Home maintenance is a constant chore. If you have anything made out of wood, chances are you will need to repair it at some point. An exterior wood filler is necessary for many different jobs. Knowing which exterior wood filler is best will help your wood last a long time.
Exterior wood fillers are very important since many times exterior wood can’t be replaced easily due to it’s location. Other times replacing certain wood items can be very costly. Below are a few examples of when you would use an exterior wood filler instead of replacing the wood.
- Exterior Window Sill
- Bottom Edges of Exterior Door Frame
- Exterior Door
- Exterior Window Frame
- House Siding
- Roof Fascia and Soffits
- Exterior Wood Posts
In the cases above, you will need to verify that you can actually repair the wood with filler or if the rot has compromised the entire wood piece. If there is no good wood for the filler to attach to, then it is best to replace the wood.
In most cases the best exterior wood filler will be epoxy based instead of a water based filler. Water based exterior fillers can break down quicker over time and doesn’t have the structural strength of epoxy.y
As a homeowner and former trim carpenter I have used different wood fillers for many years in interior and exterior projects. I’ll list the ones I recommend based on my personal experience.
Epoxy Exterior Wood Fillers
My favorite exterior wood filler for rotten wood is Elmers Wood Repair System. This system has all the components you need to stabilize the rotten wood before applying the epoxy mixture.
It is a great epoxy wood filler due to it’s ease of use. It has a 1-to-1 ratio for mixing and a working time of 20-30 minutes. Simply mix together the resin and hardener putty until it’s a solid color. After 24 hours it can be sanded, then stained or painted.
Quick Note: I used to find this in the big box stores but they no longer sell it but it is still available online.
Bondo Epoxy Wood Filler is also a good choice for any wood areas that had rotten wood. Bondo is very strong and won’t shrink.
But in comparison to the Elmer Wood Repair System, there are several things that make it harder to use for a beginner. The hardener and filler isn’t mixed on a 1-to-1 ratio so it’s a bit of a trial and error to get it right.
You also need to purchase the wood restorer separately. Lastly, the working time to use the filler is only 3-5 minutes. When you’re a novice working with epoxy wood fillers, that is not enough time before it hardens.
Again, those these issues are more about a novice using it versus someone who has years of experience using Bondo. The great thing about Bondo is that it can be used on many different types of materials.
Last epoxy product I recommend is PC-Woody wood repair epoxy paste. This epoxy has a shear strength of 850psi. Compare that to eastern pine that has a shear strength of 899. It will make a strong repair that can be drilled or screwed just like the two epoxy repair products above.
It has a 1-to-1 ratio for mixing which makes it easy to use and has a longer working time at 30-40 minutes. They even have a wood repair kit to fix and replace rotten wood damage.
Due to the high psi strength, this is also a good filler for filling larger holes or voids in wood. Like filling a large knot in a decking board.
How To Use An Epoxy Based Wood Filler For Rotten Wood
Here are the steps below to apply exterior wood filler to replace rotten wood.
- Make sure to remove or dig out any loose wood.
- If the surrounding wood is really wet, try to dry it out with a fan.
- Vacuum or use stiff brush to remove as much loose wood as possible
- Apply the wood hardener with a glue brush to all areas that the filler will touch.
- Once the hardener is dry, mix your epoxy as instructed and fill the void left behind.
- Use a putty knife to scrape away any excess.
- After the wood filler has hardened, sand away any excess.
- Paint or stain to match the remaining wood.
I have used these procedures in each of the situations above, minus decking, with good results.
Water-Based Exterior Wood Fillers
Elmers ProBond Wood Filler can be used indoors or outdoors. Even though it’s water based, it it stronger than other water based wood fillers. Unlike the epoxy wood fillers, it actually has wood fibers in it so it gives it a more natural finish than epoxy.
Since it’s water based, there’s no mixing parts, simply apply it as is to your wood for a simple repair. If you’re highly sensitive to the VOCs produced by epoxy fillers, then this is the wood filler for you.
Dap Natural Color Plastic wood filler is very similar to the elmers probond wood filler. It is a one part wood filler that can be used indoors and outdoors. It is also strong enough to be drilled into for screw anchoring.
The biggest difference is it will change colors once it’s fully dry. For a novice DIYer, this many help so you don’t sand, paint or stain before the filler is fully dry.
What To Avoid For Exterior Wood Fillers
Be careful if you’re choosing an exterior wood filler based on online recommendations only.
I’ve come across this Goodfilla water based wood filler being touted as a good exterior wood filler. On closer inspection, the product, in small print, recommends you mix this with a water based weather-proof glue if using outdoors.
I didn’t find any recommendations on the ratio to mix with the product and glue. If you already purchased this wood filler and want to use it outdoors, I recommend mixing it with Titlebond 3 glue. Titlebond is a water-based exterior glue that I have used in other exterior projects.
If you bought this and used it on an outdoor project as is, it will probably fail very soon after being exposed to the outdoor elements.
This is not to say that it isn’t a good wood filler, especially used indoors. It’s just a cautionary tale to always read the fine print on any wood filler before using it outdoors.
Epoxy Vs. Water Based Exterior Wood Fillers
Here are the most common pros and cons of both types of fillers.
|Epoxy Wood Filler Pros||Epoxy Wood Filler Cons|
|Very Strong||Can look fake if using stain|
|Best for rotten wood repair||Shouldn’t be used indoors due to higher VOCs|
|Best in wet conditions|
|Best for larger hole repairs|
|Best when painted over|
|Water Based Wood Filler Pros||Water Based Wood Filler Cons|
|Best when used in highly visible repairs||Not as strong as epoxy|
|Best for smaller cracks and holes||Won’t last as long as epoxy in wet weather|
|Looks natural and takes stain well|
I hope I was able to help decide which exterior wood filler is best for your project. Any of the products mentioned above will work well in many different situations.