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Sap coming out of wood is a common problem, especially with recently installed decks. This is especially true if you like in a hot area: sun exposure tends to increase sap leakage. So how do you stop tree sap from coming out?
Well, there’s no “direct” solution for that. Sap will come out until the wood is completely dry. But there is a workaround, and that’s what I’m going to talk about in this article.
First, you need to remove all the sap that already came out. To do this, you need to crystalize all the sap with heat, for example with a heat gun. Then, remove all crystals with a chisel. Remove any liquid remaining with a solvent like turpentine. Sand if required. Finally, seal the wood as best as possible. Since sap production can’t be stopped, this last step will keep it inside the wood by clogging up the wood pores.
Let’s start by describing tree sap. You need to know your enemy before fighting him, right? Then, we’ll get to the steps you need to take to prevent sap from leaking out of your deck/project.
What’s Tree Sap?
Sap is basically what blood is for humans. Generally, two substances go under the term sap, xylem and phloem.
Xylem contains water and nutrients. It flows from the roots all the way to the furthest tree branches. On the other hand, Phloem contains many types of organic materials, and it’s responsible for “feeding” the plant. Phloem is the sticky part that comes out of the plant, which is commonly referred to as “sap”.
Many trees give off large amounts of sap. To name a few, think of any maple species, like red maple or sugar maple. Maples are the most prolific sap producers, and their sap is notoriously edible. Pine also gives out sap, with a strong and characteristic scent.
How to Stop Sap From Coming Out of Wood? A Step-by-Step Guide
As I mentioned before, the only way to stop tree sap from coming out is by sealing the wood as best as you can. First, you need to clean the sap that already leaked. Let’s get to it.
1) Crystalize the Sap
First, you need to check the sap’s state. It can be already dry and brittle; it could also be hard on the surface, but still soft at the touch. That means it’s still liquid inside. Finally, if it just came out, it would be in that wet, sticky state that typically gets over your skin and clothes and never goes away.
For the best results, we need sap to be in a solid state. Removing liquid sap will likely cause a mess.
To turn tree sap from liquid to solid, we need to use heat to crystalize it. We are basically going to speed up the natural process. There are few ways to obtain this, the most straightforward in my opinion is by using a heat gun. Different wood saps might require shorter or longer heat exposure to crystalize, as well as different temperature levels. A good starting point is 140°F.
Make sure to always keep the heat gun moving. If you concentrate too much on the same spot, you could end up with singe marks. Keep on heating the sap until it’s completely dry. Then move onto the next step.
2) Remove the Sap
Once it’s solidified, you can remove sap crystals. Bigger chunks can be removed with your hands. When crystals don’t come off like that anymore, it’s time to use a chisel. Better if it’s a sharp, thin chisel.
Make sure the chisel is parallel to the wood surface when using it, to avoid marring the surface. Lay one face on the surface before pushing it onto the crystals. For small touches, you can also use a putty knife.
After all solid sap has been removed, there might be some liquid residuals left. In that case, you need to use a solvent to remove them. The most common choices are mineral spirits or turpentine. Make sure to use safety protections while using chemicals, such as rubber gloves, glasses, and a mask. Apply the solvent, let it work, then remove it with a rug and let the wood dry.
Before moving onto the final sealing step, it might be a good idea to do a little sanding. This will remove any imperfections created during the previous phase, plus it will help the sealer to bond better with the wood.
Before you start sanding, make sure the surface is perfectly dry and clean. Any leftover sap is likely to clog up the sandpaper, making it unusable. On top of that, if any liquid sap is still on the surface, you will end up spreading it all over the wood. This will give a blotchy look to your project once you apply the finish.
As always, if you have big scratches to remove, start with something like 80 grit sandpaper. Move up to around 120, then finally use 240 grit sandpaper to give your project a smooth feeling. Remove any dust before moving onto the next step.
4) Apply the Sealer
Finally, it’s time to seal up the wood and prevent any more sap to come out in the future. There’s a variety of choices you can make here, depending on the type of project at hand. For an outdoor deck, for example, a waterproofing sealer might be a good choice.
If your project is made of high-quality wood, a good idea might be to stain it before sealing, to bring out the wood pattern even more. Then you’ll apply the desired finish on top of it. A clear top coat is good to preserve the natural wood’s color.
For blocking sap, I really like shellac-based sealers. They provide a good level of penetration into the wood pores, which is what we need to slow the sap leakage. Make sure you apply multiple layers on the knot areas, where sap is more likely to come out.
At this point, you should have a clearer idea of what you have to do to stop sap from coming out of wood. As I said before, this is just a workaround solution.
To be fair, some sap is still likely to leak, especially from the areas with knots. The only definitive solution to it is removing the boards that keep leaking sap and replace them with dried ones.
That’s the only definitive solution to avoid this problem in the future: using completely dried wood. Best if it has been kiln-dried.
Basically, this means that wood has been dried in an oven at the right temperature and humidity conditions. This procedure reduces its moisture level to an amount that allows you to use it without problems like warping and of course sap leakage.
If you get wood from a friend, make sure its sap free before using it. If boards have been recently sawed, and kiln drying isn’t an option, leave them out to air dry. This will require some time since the temperatures won’t be as high. It could take several months to a year for it to be usable, depending on the moisture level and the wood type.