You may have heard that you can’t polyurethane over varnish, but this is not the case.
In fact, it’s possible to apply a second coat of polyurethane on varnished wood surfaces. The key is using an oil-based polyurethane rather than a water-based one.
Oil-based will adhere to the old surface very well and provide a strong protective finish for your project or furniture.
Read on to learn how to put poly over varnish appropriately.
Can You Polyurethane Over Varnish
Yes, you can polyurethane over varnish without damaging the finish. This is so because it’s hard-wearing, long-lasting and durable, and with a high resin value, which allows it to resist harsh outdoor conditions. However, be careful how you apply it as some kinds of Varnish and polyurethane won’t work well on certain types of wood.
Read also: Can You Put Polyurethane Over Danish Oil?
Tools And Materials to Apply Poly over Varnish
There’re three ways of applying polyurethane over Varnish to your workpiece, either through spraying, using a brush, or using a roller.
All these methods require a certain amount of care, and the type of product you choose may also affect the final finish.
Since I will be using the brush method, I will use the following tools and materials on my projects.
- Sanding block
- Shop vacuum
- Oil-based/Water-based polyurethane
- 120-, 180-, 220-, grit sandpaper
- 80-grit sandpaper (for refinishing jobs)
- Tack cloth
- Wet/dry sandpaper
- Automotive polishing compound
- Automotive rubbing compound
- Dry lint-free/Tack cloth
- Mineral spirits
- Distilled water for water based polys
- Quality brush – natural bristle brush for oil-based poly and a nylon bristle brush for water-based poly
How To Apply Polyurethane Over Varnish
Learning how to apply polyurethane over existing Varnish isn’t tricky, and you can even apply this material to several surfaces. It’s important to ensure the surface to be sealed against is appropriately prepared.
Let’s get to it.
Step 1: Sand the Surface
Preparing a wood surface for sealant is never only cosmetic. Careful sanding and carefully shaping a wood surface before sealing it is all about obtaining the most even, best fit with few bumps. The bonus will look better, age gracefully, and simplify future refinishing even more.
As the basic prep guidelines, ensure you have cleaned and polished your wood surface correctly, and no streaks or unevenness exists as you want to have a smooth, uniform color throughout your entire surface. Use the 80- or 100-grits sandpaper, then smoothen it with 220-grit sandpaper.
If your workpiece has unnecessary water stains, make sure you remove it. Don’t forget to work in a well-ventilated workshop for fresh air circulation.
Step 2: Remove the Dust
Dusting using a vacuum cleaner is an important part before you apply poly on oil-based varnish surfaces. If you ignore this step, it can cause the wood to start looking rotten, dingy, or fuzzy.
Use a shop vacuum that has a soft brush attachment to remove the dust. Next, wipe it with a clean, lint-free cloth moistened with mineral spirits.
Further, remove the dust using a tack cloth and proceed to the next step. Be sure to remove all the grease and wax by scrubbing the surface.
Step 3: Seal the Surface
Using oil-based poly as a sealer can help extend your woodworks’ life and protect the surfaces from water damage and stains. Sometimes, you only need one or two coats, and you’ll be set.
For this step, thin your oil-based poly first. But can you really thin polyurethane? Read our guide to find out.
Next, use two parts of poly and one part of mineral spirits. Stir the mixture using a flat stir stick, dip your natural-bristle brush about 1 inch in the mixture, then apply your poly on the wood surface.
Use long, even strokes from end to end. Wait for 24 hours for the seal to dry.
Don’t shake the can nor use an exploded-tip synthetic brush – with strands divided at the tip because it will introduce air bubbles into the poly.
Step 4: Apply the First Coat of Polyurethane
After 24 hours, apply a coat of finish from the can. Be sure not to wipe the brush on the rim of the can as it may introduce air bubbles. If you want a fast-drying surface, use water-based polyurethane, but you’ll need to apply more coats than you will with oil-based poly.
Like in the above step, spread the spar Varnish on the entire surface using long, even strokes from end to end. To add, use overlapping strokes for a uniform coat.
Step 5: Shave Off the Bumps
Once the first coat is dry (at least 12 hours), use a razor blade or a sharp chisel to cut any drips. Be careful with your blade not to cut underneath the drip and damage the surrounding surface.
Step 6: Wet Sand the First Coat
Wet sand to remove minor blemishes and dust bumps. I prefer using 400-grit sandpaper mounted to a sanding block.
When performing this step, be sure to use circular strokes.
Once the surface is smooth, wipe it using a moist cloth. You can also dry it using a clean, dust-free cloth.
Step 7: Apply the Second Coat
After 24-48 hours of applying the first coat, apply the DIY wipe on poly as the second coat. The procedures are as given in step 4. You can repeat steps 5 and 6 if needed, then apply the last coat. This time, they are extra careful not to have drips on your woodwork.
Step 8: Polish the Surface if You Wet-Sanded the Second Coat
After about 48 hours, polish the finish. I prefer using an automotive rubbing compound.
Here, dampen a clean cloth with water, then apply the automotive rubbing compound in a circular motion.
Note: This compound has a fine abrasive to help you remove any scratches left by the sandpaper.
Leave the workpiece to dry, then buff the finish using a clean, dry cloth.
To obtain a more excellent luster, the polishing compound should be applied as the final step up to seven days of drying.
Interesting read: Can you polyurethane over polycrylic?
Which Is Better—Oil-Based or Water-Based Polyurethane?
It has been said, the best way to make sure your floors and furniture will last a long time is by using polyurethane (or a similar product). This has proven to be highly durable and resistant to several different external factors.
However, there’re those carpenters who still have a few questions regarding this product.
They want to know, for instance, which is better, water-based or oil-based plastic resin? They also want to know what these two types of polyurethane are and why they are superior.
The truth of the matter is, water-based polyurethane isn’t as superior in some ways as oil-based polyurethane.
The water molecules aren’t large enough to adequately fill the space occupied by the tiny bubbles created by the bubbles of the liquid polyurethane when it’s sprayed onto a workpiece.
As a result, the water-based product can sometimes leave behind a sticky or damp residue that can prove quite tricky to remove later on.
On the other hand, the oil-based polyurethane product won’t leave anything thoroughly and adequately applied. In addition to this, you may also want to look at the cost involved with these two products.
Water-based polyurethane is cheaper than oil-based polyurethane. Therefore, if you want to save money on your flooring and furniture, it may be better to choose the water-based type of polyurethane.
Although this type of polyurethane is cheaper than the oil-based, it isn’t as durable as the latter. Therefore, if you want the best quality flooring, it would be cost-effective to opt for the water-based polyurethane product.
Read Also: Difference Between Varnish and Stain
Tips for Working with Polyurethane
Being a popular material used in finishing applications, this product can be made into a different final coat, including flooring, siding, and moldings.
The coating can harden and make sure the surface won’t be scratched or damaged when it comes in contact with abrasive materials. Here are some common tips to keep in mind when working with this material.
When spraying urethane, avoid having too much water on the surface. If there’s a lot of water vapor, then the finished surface may dry too quickly.
It’s best to have a couple of inches of water between coats but make sure they are fragile. Also, make sure not to spray more than six inches from the edge of the material.
It’s also advised to start by applying two coats and dry them thoroughly before moving to the next coat. If a single coat isn’t dry enough before proceeding, it could cause the material to bubble up or peel up.
Using oil-based polyurethane is also recommended over water-based polyurethane because the water-based product will bubble up as quickly.
Before starting any application, always have a protective mask or clothing on hand. In addition to using a mask, it’s also advised to wear a dust mask with a filtration system on the air vents located around the work area.
Before you begin working on your project, make sure you have all the necessary equipment and supplies on hand; as soon as you have everything ready and on hand, you can begin to apply your coat, starting with a light dusting to get any dust off the surface and prepare the surface for the polyurethane coat.
If the surface has been painted, make sure to wipe the entire surface down to get rid of any extra paint residue that may affect the outcome of the coating. Polishing the surface will also help to improve the overall look of the finished project.
Related read: How to use wipe on polyurethane.
How Do I Get A Smooth Finish With Polyurethane?
If you’re looking for an easy way to finish your project, consider polyurethane. You can apply this coating yourself and get a gleaming finish as an expert would.
However, if you want to learn how to do it yourself, you should have a few items before diving in.
First, you’ll need:
- Orbital sander
- 6-mil plastic sheeting
- Mineral spirits
- Synthetic sanding pads
- Wipe-on polyurethane
Draw light, squiggly pencil lines on the wood surface at every grit stage if you have those. Then, use the orbital sander for sanding the surface; once the pencil lines disappear, proceed to the next grit.
Afterward, follow the steps for applying poly as described in the step-by-step section.
To make sure the coat adheres properly, apply several layers of polyurethane.
Start by coating the surface with a single coat and wait for it to dry completely. When the coating is dry, it’s time to add a second coat. Continue putting coats over until you reach your desired thickness.
Once your polyurethane is cured, you’ll have a smooth, sturdy surface you can use again.
If you’re worried about getting an uneven finish, fret not. Polyurethane is generally smooth, which means you don’t have to worry about leveling.
Many manufacturers recommend applying a light coat of polyurethane before painting or cleaning the hardwood floors. That way, the surface is evened out throughout the entire panel. If you plan to use polishes or waxes, they will also level the floor.
Read more on the ideal interval for polyurethane coats on hardwood floors.
Is Varnish or Polyurethane the Right Finish for You?
We get asked many questions about whether it’s better to use a varnish or polyurethane on your woodworks.
Both have their benefits and disadvantages, and it comes down to your requirements for the job you are getting done.
Although both will achieve a similar effect, different types of Varnish are better suited to different jobs.
From my experience, polyurethane tends to be a little more resilient than the previous Varnish, which makes it less prone to scratching. It can also produce a gleaming finish if applied well. However, if you are looking for a relatively low-maintenance product, polyurethane isn’t a great option.
On the other hand, Varnish produces a much more consistent floor’s natural color and appearance across all workpieces, but it’s a little weaker. However, in terms of strength, it does tend to crack and peel a little easier.
So, between Varnish and poly, I’d instead get poly. It’s worth remembering that you get what you pay for. While it should help provide a high level of shine, it will begin disintegrating if left untreated for long.
If you want a genuinely spectacular shine, you may want to purchase a polyurethane product. These types of products are longer lasting than any other option and are more resistant to stains.
The only real problem with these products is, they are more expensive, but both poly and varnish are drying oil combined, making them cling perfectly.
1. Can You Poly Over Varnish Without Sanding?
Wood surfaces that have been finished with Varnish or other finishes require sanding before you can apply polyurethane over them properly. Skipping the sanding step will make the newly-painted coat bubble, peel, crack or generally not adhere.
2. Do You Apply Varnish First Then Polyurethane?
Yes, varnish should be applied before polyurethane. This is because poly is an excellent and durable material that can withstand a large amount of punishment. In addition, it’s known for its resistance to the elements, in particular, extreme temperatures and harsh chemicals. Also, it can withstand many pressures due to its open cell structure, making it ideal for applications where a high strength-to-weight ratio is required.
3. Can You Seal Over Varnish?
Yes, you can, but you must be careful if you don’t want to end up with a bubble and mess instead of a professional-looking paint job. However, sealing isn’t necessary. That’s why people prefer to seal coat the wood with a thinned mixture of the same finish.
4. Can You Paint Over Varnish?
Yes, you can paint over varnish. However, you will need to thoroughly prepare the surface before you paint on varnished wood. This includes cleaning the surface with a damp cloth and sanding it down so that the varnish is no longer glossy. You will also need to use a primer before painting and ensure that the paint you use is suitable for use on varnished surfaces.
5. Should I Use a Sealer Before Polyurethane?
Most polys don’t require sealers. If you must seal before polyurethane is applied, ensure the sealer is compatible with the Varnish.
6. Does Polyurethane Make Wood Waterproof?
Yes, polyurethane is a tried and true sealant that has waterproof properties. It will also protect your furniture from water damage, fading, cracking, ultraviolet light damage, and shrinking. Read to find out more if polyurethane is waterproof.
7. Can Water-Based Polyurethane Be Tinted?
Yes, water-based polyurethane can be tinted. If you add dye to water-based polyurethane, you can get an amber tone on your woodwork. To add, Wizard Tints can be used to give your project a more tinted color as well. Here’s how to tint water-based polyurethane.
8. Can Denatured Alcohol Ruin Polyurethane Coat?
If polyurethane is exposed to denatured alcohol, it will remain intact. This is because it has a strong bond to resist even the worst of circumstances like UV light. It’s resistant to alcohol.
9. Polyurethane Vs Varnish
The difference between varnish and polyurethane is that varnish is made from resins, oils, and solvents, while polyurethane consists of polyol and diisocyanate.
So, Can You Polyurethane Over Varnish?
The first question that comes to our mind is what about the application of polyurethane over Varnish.
The answer to this question is you can. Varnish is meant to keep workpieces clean and presentable. In such a case, applying polyurethane over Varnish may be a good idea as it can help maintain durability in the long run as it is a drying oil with some film coat.
Have further questions concerning this topic? Drop us a comment, and we will revert ASAP.
Further, here’s a comparison guide between varnish and polyurethane to help you differentiate the two.