When remodeling a bathroom, it is tempting to rush to the visible, exciting phases like hanging drywall, applying waterproofing membranes, or laying beautiful tile. However, the secret to a professional, long-lasting shower installation lies in the hidden prep work. One of the most critical—yet frequently overlooked—steps in this process is shimming the wall studs before installing drywall, backer boards, or wall panels.
Taking the time to true up your framing during the rough-in stage prevents structural failures, saves hours of frustration during tiling, and ensures a flawless aesthetic finish.
The Problem with Modern Framing
Wood is a natural, living material. In residential construction, wall studs are rarely perfectly straight, plumb, or uniform.
- Natural Imperfections: Individual studs can bow, twist, or crown as they dry out.
- Dimensional Variances: Even brand-new studs can vary slightly in thickness, creating a wall plane that steps in and out.
- Settling and Warping: Over time, older homes settle, causing entire wall sections to lean or warp out of square.
While a slight 1/4-inch bow across a 10-foot living room wall might be masked by flat paint and baseboards, that same variance in a shower enclosure can spell disaster.
The Consequences of Un-Shimmed Framing
Skipping the shimming process creates a domino effect of installation challenges and structural vulnerabilities.
1. Lippage and Uneven Tile Surfaces
Tile requires a perfectly flat substrate. If your backer board telegraphs the bumps and dips of crooked studs, your tile will follow suit. This results in “lippage”—a condition where the edges of adjacent tiles do not sit flush with one another. Lippage creates unsightly shadows, disrupts the alignment of grout lines, and ruins the look of expensive tile.
2. Excessive (and Costly) Thin-set Mortar Usage
Installers often try to fix a wavy wall by “mudding it out” by applying extra-thick layers of thin-set mortar behind the tiles to build out low spots. This practice is problematic. Thinset is engineered to be a bonding agent, not a structural leveling compound. When applied too thick, it shrinks as it cures, pulling tiles out of alignment, cracking grout, and consuming expensive material unnecessarily. Trying to save money by dot setting tiles is worse.
3. Compromised Waterproofing Membranes
Modern shower systems rely heavily on sheet or liquid-applied waterproofing membranes. If the underlying drywall or backer board bends sharply over a bowed stud, it creates a point of high tension. This tension makes it difficult to seamlessly apply sheet membranes, increases the risk of punctures, and can cause liquid membranes to cure at uneven, inadequate thicknesses.
4. Gaps and Stresses on Solid Wall Panels
If you are installing prefabricated acrylic, quartz, or composite wall panels instead of tile, flat walls are even more critical. Solid panels cannot bend to accommodate a warped wall. Forcing a rigid panel against a bowed stud creates hollow voids behind the panel, compromises adhesive contact, and puts constant stress on the joints, eventually causing the silicone caulking to split and leak.
How Shimming Transforms the Installation
Shimming involves attaching pre-made foam pr plastic shims designed just for this purpose or strips of wood, cardboard, or plastic. These are applied to the faces of low or warped studs to bring the entire wall into a single, perfectly flat, plumb plane.
[ Crooked Studs ] –> [ Add Shims ] –> [ Flat Substrate ] –> [ Perfect Tile ]
(Bowed/Uneven) (Level Plane) (No Tension/Voids) (No Lippage)
By investing a few minutes into this process, you achieve several key benefits:
- Perfect Corner Alignment: Shower corners meet at a crisp, true 90-degree angle, making corner tiles or panel joints simple to seal.
- Structural Integrity: By installing the wall board fasteners through the shims backer boards fasten securely without being subjected to bending stresses that could cause future cracking.
- Effortless Tiling: Tiles can be buttered evenly and set rapidly, transforming a tedious leveling battle into a straightforward installation. Wrapping a tile design around a corner is far easier with walls that are perfectly plumb.
- Saving Money: A bag of thinset can easily run $30 to $60. Saving just ONE bag will save you more than the cost of the shims used to flatten the wall.
- Saving Time: Since your edges are plumb, all the vertical rows of tile will be the same size. This eliminates measuring and cutting tiles individually.
Conclusion
In kitchen and shower construction, the quality of the finish is entirely dictated by the quality of the substrate. This is why the Built With Foam Wall Flattening Shim Kit was invented. Shimming wall studs may feel like tedious carpentry work, but it is the foundational step that bridges the gap between a amateurish, problematic build and a beautiful, oasis. Before you hang a single sheet of drywall or backer board, pull out your level, check your framing, and shim your way to a flawless finish.