5 Reasons You Should Never Sand Pressure Treated Wood
You’ve got pressure treated wood and you want it last and look its best throughout its life. You may have heard or read in our articles that sanding prep work is essential before staining, sealing, or finishing exterior wood, like a deck or fence.
This is true to remove mill sheen on new lumber, removing peeling stain from aged wood, or periodically re-sanding after several re-coats over the years to restore it before staining it again. The exception to this is: pressure treated lumber.
One of the pinnacle moments in my local wood restoration and deck staining business was the moment we stopped sanding pressure treated wood. Since this change, frustration with managing expectations essentially disappeared—making for a better experience for our clients and my team.
Being the thriftier choice, pressure treated wood projects become more common each year compared to woods like cedar or Ipe. This inevitably multiplies the problems associated with pressure treated wood, making it crucial for you to be clear on proper maintenance and the potential consequences before making a decision.
Here are five reasons you should never sand your pressure treated wood…
1. It Looks Terrible
Take a look at the photo above. That is a picture of a pressure treated deck I sanded personally for a client a few years ago (photo was taken immediately after staining.) This project wasn’t sanded any differently than normal practice to prove a point. This is a closeup example of how your pressure treated deck could turn out after sanding as well. It looks like the lighter areas of wood are sanded more than the rest, even after several more passes with a sander over the darker areas in attempt to even them out.
When describing pressure treated wood to clients, the two words that come up time and time again are inconsistent and unpredictable. You have literally no idea what the wood is going to look like after sanding it. It’s simply not worth the risk. After spending time, energy and money investing in a deck or fence, you should be able to enjoy it rather than feeling embarrassed hosting family and other guests with unpleasant results that could have been avoided.
2. It’s Irreversible
Hopefully you’re reading this post as research prior to doing any work and my reasons will prevent you from sanding your pressure treated lumber (and potentially ruining it.) If you’re reading this post because you’ve already sanded your deck and wondering how to fix it, the bad news is it will never look the same as when you bought it again or brand new.
Once sanded through the chemical coating of pressure treated wood, (typically a brown colour with some companies still producing a greenish hue), there is no way of getting the original finish back.
If your pressure treated lumber looks like the photo above after sanding, the urge is to sand deeper to remove all the coating to make it look more even. Seems like a simple strategy, however, some of that chemical coating is soaked into the wood all the way through— especially around knots where the pores are larger allowing the chemicals to pass through. The result: more uncontrollable two-toned wood, and more disappointment with how your project will turn out.
3. Inconsistent Quality
Like any product, quality ranges. Not all pressure treated lumber will look like the photos in this article after sanding. The problem is not only if an issue will occur, but never being able to confidently predict when and what problems will occur, as there are so many potential outcomes.
Obviously, no company will brand themselves as “low quality,” making it impossible to know which brand to choose if you’re in the purchase phase. Or, since you’re still reading this article, the more likely situation you find yourself in is: you already have pressure treated wood and researching how to best take care of it.
Perhaps you bought pressure treated wood for a project years ago and now want to stain it, or you moved to a house that already has a deck or fence with PT lumber. In either case, you have no idea what brand it is (or which brand to trust even if you did have this information.)
The good news: it doesn’t matter with pressure treated wood because it’s so unpredictable, you may as well try to predict the exact day of the next stock market crash. In fact, the only outcomes that are predictable with most PT wood is that it will likely dry out, twist, crack, and the knots will split and stick out giving your children/pets slivers when they play.
Remember, once the chemical coating is sanded, pressure treated wood will never look like new pressure treated wood again. Regardless of quality, it’s simply not worth the risk to sand pressure treated wood in the first place.
4. It’s Potentially Dangerous
Perhaps the most obvious reason not to sand pressure treated wood is the potentially harmful health consequences. You have no idea what chemicals the wood is soaked in and it doesn’t take a chemist to understand you probably shouldn’t be in direct contact with these substances.
Of course, you should be wearing the proper protection (dust mask, safety glasses, gloves, etc.), regardless if your wood is chemically treated or not. Even with a mask, you have no idea what impact leaching chemicals will have on your body over time.
I don’t trust the smell of sanding pressure treated lumber for myself or my team, nor would I recommend it for you homeowners or contractors reading this.
5. No Positive Outcomes
With a list of reasons why it’s not a good idea to sand pressure treated wood, you may be left wondering: ‘Is there ever a time where it IS a good idea to sand pressure treated wood?’
One example is re-staining a pressure treated deck that’s previously been stained with a thick or opaque / solid stain. This is a common issue for those who ‘inherit’ a pressure treated deck that’s already been stained after purchasing a new home. Maintenance is inevitable, and sanding may be the only way to get it looking good again.
(If you are familiar with my articles and the Sand & Stain System, you would already know we never recommend thicker or solid stains because they eventually peel and are a pain to maintain. Not to mention all advice adheres to the promise of our slogan: Never Peel Again.)
Another scenario is sanding pressure treated wood by ‘accident,’ inferring you sanded the wood not knowing what kind of wood it was. Even for an expert, it’s more difficult to detect what kind of wood it is after being stained (especially if it’s thicker or opaque stain.)
My hope for you in both of these examples is: the previous stain was a thin, true penetrating oil that you can simply re-coat without needing to sand (again.) If it’s a thicker finish that needs to be stripped or re-stored, you may choose to sand versus chemical stripper or paint thinner.
What’s The Solution?
The obvious solution is not to sand pressure treated wood… Here’s a recap to help guide you:
If you’re in the purchase decision phase, I would recommend investing into a wood like cedar or Ipe where it’s easier to maintain and you can get a consistent result—no matter how old or how many times it’s been stained.
If you’ve got brand new or gray / untreated pressure wood, you can choose to wash the deck with a cleaner rather than taking the risk with sanding.
If your pressure treated wood has previously been sanded, you may have to deal with how it looks until you decide to change the wood, or cover it with a thicker or opaque stain, (which I don’t recommend unless you want to deal with a peeling deck.) Otherwise, this is the only time you might want to sand a pressure treated deck (knowing that it may still look inconsistent and uneven.)
If you don’t know what kind of wood you have, get a local wood expert to analyze the wood or use the contact section to see if we’re able to help.
If you do decide to sand your pressure treated wood, consider yourself warned with the potential consequences…
