polyurethane not drying! - DIY (Do It Yourself)

Polyurethane Not Drying? A DIY Guide

A conversation from: Hotrodders Forum

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Martin raised a crucial question regarding the drying properties of polyurethane, and it led to a deeper inquiry about the differences between acrylic urethanes and polyurethanes. The discussion emphasizes the importance of understanding the chemical properties that define these products, particularly how they cure and dry. While the term "poly" suggests a variety of resins, the effective performance of polyurethane hinges on its molecular structure, which allows it to create a resilient bond under certain mixing conditions.

To clarify further, true polyurethane resins possess a unique flexibility and don’t require an additional flex agent. When compared at a microscopic level, the polymer structure of acrylic urethane resembles a ladder, while polyurethane presents a highly reinforced gable, demonstrating stronger interlinking among its molecules. This structural distinction inherently influences how these substances cure. Polyurethanes typically employ mixing ratios of 2:1, 3:1, or 1:1 for activation, in contrast to the 4:1 ratio commonly used for acrylic urethanes.

Polyurethanes tend to achieve a pencil hardness rating of 2, which contributes to superior resistance against chips and better adhesion properties. This is essential, particularly in automotive applications where exposure to harsh chemicals is prevalent, making it advantageous for use in aircraft, for example. Up to now, applying polyurethane without achieving an impressive finish was a significant challenge. However, advancements in resin technology have minimized the differences in application methods, highlighting that if users adhere to the manufacturer’s specifications, achieving a good finish should no longer be problematic even as sprays have evolved.

The improvement in clarity and gloss for polyurethanes has made them an appealing choice for restoration projects. While some products may require more time before achieving buffing quality, well-formulated polyurethanes can maintain their performance, even weeks after application. This opens a pathway for professionals who paint off-frame and need adequate time before final polishing.

If you find that your polyurethane is not drying properly, the solution lies in proper removal. Start by using acetone to strip the non-dried layer, then sand down to the base material. It’s advisable to switch brands if you continually encounter drying issues with a specific product. Based on user experiences, Minwax's clear gloss fast-drying polyurethane is a recommended choice for those using rattle cans. Additionally, the same product is available in brush-on formulas, which can be thinned for spray applications as needed.

Understanding Polyurethane Hardener and Application Techniques

It is important to mix the hardener (B-component) with the resin (A-component) in the correct proportions before use to ensure effective curing.

Steps for Coating and Sealing with PU Resin:

1. Begin by coating the surface with PU resin, combining the A and B components in the correct mixing ratio.
2. Transfer the mixture to a paint tray and mix thoroughly to ensure complete blending.
3. If color is desired, incorporate the provided WB color paste as per recommended ratios.
4. Apply the material evenly using a foam roller while scraping excess off with a scraper grid for a smooth finish.
5. Walking is permissible after 20-24 hours, and complete chemical curing typically occurs within a week.

For applications in high temperatures, consider adding water to the PU resin to counteract the formation of an orange peel texture.

Ingredients, Safety & Precautions

Warning: The B-component contains hexamethylene diisocyanate oligomers and may cause allergic reactions. Protective gear should be worn during handling, and avoid inhaling vapors.

For reliable products, Yourun Synthetic Material offers a comprehensive range of polyurethane solutions tailored to meet diverse needs.