How to Shim a Wobbly Toilet
Updated February 25, 2026
Stop a rocking toilet with plastic shims and caulk -- a 10-minute fix that prevents wax ring failure and water damage.
Overview
A toilet that rocks when you sit on it is not just annoying -- it is actively destroying the wax seal underneath. Every rock compresses and releases the wax ring. Eventually it breaks the seal and you get sewer gas, water leaks, or both. The fix takes 10 minutes: plastic shims under the base and caulk to lock everything in place. Do not ignore a wobbly toilet. A $3 pack of shims now prevents a $500 subfloor repair later.
What You'll Need
Safety First
- Do not overtighten the closet bolts trying to stop the rocking. Porcelain cracks without warning. Snug plus a quarter turn is the maximum. If tightening does not stop the wobble, shims are the answer.
- If the toilet rocks AND you see water at the base, the wax ring has already failed. Shimming alone will not fix a broken seal. You need to pull the toilet, replace the wax ring, and then shim.
Step-by-Step Instructions
- Find the Rock Direction
Sit on the toilet and shift your weight left, right, forward, and back. The toilet rocks in a specific direction -- usually side to side. The low point is where the gap is between the base and the floor. Look at the base while someone else rocks it gently. You will see the gap open and close. That is where the shim goes.
Tip: A flashlight aimed at the base from the side makes the gap visible. Even a 1/16-inch gap is enough to cause rocking. The toilet base is not perfectly flat and neither is the floor. - Insert Plastic Shims
Use plastic toilet shims ($3 for a pack of 6-8). Slide a shim into the gap from the front or side of the base. Push it in until the rocking stops. You may need shims on two sides. Test by rocking again -- the toilet should be solid with no movement in any direction. Trim the excess shim flush with the base using a utility knife or score it and snap it off.
Tip: Plastic shims only. Never use wood shims -- they absorb water, swell, rot, and eventually fail. Coins or cardboard do the same. Plastic is waterproof and permanent. - Check the Closet Bolts
While you are at it, check the closet bolt nuts. If they are loose, that alone can cause wobbling. Tighten alternating sides: a quarter turn on the left, a quarter turn on the right. Check for wobble after each round. Stop the moment the toilet is stable. Do not crank them down -- porcelain cracks from overtightening and there is zero warning before it happens.
Tip: If the closet bolt spins without tightening (nut turns but bolt spins too), the bolt has lost its grip on the flange slot. You need to hold the bolt with pliers from above while tightening the nut from below. If the flange slot is damaged, a flange repair bracket ($5-$10) gives the bolt a new anchor point. - Caulk the Base
Apply a continuous bead of silicone caulk around the base of the toilet where it meets the floor. This locks the shims in place and prevents water from getting under the base. Use kitchen/bath silicone caulk -- it stays flexible and resists mold. Smooth the bead with a wet finger. Leave a 2-inch gap at the back of the toilet (the side closest to the wall). This gap lets you see if the wax ring ever leaks -- water escapes at the uncaulked back instead of hiding under the caulked front.
Tip: Some plumbers caulk all the way around with no gap. Code in most areas actually requires caulking (it is a sanitary seal). The gap-at-the-back approach is a practical compromise: you meet the spirit of the code while keeping a leak detection point.
Pro Tips
- A toilet that was stable for years and suddenly starts wobbling may have a subfloor problem. The wood under the flange may be softening from a slow wax ring leak. Press the floor next to the toilet with your thumb. Soft or spongy? That is water damage. The subfloor needs repair before shimming will hold.
- If the floor is severely uneven (more than 1/4 inch gap under the toilet base), shimming alone may not be enough. Consider having the floor leveled with self-leveling compound before setting the toilet.
- Rubber toilet base pads ($5-$8) sit under the entire toilet base and conform to minor floor irregularities. They combine the function of shims and a gasket in one piece.
- After shimming and caulking, sit on the toilet and rock hard in every direction. If it moves even slightly, add more shims. The goal is zero movement. Any movement degrades the wax seal over time.
When to Call a Pro
Call a plumber if the subfloor around the toilet is soft, spongy, or visibly damaged (subfloor repair is needed before the toilet can be properly secured), if the flange is cracked or broken and the closet bolts cannot grip (flange repair or replacement required), or if the toilet rocks even after shimming and tightening -- the flange may be at the wrong height or the drain pipe may have shifted.
Frequently Asked Questions
When should I call a plumber to shim a wobbly toilet?
Call a plumber if the subfloor around the toilet is soft, spongy, or visibly damaged (subfloor repair is needed before the toilet can be properly secured), if the flange is cracked or broken and the closet bolts cannot grip (flange repair or replacement required), or if the toilet rocks even after shimming and tightening -- the flange may be at the wrong height or the drain pipe may have shifted.
What are some expert tips to shim a wobbly toilet?
A toilet that was stable for years and suddenly starts wobbling may have a subfloor problem. The wood under the flange may be softening from a slow wax ring leak. Press the floor next to the toilet with your thumb. Soft or spongy? That is water damage. The subfloor needs repair before shimming will hold. If the floor is severely uneven (more than 1/4 inch gap under the toilet base), shimming alone may not be enough. Consider having the floor leveled with self-leveling compound before setting the toilet. Rubber toilet base pads ($5-$8) sit under the entire toilet base and conform to minor floor irregularities. They combine the function of shims and a gasket in one piece. After shimming and caulking, sit on the toilet and rock hard in every direction. If it moves even slightly, add more shims. The goal is zero movement. Any movement degrades the wax seal over time.
What tools do I need to shim a wobbly toilet?
You will need: Plastic toilet shims ($3 for a pack at any hardware store), Utility knife (to trim shims flush with the base), Adjustable wrench (to check and tighten closet bolt nuts), Silicone caulk and caulk gun (kitchen/bath type), Flashlight (to see the gap under the base).
When should I call a professional instead of doing this myself?
Call a plumber if the subfloor around the toilet is soft, spongy, or visibly damaged (subfloor repair is needed before the toilet can be properly secured), if the flange is cracked or broken and the closet bolts cannot grip (flange repair or replacement required), or if the toilet rocks even after shimming and tightening -- the flange may be at the wrong height or the drain pipe may have shifted.
How difficult is this project?
This project is rated easy. Most homeowners with basic tools can complete it.
How long does this take?
Plan for approximately 10 - 20 minutes. First-timers may need extra time.
How much will this cost?
The estimated cost is $3 - $8. Costs vary by location and materials chosen.