Plastic Adhesives and Cements: A Complete Guide

Solvent cement does not bond two surfaces together in the conventional sense. It dissolves the surfaces of both plastic parts at the joint interface, allowing the polymer chains to intermingle. When the solvent evaporates, the two parts have effectively fused into a single continuous piece of plastic — a true molecular bond with joint strength that can approach or match the strength of the base material itself.

Solvent cementing only works on amorphous thermoplastics that are soluble in the specific solvent system being used. Acrylic, PVC, ABS, polycarbonate, and PETG are all candidates for solvent cementing with compatible products. Semi-crystalline plastics like polyethylene, polypropylene, nylon, and PTFE cannot be solvent-cemented because they are not soluble in practical solvent systems.

Structural adhesives, by contrast, are mechanical bonding systems that cure to form a solid adhesive layer between two surfaces. They work on a much broader range of materials — including many plastics that cannot be solvent-cemented — and are the correct approach when bonding dissimilar materials, when the plastic is semi-crystalline, or when the joint design requires gap-filling capability that solvent cements cannot provide. Epoxies, methacrylate adhesives, and cyanoacrylates are the most commonly used structural adhesive types in plastic fabrication.

Weld-On (IPS Corporation) and Acrifix (Evonik) are the two primary solvent cement product lines stocked at Plastic-Craft Products, each formulated for specific plastic substrates and bonding requirements.

The Weld-On line covers solvent cements for acrylic, PVC, ABS, and polycarbonate across a range of viscosities and working times. Weld-On 3 and Weld-On 4 are thin, water-like cements for acrylic-to-acrylic bonding — applied by capillary action to closely fitted joints and cured in seconds to minutes. Weld-On 16 is a thicker, paste-consistency cement for acrylic joints with small gaps or where a longer working time is needed. Weld-On 40 is a two-part methylene chloride-free system for structural acrylic bonds where maximum clarity and joint strength are both required. For PVC bonding, Weld-On 705 and compatible products provide the appropriate chemistry for both Type I and Type II PVC sheet and pipe applications.

The Acrifix line from Evonik is specifically engineered for acrylic bonding and is particularly well-suited to display fabrication, optical assemblies, and applications where joint clarity is the primary requirement. Acrifix 1S 0116 is a thin solvent cement for precision acrylic-to-acrylic bonds in close-fitting joints. Acrifix 2R 0190 is a two-component reactive adhesive that cures to a bond with high optical clarity and good UV stability — the preferred system for display cases, optical components, and fabricated acrylic assemblies where the joint must be visually invisible.

Matching the bonding system to the specific plastic is the most consequential step in any bonding specification. The compatibility matrix below covers the most common combinations encountered in fabrication:

Polyethylene, polypropylene, PTFE, nylon: Cannot be solvent-cemented. Structural adhesives or hot gas welding are required. Welding is often the more reliable joining method for polyolefin fabrications.

Dissimilar plastics: Cannot be solvent-cemented. Structural adhesives with appropriate surface preparation are required for bonding two different plastic types to each other.

Even the correct solvent cement will produce a poor result if applied incorrectly. Joint preparation is the most critical variable — the mating surfaces must be flat, clean, and free of oil, dust, and machining debris. Sanded or machined surfaces bond better than saw-cut surfaces because they provide more intimate contact between the parts.

Thin solvent cements like Weld-On 3 or Acrifix 1S 0116 are applied by capillary action: assemble the parts first, hold them in contact under light pressure, and touch the applicator to the joint line. Surface tension draws the cement into the joint, wetting both surfaces simultaneously. This technique requires closely fitted joints — gaps larger than a few thousandths of an inch will prevent the cement from wicking fully.

Curing time before handling and before applying load are separate specifications. Most thin solvent cements allow handling in minutes but require 24 to 72 hours before the joint can be subjected to stress.

When ordering plastic adhesives and cements, buyers should specify the plastic substrate being bonded, the joint configuration (butt joint, lap joint, capillary-filled close joint, or gap-filling application), the required working time, and any performance requirements for the finished joint — optical clarity, UV resistance, chemical resistance, or structural load rating.

For fabrication projects that involve both material and bonding, Plastic-Craft Products stocks Weld-On and Acrifix adhesives and cements alongside the full range of plastic sheet, rod, and tube they are designed to bond. Ordering both from a single source eliminates the compatibility uncertainty that arises when purchasing adhesives from a different distributor than the plastic, and ensures that the bonding agent is matched to the specific grade and surface condition of the material being assembled.