AND, WHAT'S WORSE ... if you purchase two or three sheets of plywood, there is an excellent chance NONE of them will be exactly the same depth, in fact, there is a good chance none of the sheets will be consistently the same depth along each edge. Rotary plywood manufacture costs less than the sliced method and it looks more like "plywood", but here are the two methods for actually making plywood. When the tree is spinning a high rate, a large blade digs into the tree deeper and deeper and at the same time a long flat vaneer is unfurreled off the blade. A select log is mounted on what is essentially just a huge lathe. Plywood manufacturers are aware of these problems. Material finished on all surfaces will expand or contract at a slower rate than raw wood, but make no mistake—finished wood will eventually acclimate to EMC levels. To compound these quality issues, some of the wood that is used to create these cores is dryer that other portions. Of the two kinds of plywoods "sliced" is the most expensive and the most attractive as it simulates boards of wood. If you install plywood sheets tightly against one another, the edges tend to pucker upwards when they expand. The cells begin to expand ever so slightly. The humps and bumps in the roof cause the light to be reflected differently from the ceramic granules on the shingles. Wood does expand and contract with temperature. Flexible paper back veneer is easy to work with and readily available. !.So, lets talk about plywood and why it is the way it is, how can we best use it and what are some alternatives. In boat restoration, its generally considered bad to encase wood in "hard" epoxy because this will constrain the outside from moving but generate a lot of internal stress. Plywood is stable; it does not expand and contract like solid wood. This means that if you are sizing a project or cutting dados, rebates etc. With a little bit of knowledge, you can predict the degree of wood movement, and take appropriate action to accomodate the movement. Plywood countertops can also expand and contract with changes in atmospheric moisture since they are made from wood. In severe cases, the sheets of plywood can actually create humps and dips between the roof framing members. If there is no gap, then the plywood will bend and buckle when it expands. Exposure to modest to moderate amounts of water will cause the EMC to gradually rise and the wood will start to expand. To prevent serious problems with your engineered floor in later life, expansion gaps should be left around the edge of the room, wherever the floor meets a fixed object such as the walls or a doorway. Most materials shrink in cold weather and expand in hot weather because the molecules slow down when cold The most notable exception, of course, is water, which expands as it freezes. So if you were to purchase a three-quarter inch 4x8 sheet of "Oak Plywood", you would have the choice of purchasing either "sliced" or "rotary". This is extremely important to know, as many residential problems are related to water in the vapor state. Events That Increase Movement Risks How to … Now ... lets talk about the "core" for a minute. Don’t worry about plywood or other man-made slabs. Traditionally plywood is the top choice – however, you’ll need to go for a thicker 12mm ply in order to ensure a rigid floor. Rotary plywood manufacture costs less than the sliced method and it looks more like "plywood", but here are the two methods for actually making plywood. Corrective measures can be expensive. When this swelling takes place after the plywood is installed, flooring, roofing, and or siding products can begin to look less than perfect. When water vapor levels rise, the cells within a piece of plywood pick up the water. Not only that, the spacing of nails on the edges of a panel are frequently different from the spacing within the panel. AND, WHAT'S WORSE ... if you purchase two or three sheets of plywood, there is an excellent chance NONE of them will be exactly the same depth, in fact, there is a good chance none of the sheets will be consistently the same depth along each edge. No matter how firm the subfloor; the plywood will expand and contract at a different rate as the tile, causing cracks to develop in the grout lines or tiles over time. Plywood is most commonly used as the substrate because it is dimensionally stable, meaning that it does not expand and contract much with changes in temperature or humidity. With a panel to expand and contract without breaking the front to season. Of course they have other challenges, like heavy weight, poor substance for using screws with and some will absorb water either from the air, or from "puddling", which makes them swell and become weak. Also, if your project has one 3/4" piece on either side and those sheets are actually 1/16th shy, your entire project will be 1/8th narrower ... see the problems this can create!!! According to the Plywood Manufactures Codes, it does not mean the plywood is exactly 3/4" ... it means the plywood will not EXEED 3/4", which means it is always somewhat less than the 3/4" ... sometimes by 1/16th" (or more). How thick should Plywood be under tile? These are placed snug against each other, and s… Wood is a natural product and as such expands and contracts with changes in moisture and temperature. No amount of sealer will stop it. He's not the only one who is disappointed in the quality of plywood ... thousands more just like him have the same comments, I hear it ALL THE TIME!!. Plywood also has more flex than MDF, so you can gently bend it to create curves; plus, plywood won’t expand, contract, or warp, even under temperature extremes. Strong winds can begin to easily pull plywood from walls or roofs in the event they have not been secured properly. This means that if you are sizing a project or cutting dados, rebates etc. The face grain of each ply, or layer, is oriented 90 degrees to the ply immediately above or below. It will also expand and contract depending on the humidity where a plywood or MDF will stay more consistent. When you purchase plywood that says its 3/4". It can absorb water in the liquid state as well as the vapor state. •Limited selection. Solution #1 - don't use plywood - I say this a bit "tongue-in-cheek" because we all know we MUST use plywood for many projects, but now we can be a bit more selective. Like all other problems that woodworkers encounter, there are solutions. The wood in winter projects will expand; the wood in summer projects will contract. This will allow engineered planks to naturally expand and contract without causing disfigurement to the overall floor. All logos and trademarks in this site are property of woodworkweb and/or their respective owner(s). Many hardwood species are available or sheets can be made using veneer. Compared to solid stock on a board-foot basis, hardwood plywood definitely is more expensive. Squirt a 3/8-inch bead of caulk … Of course they have other challenges, like heavy weight, poor substance for using screws with and some will absorb water either from the air, or from "puddling", which makes them swell and become weak. That was the hard hitting comment from an associate of mine recently. Subscribe to the FREE Ask the Builder newsletter to receive professional advice for your home. Some of these come with hardwood vaneers laminated to their face sides, others are plain. Now ... lets talk about the "core" for a minute. Solid wood isnt used because it's density is not uniform and for the fact that it can even have leaks if the boards have knots. Keep these factors in mind so you can make the best choice: •Cost. Direction Matters. In order to achieve the best results when installing plywood products, it is very important to use the proper size nail. Use a quality grade of 3/4" plywood or 1x stock boards to do this. Although engineered wood flooring is made from a combination of plywood and a solid oak lamella or top layer, it still suffers some expansion and contraction with atmospheric fluctuations. Generally speaking, these sheets are flat ANS evenly thick because of their method of manufacture. Solution #3 - Use the Medium Density Fibre (MDF) and similar versions of hardwood sheets. Wood shrinks most in the direction of the annual growth rings (tangentially), and only half as much across the rings (radially, or from the centre of the tree to the outer edge… Veneer is attached to the substrate with wood glue. Some of the cores are not well made, they may have "voids" in them, or the quality of the wood they are made from may just be of poor quality. Given sufficient time and use it may be that the protective fibreglass layer becomes damaged allowing water to permeate the surface and begin to rot the underlying plywood. "Rotary" plywood on the other hand is made quite differently. First of all there are two kinds of plywood, "sliced" and "rotary". In the spring and fall, remember that the wood will expand half your total movement allowance and contract the other half. I spend good money buying what I am assured is "good quality plywood ", so why, when I get it home, does it make me want to turn it into firewood?. Much of the problems with plywood are a result of these cores, and here's why. does expand and contract without breaking the air and contract as they disappear when installing plywood expands both lengthwise and. Sign up to my newsletter to receive expert advice for your home! Do not countersink these nails! Doors I built and installed in south Florida move quite a bit with temperatures at over 100 degrees in the summer to sometimes in the 30's in the winter. Not all plywood applications require the same size nail or spacing between nails. The first piece of wood is placed so that it rolls “up” while each subsequent layer is laid 90 degrees to the one below it, and upside-down. It is not a pretty sight. Much of the problems with plywood are a result of these cores, and here's why. Wood expands and contracts mostly across its width. If you get serious about your searching, you can find actual numbers on it. While it’s true a high quality finish will slow the rate of moisture exchange, it will not stop it. I have almost been blown off roofs on windy days when handling plywood. If you could seal the wood you would be able to use silicone to install the Corian and you may be fine. This gap will minimize or totally eliminate any puckering caused by swelling. Applied finish does not stop movement. These expansion gaps are necessary as the plywood will naturally expand and contract. An exterior elastomeric caulk works best, because it has the ability to expand and contract with the temperatures and flexing of a structure. These are then assembled on the face of the plywood core where they are glued and then sanded to make the finished sheet. These are then assembled on the face of the plywood core where they are glued and then sanded to make the finished sheet. The key to avoiding these problems is to plan for the swelling. Pucker upwards when they expand … Solution #3 - Use the Medium Density Fibre (MDF) and similar versions of hardwood sheets. They’re easy to use, and allow wood movement by sliding along a kerf in the rail as the solid wood expands and contracts. These problems are, more often than not, caused by water or water vapor. When the tree is spinning a high rate, a large blade digs into the tree deeper and deeper and at the same time a long flat vaneer is unfurreled off the blade. These boards are then laminated together using a hot press (basically a giant iron that fuses wood and glue together under heat). The re-sizing of an edge can take a few different methods, such as running all your edges vertically through your table saw to have every edge exactly the same. It is more likely than not that the wood is going to be lose in these because if you followed the instructions of the dado blade and made it exactly 3/4" ... it will be too big for the plywood. The evidence is unmistakable. Jul 10, 2013 - "Plywood is stable; it does not expand and contract like solid wood." The re-sizing of an edge can take a few different methods, such as running all your edges vertically through your table saw to have every edge exactly the same. This means that plywood expands both lengthwise and widthwise when it is subjected to excessive moisture. I hope this does not muddy the waters. That's why they call it plywood. 6. He's not the only one who is disappointed in the quality of plywood ... thousands more just like him have the same comments, I hear it ALL THE TIME! Solution #1 - don't use plywood - I say this a bit "tongue-in-cheek" because we all know we MUST use plywood for many projects, but now we can be a bit more selective. In respect to this, will tile mortar stick to wood? That was the hard hitting comment from an associate of mine recently. Particleboard and fiberboard, exposed to water directly, will expand in thickness quickly and dramatically. In fact, the installation relies on that. Wood that expands and contracts due to changes in moisture content will do so along predictable lines. Yet, what’s unique about a plywood countertop is whether it gets stains, scratches, or burns, you’ve got a way to cope! Some of the cores are not well made, they may have "voids" in them, or the quality of the wood they are made from may just be of poor quality. The shaft of the nail is slightly larger than 1/8 inch. Wood only expands and contracts in one direction; perpendicular to the grain. Most hardwood sheets of plywood use less expensive softwood cores on which to build the hardwood face of the plywood. Rarely, if ever, will the plywood return to its original shape and size. This happens because there is no other direction for them to go to relieve the swelling pressure. We cut the 4×8 sheets of ½ inch plywood to size using a circular saw. Some of these come with hardwood vaneers laminated to their face sides, others are plain. Also, if your project has one 3/4" piece on either side and those sheets are actually 1/16th shy, your entire project will be 1/8th narrower ... see the problems this can create!!! Expansion and contraction is minimal to none as the ply layers act to restrict the movement in the overall product itself. Plywood does not expand or contract. Poor quality plywood. Baltic birch plywood panels (a type of plywood consisting of birch veneers throughout) are sometimes sold as 5 x 5-ft. panels. Some of these veneer sheets within the plywood expand or contract depending on how wet they were when they were used to make the "cores", and what the atmospheric conditions are where they are stored. Now I know this sounds tedious, but it's not that bad, and considering all the time you save by using plywood, you can afford to use up a bit of that time making it perfect. Plywood is made by cutting thin layers of a tree all the way around its circumference. It is this veneer that is then glued to the plywood core, then sanded to make the finished sheet.
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