木材の動きを理解する - プロジェクトを守る鍵

What is the key to preventing most of the damage to wood projects?

Understanding wood movement. Wood takes on and gives off moisture as the humidity and temperature around it change, and it swells and shrinks as it does.

If you don’t understand and plan for wood movement, it can spoil your project with warping and cracking.

Whether you’re using wood for furniture, flooring, cabinetry, or some other application, you’ll want to understand wood movement so you can plan for it before it causes problems. The following sections will show you how:

• 木材の動きの種類
• 木材の動きに影響を与える要因
• 木材の選択と準備
• 木材の動きに関する設計上の考慮事項
• 木材仕上げ
• 木材のメンテナンス
• トラブルシューティングと修理

まず、木材が動くさまざまな方法を見てみましょう。

木材の動きの種類

Wood movement is caused mainly by changes in moisture content. As wood absorbs moisture, it swells, and as it releases moisture, it shrinks.

How much it moves depends on direction. Wood moves very little along its length. Most movement happens across the grain, and tangential movement (parallel to the growth rings) is about twice as great as radial movement (across the rings).¹ That’s why quartersawn lumber shrinks and swells less in width than plainsawn lumber.¹

Keeping these differences in mind throughout the woodworking process can help prevent moisture-related damage in the long run.

木材の動きに影響を与える要因

Wood moves toward its 平衡水分含有量 (EMC), the moisture content at which it is neither gaining nor losing moisture in its surrounding environment. Until it reaches EMC, wood will continue to swell or shrink. Changes in temperature and humidity change the EMC, so they lead directly to changes in the wood’s moisture content and to wood movement.

To minimize movement after you complete a woodworking project, make sure the wood is acclimated to its environment beforehand.

The wood itself also plays a role. Some species move much more than others as their moisture content changes. Going from green to oven-dry, for example, true mahogany shrinks about 4.1% tangentially and teak about 5.8%, compared with 8.6% for northern red oak and 9.9% for sugar maple.¹

By taking these factors into account throughout the woodworking process, you can minimize moisture damage in the long term.

木材の選択と準備

As you plan your project, whether you’re building furniture, installing a hardwood floor, or taking on outdoor construction, here are some ways to account for wood movement.

適切な木材の種類を選択する

As mentioned above, some wood species are more stable and less prone to movement, which makes them better suited for projects where wood movement is a significant concern. For indoor projects like furniture making and hardwood flooring installation, choosing a stable species helps your work last.

検討している種について時間をかけて調べましょう。役に立つ情報源の一つは 木材ハンドブック published by the USDA Forest Service’s Forest Products Laboratory. Chapter 2 describes commercially important wood species, and Chapter 4 covers how moisture affects wood, including shrinkage values for many species.

乾燥木材を選ぶ

Kiln-dried lumber is dried in a controlled environment to a target moisture content, which reduces later shrinkage and gives you a more stable product.

Keep in mind that a “KD” (kiln-dried) or “S-DRY” (surfaced dry) grade stamp on softwood lumber generally means a maximum moisture content of 19%, or 15% for lumber stamped KD 15.¹ That’s well above the moisture content recommended for interior woodwork and furniture, so check the wood yourself rather than relying on the stamp.

柾目木材を選ぶ

Because wood moves more in some directions than others, the way a board is cut matters. Quartersawn wood has its growth rings at 45 to 90 degrees to the board’s wide face. Compared with plainsawn lumber, it shrinks and swells less in width and cups, checks, and splits less.¹

水分含有量を確認する

木材の水分含有量を推測するだけでは不十分です。 木材水分計 正確で信頼できるデータを取得するため。

木材の水分含有量を測定するために使用できるメーターは 2 種類あります。ピン型水分計または ピンレス水分計. Both can provide accurate readings if you use a high-quality meter. A pinless meter is often preferable because it doesn’t leave pinholes in your wood, and pinless meters generally take readings faster than pin meters.

水分含有量はいつ測定すればよいですか?

Do it before you buy the wood and again before you begin your project.

Check that the reading is as close as possible to the EMC where the finished piece will be used. In most of the U.S., the 木材ハンドブック recommends an average moisture content of about 8% (6% to 10% for individual pieces) for interior woodwork, flooring, and furniture, and about 12% (9% to 14%) for exterior uses. The interior average is about 6% in the dry Southwest and about 11% in damp, warm coastal areas.¹

使用する EMCチャート to find the average EMC for your area.

木材の水分含有量が EMC から大きく離れている場合は、時間をかけて乾燥させるよりも、他の木材を探したほうがよいかもしれません。

しかし、その数字がほんの数ポイントずれているだけなら、慣れるのに時間をかけるだけで十分です。

木材を順応させる

Letting wood acclimate to its final environment before use helps stabilize its moisture content and reduces the chance of movement-related problems.

Acclimation involves storing wood in the space where it will be used, with good air circulation and the temperature and humidity at normal living conditions.

Acclimation time varies with species, thickness, starting moisture content, and conditions, so don’t go by the calendar alone.

木材の準備ができたかどうかはどうやってわかりますか?

Use your wood moisture meter to see whether the wood has reached the EMC.

そうして初めて、安全に作業を始めることができます。そして、その場合でも、木材の動きに注意してください。

木材の動きに関する設計上の考慮事項

By managing moisture content before you begin your project, you’ve set yourself up to avoid most movement problems. But wood will still move as the seasons change, so plan for it during the woodworking process too.

When designing and building wood projects, allow for expansion and contraction by leaving enough space between components. This prevents undue stress on joints and fasteners, which could lead to warping or cracking.

And since wood expands and contracts mainly across the grain, try to align your components with similar grain directions. This helps prevent differential movement and reduces the risk of problems.

You can also accommodate movement with the type of joinery you use. Here are some examples:

• フローティングパネル: In cabinet doors or other panel assemblies, floating panels allow for wood movement without stressing the frame or causing cracks.
• ブレッドボードの端: These are used on tabletops and other large surfaces to help keep them flat. Attach them so the top can still move across its width, typically by gluing only at the center.
• スライディングダブテール： This type of joint allows for movement along the joint’s length.
• 舌と溝のジョイント: Commonly used in flooring and paneling, tongue and groove joints allow for expansion and contraction while keeping a tight, even appearance.

次に、特定のプロジェクトに関する考慮事項をいくつか見てみましょう。

フローリングとパネル

Account for expansion and contraction to prevent buckling or gaps. Follow the flooring manufacturer’s installation instructions, including expansion spacing and underlayment.

家具の建設

• ケース商品： When building case goods like dressers and bookshelves, consider using frame-and-panel construction.
• テーブルと椅子: Use appropriate joinery and allow for expansion and contraction in critical areas, such as where a solid-wood top attaches to its base.
• ベッド： ヘッドボードとフットボードには、フローティングパネルまたはスラットデザインを使用します。

アウトドアプロジェクト

• デッキとフェンス： Choose wood species with decay resistance. Leave proper spacing between boards for expansion and contraction.
• ガーデン家具: Use stable species, durable finishes, and joinery that allows for movement.
• パーゴラとガゼボ: Build pergolas and gazebos with strong joinery and adequate spacing.

構造部品の取り付けと接続が完了したら、仕上げとメンテナンスに関する湿気関連のポイントをいくつか示します。

木材仕上げ

Finishes such as varnish, lacquer, and paint slow down changes in the wood’s moisture content, but they can’t prevent them.¹ Even a well-finished piece will move as humidity changes, so it’s still important to keep indoor humidity at reasonable levels.

仕上げのオプションは次のとおりです。

• Film-forming finishes: Varnishes, polyurethanes, and lacquers build a protective film on the surface. They come in both oil-based and water-based versions, and water-based finishes generally dry faster.
• Penetrating oil finishes: Natural oils like linseed or tung oil soak into the wood rather than forming a film, and they give a low-sheen, natural appearance.

Apply the same finish to all sides of a piece, including undersides and end grain, so moisture moves in and out as evenly as possible. Prepare the surface by sanding and cleaning it thoroughly, follow the manufacturer’s instructions, and allow the finish to dry and cure fully.

木材のメンテナンス

To maintain the quality and longevity of your wood projects, follow these wood care practices:

• 表面保護： Use coasters, placemats, or other protective barriers to prevent direct contact between hot, cold, or wet items and the wood surface. This helps avoid moisture-related issues and other damage.
• 直射日光を避ける: Light changes the color of wood over time, and direct sun can heat and dry one side of a piece faster than the other. Position your wood projects away from direct sunlight, or use blinds or curtains to reduce exposure.
• こぼれた場合はすぐに対処してください: Wipe up spills promptly to keep moisture from penetrating the wood and causing warping or cracking.
• 適切な洗浄製品を使用してください。 Choose mild, wood-safe cleaning solutions for your wood surfaces. Avoid harsh chemicals that may damage the wood or the finish.
• 定期検査： Periodically check your wood projects for signs of damage or wear, such as loose joints, lifting veneers, or worn finishes. Address these issues promptly to maintain the integrity and appearance of your woodwork.

トラブルシューティングと修復

一生懸命に作業した後、木工作品に反りやひび割れが見られたらどうしますか？問題解決の第一歩は、その原因を突き止めることです。

次のことを行います。

• Measure the moisture content of the affected wood with your moisture meter and compare it with unaffected areas.
• Investigate the surrounding environment for moisture sources, such as leaks or high humidity.
• Assess the impact of other environmental factors, such as sunlight exposure or temperature swings.

Whether the cause is moisture, design, or the environment, fix the underlying problem first. Depending on the damage, you may be able to repair the piece, or you may need to replace the affected parts or boards with properly dried wood.

Use this guide as your starting point. By accounting for moisture ahead of time, you’ll save yourself the time, money, and headache of fixing problems later on.

Measure moisture content with a quality moisture meter, and take these steps to keep your wood projects beautiful and durable.

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ロン・スミス

ワグナーメーターの営業マネージャーであるロンは、様々な業界の計測機器および測定システムにおいて35年以上の経験を積んでいます。これまで、計測機器メーカーにおいて、地域営業マネージャー、製品・プロジェクトマネージャー、営業マネージャーを歴任してきました。

最終更新日: 8 年 2026 月 XNUMX 日