What method can reduce warping when repairing large, flat surfaces with polyester resins?

Using short strips of fiberglass when repairing large, flat surfaces with polyester resins is effective in reducing warping due to several reasons related to how the material is applied and cured. Short strips allow for better handling and manipulation, minimizing stress concentrations that can lead to warping. When working with large surfaces, using shorter sections helps in distributing the forces evenly across the repair area. This ensures that as the resin cures and shrinks, the stress does not accumulate at any one point, preventing deformation.

In contrast, employing long strips of fiberglass can increase the likelihood of warping, as the length of the strip can allow for tension buildup along the edges and an uneven cure across the surface. Applying heat may not always lead to the desired outcome in terms of reducing warping, as uneven heating can cause localized softening and lead to further structural issues. Prior sanding prepares the surface but does not inherently address warping issues related to the application method of the repair material. Thus, using short strips is the most effective strategy to prevent warping in this type of repair.