Plywood has many uses in carpentry and woodworking as they are easy to install and detach. It pays to know which type of plywood can serve its purpose for decades and the factors that influence its functionality. The right choice of plywood may impact the quality of your project. Keep reading and find out the best plywood for the outdoors.
How Strong Is a Plywood?
The answer depends on the type of plywood you are using. It does not say that branded plywood offers resilience against weather or moisture. The brand may play a role, but many plywood products of the unknown brand offer extended, lasting benefits to your project.
Branded plywood usually comes from China or small manufacturers, and importers re-brand them as their in-house products. So, it is untrue that branded plywood is a premium quality product. Retailers hype the branded plywood compromising the quality instead.
Exterior plywood is the best material for outdoors as it can withstand extreme conditions for outdoor use. It is excellent for walkways, decks, garages, benches, gazebos, cabanas, sheds, planters, outdoor shelving, and furniture. This plywood is resistant to water, flooding, and humidity.
Manufacturers apply waterproof glue in between the wood layers to reinforce the plywood. Although not as strong as hardwood as the surface has visible flaws and knots, this material is a good alternative for outdoor uses.
Tips on Identifying the Best Plywood to Be Used Outdoor
Know the Purpose of Using it
The deciding factor when to use plywood depends on your purpose. Choose a Gurjan or waterproof plywood if you use it for wet areas like the bathroom and kitchen. If you use it for furniture in your home interior, look for MR or commercial-grade plywood.
If you are using it for outdoor use, choose a Douglas fir plywood as it is resilient to moisture and weather and adds aesthetics to your furniture piece.
Buy from a Wholesaler
Buying plywood from a stockist or wholesaler means you get a good bargain over buying from retailers. Wholesalers have an extensive catalog of plywood sheets from different manufacturers; among the plywood that you can opt for include MR Grade Plywood, Gurjan Plywood, T1-11, CDX, and OSB.
You can compare the quality and price by checking the full plywood sheets from a wholesaler. Retailers offer a limited number of plywood sheets, where you only choose from one sheet or trade sample.
Look for Grade Certification
Good quality plywood does not always have to be exterior; it should have a product certification. Each country that produces plywood has different compliance marks, for example, the ISI mark if it comes from India. MR Grade plywood has an IS: 303 marks, while waterproof plywood has an IS: 710 marks.
You can also identify the manufacturer by looking at the CML number below the ISI mark. There are four plywood veneer grades in the United States: Grade A, Grade B, Grade C, and Grade D, with the fifth grade known as C-plugged.
Examine the Quality
The look of a plywood sheet can be deceiving. You must scrutinize the sheet to determine its quality. Run your fingers on the surface of the wood to see if it is smooth, and check if it has a wood face veneer.
The plywood should have a uniform thickness in all its layers and corners. Lift one side of the plywood to determine which part is heavy or light; heavy plywood carries extra density.
Examine the sides to find the core layers; make sure each layer does not have core gaps and overlapping. Well-made plywood should not bend, and the center is not hollow. Knock the plywood’s center; if it produces a different sound in all its parts, it means it is not recessed.
Hollow plywood does not offer firm support and easily bends and warps. One of the best methods of determining the quality of the wood is to test a small cut piece. Complete core plywood has enough nail-holding capacity.
Pros & Cons of Exterior Plywood
Exterior plywood guarantees its long-lasting benefits in outdoor furniture and other uses outside your home. Plywood manufacturers treated the plywood with chemicals.
Composite wood plywood, including exterior plywood, consists of wood resin boards that act as a bonding material. The calculation of adhesive formulation is phr or parts per hundred resin.
Its chemical composition includes 100phr for phenolic resin, 0-10phr for extender, 0-20 phr for water, 5-10 phr for filler, 0-5.0phr for hardener (CH2O), and 3-10phr for solubilizer (NaOH). It consists of 730 to 5880 process pressure (psi) and a process temperature of 100 to 150 degrees C.
The difference between regular and exterior plywood is that exterior plywood has waterproof gluing between each layer for reinforcement. This method makes the plywood resistant to extreme conditions and elements. It is durable for indoor and outdoor uses, adding aesthetic value to the furniture pieces or exterior constructions.
Its disadvantage is that it lacks a rustic look compared to hardwood, as there are visible knots and tarnishes on the surface. However, many types of exterior plywood are available today.
One is marine-grade plywood for boat building, and the other is exterior wood structures. It can stand against moisture and humidity compared to ACX and oriented strand board (OSB).
Moisture: Biggest Enemy of Exterior Plywood
Moisture is the biggest culprit, which is why some people dislike using plywood outdoors. It can take a toll on outdoor structures and furniture pieces, even if the plywood has several adhesive layers. Suppose you cannot do away with plywood for your outside facilities. In that case, the best remedy is to select the best plywood with a high moisture-repellency property carefully.
The best way to protect the plywood from moisture is to prevent it from directly contacting water. The plywood warps and deforms once the water penetrates the surface. Proper installation of plywood can extend its lifespan, ensuring that no amount of water or moisture seeps into the layers.
Types of Plywood You Can Use on Outdoor
1) Marine-Grade Plywood
Building contractors and professional woodworkers prefer marine plywood for interior and outside structures. It has superior performance as the wood is more durable than other types of plywood. It is sometimes known as boiling waterproof plywood (BWP) as it can stand for three days of boiling water exposure. Hence, it is a popular plywood for constructing marine vessels.
Marine plywood can be a good material for wet areas in your home, such as the bathroom and kitchen, if you are on a tight budget. It is excellent for wall cladding and insulation. This plywood type tops the list of materials for cupboard requirements in wet areas due to its resistance against building water.
Most marine plywood uses Douglas fir or Western Larch wood and a strong adhesive called WBP or phenolic glue. The veneers in layers of marine plywood are premium quality without gaps, blemishes, and hollows.
Each core layer of marine plywood uses a single-core veneer to provide extra strength to the structure. Aside from boat building, marine plywood is the best material for building outdoor tables, benches, decks, planters, and porches.
2) Aircraft Plywood
Aircraft plywood is a top-grade plywood commonly used for aircraft construction. It was a popular material in aircraft building during World War II. This plywood type could be hardwood plywood or thin birch plywood with a width of 1.8mm. Both inner and face veneer plies are free of blemish and knots. The core layers of aircraft plywood do not have gaps and hollow sounds.
The downside of this plywood is that the back veneers are not as good as the face veneers due to some open defects, but they can still have the same quality as the face veneers. Manufacturers of aircraft plywood use a strong adhesive to glue the layers, such as WBP phenol formaldehyde and WBP melamine formaldehyde.
The best tree species to produce aircraft plywood include Douglas fir, beech, walnut, hard maple, mahogany, and birch. Aside from aircraft construction, this plywood is ideal for boat building, furniture making, model boats, toys, wooden crafts, and musical instruments.
3) CDX Plywood
Contractors use CDX plywood in roof and exterior wall constructions. It consists of one side with veneer Grade C and another with veneer Grade D. Both sides bond together using glue to withstand moisture. Some people need clarification about CDX if it is a pressure-treated, outdoor or exterior plywood due to the letter X in its name.
X stands for the type of adhesive it uses to glue the veneers and does not stand for the exterior. The glue makes the plywood stand against exposure to moisture for a short time, not for the long term. Building professionals cover it with shingles, siding, or bricks to make it stand for long hours from moisture.
CDX has a thickness of 3/4, 5/8, and 1/2 inches. It is suitable outdoors, as shown in its X marks, and can survive against extreme conditions if it has a urethane finish coating.
4) OSB Wood Panels
These wood panels resemble plywood with perpendicular layers consisting of fifty wood strand layers. Oriented strand board offers extra strength due to the wood strands and adhesive hot-pressed into the wood sheets, aligned in every layer. It is more advantageous than plywood as it comes in larger panels, which is less costly.
OSB is excellent for wall, sub-flooring, roof sheathing, and roof decking. It offers more shear strength than regular plywood. These wood panels do not possess core gaps and are sustainable as the manufacturers source them from sustainably grown trees and not harvested from forests.
5) Pressure-treated Plywood
Pressure-treated plywood can last for years due to its resistance to insect infestation and rotting. It is improved plywood treated with chemicals under high pressure to stand against infestation from termites, wood borers, mildew, and mold. Manufacturers use chemicals in treating regular plywood, such as copper azole, chromate copper arsenate, and ammoniacal copper quat.
6) T1-11
T1-11 has been a popular siding material since its introduction in the 1960s. It offers a natural wood-grained look, ready for stain or paint coating. The downside of this exterior grade plywood is that it is prone to water damage due to its composition and fabrication process. It is not resistant to moisture, making its lifespan short. It needs proper installation and sealing to prevent damage in the long run.
Conclusion
Plywood does not have the longevity and durability that hardwood has. It cannot last for years if it has prolonged exposure to moisture and harsh conditions if you use it for outdoor furniture and wooden structures. The best plywood for outdoor can serve for years, given they have been treated with chemicals to thwart pests and mildews and to stand against moisture. Moisture is the number one culprit of plywood deterioration. There are many plywood types and alternatives that you can use outdoors that can last for 35 to 50 years. Our guide above can help you decide which plywood is suitable for your project.