Should You Sand Between Layers of Putty or Resin Repairs?

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Do I Need to Sand Between Layers When Using Putty or Resin?

Sanding between layers when working with resins or putties is a simple step that makes a significant difference to both the quality and longevity of your repair. Here’s what you need to know about this crucial process.

Why Sanding Between Layers Matters

Each coat of resin or putty needs a surface it can grip to. Light sanding slightly roughens the cured layer, improving adhesion for any following coats. This is particularly important with thicker repairs or when building up multiple layers, as a glossy or uneven surface may prevent the next layer from bonding properly.

Besides strengthening the repair, sanding minimises the risk of weak spots or delamination, meaning your finished repair is more uniform and robust.

How to Sand Between Layers

Allow each layer to cure according to product instructions before sanding.
Use fine to medium grit sandpaper (typically 120–240 grit) to create a smooth, slightly matte surface.
Wipe away sanding dust with a clean, dry cloth – any remaining debris can affect the next coat’s finish.
Repeat the process for each new layer until the repair reaches your desired thickness and uniformity.

For example, the CROP 2K Fiberglass Putty – 750 ml + Hardener is designed to be easily sanded after curing, making a smooth result simple to achieve before priming or painting.

When This Step Is Crucial

Sanding between layers is especially important for repairs that require strength and a seamless finish, such as cracks, deep cavities, or structural fixes on water softener resins, car bodywork, and rigid plastic or fibreglass surfaces. Skipping this step can leave the repair looking uneven or lead to peeling and reduced durability.

Related guides

How To Repair A Perforated Water Softener Resin

By taking the time to sand between layers, you’re setting your repair up for a neat, long-lasting result. This attention to detail is a key part of tackling challenging fixes, such as those discussed in our guide on repairing perforated water softener resin.