How to Solve Inner Corner Cracking, Peeling and Delamination during Colorful Paint Construction?

Netizen’s question:

Why do inner corners often crack during stone-like paint spraying?

Analysis：

During the intermediate coating construction of colorful paint, inner corners, recessed parts of Roman columns and other hard-to-spray areas are prone to repeated spraying, resulting in excessively thick paint films. The paint film will shrink during vitrification and drying. When the film is too thick, there is a big difference in shrinkage ratio between the surface and inner layers, which eventually causes cracking.

Construction Solutions

To avoid such problems during colorful paint spraying, the following two methods can be adopted:

1. Shielding. Shield areas that do not need spraying to avoid repeated over-spraying.
2. Pre-spraying with thin coats. For hard-to-construct positions, apply one thin coat in advance before large-area construction, and keep subsequent spraying thin on these areas.

Q：

Why do blistering, peeling and delamination occur after the application of colorful paint?

This problem can be divided into two cases based on whether chalking occurs on the back of the paint film.

Paint film with chalking

Analysis

1. Insufficient strength of the putty layer. Colorful paint shrinks during vitrification and drying, and its paint film features high flexibility. Weak putty layers easily lead to delamination, especially at partition lines.
2. Late removal of partition tape causes cracks on the paint film and weakens its adhesion to the base. Soaked by rainwater later, the coating will suffer blistering and delamination.

Construction Solutions

1. Select type P exterior wall putty complying with national standard JC/T157-2009 Putty for Exterior Building.
2. Remove the partition adhesive tape within 30 minutes after intermediate coating construction.
3. Conduct sufficient water curing after putty polishing to fully cure cement ingredients and enhance the strength of putty.

No Chalking on Paint Film

Analysis: Poor construction environment leads to insufficient solid content or failed vitrification of the paint film.

1. Excessively low temperature prevents paint film vitrification and effective adhesion, which is usually accompanied by cracking.
2. Excessively high humidity. If uncured paint film gets wet by rain after spraying, unformed coating will be washed away directly. For formed film, rainwater penetrates inside and washes away solid components, reducing adhesion strength. Moisture accumulates between paint film and putty layer, causing blistering, hollowing, cracking and delamination. Such defects often occur on water-prone horizontal surfaces like window sills and cornice boards.

Solutions:

1. The film-forming temperature for coatings shall be above 5℃ (excluding special coatings). Keep construction temperature over 5℃ and avoid low-temperature periods in cold areas.
2. Keep a close eye on weather conditions before construction.