Is Polyurethane Waterproof?
Yes, it is, but to a certain degree. And, that certain degree further depends on several facts, including, physical properties, thermoset, and how it is applied. Based on those factors, some polyurethanes may have more absorbance capacity than others. Practically, polyurethane even may have zero absorption capacity compared to many other available alternatives determined by the key factors as said.
What is it then?
Actually, you instead can call it water-repellent, as the polyurethane layer (after dries) creates a protective film that only repels water. Water can still penetrate the wood through the topcoat, although it will be difficult to soak through it. Nonetheless, polyurethane provides an excellent surface protection for wood, protecting it from scratches, discoloration, mold, and fungus.
Does Polyurethane Protect Wood from Water?
As said, adding polyurethane to your wooden furniture won’t actually make it waterproof – just prevent wet insertion for a certain time. However, it does give it extra durability and offers a higher level of protection, as it forms a plastic-like layer that resists weakening due to the wood’s constant expansion and contraction. But don’t forget that, whether oil-based or waterborne, it will not completely seal the wood, and it may still reveal weak points as it ages.
If water pools on the polyurethane-coated wood, it can penetrate it and cause damage. Therefore, it is vital to wipe any spills off immediately. This protective film has microscopic pores and makes it difficult for water to penetrate the wood. However, the protection provided by polyurethane is limited to a few days, and it is not waterproof in the long run. While polyurethane is similar to varnish, it is less competent in terms of waterproofing than varnish, particularly oil-based ones. But, of course, it is harder and more durable and water-protective than shellac.
Successful Wood Waterproofing
In another content, we have discussed the process of waterproofing wood. Here in brief you’ll get just what you can use for the purpose.
1. Use Wood Oil
A good way to waterproof wood is by applying wood oil. Any oil which is made from Tung oil and polymerized Linseed oil perform great to prevent wet insertion in wooden surfaces. While it requires more time to cure than Tung oil, it’s cheap and gives a beautiful glossy finish. While you need to apply three or more coats of a wood oil, it dries much faster and cheaper than polyurethane.
2. Use Sealer or Varnish
Appling oil-based varnish or sealer over polyurethane coats on wood is another excellent way to make the wooden stuff waterproof. It keeps the surface free from scratch at the same time. For outdoor and wet area uses, consider marine varnish first. It contains UV absorbers, which means it will resist damage caused by sunlight.
To protect your wooden furniture from UV damage, you should apply an exterior wood stain sealer every year or two. Alkyd-based stain sealants, on the other hand, will leave a light coating, so they’re better suited for interior wood items.
3. Use Stain-Sealer Combo
The use of a stain-sealer combo is beneficial when you want to protect your wood surfaces and preserve the natural beauty of the wood. Unlike painting, staining will not fade away over time. It will retain its natural beauty and make it more attractive. However, if you plan to place your rocking chair outside, it is not necessary to use a stain-sealer combo.
Stains and sealers protect wood from water and mold. Depending on the type of wood, different stains will provide different protection. Water-based stains will provide better protection against the harmful effects of ultraviolet rays and molds. A stain-sealer combo will give you the ultimate protection for your wood.
A two-in-one stain-sealer combo will seep into the fibers of wood, preventing cracking, peeling, and chipping. It also dries quickly, leaving a flat finish that is attractive and durable. It also resists the effects of water damage, mold, and mildew. In addition, a high-quality stain is designed to preserve the wood’s grain while giving it a beautiful finish.
Are Shiny or Glossy Finishes More Water-Resistant?
Floors with shinier surfaces are less water resistant than those with matte or satin finishes. High gloss, semi-gloss, satin, and matte sheen levels all score equally in terms of durability. However, less glossy surfaces conceal flaws better and retain their aesthetic value longer than their glossier cousins. The more light a floor reflects, the more easily scratches and dents are shown. The glossier the floor, the more light it reflects.
What Happens if Polyurethane Gets Wet?
Constant wetness on polyurethaned surface lead the water penetration inside wood (if not sealed by either way as said above). This can ultimately result in warping, swelling and wearing off of the poly finish and discoloration, e.g., the wood may turn gray and at the end black.
Can Polyurethane Prevent Water Rings?
Although polyurethane has an incredible capacity to repel water, it still can not effectively fight against water ring damage like most other finishes. To make it more difficult for moisture to penetrate the coat, however, think about adding additional coats of polyurethane finish. Remember, wood becomes more water-resistant the more layers of poly there are.
Water Absorption by Polyurethane Compared to Other Materials
Polyurethane differs from other urethanes because they don’t have the traditional hard and soft segments. Water is incorporated during the foaming process, increasing the urea content and hydrogen bonding interactions. The materials are composed of low-molecular-weight tri and tetrafunctional alcohols with carbamate and urea linkages that are higher than those in SMP (Shape-memory polymers).
In laboratory tests, the effect of water on polyurethane foam was investigated. It was found that the polyurethane foams’ tensile strength decreased when exposed to moisture. The effect was most pronounced after an exposure to 8% moisture and five degrees Celsius. At the same time, moisture saturation was reached after six hours of exposure to low humidity. These results are in line with other studies. Polyurethanes have good electrical insulating properties. The hardness of the polymer also affects its resilience. The lowest rebound compounds are generally used for shock-absorbing elastomer applications. However, compounds with 40-65% resilience are best suited for applications with high frequency vibrations. High resilience compounds provide more toughness and resist high frequencies. Moreover, the polymer bonds well to a wide range of materials during manufacturing, so it is highly versatile.
Is Polyurethane waterproof, then? Sadly, no, although it is among the best and most durable wood treatments available. Additionally, it may effectively repel water while shielding the wood’s surface from dings, mold, and fungi. If you just add some stain-sealer, tung oil, or varnish, the water-repellence will be easily turned into waterproofed.