Causes And Solutions For Air Bubbles And Delamination in The Hand Lay-up Process Of Fiberglass Mat

When performing hand lay-up of chopped strand mat, air bubbles and delamination are more likely to occur due to the mat's loose texture and uneven impregnation rate. This article will focus on four key aspects: raw materials, operating methods, environmental conditions, and curing systems. It will thoroughly explain the causes and provide solutions to help you avoid pitfalls in your production process.

 

I. First, understand the difference between bubbles and delamination.

 

Many workers confuse bubbles and delamination during construction, but their causes, manifestations, and hazards are different.

Bubbles: These are mostly tiny voids inside or on the surface of the product, visible to the naked eye, and raised to the touch. They mainly affect appearance and airtightness.

 

Delamination: This occurs when layers are not firmly bonded, resulting in delamination and hollow areas. A light tap produces a hollow sound. It is a structural defect that directly reduces strength.

 

Both often occur simultaneously: incomplete bubble removal → insufficient resin impregnation → ultimately leading to delamination, a typical "failure chain."

 

II. Bubbles in Hand Lay-up: 7 Major Causes + Corresponding Solutions

 

Bubbles are the most common problem in hand lay-up processes. The root causes are basically insufficient impregnation, air trapping, and poor venting.

 

1. Resin Too Thick, Viscosity Too High

High resin viscosity results in slow flow, preventing rapid impregnation of the fiberglass mat. Air is trapped inside the fibers, forming dense small bubbles.

Solutions:Add appropriate thinner or reactive thinner to control viscosity; preheat resin before winter construction.

 

2. Incorrect order of applying adhesive and rolling:
Laying the felt before applying resin is most likely to trap air.

Solution: Adhere to the standard procedure of applying primer first → laying the felt → applying adhesive again → rolling to remove air.

 

3. Improper rolling tools or insufficient pressure:
Rollers that are too hard, have excessively long nap, or apply insufficient pressure will not completely expel air from the felt.

Solution: Use a defoaming roller or a hard rubber roller, rolling multiple times in one direction, avoiding back-and-forth rolling.

 

4. Damp or oily chopped strand mat:
Damp or contaminated felt will hinder impregnation and create air bubbles.

Solution: Keep fiberglass felt dry; check for moisture and dirt before use.

 

5. Applying too thick an adhesive layer:
If the adhesive layer is too thick, internal air bubbles cannot rise and escape. Solutions:

6. Too Fast Curing

Gelging is too fast; air bubbles haven't escaped before curing.

Solution: Adjust the ratio of accelerator and hardener to avoid rapid curing at high temperatures.

 

7. High Airflow and Dust in the Environment

Wind causes premature skinning, sealing internal air bubbles.

Solution: Maintain a windless, dust-free, and temperature-stable workshop.

 

III. Product Delamination: 5 Core Causes + Thorough Solutions

 

Delamination is more serious than air bubbles and represents adhesive failure, mainly occurring between layers, at corners, and in areas of varying thickness.

 

1. Incomplete Impregnation Between Layers, Dry Felt, Dry Spots

Chopted strand mat is not fully impregnated with resin, resulting in "dry strands," preventing bonding between layers.

Solution: Ensure each layer of mat is fully impregnated with adhesive, free of white spots and dry spots, before applying the next layer.

 

2. Excessive Interval Between Layer Laying

If the previous layer has already cured or partially cured, laying a new layer will cause delamination.

Solution: Control the laying rhythm; continue laying the next layer while it is still surface dry but not fully gelled.

 

3. Difficulty in Air Venting at Corners, Curved Surfaces, and Complex Structures

Uneven areas are most prone to air pockets and insufficient adhesive, leading to delamination.

Solution: For complex areas, apply adhesive first, then lay the felt, and repeatedly roll it. If necessary, cut openings to eliminate wrinkles.

 

4. Inaccurate Resin Proportioning

Insufficient hardener leads to incomplete curing and insufficient interlayer strength; insufficient accelerator results in slow curing and susceptibility to delamination due to disturbance.

Solution: Strictly adhere to the mixing ratio; mix only what is needed; do not use expired adhesive.

 

5. Uneven or Wrinkled Chopped Strand Mat Laying

Wrinkles inevitably lead to insufficient adhesive and air pockets, ultimately resulting in delamination.

 

Solution: Lay the mat flat, firmly, and wrinkle-free; press the edges firmly.

 

IV. Perfecting the Hand Lay-up Process in One Go: Standard Operating Procedures

 

The most effective way to fundamentally eliminate air bubbles and delamination is to follow standardized procedures.

1. Mold Cleaning: Ensure the mold is clean, dry, and free of oil. Apply a release agent evenly.

2. Resin Preparation: Mix the resin, accelerator, and hardener according to the specified ratio and stir thoroughly.

3. Primer Application: Apply a thin layer of adhesive to the mold surface to improve adhesion.

4. Chopped Strand Mat Laying: Lay the mat flat, without wrinkles or warping.

5. Resin Impregnation and Rolling: Apply one layer of adhesive and roll it over to ensure complete saturation.

6. Layered Application: Apply multiple thin coats, rolling over each layer to remove air bubbles.

7. Room Temperature Curing: Maintain a stable environment and avoid disturbance.

 

V. Summary: Three Key Points for Successful Hand Lay-up

 

The hand lay-up process for chopped strand mat (CSM) may seem simple, but to produce high-quality products, the core principles are:

First, the resin must be thoroughly impregnated; insufficient impregnation will inevitably lead to problems.

 

Second, air must be completely removed; failure to remove air will result in air bubbles.

 

Third, the layers must be continuous; avoid gaps or excessively long intervals between layers.

 

By ensuring these three points are addressed, common defects such as air bubbles, delamination, hollow areas, and detachment can be largely avoided, significantly improving the product's appearance, strength, and airtightness. Hand lay-up is a technique combining experience and attention to detail; careful observation, adjustments, and adherence to standards will ensure the consistent production of high-quality fiberglass products.