Wood does expand and contract with temperature. You can see this orientation and layering when you look closely at the edge of a piece of plywood. Rarely, if ever, will the plywood return to its original shape and size. DIY Frequently Asked Questions / Will OSB expand and contract like plywood? Wood, because of its cellular and fibrous structure, can readily absorb water. These expansion gaps are necessary as the plywood will naturally expand and contract. While it’s true a high quality finish will slow the rate of moisture exchange, it will not stop it. Plywood is made by cutting thin layers of a tree all the way around its circumference. OSB has a tendency to expand and contract, although manufacturers have come out with better resins that have made them more and more stable. This is extremely important to know, as many residential problems are related to water in the vapor state. Many people have seen plywood swell. This happens because there is no other direction for them to go to relieve the swelling pressure. In severe cases, the sheets of plywood can actually create humps and dips between the roof framing members. 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. This is with keeping a MC (depending on species) of 6% year-round. Wood only expands and contracts in one direction; perpendicular to the grain. If you could seal the wood you would be able to use silicone to install the Corian and you may be fine. This means that on a piece of 4 x 8 plywood, you can experience expansion due to swelling across the 4 foot dimension as well as the 8 foot dimension. No amount of sealer will stop it. Baltic birch plywood panels (a type of plywood consisting of birch veneers throughout) are sometimes sold as 5 x 5-ft. panels. These are placed snug against each other, and s… Its best to use MDF then veneer over the top with the finish of your choice. Plywood manufacturers are aware of these problems. 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. Solution #3 - Use the Medium Density Fibre (MDF) and similar versions of hardwood sheets. Applied finish does not stop movement. 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!!! !.So, lets talk about plywood and why it is the way it is, how can we best use it and what are some alternatives. This means that if you are sizing a project or cutting dados, rebates etc. These problems are, more often than not, caused by water or water vapor. Individual pieces of plywood buckle, twist and sometimes bubble or delaminate. 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. While you can lay tile directly over a concrete slab using thin-set adhesive, don't make the mistake of applying tile directly to a plywood subfloor. Events That Increase Movement Risks 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". 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. Jul 10, 2013 - "Plywood is stable; it does not expand and contract like solid wood." In fact, the installation relies on that. The key to avoiding these problems is to plan for the swelling. 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. - Woodworkers Source The evidence is unmistakable. Measure Width in inches. Wet air expands wood, dry air shrinks it. 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. If you install plywood sheets tightly against one another, the edges tend to pucker upwards when they expand. Keep these factors in mind so you can make the best choice: •Cost. Some of these come with hardwood vaneers laminated to their face sides, others are plain. Don't forget, plywood has the face grain aligned in two directions! 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. Know that wider boards expand and contract more than narrower ones. Plywood, particleboard and fiberboard are more dimensionally stable. Plywood countertops can also expand and contract with changes in atmospheric moisture since they are made from wood. Some of these come with hardwood vaneers laminated to their face sides, others are plain. 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). Like all other problems that woodworkers encounter, there are solutions. These terms are used when talking about the face of the plywood. The main issue with using a non-marine plywood is the eternal problem of time. Solution #2 - re-manufacture the width of each edge of plywood you will use. Of the two kinds of plywoods "sliced" is the most expensive and the most attractive as it simulates boards of wood. Don’t worry about plywood or other man-made slabs. Corrective measures can be expensive. 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?. 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?. 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. It is this veneer that is then glued to the plywood core, then sanded to make the finished sheet. 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. The shaft of the nail is slightly larger than 1/8 inch. We left approximately 1/16″ inch of space between each plywood sheet, and between the plywood and the van walls. Yet, what’s unique about a plywood countertop is whether it gets stains, scratches, or burns, you’ve got a way to cope! In other words, the wood will still expand and contract with temperature and humidity. 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. Like all other problems that woodworkers encounter, there are solutions. I have almost been blown off roofs on windy days when handling plywood. When you purchase plywood that says its 3/4". Plywood does not expand/contract the same as hardwood. They don’t have the seasonal movement that solid wood does. 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. 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. 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 hardwood sheets of plywood use less expensive softwood cores on which to build the hardwood face of the plywood. Wood is a natural product and as such expands and contracts with changes in moisture and temperature. Hardwood plywood does have its limitations. You must check before you nail. These are then assembled on the face of the plywood core where they are glued and then sanded to make the finished sheet. does expand and contract without breaking the air and contract as they disappear when installing plywood expands both lengthwise and. It will also expand and contract depending on the humidity where a plywood or MDF will stay more consistent. This expansion is greatest along the face of the grain of a piece of wood. Flexible paper back veneer is easy to work with and readily available. Also consider the time of year. Click to see full answer. 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!!! Use a quality grade of 3/4" plywood or 1x stock boards to do this. When installing OSB as a subflooring or roof decking, space the panels 1/4” apart. That was the hard hitting comment from an associate of mine recently. Solution #3 - Use the Medium Density Fibre (MDF) and similar versions of hardwood sheets. Poor quality plywood. 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. An exterior elastomeric caulk works best, because it has the ability to expand and contract with the temperatures and flexing of a structure. Many hardwood species are available or sheets can be made using veneer. 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. Squirt a 3/8-inch bead of caulk … Direction Matters. 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. It can absorb water in the liquid state as well as the vapor state. Much of the problems with plywood are a result of these cores, and here's why. Install the blocking flush with your cabinet tops by first drilling pilot holes at an angle through the blocking and then screwing the blocking to your cabinets. In order to achieve the best results when installing plywood products, it is very important to use the proper size nail. 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. Most hardwood sheets of plywood use less expensive softwood cores on which to build the hardwood face of the plywood. Virtually every one recommends that you, your carpenter or builder create a 1/8 inch gap around all edges when installing plywood. "Rotary" plywood on the other hand is made quite differently. All logos and trademarks in this site are property of woodworkweb and/or their respective owner(s). These are then assembled on the face of the plywood core where they are glued and then sanded to make the finished sheet. 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. That was the hard hitting comment from an associate of mine recently. The wood in winter projects will expand; the wood in summer projects will contract. 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. PLYWOOD - The Good, the Bad the Alternative, As an Amazon Associate I earn from qualifying purchases, Woodworkweb is a participant in the GoAffPro Affiliate Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to the partner site. If you sealed all sides and edges of the wood you would cut down on the changes in the wood. Compared to solid stock on a board-foot basis, hardwood plywood definitely is more expensive. If you get serious about your searching, you can find actual numbers on it. In any case, to bond tile to wood, you must use a flexible thin-set mortar with a latex additive. While you can lay tile directly over a concrete slab using thin-set adhesive, don’t make the mistake of applying tile directly to a plywood subfloor. All rights reserved unless otherwise provided as noted, please report any copyright infringements to the email noted elswhere on this site. It is not a pretty sight. 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. The exception to the rule is a floating floor. And when it was in a hot dry environment the Corian would expand and the wood would contract and crack the Corian. Traditionally plywood is the top choice – however, you’ll need to go for a thicker 12mm ply in order to ensure a rigid floor. Exposure to modest to moderate amounts of water will cause the EMC to gradually rise and the wood will start to expand. Particleboard and fiberboard, exposed to water directly, will expand in thickness quickly and dramatically. Pucker upwards when they expand … When water vapor levels rise, the cells within a piece of plywood pick up the water. 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! Not only that, the spacing of nails on the edges of a panel are frequently different from the spacing within the panel. How to … Wood that expands and contracts due to changes in moisture content will do so along predictable lines. A select log is mounted on what is essentially just a huge lathe. Like anything you do in woodworking selecting materials is half the battle and knowing what to look for and what application you are working on will go a long way in helping you select the right materials. Use a 16d sinker nail for this purpose. Knowing this, it is important that you plan for this expansion. 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. As wood expands (swells) and contracts with changes in humidity, the finish at joints will crack. 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. Engineered floors do not require the expansion area solid products need due to the way they are constructed in cross ply layers similar to plywood. 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. The humps and bumps in the roof cause the light to be reflected differently from the ceramic granules on the shingles. This will allow engineered planks to naturally expand and contract without causing disfigurement to the overall floor. You have to search very hard because the numbers are so small that nobody pays any attention to it. The cells begin to expand ever so slightly. This is accomplished quite easily if you simply follow established guidelines offered by plywood manufacturers and associations. Expansion and contraction is minimal to none as the ply layers act to restrict the movement in the overall product itself. When you purchase plywood that says its 3/4". A select log is mounted on what is essentially just a huge lathe. 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. 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. Do not countersink these nails! If the plywood is required structurally then this becomes a messy problem indeed. The cells begin to expand ever so slightly. In respect to this, will tile mortar stick to wood? 6. •Limited selection. How thick should Plywood be under tile? 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!!. So ... what's the difference other than price you ask ... whew, a LOT ....... Of the two kinds of plywoods "sliced" is the most expensive and the most attractive as it simulates boards of wood. Step 2: Find the average yearly change in moisture content. Strong winds can begin to easily pull plywood from walls or roofs in the event they have not been secured properly. To compound these quality issues, some of the wood that is used to create these cores is dryer that other portions. 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. Don't forget, plywood has the face grain aligned in two directions! If there is no gap, then the plywood will bend and buckle when it expands. Much of the problems with plywood are a result of these cores, and here's why. Subscribe to the FREE Ask the Builder newsletter to receive professional advice for your home. Now ... lets talk about the "core" for a minute. "Sliced" plywood is just as it says, slices of wood are sheared off with a giant knife, just like slicing cheese. Cut the tip off of a tube of elastomeric caulk using a utility knife. 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. Well, that's the story of plywood ... love it or hate it, it remains a great product for many applications, but not necessarily the only product. This expansion is greatest along the face of the grain of a piece of wood. Wood expands and contracts mostly across its width. Complete the form below and each week you'll get: Unsubscribe at any time. We respect your email privacy. Now ... lets talk about the "core" for a minute. Generally speaking, these sheets are flat ANS evenly thick because of their method of manufacture. This means that if you are sizing a project or cutting dados, rebates etc. When the moisture content changes the top will bow – always. 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… 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. 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). This gap will minimize or totally eliminate any puckering caused by swelling. It is this veneer that is then glued to the plywood core, then sanded to make the finished sheet. Veneer is attached to the substrate with wood glue. When you purchase plywood that says its 3/4". The face grain of each ply, or layer, is oriented 90 degrees to the ply immediately above or below. A 4 x 8 piece of plywood when exposed to wind forces is nothing more than a large sail. First of all there are two kinds of plywood, "sliced" and "rotary". When this swelling takes place after the plywood is installed, flooring, roofing, and or siding products can begin to look less than perfect. These boards are then laminated together using a hot press (basically a giant iron that fuses wood and glue together under heat). I have seen hundreds of houses where the roofing plywood has been installed improperly. With such small numbers, mm show the differences best) These are designed to not react at all to standard indoor environmental changes. They’re easy to use, and allow wood movement by sliding along a kerf in the rail as the solid wood expands and contracts. "Rotary" plywood on the other hand is made quite differently. 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.
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