How to Stop Sap From Coming Out of Wood? A Guide for Untreated Wood.


When you build that new piece of furniture or put down a new outdoor deck, one of the unexpected problems that might come up is sap coming out of the wood.

The main way to stop sap from wood is to heat the wood and seal it properly. Pine and fir are the worst offenders. Kiln drying wood to 170 F will crystallize most of the sap and prevent oozing. If you aren’t able to buy kiln-dried wood, then if possible, heat the wood with a heat gun until the sap crystallizes, then seal the wood with the sealer of choice. Clean the Sap off the wood with a Solvent first.

The initial moisture content of your wood can be the main contributor to sap. Check out my article on How dry should wood be for woodworking for more information.

There are many things that you will quickly learn when working with fresher woods. One of the most frustrating things is that when sap appears after a project has been complete, there is extraordinarily little that can be done.

If you can’t buy kiln-dried wood and have a small piece of wood your working on, you can carefully heat it with a heat gun to crystallize the sap. I recommend the 1500 Watt Porter Cable heat gun due to its lower price. (Check here for the current price on AmazonOpens in a new tab.)

All trees have sap in them. It is how the tree transports nutrients throughout itself, which is why you need to ensure the wood is dried correctly before working with the wood.

Here’s how sap can be treated and why it is such a big problem. 

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Why is sap coming out of the wood?

As said before, all trees have sap, and this means that every single piece of wood you can use to create something will have sap in it as well. The causes of sap coming out from a finished piece of wood is vast, with many people reporting that they’ve never seen sap on their projects, while others seem to be continuously stuck with it. 

If you are using green wood that has not been dried properly or completely the sap will get stuck in pockets and seams throughout the wood. It might seem fine while working on the piece, and once you start sanding or working on the wood, you may not even notice any problems with the wood.

However, once heated by the sun, indoor heating, or just a heat gun, the sap will start to melt and solidify. Slowly but surely gathering on the wood pieces that you have worked on, this is why the standard practice for woodworking is to let the wood dry(either kiln-dried or air-dried). See my article on How dry lumber should be for woodworking for specifics. (link to article here)

Can you apply stain over the sap?

If your finished piece is already past the point of no return, then you will have to apply the finishing’s you want on your piece. This can mean using very thick layers of paint, oils, or stains, which will work perfectly well.

You can stain your wood if there is sap coming out of it, but the areas where sap has congealed will not react the same way as the wood. In extreme cases, this can leave large areas of your piece unstained and untreated. 

To overcome this, you need to sand down the piece, ensuring there is no sap congealing anywhere on the work. Then immediately apply the stain or oil you want in the wood. This will effectively stain the wood; however it will not stop more sap from appearing down the line. 

Why is there more sap coming from the deck?

Furniture can show symptoms of sap oozing out of them, with some smaller pieces of art, also showing the effect of improper treatment. However, commonly the DIYer will face sap seeping out of almost every single part of their deck.


The sun is continuously baking the deck, making the sap ooze out and become congealed in many spots. Any DIYer that has used inexpensive wood for their deck will know the horror of going outside one afternoon and suddenly having sticky feet. 

The only way to overcome sap leaking form a deck is to try several different treatments, scarping off the sap as it appears, and reapplying any drying or oiling agents you may think is sufficient. 

Can you paint over the seeping sap?

You can always paint over sap, making your piece look slightly bumpy in spots but never losing its shine. However, as time goes on, your paint will start to peel and bubble. The sap that oozes out of wood is under a lot of pressure and will easily overcome the bonding structures of paint.

Paint is probably one of the worst affected treatments on wood that can be harmed by sap seeping out of wood. This is because the sap comes from the inside of the wood and will rarely bleed through the paint with oils or stains. 

Pushing the paint and damaging the paint in a way that is almost impossible to fix properly ever again. 

What are the ways of cleaning the sap?

There are several methods to clean sap off wood, with the only tried and tested way is to scrape the sap off after it has dried. One of the challenges of having untreated lumber is that the sap will be soft and sticky, making it a big pain to deal with. 

Once the sap has hardened, it can be relatively easy to scrape off. If you would like to try and get sap out of your wood without sending it to be treated or risking your finished piece to be damaged, you can use a heat gun. Heating the sap and getting it to ooze out of the wood is an easy way of getting rid of sap in smaller pieces of wood. 

Once you scrape off the excess sap, use a cleaning solvent like mineral oil or turpentine to clean the rest of the sap off. Sand the surface down to 240 grit, and than apply a sealer to the surface. Shellac works the best because you can put a layer of shellac on the bare wood, than stain, paint or varnish over the shellac.

How long will the sap be oozing out of the deck?

Wooden decks are hard to predict and knowing how long the sap problem will be there is impossible to know. Fortunately, there are many tests and storied of how long it has taken other decks to become perfectly sap free.

Usually, between a year and 20 years of natural waiting for the sap to finish oozing out, which means you may never see the sap stop bleeding while you are using the current deck. Many DIYers end up buying proper wood and rebuilding their decks to overcome the problem of sap.

What types of wood have more sap?

All wood has sap, with pine an fir being especially sap filled wood, but there are many kinds of wood we work with from day to day that does not have a trace of it in them. This is because the wood has undergone proper treatments before being sold, and here are the telltale signs that the wood you are using is not all it is advertised as.

  • Fresh wood: The wood with the most sap, new wood will always start seeping and oozing within a few days of use.
  • Untreated wood: Many chemicals are used when preparing wood, and if even one of these has not been done correctly, the sap in your wood will still be present. 
  • Incorrect drying: Drying can be done in mainly two ways, naturally with the sun or Kiln Dried. If any of these have not been done correctly, you will know by the sap oozing out. 
  • Not enough drying: Many times, people forget that some parts of wood need to be left longer. Other times, the type of wood determines how long you need to ‘cook’ the wood. If the people making the wood are entirely unaware of these differences, you will get wood that oozes and leaks sap everywhere.

Conclusion

The best way from treating sap is not to have sap at all, but if you are unfortunate enough to experience wood with sap still in it, you will find there are many ways to treat them. Some are extreme, while others require a lot of elbow grease, be sure you don’t scratch that smooth new surface you just spent hours making!

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