Good quality stones must

🪨 Understanding the Qualities of Good Building Stone

Selecting the right stone for construction is crucial for the longevity and safety of a structure. A good quality building stone must possess several key properties to withstand environmental forces and the test of time.

🔬 Detailed Analysis of the Options

Let's break down why each of these properties is essential.

A. Be Durable

Durability is the ability of a stone to resist the combined action of weathering forces like rain, wind, heat, and frost over a long period without disintegrating or decomposing. A durable stone maintains its strength, appearance, and structural integrity for decades or even centuries. This is arguably the most important overall quality.

B. Be Free From Clay

The presence of clay within the pores of a stone is highly undesirable. Clay readily absorbs water, causing the stone to become weak. More importantly, clay can cause the stone to swell when wet and shrink when dry, leading to gradual disintegration. Stones with clay impurities are not durable and will weather quickly.

C. Resist Action of Acids

Atmospheric pollution, particularly in industrial areas, can lead to "acid rain". This rain contains dissolved acids (like sulphuric and nitric acid) that can react with and degrade certain types of stone. Good quality stone, especially for exterior use, must be able to resist these chemical attacks to avoid pitting, discoloration, and loss of strength. Silicious stones like granite and quartzite are excellent in this regard, while calcareous stones like limestone and marble are more vulnerable.

✅ Other Important Qualities of Good Building Stone

Besides the options listed, several other factors are considered when selecting stone:

• Strength: The stone must have sufficient crushing strength to safely carry the load imposed on it (typically > 100 N/mm² for structural use).
• Hardness: The ability to resist scratching and abrasion. This is crucial for floors, steps, and pavements.
• Toughness: The ability to resist impact and shock loads.
• Low Water Absorption: Good stone should absorb very little water (typically < 5%). High water absorption can lead to decay and frost damage.
• Good Appearance: For facing work, the stone should have a uniform color and texture and be free from flaws like cracks or patches.
• Ease of Dressing: The stone should be workable, meaning it can be cut, shaped, and finished to the desired size and form without too much cost or effort.

💡 Study Tips

• Think "Long-Term": The goal of using stone is permanence. All the qualities listed (durability, no clay, acid resistance) contribute to making the stone last a very long time.
• Clay is the Enemy: In both bricks and stones, remember that clay within the material is a major weakness because it absorbs water and causes decay.
-
• "All of the above" questions: When you see an "all of the above" option, carefully check if each individual statement is a desirable quality. If they all sound like good things, "all of the above" is often the correct choice.