Polyurethane is one of the most efficient agents for wood protection. Attaining the desired protection comes through proper application. Your skill, expertise and caution can not only ensure that – but a worthy polyurethane brush is also essential for a flawless painting and finish.
Why Use a Polyurethane Brush?
As a synthetic resin, polyurethane needs to be applied carefully. Brushes have proven to be the best applicator for polyurethane in most areas except those where spray or any other method is more useful. Ease of use is probably the foremost reason why one should use it for painting or finishing polyurethane, whether it’s oil-based or waterborne. It enables even novice users to achieve the desired, or at least, a reliable result.
The fine brush bristles (or foam) stroke excellently on even and straight surfaces, leaving no spots, marks and lines. Neither does brushing require you to wrap your hands with a towel soaked in polyurethane nor does it force you to reload the sprayer repeatedly. You just need to be careful about applying an excessive amount than required. But remember, you hardly get these benefits unless it’s a quality polyurethane brush.
Brush Types – Which is the Best Applicator for Polyurethane?
Materially there are two types of polyurethane brush – Bristle and Foam. Bristol brushes can be made in two ways – from natural bristles (made from animal hair) and synthetic bristles (made of nylon, polyester, or a blend of the two).
The question is, which is more suitable for applying polyurethane?
Well, there is a conventional understanding – “Natural bristle brush is better for working with oil-based polys, and synthetic filament brush performs great with water-based (also include oil-modified) polys.” But this might be relative, where you may find natural bristles working well for waterborne poly (as long as the finish doesn’t splay the bristles) and synthetic bristles for oil-based polys. However, painting with foam brushes or rollers can give you a controlled finish (as they prevent over-application of the solvent), but they create bubbles.
The conclusion is bristle brush is better if you can stroke well and wipe off the excess polyurethane ideally while application and the foam brush is better if you can control the bubbles efficiently. In addition, do not forget to comply with the instructions coming from the polyurethane manufacturer.
Selected Applicators – Best Brushes for Polyurethane
As we know, a brush is the best applicator for polyurethane indoor and outdoor, so let’s come across the right brushes among the wide variety available. Considering the application (how and where) and efficiency, we’ve shortlisted the best polyurethane brushes through our research. Each type includes not one but multiple similar-quality brushes (alternative to each other) so that users can choose one if not another.
Best Natural Bristle Brush for Poly – Purdy Ox-Hair
Best Synthetic Bristle Brush for Poly – Purdy XL Glide
Best Polyurethane Brush for Large Coverage – Wooster Brush Q3108-4
Best Polyurethane Paint Brush for Arts & Crafts – Pro Grade Chip
What Makes a Brush Right Applicator for Polyurethane
Why and how you will use a brush first determines which type of brush can be the right choice for the job. With this in mind at the beginning, you can narrow down the possible justification parameters for a suitable brush. For example, if you need to handle tight corners of a cabinet, a bristle brush is better than a foam brush, as the latter can not reach tough places.
Then look into the bristle. Brushes with fine bristles are always welcome, as they show excellence in working with both oil and waterborne polys. However, natural or synthetic filament doesn’t matter if you get the right softness, shape, size and durability in a brush required for your project. But natural bristles indeed offer better smoothness and fewer marks.
Now it comes about the brush size and shape. The intended purpose of using a brush or the type of project determines what should be the right size and shape. Usually, you will find these sizes – 1”, 1.5”, 2”, 2.5”, 3”, 3.5”, and 4”. 2-inch brushes and smaller ones are suitable for tricky projects with awkward and tight corners, where the angular shape is also an affirmative feature. 2-inch to 3-inch are excellent for most woodworking projects. But for covering larger surfaces, a 4-inch brush is recommended.
Check if the ferrule is strong and durable enough. A ferrule is the metal part of a paintbrush that connects bristles with the handle. It can be made of steel or aluminum. If it doesn’t seem strong enough and holding the bristles firmly, it’s best to avoid that brush. Otherwise, a strong chance is there to see the bristles bend, break, or detach from the brush soon. The weirdest thing that can happen is that the detached bristles can be stuck on the painted surface during finishing, which is quite annoying to remove and harmful for the project.
A comfortable and firm-to-grip handle is another sign of a good poly applicator. An easy-grip handle allows the applicator to control strokes, leading to making the application precise. Remember, a small-handle brush works well for small projects, while a large-handle brush is a must for big projects.
Polyurethane Sheen and Brush Suitability
When painting or finishing polyurethane, the sheen is significant, and you can target any – matte, satin, semi-gloss, or high-gloss – that is most suitable to your project. You don’t need to worry much about matte or satin, as the two keep fewer defects visible. So, using a non-fine bristle brush does not pose much risk.
But the gloss sheen, especially a high-gloss one, tends to show more defects such as lines and marks. Therefore, using a fine-bristle brush that strokes pretty smoothly is necessary to avoid marks or lines.
Simple Tips for Using a Polyurethane Brush
We have explained elsewhere how to apply polyurethane using a brush. Here we’re just providing you with some tips for using a polyurethane brush, whether for painting or finishing anywhere, from interior table to exterior deck.
- Dip the brush in mineral spirits before using oil-based poly or water before using a water-based finish. It will help you clean the brush quickly and go longer in between cleaning.
- Roll the handle rapidly between your hands after dipping the brush into water, spirit, or polyurethane, whatever the case, to eliminate extra.
- Pour some polyurethane finish (as much as you feel required for the project) into a separate container from the original can or container. It prevents the dirt and dust particles collected by the brush.
- Dip the brush about one-third and gently slap against the inside of the polyurethane container. The brush will stay dry and tough to offer coats accurately if you scrap bristles over the container edge.
- When bruising polyurethane, go with the grain to keep the appearance even and smooth.
Brushing Polyurethane: Problems and Troubleshoots
Even if there are some minor problems (quite insignificant), you may have to deal with five or six major problems during polyurethane brushing, as given below along with solutions.
The most common problem you may encounter while applying poly is brush marks or lines. Sanding and reapplying a skinny layer of polyurethane is how you can fix this. First, remove all dust particles from the painted surface with a soft and clean cloth. Next, use small or mid-grit sandpaper. After that, spread the required amount of water poly (if the previous finish is water-based), or wipe on with oil poly (if the previous finish is oil-based.
Bubbles appear when brushing (mainly with foam brushes) due to moisture emitted by the substrate or by turbulence of the polyurethane paintbrush. You can control bubbles by applying in moderate temperatures and prevent bubbles by brushing slowly. But if you still find some bubbles hardened inside the finish, flatten those using 220-grit sandpapers and then recoat polyurethane slowly.
Cracks can appear if you apply a thick coat on quite a hot day and if it dries promptly. Flatten the cracked areas with 220-grit sandpaper, wait until it’s a moderate temperature, and then spread a thinner layer of similar polyurethane.
Drips, usually caused by applying too much paint in a single coat, are the fundamental reason for brush marks. When you continue brushing to remove drips, it leaves brush marks. So, it is essential to prevent drips.
When you notice drips on the finished surface, stop brushing instantly, and wait till the finish gets dry. Then scrape the drips off using a razor or sand those with 220-grit sandpaper before you recoat.
Separated and Bead Forming Finish
While coating, you may discover that the finish is falling apart or forming into beads. If you find this, scrape the poly horizontally using a pull scraper when the finish is still wet and wash the wooden surface with a solvent (e.g. mineral spirit) for oil polys or by water for water polys.
The defect is usually caused by silicone existing in the substrate left by wax or polish on the wood surface. We suggest sanding the surface pretty well before applying finish and adding a leveling agent to the polyurethane to prevent such occurrences.
Cloudy Finish (Blushing)
This defect results from moisture in the wood or environment (wet, hot, and humid conditions) where you are applying. Blushing occurs more likely in solvent-based finishes, so oil-based polys are at significant risk, not waterborne options.
Unfortunately, there is no alternative but to remove the finish with sandpapers or an oscillating tool once it turns cloudy. But you can prevent this by ensuring dryness in wood and balancing the humidity and temperature of the surrounding environment where you’re applying.
Can You Reuse Polyurethane Paint Brush?
Yes, you can use a paint brush for applying polyurethane more than once. Then, all you need is to clean it properly using the proper paint thinner or water, as the case demands.
How to Clean Polyurethane Brush?
Only a few cautious steps are reasonable enough to clean your paintbrush or polyurethane brush and keep it reusable. These are in brief-
- Rinse well immediately after use;
- Clean with soap and water if you use it for waterborne finishes, including polys;
- Use mineral spirits to clean if you use it for oil-based poly and other finishes;
- In both cases, follow the safety instructions by the manufacturer.
- Let the brush fully dry;
- Store in its designated package or box between uses.
Can You Use Polyurethane Brushes for Varnish & Other Finishes?
Of course, you can use them for any interior or exterior finish, but that should be bristle-featured brushes. For oil-based varnish, you can use any natural-bristle brush or a fine synthetic-bristle brush with flagged tips.
On the other hand, the synthetic-bristle brush should be your first choice for water-based varnishes, as natural bristles splay when soaked into water or waterborne solutions. Avoid form brushes, but for larger projects, you can use rollers.
Can You Use Polyurethane Brush to Apply Adhesives Too?
Avoid using it for applying glue if you have an expensive polyurethane paint brush. But yes, you can feel free to use inexpensive polyurethane brushes if the glue is relatively thin. It’s best to learn the range of uses of your brush before applying it for any other purpose.
Having the best brush for polyurethane creates a significant difference to the entire project, from staining to finishing. The right brush ensures a smooth, even and precise finish. You will also find it easier and comfortable to work with. Last but not least, a quality brush does not cost much from your bucks!