How to work with plywood correctly

Plywood can be processed in a variety of ways, both with standard hand and electric woodworking tools. However, it should be noted that the glue in the plywood board causes rapid wear on the cutting tools, so it is recommended to use hard metal tools. Plywood can also be cut with modern laser cutting systems and hydraulic systems at 3500 bar.

Sawing

The best sawing result is obtained with a band or circular saw. To get a clean cut, sawing must be done correctly. First, sawing is performed across the direction of the fibers of the front side, then along. This method avoids splitting corners. On the best, front side of plywood, sawing is done with a hand or band saw, on the back side – with a circular or contour saw. When sawing with a circular saw, a high speed and low feed rate are recommended. The penetration limit of the saw blade teeth should be small.

Drilling

Smooth-edged holes are obtained if the drill is sharp enough and equipped with a front cutter. Start drilling from the front. Splitting on the back of the board can be avoided by using a backing sheet.

Using nails

For panels for walls, ceilings and floors, threaded nails or special screws are best suited, preferably with the head hidden or depressed. Ordinary wire nails are also suitable for covert nails. Acid resistant nails are recommended for nailing external cladding panels as they provide better protection against rust on the panel surface.

The length of the nails should be 2.5-3 panel thicknesses. The spacing between nails for panels for walls and ceilings is considered suitable – 10-20 cm along the edges, 20-30 cm – in the middle, depending on the load and the type of nails. In floor panels, the spacing should be 20-30 cm along the edges and 40-50 cm in the middle. Due to the fact that the structure of the plywood board is a strip of veneer with crosswise grain, nails can be driven close to the edge. A distance of 12-15 mm to the edge of the panel is considered suitable.

In stress-resistant structures, the strength and retention of the nails plays an important role in their integrity. The nails need to be driven in the correct order, they need to be long with large heads. Screws can be used. As noted above, structural fixation can also be improved by using glue at the joints..

Screw connections

In many applications, plywood panels are fastened with screws. In decoration, cabinetry, exhibition stands and shipbuilding, screws are preferred. Auxiliary holes can be pre-drilled, with the hole in the panel matching the screw diameter and the smaller hole in the frame; the diameter of the latter will be half of the previous one. The head of the screwed-in screw must not penetrate the face veneer. Washers must be used if domed nails are used. When attaching sheathing plywood to metal structural components, special screws can be used to secure the plywood board from the back without damaging the front.

Floor panels for freight containers and trailers are usually attached to the metal chassis using self-tapping screws. For example, plywood boards 27 mm thick can be fixed with M6x40 mm screws. The screw first penetrates the plywood board and then cuts the threads in the metal. This method is fast enough.

Thin plywood panels for transport engineering are also easily attached to the metal structure using the aforementioned self-tapping screws. Plywood boards are easily bolted. The bolt hole should be 2 mm larger than the bolt diameter. There should be washers and nuts under the bolt heads to protect the panel surface. To avoid damaging the wood under the bolt, do not over tighten the bolt. Where plywood is used outdoors, an overtightened bolt may press into the board surface and swell with moisture. This will cause cracks in the plywood surface around the bolt..

Locks, hinges, shelves, etc. can be easily and securely attached to the plywood surface from any side or edge. The most durable is fastening with clamping devices. If it is necessary to place screws on the edges of the panels, the holes for them must be pre-drilled.

Mounting

Plywood can be attached to the structure with glue, nails, staples, screws, rivets or bolts. When choosing a fastening method, it is important to consider the operating conditions, the required strength and appearance. Prior to installation, the plywood board must be prepared in terms of its end-use conditions, and precautions must be taken to prevent possible expansion or contraction of the board due to moisture or temperature changes. A gap of 2 mm at the joints is considered necessary. An elastic core can be used, for example, between the edge of the panel and the steel frame of the structure. In heated structures, ensure adequate ventilation of the plywood board.

Connection types

Joints and joints are important components of plywood structures. There are many types of plywood board joints: tongue-and-groove, tongue-and-groove and others. When done correctly, they provide the structural integrity of the walls, floor and supporting elements. The ends of the plywood board are usually the most sensitive part, so special attention must be paid to the processing of joints, especially if the plywood is intended for outdoor use..

In walls and ceilings, butt, open, tongue-and-groove, folded and strip joints are recommended. In outdoor applications, the various strip joints provide the best protection against external influences. Vertical and horizontal profiles made of aluminum effectively protect the edges of the plywood board. Resistance to rust makes them a suitable material for facades. However, if an open joint is preferred for architectural reasons in outdoor applications, the edges must be properly finished. Approximately 2 mm / m must be maintained for panel expansion. In butt joints, this distance should be 3-6 mm. The tongue and groove joint is usually used for floors and panels that go under roofs. It effectively prevents the panels from lifting and damaging the roofing materials, and is able to withstand higher loads than a conventional butt joint. The panel is fixed by secret nailing.

The best load-bearing capacity is obtained by using a stepped profile or similar special profile with flanges supporting the edges of the adjacent panels. Such profiles are used, for example, in the construction of floors for containers for the transport of goods or trailers..

Gluing

Raw plywood is usually glued with any wood glue. The choice of adhesive depends on the way of working, the moisture content during the end use and the required strength. Common types of glue: PVA, phenol, epoxy resin, polyurethane, etc. PVA glue is suitable for indoor use. This adhesive is colorless and has good adhesion strength. Phenol and epoxy adhesive have a high bonding strength that can withstand harsh environmental conditions. When bonding plywood to metal, epoxy type glue is recommended. Contact adhesives are commonly used for bonding large surfaces and for veneered plywood intended for indoor use.

It is not recommended to glue film faced plywood. Film-coated plywood is not capable of long-term adhesion. If film-coated plywood is attached with glue, the surface to be glued must first be sanded down to a layer of wood, for example, with sanding paper. It is desirable that the glue is epoxy. The surface to be glued must be dry and clean..

The adhesive should be applied evenly to both surfaces to be bonded with a roller or brush. The desired pressure force is achieved with clamps, screws or nails. Suitable nail spacing is 1 nail per 40 cm2. Any excess glue should be removed before it hardens. Always read the adhesive manufacturer’s instructions carefully..

Grinding

The surface of plywood is usually sanded with relatively coarse abrasive paper (# 80-100) perpendicular to the grain of the wood. If an extremely smooth finish is required, for example for high-quality varnishing, we recommend sanding with fine-grained paper in the longitudinal direction of the wood grain.

Surface finish

The sanded, flat plywood surface provides an excellent base for subsequent finishing. Plywood can be laminated, laminated, painted, impregnated with special paint or mortar, etc. When choosing paint or primer, it is important to consider the tendency for cracks in veneers. The surface can also be covered with laminate or fine wood veneer. The use of a thin film is possible. Plywood can also be wallpapered. If plywood boards were stored in high humidity conditions, they must be dried to normal moisture content before finishing. The surface should be thoroughly cleaned of dust from previous treatment. This procedure must be repeated before each finishing step. Depending on the required quality, 1-2 layers of coating are applied.

Edging

To level the board edges after sawing, they can be slightly trimmed. The best result is achieved by paving from the corners towards the middle, thereby avoiding splitting at the corners. Panel edges can also be sanded. The ends are painted 2-3 times with acrylic paint with special additives.

Primer

Wood is a natural material that expands and contracts depending on the complex effects of ambient temperature and humidity (despite the transverse veneer layers inside the slab). Cracks are observed on the inside of the face veneer, which expand and contract under the influence of moisture changes. For these reasons, a preliminary primer is necessary for subsequent painting. Flexible paints are used and the correct color combination is important.

Painting the backing paper completely prevents the formation of cracks on the paint layer due to moisture In high humidity and outdoor applications, plywood boards should be painted on the back. In such conditions, end-face processing is important and must be carried out especially carefully and several times. Plywood intended for outdoor use must be painted with special paints.

Painting

The paint application gives the plywood a natural textured pattern. The surface of the board can also be painted completely, without the appearance of wood grain. The paint is applied by brush or spray. Colored plywood is acceptable for both interior and exterior decoration. But before the final painting, the surface must be treated with a special solution to prevent the appearance of blue stains and fungi, since the biological resistance of transparent paints is limited due to the minimum content of a binder.

Varnishing

Birch plywood with a varnished surface is pleasant to look at and is easy to keep clean. Before varnishing, the panel surface should be sanded with fine-grained emery paper. Sanding dust must be carefully removed and the surface covered with diluted varnish.

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