Installing new cabinets can be a tricky process, especially when it comes to getting them level and secure. Many cabinet installers use shims during the installation process to help level and stabilize the cabinets. But do you actually leave the shims in place under the cabinets when the job is done? Here is a detailed look at whether or not you should leave shims under cabinets after installation.

What Are Shims and Why Are They Used Under Cabinets?

Shims are thin, tapered wedges made of wood, plastic, or metal that are inserted between cabinets and the floor or wall during installation. Shims serve several important purposes:

• Leveling cabinets – Floors and walls are rarely perfectly level and flat. Shims compensate for any uneven spots, allowing the installer to level cabinets side-to-side and front-to-back.
• Filling gaps – Small gaps inevitably occur between cabinets and floors/walls. Shims take up space in these gaps, providing a tighter fit.
• Securing cabinets – Shims wedged firmly under cabinets help hold them in place once level and stabilized. The friction helps prevent movement.
• Reducing vibration – Shims minimize contact between cabinets and floors/walls, which dampens vibrations that can cause rattling inside cabinets.

In short, shims make installing cabinets easier while also creating a more secure and sturdy finished product. Installing cabinets without shims would be extremely difficult and result in a sloppy final installation.

Should Shims Be Left Under Permanently Installed Cabinets?

Whether shims should remain under permanently installed cabinets is a matter of debate among installers. There are good arguments on both sides. Here are the pros and cons of leaving vs. removing shims after cabinet installation:

Reasons to Leave Shims Under Cabinets

• Maintains cabinet stability – Leaving shims in place ensures cabinets stay firmly wedged. This prevents rocking or shifting out of position over time.
• Prevents future rattling – Shims minimize contact with the floor, reducing transfer of vibrations that could loosen cabinets or cause rattling inside.
• Reduces cabinet sag – Long-term moisture exposure can cause some cabinet substrates to sag slightly. Shims provide ongoing support.
• Simplifies leveling process – With shims remaining, installers don’t have to perfectly match cabinet bottoms to the floor. The shims compensate for slight variations.
• Saves time – Removing shims requires carefully sliding cabinets out to access the underside. Leaving them in place is faster.

Reasons to Remove Shims After Installation

• Allows floor to fully support cabinets – With shims removed, the entire bottom of the cabinet rests directly on the floor for maximum stability.
• Prevents compressed or crushed shims – Over years of use, cabinet weight and shifting could flatten shims so they no longer fill the gap effectively.
• Avoids debris accumulation – Dust and dirt can collect on top of shims left under cabinets, which could lead to insect/rodent issues.
• Provides better cleaning access – Homeowners can more easily clean under cabinets if shims are removed.
• Enables floor leveling for future – With shims gone, any sections of uneven floor can be flattened for future cabinet or appliance projects.
• Looks more finished – Some homeowners prefer the appearance of cabinets sitting directly on the floor without shims underneath.

Best Practices for Shims Under New Cabinets

Most expert cabinet installers recommend removing shims after installing permanent cabinets whenever possible and practical. This ensures the floor bears the full weight rather than shims taking up space between the cabinets and floor.

However, leaving shims under very long spans of cabinets is usually advised, as they provide ongoing support against sagging. For most standard cabinet runs of under 10 feet, shims can and should be removed.

Here are some best practices to follow when using shims under newly installed cabinets:

• Use high-quality, kiln-dried wood shims that resist compressing or warping over time. Stay away from low-quality bargain shims.
• Place shims as close to cabinet corners as possible for most stability. Also shim near appliance cutouts or other heavy areas.
• Gently hammer shims in at slight angles rather than straight in to “lock” cabinets in place.
• Check for gaps after driving in shims. Add additional shims until any gaps close.
• After installation, slide cabinets back gently to access and remove shims. Pull them straight out rather than hammering them sideways.
• For long spans, only remove shims at ends and periodic sections rather than the entire length.
• Consider leaving shims only under problem spots with vibration or instability issues.
• Sweep and vacuum under cabinets after removing shims to clean up any dust, dirt, or debris.
• Fill any unfilled gaps with small wood wedges after removing shims for an extra-secure fit.

Frequently Asked Questions About Cabinet Shims

Many homeowners and DIYers have additional questions about proper use of shims during kitchen cabinet installations. Here are answers to some of the most common questions.

Should I use shims when installing new cabinets?

Yes, using shims is an essential part of the cabinet installation process. Shims allow installers to perfectly level and stabilize cabinets even on uneven floors. Attempting to install cabinets without shims will likely result in a crooked, insecure finished product.

What material should I choose for cabinet shims?

Expert cabinet installers strongly advise using wood shims, which better resist compression and hold shape compared to plastic or metal. Choose kiln-dried hardwood shims rather than cheaper softwood which can compress and warp.

Is there a certain thickness of shim I should use?

Most cabinet installers use a standard shim thickness of around 1/8 inch. Use multiple shims if a thicker amount is needed for leveling. For especially unlevel floors, consider using up to 1/4 inch thickness in problem spots.

Where exactly should I place shims under new cabinets?

Focus on shimming near the corners and under major weight-bearing areas like appliance openings. Also shim cabinets 24 inches or longer in length every few feet. Avoid just shimming the very center, which can create a weak, unsupported span.

Should I hammer shims straight in or at an angle?

Angling shims slightly (about 15 degrees) allows them to wedge firmly in place and “lock” the cabinets. Hammering them straight in risks not achieving a tight fit. Gently tap angled shims in until any gaps disappear.

How can I remove shims without damaging new cabinets?

Carefully slide cabinets back just enough to access shims, then gently pull them straight out rather than hammering them sideways to remove. Take care not to scratch cabinet surfaces. Removing shims can take practice and patience.

Is there an easy way to clean under cabinets after removing shims?

Use a strong vacuum with crevice tool to remove dirt, dust, small wood pieces, etc. You can also sweep thoroughly before vacuuming. Make sure to clean up any debris left under cabinets from pulling out shims.

Signs It’s Time to Remove and Replace Shims

Over time, even properly installed shims can begin failing at their job of stabilizing cabinets. Here are some signs that existing shims under cabinets may need to be replaced:

• Loose cabinets – If the cabinets rock or shift when opening doors or drawers, shims may be compressing and loosening.
• Visible gaps – Gaps that reappear between cabinets and floor indicate shims have flattened and no longer fill space.
• Rattling cabinets – Shims help minimize vibration transfer, so rattling could mean they need replacement.
• Warped shims – Humidity can cause low-quality shims to swell, warp, and crack.
• Insect/rodent issues – Small wood pieces from old shims can attract pests if left under cabinets.
• Sagging cabinets – If cabinets droop in the middle, shims may be failing to support weight.
• Floor work needed – Old shims must be removed to level uneven floors for new cabinet or appliance installations.

How to Shim Under Cabinets Like a Pro

Installing kitchen cabinets is a difficult job that’s nearly impossible for amateurs to do smoothly without shims. Here is a summary of pro tips for shimming under cabinets like an expert:

• Use high-quality kiln-dried hardwood rather than softwood or composite shims that compress.
• Make sure cabinets are pre-level and secure to each other with screws/nails before shimming.
• Shim near corners and heavy spots first, working outward. Shim entire runs of over 24”.
• Gently hammer angled shims to wedge them into gaps. Check for tightness.
• Add additional shims until cabinets are fully level and stable with gaps eliminated.
• For long spans, only remove some shims after installing. Leave some for support.
• Carefully pull shims straight out when removing rather than hammering sideways.
• Vacuum and sweep thoroughly under cabinets to remove all debris once shims are gone.
• Consider leaving some problem shims that control vibration or instability issues.

Conclusion

Installing kitchen cabinets is a challenging process that requires proper use of shims to level, secure, and stabilize them. While opinions vary, most experts recommend removing shims after installation whenever feasible to allow the floor to fully support cabinets. However, some shims should remain under very long spans to prevent sagging over time. With high-quality shims installed carefully by a skilled professional, your new cabinets will enjoy a lifetime of functionality and beauty.

When Should You Shim Under Cabinets?

Shimming under cabinets is an important part of ensuring a quality installation. There are certain situations that definitely call for utilizing shims during the cabinet installation process:

Uneven Floors

One of the most common reasons to use shims is when installing cabinets on an uneven floor. Even slightly uneven floors can make cabinets unstable and prone to rocking or tipping if not properly shimmed. Careful shimming allows cabinets to be leveled despite imperfections in the floor’s surface.

Professional cabinet installers always come prepared with an array of shim thickness options to handle variances in floor flatness. Attempting cabinet installation on uneven floors without shimming virtually guarantees a sloppy, unprofessional finished look.

Filling Gaps Around Cabinets

Gaps inevitably occur between the bottoms of cabinet boxes and the floor or walls during installation. Leaving these gaps can make cabinets feel loose and insecure. Shims are an easy solution for filling small gaps around the perimeter of cabinets for a tighter fit.

Driving in shims around the edges also reduces reverberation and “chatter” within the cabinets that can occur when they are installed directly against the floor or walls. Shims minimize contact and dampen vibrations.

Securing Cabinets Together

Attaching cabinets together with nails or screws is not always enough to prevent subtle shifting or misalignment, especially on uneven surfaces. Strategically placed shims wedged between cabinets provides extra holding power. The friction applied by shims prevents individual cabinets from slipping out of position.

Supporting Appliance Cutouts

Heavier appliances like ovens and microwaves require extra support when installed into cabinet cutouts. Shimming beneath the sides of the cutouts helps bear the load and prevent sagging or distortion over time. Shims also minimize direct contact between the appliance and cabinet for a vibration-free fit.

Bridging Large Floor Spaces

Spanning longer open floor spaces between walls with a continuous cabinet run increases the chance of cabinets sagging in the middle over time. Placing periodic shims under cabinets when they are over 8 to 10 feet long provides ongoing reinforcement against drooping or bowing.

Stabilizing Corner Cabinets

The triangular shape of corner cabinets leaves them prone to instability on two sides. Generous shimming in the corner where the cabinets meet the walls on both sides is important for maximizing sturdiness and preventing shifting out of square.

Leveling Individual Cabinets

Sometimes just one cabinet in a run winds up slightly out of level with the rest. Targeted shims under just the problem cabinet is an easy fix to bring it back into plane with the surrounding cabinets. This avoids having to tweak multiple adjacent cabinets.

When Working Alone

Installing cabinets solo makes keeping them properly aligned very challenging when fastening together. Using shims provides temporary support and friction that substitutes for an extra set of hands. The shims hold cabinets steady until fasteners are in place.

Conclusion

Any time the floor is uneven, gaps are present, appliances are being integrated, or extra support is needed, shimming during cabinet installation is strongly advised. Experienced installers rely on shims to simplify the alignment process and create secure, level cabinetry that stays rigidly in place for the long term.

What Are the Best Materials for Shims?

Shims come in a variety of materials, each with pros and cons. The type of shim used during cabinet installation plays a big role in creating a stable, long-lasting finished product. Here is an overview of the most common shim materials to help identify the ideal choice:

Wood Shims

Wood shims are a cabinet installer’s first choice. Wood offers numerous advantages:

Strength – Wood shims made from dense hardwoods do not compress or flatten easily under pressure like softer materials. This allows them to maintain the desired thickness for filling gaps.

Friction – The texture of wood shims creates friction against cabinets and floors that keeps them from slipping out of place after installation.

Workability – Wood shims can be easily filed or sanded if adjustment to their size or shape is needed during installation.

Appearance – For homeowners who prefer a look of quality, an all-wood shim installation under cabinets has natural appeal.

The downsides of wood shims include potential instability when exposed to moisture and the fact that they can split if hammered in too aggressively. Overall, wood is the first choice for professional cabinet jobs.

Plastic Shims

Plastic shims offer consistency and convenience:

Uniformity – Molded plastic shims have precise, uniform thickness and shape from one shim to the next. This allows for fast, predictable shimming.

Easy availability – Plastic shims are widely available at any hardware store. There is no need to source specialty wood shims.

Moisture resistance – Plastic will not swell or deteriorate due to minor humidity exposure during installation like wood can.

However, plastic shims lack strength compared to wood, and their slippery surfaces provide very little friction. Plastic works acceptably for quick, temporary jobs but not for permanent professional cabinet installation.

Metal Shims

Steel or aluminum are sometimes used as shim material:

Strength – Metal shims resist compression and deformation under heavy cabinet loads.

Thin profile – Metal can be rolled very thin while maintaining strength, allowing quick shimming in tight spots.

Adaptability – Metal shims are available in convenient folding designs.

On the downside, metal shims lack friction and their hardness makes precise adjustment very difficult. Special metal tools are required for on-site modifications. Metal conducts noise more readily than wood or plastic. Overall, metal shims are rarely seen in cabinet work.

Composite Shims

Newer on the market are composite shims made from laminated layers of wood veneer, fiberboard, and plastic. Composite shims offer a balance of properties:

Strength – More resistant to compressing than plastic alone.

Low friction – Slides smoothly into place but maintains its position.

Thin profile – Can be produced in thinner dimensions than solid wood.

Consistency – Even thickness and shape from one shim to the next.

Workability – Can be trimmed/sanded if needed.

The compromise performance of composites leaves them still inferior to wood for permanent cabinet shimming in most installers’ opinions. But composite shims are superior to plastic or metal alternatives.

Conclusion

Wood shims remain the gold standard based on their strength, workability, and friction. But plastic and composites work acceptably for less demanding DIY cabinet projects. Metal shims are rarely used in cabinetry. Making sure you use the optimal shim material for permanent or temporary shimming is key to long-term cabinet stability.

What Are the Best Places to Shim Under Cabinets?

Strategically shimming in the ideal locations is just as important as choosing the right shim material. Paying attention to where shims are placed under cabinets can prevent problems down the road. Here are the most crucial locations professional installers make sure to shim:

Near Cabinet Corners

The corners of the cabinet box take the brunt of weight and movement forces. Shim placement right next to the inside and outside corners is critical. This stabilizes both the sides and front/back near the most vulnerable joints.

Well-shimmed corners also minimize likelihood of cabinets pulling out of square over time. Taking the time to shim carefully at corners makes the rest of the installation process easier.

Under Appliances

Any cabinet cutouts for appliances – especially heavy ones like stoves and microwaves – need extra reinforcement to prevent sagging. Placing shims under the sides of appliance openings provides solid support.

Shims also minimize direct contact between the appliance and cabinet edges. This reduces noise and vibration transfer. Sturdy shimming at appliance cutouts prevents cracking or distortion.

Mid-Span On Long Runs

Long straight cabinet runs over 8 feet or more should be shimmed every 2 to 3 feet along their length. Centers and corners alone are not enough. This periodic mid-span shimming prevents noticeable drooping in the middle over time.

For the longest runs of more than 12 feet, permanent shims left in place mid-span are recommended even after general removal. This provides lasting support against gradual sagging.

Between Cabinets And Wall

Any gaps between the cabinet sides or backs and adjacent walls allow too much