Glossary
Extra thin cement
A watery, fast-acting plastic cement drawn into a closed seam by capillary action rather than brushed on thickly.
Extra thin cement is a low-viscosity version of plastic cement, thin enough that it behaves almost like water when touched to a seam. Rather than applying it directly to a part before joining, the usual method is to hold the two halves together first and run a fine brush loaded with cement along the seam line, letting capillary action pull the liquid into the joint on its own.
This capillary approach is what makes extra thin cement popular for clean panel lines and tight-fitting parts, since it leaves almost no visible bead of excess plastic once the joint sets. It also sets noticeably faster than tube cement, often within a minute or two, which suits builders working through many small joints on one model in a single session rather than holding each part for long periods.
The main risk is that the thin liquid can wick further than intended, running into a panel line or a clear part where it will fog or mar the surface if you are not careful with the brush. A common mistake is using too much on a first attempt, so it helps to practice the capillary technique on spare sprue material before using it on a visible seam.