Caulk is a great fixing solution for all sorts of problems around the home. The thick material can be used to fill gaps around windows and doors, patch small holes and cracks, and repair roof tiles to keep your home waterproof. It’s especially good for any exterior wood projects, but it’s crucial that you buy the right product. If you use the wrong type of exterior caulk for wood, or you pick a low-quality product, it will not
What to Consider When Buying Exterior Caulk?
It can be a bit overwhelming buying caulk because there are so many options out there. But you can narrow down your choices if you consider a few simple questions.
Type of Caulking
There are a lot of different types of caulking, each suited to certain jobs. Before you make a choice, you need to understand what they are and the pros and cons of each. The main types of caulk are:
- Latex Caulk – Latex caulk is the cheapest option and you can get specific exterior latex caulk products. It’s good for filling in cracks, but it doesn’t last as long as other types. It also doesn’t do well when contracting and expanding, so it’s not good for places with extreme temperature fluctuations between the seasons.
- Acrylic Latex Caulk (Painters Caulk) – This is the most common type of caulk that is used to fix small gaps and cracks in wood, drywall, and masonry. It can then be painted over. However, standard products are only suited for interior use. You need to look for a specific exterior acrylic latex caulk, which has additional ingredients to make it waterproof.
- Vinyl Latex Caulk – Vinyl latex caulk is very similar to painters caulk in terms of how it is used. But it is a lot more durable and, unlike painters caulk, it is not water soluble, so it can be used outside.
- Siliconized Acrylic Sealant – This type of caulk has the extra durability you expect from silicone, but the easy application and good texture of acrylic. It is usually used for indoor applications that require a watertight seal. It can be used for exterior purposes, but it isn’t the best choice and won’t last as long as other types of caulk.
- Pure Silicone – Pure silicone is normally used in bathrooms because it is incredibly watertight. This makes it great for some exterior applications, but not all. It does not adhere well to porous materials like wood and masonry. It can also be more difficult to work with and it doesn’t take paint that well at all.
- Polyurethane Caulk – Exterior polyurethane caulk is a brilliant choice. It’s very flexible like silicone, it has great UV resistance (so won’t turn yellow over time), and it takes paint very well. It’s one of the most expensive choices but it’s worth it if you want a long-lasting repair.
- Butyl Rubber Exterior Caulk – This type of caulk is usually used for commercial applications as it’s a very heavy-duty product but it can be used by DIYers too. It’s very flexible and tough, so it withstands the elements well, but it can be hard to clean off and replace without using paint thinners.
Polyurethane caulk or vinyl latex caulk are both good options for general wood projects outdoors. You could also consider Butyl rubber caulk if you need something a bit stronger. Always consider what your specific needs are and which type of caulk best meets them.
Is it Paintable?
Not all types of caulk are paintable. Think about what job you are doing and whether it is important that you can paint the caulk. For example, if you are filling cracks in a window frame, you need to paint over it afterwards so the repair blends in and you can’t see it. But if you’re using caulk somewhere that won’t be visible, you may want to prioritize durability and choose an option that can’t be painted.
What Color is it?
It doesn’t necessarily matter if the caulk isn’t paintable because many of them come in a variety of colors. When using a type of caulk that can’t be painted, look at different brands and see who offers the best range of colors. Remember, you’re looking for something that matches the color of the wood as closely as possible.
Is the Caulking Weatherproof?
This is perhaps one of the most important things to consider. You’re using the caulk on exterior wood and if it is not weatherproof, you will have to replace it over and over. For wood, polyurethane caulk is one of the best weatherproof options.
How Durable Is It?
Weather resistance is the main concern with exterior caulk, but you need to think about durability too. Latex and acrylic caulks do not expand and contract very well with temperature changes, so they are prone to cracking. Silicone tends to be more durable and flexible, but won’t work well on wood. Polyurethane, on the other hand, works well on most materials and is very flexible, so it should last a long time.
Is it Easy to Work With?
Some caulk has a much easier texture to work with. It fills gaps and leaves a nice smooth finish, but some types of caulk are a bit trickier to deal with. Getting a good finish with something like pure silicone is much harder than it is with acrylic latex caulk, for example. If you’re quite experienced, you don’t need to worry that much about the usability, but if you haven’t used caulk in the past, it’s worth thinking about.
Consider where you are trying to put the caulk too. If it’s in a hard to reach spot, it’s best to use a caulk that is easy to work with or you’ll end up with a mess on your hands.
Drying and Curing Times
Finally, think about the drying and curing times. If you get a lot of rain where you live and you need to finish the job quickly, pick caulk with a short drying time. Most types will dry in 30 minutes to an hour, but the curing time can vary from 8 hours all the way up to 6 hours. Ideally, you want it to be fully cured before it is exposed to any rain.
10 Best Exterior Caulks for Wood
So, now you know how to pick the right caulk for your exterior wood projects. But you might still be a bit lost and there are a lot of bad products out there. This list of the best exterior caulks for wood will help you find the perfect product.
1. OSI Quad 
OSI Quad is a very popular exterior wood caulk that is normally used for sealing windows and doors. It has a unique formula of elastomeric polymers and high quality synthetic resins, making it different from a lot of the standard caulk products you will find. It also means that it’s incredibly tough and will give you a great weather-resistant, flexible finish that resists cracking. It is also specifically formulated to prevent yellowing in the sun, and it won’t collect dust and dirt either.
If you have any cracks in window frames and doors, or you need to reseal the edges, this is the perfect product. It’s not great for filling in nail holes or large cracks, but it can handle some small wood repairs.
Once it has cured, it can be painted with latex paint. The manufacturers also offer an online color match service, which can produce a match for over 9,200 colors, making it perfect for any job.
2. Sashco Big Stretch Caulk
Sashco Big Stretch Caulk is perfect for any application where flexibility is a priority. It’s an excellent multi purpose caulk that can be used for interior and exterior applications on a variety of materials, including wood. It’s a water-based sealant that is incredibly stretchy, so when wood expands and contracts, the caulk won’t crack. That means this will last you a lot longer than other caulks without the need to reapply. It comes in a good range of colors and can be painted too.
The other great thing about this caulk is how easy it is to use. The consistency is quite thin compared to other caulks and it fills gaps very easily. You’ll get a nice even finish, even if you’re not that experienced, and it will last for years to come.
In terms of the level of skill required compared with the end result, this is one of the best caulks on the market.
3. Gorilla Waterproof Caulk & Seal 100% Silicone Sealant
Gorilla have a reputation for tough products and their Waterproof Caulk and Seal 100% Silicone Sealant is no exception. This silicone sealant works well for interior and exterior projects and it bonds especially well to wood. It isn’t ideal for all projects but it does, however, dry in just 30 minutes, so if you need to quickly seal something before it rains again, this is the way to go.
It is a simple, clear sealant that is not paintable and it has quite a shiny finish to it, so it doesn’t look the best when compared with other caulks. Use this for practical applications, preferably where it won’t be visible. But if you need something that looks nice and blends in with the surrounding wood, consider other options.
4. Sikaflex Construction Sealant
Sikaflex Construction Sealant is a polyurethane sealant that is brilliant for exterior wood projects. It’s designed for weatherproofing joints, so it’s brilliant for wooden window frames and doors. The flexibility on this caulk is great too, so it will last for years to come without a single crack.
In terms of application and the flexibility that it offers, this polyurethane sealant is very similar to a high-quality silicone one. However, because it’s polyurethane, you can paint over it too. It goes on fairly easily but a small dab of water on your finger can help you get a nice smooth joint.
Although it doesn’t have any of the frills that other products have, like extra quick drying times, this is a very reliable polyurethane caulk that can handle most exterior wood jobs.
5. OSI Quad Max
OSI Quad Max is the more advanced version of the standard OSI Quad, and it’s best used for more heavy-duty jobs. The normal OSI Quad is suitable for use on most materials, but not all. Quad Max, on the other hand, can be used on anything, including more difficult materials like glass, fiber cement, stone, stucco, and all types of wood. Although OSI Quad does work on wood, the Quad Max will give you a stronger bond. You can also use it for applications where you are working with wood alongside another material.
OSI Quad Max is also 5 times stretchier and more temperature-resistant than the normal caulk, so it will last longer. If you are using it in an area that is likely to see a lot of movement, the Quad Max is the way to go.
As you would expect, the Quad Max is more expensive, but that is because it is tougher and it can be used on anything you like.
6. Sika Sikaflex-221
Sika Sikaflex-221 is a more robust alternative to the standard Sikaflex Construction Sealant. It’s another polyurethane caulk that can be used on a range of materials, including exterior wood. It can be painted but it’s also available in 3 colors; black, white, and aluminum gray. This is designed for use on trailers and caravans but it’s generally good for any applications where more movement is likely. It’s flexible and tear-resistant, making it better for repairs that are likely to be put under a lot of stress.
When you are sealing around a window or door, a standard Sikaflex Construction Sealant does the job just fine. But for more specialist jobs, it’s worth spending a little bit more on the Sika Sikaflex-221.
7. Top Gun 400 Sealant
Top Gun 400 Sealant is an acrylic urethane caulk that offers very strong adhesion and exceptional flexibility. It can stretch up to 800% of its normal size without breaking! It also takes paint better than most caulk products out there. This is ideal for filling any areas outside the home because you get a fully airtight and watertight seal that lasts a long time. It is dirt-resistant too, so it will stay nice and clean, even if you don’t paint it.
If you are looking for the most flexible option that still looks excellent when painted, you can’t go far wrong with Top Gun 400 Sealant.
8. Sashco Sealants Clear Lexel Adhesive Caulk
If you need a caulk that works well on difficult surfaces in wet conditions, Sashco Sealants Clear Lexel Adhesive Caulk is excellent. It is an interior and exterior sealant that gives a flexible, rubber-like finish that won’t crack over time. Once dried, it offers 400% flexibility in joints, so it will last a long time. It is completely clear and barely visible, especially when compared with silicone or other types of caulk. This is ideal if you want an invisible repair that won’t show up at all. However, if you need to, you can paint this caulk very easily too.
Lexel caulk is also amazingly waterproof, so you can even apply it in wet weather. It won’t hold up if it is completely submerged (in a swimming pool, for example), but it will stand up to any other weather conditions.
This is one of the best caulks money can buy and when applied properly, it’s durable, flexible, and looks great. However, it can be difficult to get good results because it’s tricky to apply. It’s much stickier than other products and if you’re not that experienced, you may struggle.
9. Red Devil 100% Silicone Sealant Architectural Grade
Silicone is not always the best choice for wood because it doesn’t adhere that well. But Red Devil 100% Silicone is an architectural grade caulk that does bond well to wood. It is an excellent product for fixing cracks and chips, but bear in mind that it can’t be painted over. So, if you’re looking for aesthetic repairs that blend in, this may not be the best choice.
Many silicone products contain a lot of mineral spirits and other solvents. When they dry, they don’t have the same durability that you get from 100% silicone. Although silicone may not always be the right choice for wood, it can be useful sometimes. But if you are going to use it, make sure you invest in good quality silicone like Red Devil.
10. Dap Alex Plus Acrylic Latex Caulk Plus Silicone
Dap Alex Plus Acrylic Latex Caulk Plus Silicone is a tough all-purpose acrylic latex caulk with silicone additives, which improve flexibility and strength. This is better than a standard silicone because acrylic latex bonds better to wood, but you still get the benefits of a good silicone. This is an incredibly fast-drying caulk too, so if you’re in a rush, you can paint over it in just half an hour.
It gives you an excellent waterproof seal and it’s flexible, so you’ll get a long-lasting repair. As all-purpose caulk products go, this is one of the best that money can buy.
Exterior Caulk for Wood FAQs
Can All Caulking Be Painted?
No, not all caulking can be painted. Silicone caulk cannot usually be painted and will need to be covered with a different type of caulk first. If you try to paint straight onto it, the paint will peel in no time at all. Acrylic and latex caulk, on the other hand, both take paint very well, but some may require a primer. Butyl-rubber caulk can also be painted well and doesn’t require a primer.
Before painting any caulk, it is important to make sure that it has cured properly. If you seal it before it is fully cured, it will not finish drying properly and it won’t perform properly. When using it outdoors, this means that it may not be properly water-resistant.
Can You Apply Caulking to Wet Wood?
In most cases, the answer is no. Applying caulking to wet surfaces is a bad idea and it won’t bond properly. With wood, you may also be sealing over mildew and rot, which will continue to spread. There are, however, some specialist caulks that are designed to be applied in wet conditions, like the Sashco Lexel Silicone.
As a general rule, you should always avoid using caulk on wet wood unless you absolutely have to. In that case, buy a product that is specifically designed to bond to wet surfaces.
Can You Fill Wooden Holes With Caulking?
Yes, caulking is a good choice for filling holes in wood. As long as you’re using the right type of caulk, it’s easy to fill small holes. However, if the caulk doesn’t bond to itself very well, you won’t be able to use it on large holes and you will need a filler instead. Usually, caulk is better for repairing small holes and cracks along the edge of a wooden surface, while filler performs better on a flat surface.
What is a Bead of Caulking?
A bead of caulking simply means a line of caulk. The width of the bead varies depending on the width of the nozzle. When you are cutting the end off, you can determine how wide the bead will be. Cutting closer to the top of the nozzle creates a smaller bead. Just bear in mind that the bead will shrink slightly when drying, and it should never be smaller than ¼ inch.
How Long Does Caulking Last on Wooden Surfaces?
The lifespan of exterior caulk on wooden surfaces always depends on the quality of the caulk, the weather conditions, and how well it has applied. If the caulk is painted over, it is protected by the paint and should last 7-10 years (the average lifespan of the pain) before it needs to be reapplied. Usually, you should re-caulk every time you paint the wood again. On unpainted wood, acrylic and latex caulks last roughly 5 years before they start to degrade, but some products will last longer.
It’s a good idea to check the caulk on wooden surfaces regularly to see if there are any signs of damage. If it is peeling or cracking, and there are small gaps appearing around the edges, it’s time to reapply.
Can You Apply Caulking on Wood During a Freeze?
It depends on the type of caulk that you are using. Latex caulk is not designed for use in temperatures below 5 degrees Celsius. Using it in cold temperatures will prevent it from bonding properly. However, other types of caulk are suitable for use in temperatures below zero, so you can use them during a freeze.
To be safe, always check the guidelines on the tube. The instructions will always tell you the optimum temperature range for application.
Can You Apply Caulking to Painted and Stained Wood Surfaces?
Yes, you can apply certain types of caulking to painted and stained wood surfaces. Acrylic and latex caulk will bond well to the paint, but consider how you are going to touch up the paint afterwards. Silicone, for example, won’t take paint or stain, so you won’t be able to match the color.
Final Thoughts
Caulk is a simple fix for a lot of exterior wooden surfaces, especially window and door frames. For best results, you need to choose the right type of caulk that bonds well to wood and holds up against the weather. As a general rule, I would go for acrylic latex products because they are durable and they take paint well, so they blend in perfectly.
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.