moisture and other water-related damages, which may indirectly cause sap to come out.

Effects of Wood Type on Sap Coming Out of Wood

The sap is a natural part of a tree, so it wouldn’t be wrong to say that all types of wood contain tree sap. On the other hand, the type of the tree determines its sap content, meaning that some kinds of wood have more tree sap than others.

While hardwoods such as mahogany and walnut have a lesser sap content in comparison to softwoods such as pine and fir, softwoods are often the primary choice for all kinds of woodwork, ranging from furniture to deck boards due to their high availability and affordable prices.

Considering that these woods have a vast amount of sap in them, there is no surprise that the tree sap eventually comes out if it hasn’t been dried out, even when proper sealing techniques are applied. While sealing provides a certain level of resistance that keeps the sap inside the wood for a while, active tree sap can eventually make its way out.

While sap is less of a problem in hardwoods, which technically makes them more suitable for flooring, their high price point often causes people to steer away from them.

Effects of Heat on Sap Coming Out of Wood

Earlier, we have mentioned how you can use heat to crystallize the sap and stop it from leaking. In fact, the kiln drying process also utilizes heat to dry the wood and crystallize the sap inside, which is also called setting the sap.

Unfortunately, the combination of heat and sap is a double-edged sword, with heat also being responsible for sap coming out of wood to a certain extent.

Until the target temperature of 160 – 170 degrees Fahrenheit is reached for crystallization, heat causes sap to melt. As the heat from the sun is never enough to bring the sap to crystallization temperature, dry heat often causes sap to melt and start leaking.

Because of this, you’ll notice that people often experience sap leaking out of their deck boards during the times of the year where temperatures are high.

How to Remove Sap From Wood?

Getting the wet and sticky sap off wood is a nightmare that we all had to experience at some point. On the other hand, it’s quite straightforward to remove dry sap as all it takes is a little bit of scraping.

So, we should use this fact to our advantage and start the removal process by drying the sap. As we have mentioned a few times earlier, the temperature (160 – 170 degrees Fahrenheit) that is required to crystallize sap can easily be provided by a heat gun.

By simply aiming your heat gun at the areas where sap is located, you can cause the sap to crystallize in a few minutes. After crystallization occurs, all you have to do is to scrape the dry sap off the wood with the tool of your choice.

If removing the dried sap leaves residue on the wood, you can get it off with the help of a solvent such as acetone.

Why Is Sap Coming Out of My Deck?

If your deck suddenly started oozing sap despite it never being a problem for so many years, it can cause a serious amount of frustration and confusion.

There is a reasonable explanation as to why this is happening, but unfortunately, it’s not an explanation that you will enjoy hearing.

Simply put, your wood hasn’t been properly dried, meaning that the sap inside hasn’t crystallized. While the seal has successfully stopped sap from leaking for a long amount of time, the wet sap most likely made its way out due to factors such as changes in temperature and the seal losing its effectiveness over time. With woods where sap hasn’t been set, it’s only a matter of time until sap starts making its way out.

Depending on the extent of leakage, you can remedy the situation by scraping the sap off and re-staining, sealing the knots that bleed sap, or replacing the boards completely.

Will Sap Keep Coming Out of Wood Forever?

The frustration of having to deal with sap coming out of your wood over and over can prompt you to wonder whether the sap leakage will be stopping at a certain point or not.

Truth be told, waiting for the sap leakage to stop by itself can take tens of years, depending on the type of wood used. For this reason, it’s better to do something about your sap problem rather than trying to wait it out.

While small amounts of sap leakage can be stopped by crystallizing the sap and sealing the knots, in cases where your entire deck is oozing sap, it’s most likely better to replace the boards altogether with wood that has been properly dried.

Wrapping Up

Dealing with sap can dampen your mood, but it’s not a problem without a solution. Whether you’re dealing with tree sap in your current project or you’re looking to avoid having to deal with tree sap in your future projects, there are plenty of things you can do.

While processes such as sealing the wood can slow the leakage of sap down, preventing tree sap from coming out usually comes down to drying the sap out by exposing your wood to high temperatures where it hardens and crystallizes.

At the end of the day, prevention is the best thing to do when it comes to dealing with sap leakage, which is why you should be showing extra care to the wood you are buying if you don’t want to deal with this problem.