When the putty is scraped off, dense air bubbles appear, but no deep air holes can be found on the base surface. What's going on?

The common putty layer bubbling problem in wall decoration can be analyzed and solved from the following aspects:

Bubbling on the mortar surface: If dense bubbles appear when the putty is scraped but there are no deep air holes on the base surface, it is likely that the mortar surface is too rough and the air cannot be effectively discharged when the putty is scraped, thus forming bubbles. The solution is to use a liquid reinforcement before scraping the putty to facilitate exhaust, and then scrape the putty again, which will greatly reduce air bubbles.

Blistering of air holes on the base surface: If bubbles appear on the base surface, bulge very high and are deep inside after being punctured, it is likely that the air holes on the base surface are sealed. When applying putty on the cement surface of the cast-in-place slab, since the air holes are sealed by the putty, the air inside is compressed, forming accumulated potential energy. When the scraper leaves the air hole, the compressed air will rebound and push up the putty to form bubbles. The solution is to use low-viscosity coarse putty or quick-forming plaster for the first pass to avoid the generation of bubbles.

Bubbles in the second coat of putty: If this happens, it is likely that the first coat of putty did not eliminate the bubbles. When scraping the second coat, you habitually use a spatula to flatten it and break the bubbles in the first coat. New bubbles continue to form on the same gas hole. The solution is not to shovel out the first air hole, and continue to use leveling putty or gypsum to cover up the air holes.

Blistering when scraping the overlay putty: If the base putty formula is inappropriate or there are pinholes on the surface, blistering will occur when scraping the overlay putty. The solution is to replace the leveling putty.

In addition, there is a non-bubble blistering problem, which is usually caused by the separation of the surface layer and the inner layer, similar to the bubbles that appear after the skin is burned. This may be due to the fact that the old wall or poor-quality interior wall putty is not water-resistant or has pulverization, and cannot withstand the moisture intrusion of the second putty, causing it to lose its structural strength, and is damaged by the second putty scraper and causes blistering. The solution is to use sealing wall cement on the first putty (it needs to be eradicated in serious cases), and add water retaining agent and adhesive to the second putty to solve the problem.

For blistering problems caused by other reasons, you can try to use a good filled low-viscosity leveling putty for the first pass.