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Difficulty: HardWeakening Arguments

To protect 14th-century sandstone monuments from winter freeze-thaw weathering, municipal heritage conservators plan to apply a hydrophobic silicone nanofilm across the exterior surfaces of all downtown stone structures. Laboratory tests confirm that the nanofilm prevents external rainwater from penetrating sandstone pores by up to 98 percent. The conservators conclude that applying this coating will significantly reduce the rate of structural cracking and surface spalling caused by freeze-thaw cycles over the next decade.

Which of the following, if true, most seriously weakens the conservators' argument?

  1. Groundwater drawn up through the porous foundations of sandstone monuments evaporates primarily through exterior stone surfaces, and the nanofilm prevents trapped internal moisture from escaping.Answer
  2. B
    Synthetic sealants previously tested on modern concrete structures required reapplication every three years, whereas the new nanofilm maintains its water repellency for fifteen years.
  3. C
    The total financial cost of coating all downtown sandstone monuments exceeds the annual emergency repairs budget of the heritage conservation department.
  4. D
    Nearby granite architectural structures suffer significantly lower rates of spalling and surface cracking during severe winters than untreated sandstone monuments do.
  5. E
    The chemical application procedure temporarily alters the natural surface hue of historic sandstone for several weeks before curing into an invisible layer.

Answer

The argument is most seriously weakened by the statement that groundwater drawn up through porous foundations evaporates through exterior surfaces and that the nanofilm prevents this internal moisture from escaping.
The conservators assume that blocking external rainwater will prevent water from collecting and freezing inside the sandstone. The correct option reveals that moisture also enters the monuments from below via groundwater. Because the nanofilm creates an impermeable seal, this rising groundwater becomes trapped beneath the stone surface, where it will freeze during winter and cause severe internal cracking and spalling. This directly negates the expected benefit of the plan.

Step-by-Step Solution

1
Deconstruct the argument structure into premise and conclusion
Premise: Hydrophobic nanofilm stops 98% of external rainwater from penetrating sandstone. Conclusion: Applying the nanofilm will significantly reduce freeze-thaw cracking and spalling over the next decade.
Identifying the explicit logical bridge allows us to uncover the unstated assumption.
2
Identify the central unstated assumption of the author
The argument assumes that external rainwater is the sole or primary source of water responsible for freeze-thaw damage inside the sandstone.
Weakening questions require finding evidence that demonstrates why the premise might fail to guarantee the conclusion.
3
Evaluate the impact of new information on the underlying assumption
If groundwater enters through foundations and cannot escape due to the barrier, trapped internal moisture will freeze and expand, exacerbating structural damage despite keeping rainwater out.
Demonstrating an alternative cause of severe moisture damage directly breaks the connection between keeping rainwater out and preventing freeze-thaw cracking.

Key Concept

Weakening Causal Arguments by Identifying Trapped Alternative Factors
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Topics

Weakening Arguments

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