All wood contains sap and when it is exposed to heat, it will often start to leak through. This is a particularly common problem with wooden decking and it can ruin the nice finish on the surface.
Unfortunately, you cannot stop sap altogether as it is a natural feature of the wood. However, properly treating and drying the wood will reduce the chances of leakage. You can also use a heat gun to crystallize and scrape off leaking sap.
If you are experiencing problems with sap leakage and you don’t know what to do, this article will give you some great tips on how to manage the problem.
Why is Sap Coming Out of my Wood Deck?
Tree sap is an organic fluid that can be found in all types of trees. However, some types of wood are more likely to have issues with sap.
There are several different reasons why you could be experiencing excess sap coming out of your wood deck boards. When the wood is cut, the sap still remains inside the boards. In most cases, if the wood has been heat-treated and dried properly, the sap will be crystallized inside and will not run.
However, if the wood is exposed to heat or the humidity changes drastically, it can start to melt and seep out of the wood onto the surface of your deck. So, if you live somewhere with a warm climate, you are more likely to experience this. The same is true if you use a heat gun to strip off paint or sealer, so it’s best to use a chemical stripper instead.
In some cases, it may be that the wood has not been dried properly before the deck was laid. Always double-check that the wood is completely dried and it has been treated properly before using it if you want to reduce the chances of sap leakage.
What Types of Wood Can Leak Sap?
Technically, all types of wood can leak sap because all trees contain some sap. However, certain trees have more than others, so it’s more likely to be an issue. Pine and fir tend to be the worst when it comes to sap leakage.
If the wood is fresh, it will start leaking sap a few days after being cut. This is why it must be dried and treated before use. If you have any fresh wood, give some time for the sap to stop leaking before you do anything with it.
Wood is often treated with certain chemicals to limit the amount of sap that is present. If you are using untreated wood, expect to deal with more sap.
Many people find that pressure-treated wood of any kind leaks a lot of sap too, especially around the knots.
How to Stop Sap from Coming Out of Deck Boards
Unfortunately, there is no way to completely stop sap from coming out of wood. The key to managing the problem with deck boards is to treat the wood properly. If possible, always try to use kiln-dried wood for your deck because the sap will be properly crystalized and less likely to leak through.
If the deck is already in place and you notice sap leaking through, your best option is to recrystallize the sap. You can use a heat gun to gently heat the sap until it hardens and you are able to scrape it off.
Bear in mind that sap will continue coming out of freshly cut wood for a month or two, in some cases. So, it is best to lay the deck when the weather is good and you are able to give it some time to dry properly and release all of the sap before you finish it. That way, once the protective layer of stain, paint, or sealer goes on, you shouldn’t get any more sap coming through. So, leave the deck and then clean away any sap as and when it leaks out.
Once you have dealt with the sap, you can think about refinishing the wood. Use 240 grit sandpaper to remove any residual layers of sap and create a smooth surface. You can then stain or paint as you would like and this should cover the areas of sap. However, keep in mind that if there are any large congealed areas of sap, they will still be visible.
If you find that this is a constant problem because the deck is regularly exposed to direct sunlight, consider adding some shade to your deck area.
Alternative Options to Removing Sap from Wood
Crystallizing the sap is a good option for removing it but you can also clean it off if it is still very fresh. Runny sap can be washed off using an oil soap. Start by using a metal scraper to remove the majority of the sap, and then apply the undiluted soap to the area and scrub with a soft brush. Rinse with warm water afterward and repeat the process if necessary. You can use acetone to get rid of any small marks that did not come off with the soap.
If the sap has cooled and hardened on the wood, you should be able to use a chisel to gently pop the solid pieces of sap off the wood. Be careful when doing this so you don’t accidentally damage your deck. Afterward, you should be left with a faint residue that can be wiped off with some acetone. If you think that this method may be easier, you can harden fresh sap with an ice cube and then follow the same steps.
Can You Apply Deck Stain Over the Sap?
Yes, you can, but it’s always best to remove the sap before refinishing your deck. It is better for the wood to have a clean surface that will absorb the new treatment properly. The sap will not take the stain like the wood does, so your deck will be left unprotected and there will be small gaps where moisture can still get in.
To avoid this, make sure to sand the decking properly and get rid of any areas of congealed sap. Then, immediately apply the stain according to the manufacturer’s guidelines before the sap comes back through.
Can You Apply Sealer Over Sap?
Yes, you can apply a sealer over sap. In fact, it can be an effective way to stop it from leaking out of your deck. But it is especially important that you prepare the surface properly beforehand so you get a complete seal.
Start by cleaning off the sap and then sand the boards too. That way, you can ensure that there is no residue left over and you get a complete seal that stops any sap leaking through.
Can You Paint Over the Sap?
Yes, it is possible to paint over the sap on your deck. Start by using some acetone to remove any small marks of sap that are hard to reach with a cleaner. Then follow up with sanding the area down so there is no residue left behind. Use high-quality exterior paint that will be able to stand up well against sun exposure.
If you have large areas of congealed spa that are difficult to remove completely, painting can be a good option for getting rid of them. You will still have bumpy areas but they won’t be hugely noticeable. Just bear in mind that the sap may continue oozing out of the wood and this will cause the paint to peel and bubble, so you will need to reapply more often.
Ideally, you should work on removing as much of the sap as possible before you apply any paint, but if that isn’t an option, you can just keep covering it.
How Can You Stop Sap from Coming Out of Painted Wood?
If you want to stop sap from coming out of painted wood, you need to prepare it properly before the paint goes on. Firstly, remove all of the sap that you can see, and give the wood plenty of time to dry. This will also give it a chance to release more sap if it’s going to. Once you are completely happy that the sap is gone and no more is coming out, then you can start preparing the surface.
An oil-based primer is the best option here. Apply multiple coats for the best protection and then use high-quality latex paint over the top. As long as you give the wood long enough to dry properly and you prepare the surface well, you should be able to avoid more problems with sap in the future.
How to Stop Sap from Coming Out of Wood Siding?
Just like your decking, you should make sure that your wood siding is properly treated and dried before you use it. But sap may still seep through regardless.
You can use the same method of scraping off hard sap and then using turpentine to wipe away residue on your wooden siding. If you plan to paint the siding, you should also use a stain-resistant primer on the knotted areas first. Although this will not give you complete protection, it does make the sap less obvious when it first starts seeping through.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.