Achieving that flawless finish on your wood project isn’t just about your craftsmanship; it’s also about choosing the right sealant to enhance durability and aesthetics. And it’s paramount to ensure protection, especially for outdoor pieces.
But how can you be sure you’ve picked the right sealant? And how do you seal painted wood for outdoor use? In this article, I’ll share expert recommendations to guide you through the process!
Why Do You Need to Seal Painted Wood?
Using a polyurethane sealant is essential for outdoor use to make your wooden furniture last longer than ordinary. There are different sealers that you can choose from, which I’ll discuss further later.
But you should know that a sealant is not made for every wooden surface, especially those with existing polyurethane products like paint, or wax.
When Not to Seal Painted Wood
When working with wooden surfaces painted with oil-based or latex paints, there’s a unique interplay that can alter the color results when you apply a polyurethane coating.
For this reason, I’d advise against using polyurethane sealant on lightly sanded painted wood under certain circumstances. Let’s delve into those condition:
Wood Has an Existing Sealant
Before sealing the wood, you have to remove the old sealant.
When a new sealant is applied over an old one, the surface will turn messy and unappealing. Also, the bond of the new sealant is not as strong when compared to applying it to a clean surface.
Waterproof Paint Was Used
The best waterproof paints for wood are used to protect the surface from water and moisture penetrating it. So anything that you put over the waterproofing will not be drenched into the surface. This includes sealant products.
With a Unique Finish
Any wooden surface with a unique finish cannot be brushed with sealant. Finishing products contain chemicals and compounds that contradict the components of sealant. Therefore, sealant products cannot be combined with painted wood with a unique finish.
When to Seal Painted Wood
On a side note, you can apply a sealant over a painted wood surface, given that the following conditions are met.
If you have applied chalk or milk paint, you must use a sealant to protect the surface. You can also use sealant with lead-based. Lastly, you can use sealant to add different tones or shades.
(But what’s the best sealer for redwood? Check this review next!)
Benefits of Sealing Painted Wood
You can also use sealant for painted finishes for the following fundamental reasons.
Preserving the Finish
The final appearance of furniture and floorings varies on the finishing products you use. If you’re aiming for a specific final color, look, or texture, the right finishing products will help you achieve these goals.
And to preserve the finish, it’s imperative that you use sealant products on top as the final layer.
Preventing Mold Growth
Any wood surface can develop mold because of moisture, air, and contaminants trapped together on the surface. You can prevent mold and fungi from accumulating if you are going to use sealant.
Getting a Glossy Finish
You should discredit the idea that sealant reduces the gloss effect of the finish. Sealing wood with high-gloss components can improve the gloss finish of a surface.
Can You Seal Any Type Of Wood?
As I mentioned earlier, there are certain conditions that you should not apply sealant if it has an existing sealant. Also, if the painted wood has a unique finish or waterproofing applied to it.
When to Paint and Seal Bare Wood Projects
For these projects, you need to prepare it thoroughly, from cleaning to finishing. But finishing needs sealing to ensure that the finished surface will not get damaged. Again, the sealant protects and maintains the final appearance of your wooden surface.
Here are the important things you should know when preparing bare lumber for your wooden project:
Using a moisture meter, you should check the moisture content of bare wood surfaces using a moisture meter. The moisture content affects the absorption of coating products. For exterior wood surfaces, the ideal is 15-20%, and for interior surfaces, the maximum is 15%.
I’d strongly advise against using water to get rid of grains and other imperfections. Adding water introduces unnecessary moisture to the surface.
Before proceeding further, always prime your wood. I’ve often found that shellac-based primers offer superior adhesion for sealing products. They’re especially effective in prepping and sealing knots. If any sap dries from the primer, make sure to remove it and then apply a sealer over that spot to ensure a smooth finish.
The last preparation you need to seal it is sanding. After filling the holes and cracks, sanding should be done in the direction of the grain using 150-220g sandpaper.
Sealing Painted Wood: Detailed Step-by-Step Guide
The next thing you must understand is how to seal painted wood for outdoor use properly. I listed the things you’ll need, safety measures to be mindful of, and the detailed steps of the entire process.
Safety Considerations
For safety considerations, make sure that your workstation is well-ventilated. You can wear masks to prevent breathing in and use goggles to protect your eyes from droplets of volatile organic compounds (VOCs) from sealants.
Have your brushes with oil-based sealers cleaned with thinner or mineral spirits. You can use water and soap to clean brushes with water-based wood sealant. Also, separate the disposal of waste materials from regular waste so it will not be hazardous.
What You'll Need
For materials, you will need the following:
- Sealers (water or oil-based polyurethane)
- Cleaning agent (Trisodium Phosphate/ TSP)
- Paint stripper/thinner or mineral spirits
Some tools and equipment you need for sealing painted wood projects:
- Paintbrush
- Tack cloth
- Sandpaper (220-320g, 400g)
- Sander
- Stir sticks
- Bucket
- Sponge or lint-free rags
- Gloves (rubber or latex)
Step #1: Clean Your Painted Wood
Using your bucket and warm water, make a cleaning solution by mixing the TSP with your stir sticks. Make sure you are wearing gloves before you dip the sponge or rag in the solution.
Squeeze to remove the water from the rag and wipe the surface to remove the impurities like oil and dirt.
Step #2: Prepare Your Preferred Sealant
Prepare your wood sealant if you prefer oil-based or water-based polyurethane paints. Oil-based polyurethane sealant products are ideal for outdoor surfaces, while water-based sealants are susceptible to moisture and water.
Step #3: Sand Your Painted Wood Lightly
If the surface is rough and there are visible imperfections, you can sand the surface using 220-230g sandpaper. Sanding the surface can achieve a smooth finish.
Step #4: Remove the Dust
Dust on the wooded surface can hinder sealant application. So using your cloth, wipe the surface until all wooden particles are removed. A tack cloth is better than ordinary cloth because the former’s texture is sticky, and it can remove the smallest particles on the surface.
Step #5: Apply Your Polyurethane Sealer
Now, you can apply your preferred polyurethane sealer using a brush or rag. Depending on your choice of poly, you can use either of the two application tools.
When using the rag, you have to soak it in the sealant and then smooth it on the surface. Make sure you apply sealant on the end of the exposed cut of the lumber because this is the most absorbent part.
Step #6: Sand the Cured Polyurethane
The drying and curing time of polyurethane sealers depends on the type of sealant. But after it is properly cured, you need to sand the coats using 400g sandpaper. Sanding the cured sealers will give it a smoother finish.
Step #7: Remove the Polyurethane Dust
After sanding the cured polyurethane, use a tack cloth again to remove the poly dust. This will ensure that the surface is thoroughly cleaned.
Step #8: Re-Apply More Coats of Polyurethane Sealer
Add another coat of sealer to increase the appearance (gloss) and adhesion and add durability to the surface. If you decide to add multiple layers, you have to wait in between to dry it completely.
Step #9: Let the Wood Dry
Finally, when you are satisfied with your finished product, you need to cure the wood. Depending on the layers of your coat and the type of sealant products, you have to wait to dry it.
Choosing the Right Sealant for Painted Wood
You need the right sealant to achieve the result on your painted wood. Here are the sealant products you can choose from.
Oil-Based Polyurethane
Sealant products offer oil-based paints or solvent-based polyurethane that can make your it more durable. It is cheaper rather than water-based polyurethane and glossier than other sealants.
However, it emits VOCs compared to others, but it dissipates in a few hours after application. You also have to wait more time to dry the solvent-based poly.
Water-Based Polyurethane
If you want to have the best alternative for solvent-based, you can use water-based polyurethane. It is the ideal sealant for decorative furniture, which offers a natural sheen and has a milky look. You need synthetic brushes to apply this solvent.
Polycrylic Sealants
As a water-based sealant, polycrylic sealants are not durable as polyurethane. But it contains resins that protect the painted surface.
You can choose clear, satin, or high-gloss finishes, which you clean easily. However, you cannot use this with oil-based as it has less adhesion.
Paint and Sealer Product Combo
If you have white furniture or light-colored outdoor wood, then this paint and sealer product combo can give you the finish you want. You do not need primer or top coats for this sealant.
But you should follow the instructions from the manufacturers, particularly in the preparation and application. It does not stain and has less chance of discoloration because of its clear color.
Epoxy
Looking for a sealant that can last more than a decade or at least five years? Well, you can use epoxy sealant as it offers multipurpose sealing on surfaces. This is a sealant that can repel water and protect the surface from ultraviolet rays.
Its durability can be measured in the fact that boatbuilders use it. You can use clear or colored epoxy. But buying epoxy is expensive as compared to other sealant products.
Exterior Oils
Exterior oils refer to natural oils which can be used to seal the wood. Some exterior oils that you can add to it as sealant are oils from linseed, tung, coconut, and walnut.
You can also combine these oils with mineral spirits and other components for the paints. Danish oil and teak oil are some of the popular blended products of natural oils and polyurethane.
Shellac
This sealant is ideal for artifacts and outdoor furniture and is suitable for walnut, fine, veneer, and mahogany wooden surfaces. The only issues with Shellac products are you cannot dissolve them in water and solvents, and it does not offer additional durability.
You need clog spray equipment if you’re going to use it. It is not advisable to use it with a paintbrush.
Varnish
One of the common sealants you can use is varnish which you can use for floors, cabinets, and furniture. You can choose from lacquer, alkyd [1], polyurethane, shellac, and resins based on your varnish. Varnish is ideal if you want a clear and transparent finish.
Wax
Aside it offers protection, and you can use the wax to create a more appealing appearance for your wooden furniture. It also adds a multi-layer of protection to the surface. However, you need to buff the surface after application. Otherwise, it will look dull.
Lacquer
The appearance of this sealant can be distinguished from dull to medium to high-gloss. You can use this sealant for wooden furniture with a natural bristle brush tool.
Stain
Wood stain is another common sealant because it offers pigmentation to the surface. You can have your furniture a unique pattern finish, particularly the kinds of oak and ash. It also includes a binding property to provide adhesion.
Enamel
Enamel is famous for providing the final touch of the wood surface. Its texture before the application is similar to nail polish. Once applied, it gives the surface a robust, protective shell, ensuring durability and shine.
Why Seal Woods with Exterior Paints for Outdoor Use?
Outdoor surfaces are exposed to extreme weather conditions, so it needs additional protection.
Without a good sealant, they can deteriorate quickly, fading and becoming an eyesore right outside your home. That said, I can’t stress enough how vital a sealant is to achieving that long-lasting, polished finish.
Here are the basic steps to seal your wood’s exterior paint.:
How To Seal Painted Wood For Exterior Use
Step #1: Before the application of sealant, you need to prepare the surface. Make sure that it’s dry, and if there are imperfections on the surface, you can sand the area. Wipe the surface using the tack cloth.
Step #2: Prepare your sealant solution using a long stick and a clean bucket. Ensure that you stir the sealant inside the bucket in one direction slowly. For instance, if you stir it clockwise or counter-clockwise, stay in that direction to prevent air bubbles into the sealant.
Step #3: You can apply the sealant on the surface. Make sure you only brush a thin layer as your first coat. If you opt to apply a second layer, make sure that no bubbles, drips, or accumulation of sealant on the surface.
Step #4: Let it cure properly. If the surface is dried completely, you can now sand slightly. This will keep the surface super smooth. Just remove the dust with a clean cloth for the perfect appearance of your wood project.
Step#5: Finally, apply the final coat to achieve the results you’re yearning for.
Next Readings:
Key Things to Consider When Sealing Painted Wood
Before you seal painted wood for outdoor use, you of course need to ensure both your and your crew’s safety. Polyurethane products are highly flammable, so make sure you use a small amount of the suggested quantities.
Also, after you use the thinners and finishes, you should close the cans immediately.
Your brush should have bristles that have splits, and they should have different lengths. For water-based finishes, synthetic bristles are ideal to use, whereas, for solvent or oil-based, you can use natural bristles. Choose a brush with non-corrosive metal or plastic handle.
There you have it, the must-know sealing techniques on painted wood.
How to Ensure Your Paint Job Will Last
But how would you want your painted job to last longer? There are a few things you need to do before and after your sealing and painting job.
To ensure that it will last longer, you have to remove damaged paint before you apply a new coat. By scraping it off, you will give your new coat a good adhesion to the wood. You can use sandpaper to smoothen the surface.
For holes and cracks, apply a wood filler first to level the surface. Wait for the fillers to get dry before sanding and coating.
The technique you use matters immensely. Getting your strokes right can be the difference between a patchy finish and an even, smooth coat. And don’t even get me started on timing!
To prevent moisture or air bubbles from forming, it’s crucial to paint under the right conditions. Personally, I’d suggest painting when the weather is cool and dry for the best results.
And to give it a long life span, make sure to use primers and undercoats before applying your preferred top coats. Then give it a final touch using a wood sealer.
Common Mistakes When Sealing Painted Wood
To make sure everything your doing is in order and on the correct path, here is the list of common mistakes that our pro painters are avoiding.
Make sure you pick the right color for your wood. Oil-based paint, flat latex paint, and chalk paint have their ideal usage and proper techniques.
Also, avoid layering over an old coat. The previous coat has less adhesion, so the new coat will fall off eventually.
Last but not least is using a low-quality paintbrush. The bristles of a cheap brush can easily fall off and get mixed during the application. Also, you have to start from top to bottom so you can flatten the surface easier.
FAQ
What is the best outdoor sealer for painted wood?
The best outdoor sealer for painted wood is a polyurethane topcoat. I hgihly recommend using a clear poly that will seal and prolong the exterior paint.
Can you weatherproof painted wood?
Yes, you can weatherproof painted wood by using the appropriate sealant. You can apply two or more coats for outdoor surfaces to give sufficient protection against extreme weather conditions.
You can also use outdoor-grade paints or varnishes to enhance the wood’s durability and ensure its longevity in outdoor settings or areas prone to exposure.
Do I need to seal the exterior wood after painting?
Yes, you need to seal the exterior wood after painting. Make sure that the paint is cured or dried before using the wood sealer.
How do you seal acrylic paint on wood for outdoor use?
You can seal acrylic paint on wood for outdoor use by using a polyurethane sealant. It gives a durable layer of protection.
Interesting Read: Can You Apply Acrylic Paint on Your Face?
Can you use polyurethane outdoors?
Polyurethane products are suitable for outdoor surfaces. It offers durability and extension of it.
Can you put poly over a painted deck?
Polyurethane products are versatile, so you can have multiple coats of poly over a painted deck. Most paints absorb oil-based and water-based polyurethane.
Can paint protect wood?
Paint is a good barrier layer for wood. But your paint needs a sealant to have additional protection against tears and extreme heat, and cold.
Can you combine sealer and paint?
It is not recommended that you combine sealer and paint. You can mix them, but the results render a poor-quality finish. So you should stick in using sealer and paint separately.
How do you preserve your old painted wooden surface?
Using soap and clean water will preserve your old painted wooden surface. Using alcohol-based or any liquid can compromise the pain on the surface.
Can you put deck stain over paint?
Technically, you can apply deck stain over paint, but it won’t work the way you might hope. Deck stain isn’t designed to cover paint. Instead of a cohesive, blended look, you’ll end up with a distressed appearance.
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Conclusion
At this point, you already know how to seal painted wood for outdoor use. There are many things to be mindful of, but I’m confident that you’ll do it successfully with this guide. Your paint job will surely turn out what you expected.
You've probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.
Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.
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