Polyurethane is the newest lab-technology product compared to other finishes like shellac, varnish, and lacquer.
It is better in some ways, like being more resistant to moisture and chemical. Ways how to apply water-based polyurethane and oil-based ones are also easy.
Based on the materials, the products belong to three types, oil-based, water-based, and water-based oil-modified.
- The oil-based one tends to warm up the wood color as it turns the color slightly amber.
- It takes more time to dry but creates a smoother and more durable finish. Yet the production releases more volatile organic compounds (VOC).
- For the ‘greener’ option, water-based polyurethane was created. Its finish is crystal clear and creates a plastic-like effect. It dries faster than the oil-based one but needs more layers.
- Lastly, the mixed one has similar characteristics to both types. It dries fast, has low VOC, and changes into amber. The only difference is the cloudy look.
Pros and cons of water-based polyurethane
As this writing focuses on the water-based one, here are the pros and cons of water-based polyurethane.
- It gives a clear look.
- It dries quickly.
- The ways how to apply water-based polyurethane are easy.
- It has no odor.
- It is good to preserve the color and pattern of the wood, unlike the oil-based that changes into amber.
- It creates a flexible finish after several coats.
- Even with only water, it is easy to clean.
- It is prone to getting scrapes, is not too resistant to heat and moisture, and is less durable.
- It isn’t easy to spot the previous application on the surface.
- It needs more layers as few coats are quite invisible.
The basic techniques of how to apply water-based polyurethane
- Preparing the surface: sanding and cleaning the surface is a must because it prepares the adhesion for the polyurethane to stick. If there is already a current coat on the surface, sand the coat a little bit to prepare the adhesion.
- Then how do you apply water-based polyurethane to the floor? Use an edger or orbital palm sander to smooth the edges. When every inch is ready, it is time to vacuum or clean from any debris left.
- If there are any cracks or gaps, fill them with wood filler. Then, let it dry and set. Sand the filler and clean the wood again.
- Preparing the water-based polyurethane: several brands require a thinning process for the polyurethane. Hence, read the directions. If you want to add thinner, add no more than 10%. To get rid of lumps, strain the poly first.
- Applying the first coat: damp any applicators that you use. Apply it evenly following the grains. Don’t press the surface too hard. For the floor, use a cut-in-pad for the edge. Get rid of any puddles if it’s already 5 minutes before it sets.
- For the normal temperature, wind flows, and humidity, 2 hours are enough for the surface to dry. Inspect all the surfaces; if it is good, tack it.
- Within 10 hours, the current layer will adhere to the new one. After the final layer, let the wood cure for 30-60 days.
When to Use Water-Based Polyurethane
If you don’t like dealing with messy, smelly solvents, you should use water-based polyurethane.
Water-based polyurethanes might be what you need if all you need is a thinner, more flexible coating; it’s simple to apply and even simpler to clean up after.
Even one coat of polyurethane made with oil is thick, but one or two coats of polyurethane made with water are almost invisible and don’t build up at all.
In the same way, if you want the water-based product to look like a hard shell, you have to use a lot of coats.
Problems while applying the water-based polyurethane
The major problem of how to apply water-based polyurethane is air bubbles. Water in its nature creates air bubbles and puddles. They could make the result uneven and bumpy.
Please read the related article: How to Apply Polyurethane without Bubbles
Besides, the liquid also could raise the wood grain and create lint. Moreover, the liquid may not flow out properly when the temperature is too hot.
Adding improper thinner could also make the finish crystallized.
Those problems could be avoided by preparing well, especially the sanding process and the right applicator choice.
Failed water-based application and ways to fix the wood
Once the problems appear, the ruined finish might have spots, bubbles, bumps, or ugly brush marks.
The clarity might also be uneven as some parts are clear while others are cloudy.
There are three ways to fix the failing finish. The first one is by sanding the ruined part. You can use high grit one like 400 or more.
To avoid more damage, high grit sanding sponge of at least 220 can be the safest option. The second is using steel wool, and the last and least-expected one is restarting the surface.
Tips on how to apply water-based polyurethane
- Check the product details carefully. As some products require thinning and others do not, knowing what is best for the application is a must.
- Apply the polyurethane indoors as bugs, dust, and other flying things might ruin the surface.
- Use flat and horizontal surfaces since the vertical ones could cause runs and drips.
- No shaking the product before applying the polyurethane. To mix the fluid, a gentle stir is enough.
- During the curing process, put the wood on the bright side. Hence you can spot the surface if there are any failures.
Best applicator for applying water-based polyurethane
Besides the steps of applying water-based polyurethane, getting the right is also crucial.
One of the causes of bubbles is the air in the brush. Different woods have different characteristics also, and each requires a certain applicator. For the flat surface, the brush is okay.
Yet a cloth is necessary for the round, vertical, or contoured surface to prevent drips. For a wider surface, rollers and T-bars are the best options.
Some claim that T-bars are better than rollers for polyurethane. For the brush-marks-free finish, use the stain pad.
Yet you still need to check the materials of the cloth whether it could absorb and release the polyurethane well or not.
Use Synthetic Abrasives, Not Steel Wool. Synthetic wool comes in different grades and is easy to find in stores that sell water-based finishes.
Between coats, you can use coarse to medium synthetic wool. To get the last layer off, switch to fine and extra fine.
Good varnish to pair with water-based polyurethane
If you want to go creative, put different varnish before or after the water-based polyurethane. However, some varnishes cannot go well with water-based polyurethane. An example is any oil-based varnish product.
Water doesn’t blend with oil and applies to the water-based varnish. Applying water-based application over the oil-based polyurethane might work. Yet the opposite doesn’t.
The most recommended coat before applying the water-based polyurethane is shellac.
Ways of applying water-based polyurethane over varnish are quite similar to the previous one. The key is to create adhesion of the current layer of varnish.