# Replace with Layer {% embed url="" %} Use this tool to apply a new material and change the thickness of a wall, slab or roof. If your wall, slab or roof will consist of multiple material layers, choose one to be the ‘core’ layer. Typically this will be the structural layer, e.g. bricks in a cavity wall or studs in a stud wall. 1. Under the *Detail* icon, click *Replace with Layer* 2. Select one or more walls, roofs or slabs 3. Choose a material. Your [project material libraries](/documentation/qonic-dashboard/libraries/material-libraries.md) will be displayed here, as well as the materials already in the currently open model. 4. Enter a thickness 5. (optional) Click 'show preview'. The selected walls will now become transparent, and a preview of the new material will be visible on top of it. Hovering the cursor over this preview will highlight it in blue. Left-click the highlighted preview to change the alignment if the thickness has changed.\ **Note:** previews of adjacent walls will be grouped together so that you can change the alignment of multiple walls at the same time. 6. Click *Apply* or press *Enter* The new material and thickness will now be applied to the selected building elements. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://help.qonic.com/documentation/qonic-application/modeling/modifying/material-layer-editing/replace-with-layer.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.