Lab / experiment Grade 11 Health & Consumer Science

After the Ellisfield Burst Pipe: A Mold-Prevention Drying Lab

Groups dry wet cloths in a fan draft, in still air, and under cover, then model drying with ratios and logarithms to explain why hidden wet materials grow mold.

Grade: Grade 11
Subject: Health & Consumer Science
Material: Lab / experiment
Time: 2 sessions, ~95 min total
Prep: Moderate prep
Materials: Three identical cotton washcloths per group, same brand and size, Kitchen or lab scale that reads to 1 gram, 1 per group, Plastic tub holding about 3 liters of room-temperature tap water, 1 per group, Box fan with a low setting, 1 per class or 1 for every two groups, Two wire cooling racks per group, Plastic tray and an upside-down plastic storage container large enough to cover a folded washcloth, 1 per group, Three index cards marked Fan, Still, and Covered, 1 set per group, Masking tape and a permanent marker for labels, Timer or stopwatch, Paper towels for spills, Calculators with a log key, or a spreadsheet

Standards

HSF-LE.A.1 Common Core Math

Distinguish between situations that can be modeled with linear functions and with exponential functions, recognizing that linear functions grow by equal differences over equal intervals and exponential functions grow by equal factors over equal intervals.

How this material aligns: Question 3 has students compare successive differences and successive ratios in their own Fan cloth data to choose a linear or an exponential model, and question 4 has them find the constant 10-minute factor in the pilot Fan cloth data.

All materials for HSF-LE.A.1 →

HSF-LE.A.2 Common Core Math

Construct linear and exponential functions, including arithmetic and geometric sequences, given a graph, a description of a relationship, or two input-output pairs.

How this material aligns: Question 5 has students construct an exponential model for the pilot Fan cloth from its starting water and the constant ratio they read from the data table, then use it to predict a later value.

All materials for HSF-LE.A.2 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-24.

Objectives

Students will measure the water lost by identical wet cloths drying under three conditions and express each result as a fraction of the starting water.
Students will decide whether a linear or an exponential model better describes drying data by comparing successive differences and ratios.
Students will construct an exponential drying model and solve it with logarithms to predict how long a material takes to reach a target moisture level.
Students will use their data to explain why wet materials that cannot dry quickly should be removed after a leak to prevent mold and protect people with asthma and allergies.

Vocabulary

Evaporation: Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
Humidity: Humidity is the amount of water vapor floating in the air. Air that feels sticky and damp has high humidity, while dry air has low humidity.

Also: porous, mold spores, exponential decay, ratio, moisture control

Teacher overview

In the fictional town of Ellisfield, a corroded supply pipe in the basement of an old apartment building burst overnight and soaked the carpet, the carpet pad, and the lower edge of the drywall in two ground-floor units. The building manager now has to decide which materials can be dried in place and which have to be torn out, and that is a health decision, because mold grows on materials that stay wet. In this lab, students model three situations with identical cotton cloths: one drying in moving air, one in still air, and one covered the way a carpet pad sits under a rug. They track the water each cloth loses, model the drying mathematically, and use the models to support a cleanup plan.

Teaching note: the misconception this lab targets is the belief that a material which feels dry on its surface is dry inside, so a rug that feels dry the next morning can be left where it is. The covered cloth usually still holds most of its water at the 24-hour reading even when its top layer feels only slightly damp, which gives students direct evidence for why water-damage guidance stresses removing or opening up materials that cannot dry quickly. A second point is worth raising during the analysis. Real drying curves are not perfectly exponential, because cloth often loses water at a nearly steady rate while its surface stays wet and then slows as it dries. Groups may therefore find that a linear model fits their first 40 minutes about as well as an exponential one, and that result should be discussed as a finding rather than marked as an error.

After the Ellisfield Burst Pipe: A Mold-Prevention Drying Lab — Grade 11 Health & Consumer Science

Name: ____________________________ Date: ______________

Procedure

Background: mold spores float in nearly all indoor and outdoor air, and they start to grow when they land on a surface that stays damp. After a leak, the most important step in preventing mold is drying wet materials as fast as possible. Mold growing indoors can set off allergy symptoms and asthma attacks. It is a particular concern for people with asthma, for infants and young children, for older adults, and for anyone with a weakened immune system. In this lab, each cloth stands for a material in the flooded Ellisfield apartments. The Fan cloth stands for carpet pulled up and spread out with a fan blowing across it. The Still cloth stands for carpet spread out in a closed room with no fan. The Covered cloth stands for carpet pad left under a rug, or insulation left behind drywall.

Label three identical washcloths 1, 2, and 3 with a small tape tag on one corner. The cloths must match in size and material, because thickness changes drying time.
Weigh each dry cloth and record its dry mass to the nearest gram in Table 1.
Shuffle the Fan, Still, and Covered cards and deal one to each cloth. Record which condition each cloth received. Random assignment keeps any small difference between cloths from lining up with one condition.
Soak each cloth in the tub for 1 minute. Lift it out, hold it over the tub, and wring it with both hands until it stops dripping. Wring all three cloths the same way.
Weigh each wet cloth right away and record the mass in the row for 0 minutes.
Set up the three conditions:
- Fan: lay the cloth flat on a wire rack about 1 meter in front of the box fan, set on low.
- Still: lay the cloth flat on a second rack in a part of the room away from the fan, vents, and windows.
- Covered: fold the cloth in quarters, set it on the plastic tray, and cover it with the upside-down storage container.
Safety: keep the fan and its cord well away from the tub and the wet cloths, and plug the fan into an outlet the water cannot reach. Wipe up drips on the floor at once, since a wet floor is a slipping hazard.
Start the timer. Every 10 minutes for 40 minutes, weigh each cloth and put it back in its place the same way it was. Work quickly so that no cloth is away from its condition for more than a minute.
At the end of class, turn the fan off and leave all three cloths in place overnight. The Fan cloth will dry in still air overnight, so keep that in mind when you read its 24-hour result.
At the start of the next class, press a dry paper towel on top of the Covered cloth and note whether the top feels dry, damp, or wet. Then unfold it and feel the inner layers. Weigh all three cloths and record the 24-hour masses.
For every reading, find the water remaining: water remaining = mass at that time minus dry mass. Then find the fraction remaining: water remaining divided by the water at 0 minutes. Record both in Table 2.
Do not use carpet, cloth, or other materials from a real leak or flood in this lab. Water from floods and sewer backups can carry germs, and cleaning up after it calls for different precautions.

Data & Analysis

Table 1: Cloth masses (grams)

Reading	Cloth 1 (condition: ____ )	Cloth 2 (condition: ____ )	Cloth 3 (condition: ____ )
Dry mass
0 minutes (wet)
10 minutes
20 minutes
30 minutes
40 minutes
24 hours

Table 2: Water remaining in grams, and fraction of the starting water remaining

Reading	Fan: fraction	Still: fraction	Covered: fraction
0 minutes	1.00	1.00	1.00
10 minutes
20 minutes
30 minutes
40 minutes
24 hours

Covered cloth at 24 hours: the top felt (dry / damp / wet), and the inner layers felt (dry / damp / wet).

Part A: Your group's data

What fraction of its starting water did your Fan cloth still hold at 40 minutes?
What fraction of its starting water did your Covered cloth still hold at the 24-hour reading?
For your Fan cloth, find the difference and the ratio between each pair of back-to-back 10-minute readings of water remaining. Were the differences closer to constant, or were the ratios? Based on that, is a linear model or an exponential model the better fit for your first 40 minutes?

Part B: Reference data from a pilot group

Suppose a pilot group in Ellisfield ran this lab with three cloths that each held 80 grams of water at 0 minutes. Their water-remaining results are below.

Time (minutes)	Fan cloth water (g)	Still cloth water (g)	Covered cloth water (g)
0	80	80	80
10	64	76	80
20	51	71	79
30	41	67	79
40	33	63	78

Divide each of the pilot Fan cloth's readings by the reading 10 minutes before it. What ratio, rounded to one decimal place, describes the Fan cloth?
Using the starting water of 80 grams and the ratio from question 4, write an exponential model for the pilot Fan cloth, W = a(b)^n, where W is the water remaining in grams and n is the number of 10-minute intervals since 0 minutes. Use your model to predict the water remaining at 60 minutes.
Use your model from question 5 and logarithms to find how many minutes it would take the pilot Fan cloth to fall to 8 grams, which is 10 percent of its starting water. Round to the nearest minute.
Over the 40 minutes, how many grams of water did the pilot Still cloth lose per 10 minutes, on average?
What fraction of its starting water did the pilot Covered cloth still hold at 40 minutes?

Part C: What the data mean for health

Explain, in terms of evaporation, why the Fan cloth dried fastest and the Covered cloth barely dried at all.
The Covered cloth stands for carpet pad under a rug or insulation behind drywall. Use your data and the pilot data to explain why water-damage guidance tells people to remove or open up wet materials that cannot be dried quickly, and explain how that protects the health of the people who live in the apartment.
Name one way the cloth model differs from a real flooded apartment, and explain whether that difference would make real drying faster or slower.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: Accept the fraction calculated from the student's own Table 2 (water remaining at 40 minutes divided by water at 0 minutes).
The value should be clearly lower than the Still cloth's fraction at 40 minutes. If it is not, check whether the Fan cloth was folded, set too far from the fan, or weighed slowly.
Answer: Accept the student's own value; it should be much higher than the Fan and Still fractions at 24 hours, and it is often close to 1.
Many groups also report that the top of the Covered cloth felt only damp while the inner layers were wet, which is the observation the teaching note is built on.
Answer: Accept either model when the choice matches the student's own differences and ratios.
If the ratios stayed about the same while the differences shrank, the exponential model fits better. If the differences stayed about the same, a linear model fits the first 40 minutes. Strong answers note that 40 minutes is a short window and that drying often slows later, so the 24-hour reading is useful for checking the choice.
Answer: 0.8.
64 ÷ 80 = 0.80, 51 ÷ 64 ≈ 0.80, 41 ÷ 51 ≈ 0.80, and 33 ÷ 41 ≈ 0.80. Each 10-minute interval leaves about 0.8 of the water that was there before, so the Fan cloth loses about 20 percent of its remaining water every 10 minutes.
Answer: 21 grams.
The model is W = 80(0.8)^n. Sixty minutes is 6 intervals, so W = 80 × 0.8^6 = 80 × 0.262144 = 20.97, which rounds to 21 grams.
Answer: 103 minutes.
Set 80(0.8)^n = 8, so 0.8^n = 0.1. Then n = log 0.1 ÷ log 0.8 = (−1) ÷ (−0.0969) ≈ 10.32 intervals. At 10 minutes per interval, that is about 103.2 minutes, or 103 minutes.
Answer: 4.25 grams.
The Still cloth went from 80 grams to 63 grams, a loss of 17 grams over 4 intervals, and 17 ÷ 4 = 4.25 grams per 10 minutes. Its differences (4, 5, 4, 4) are close to constant, so a linear model describes this short window well.
Answer: 0.975.
78 ÷ 80 = 0.975, so after 40 minutes the Covered cloth still held 97.5 percent of its water.
Answer: Moving air carries damp air away from the Fan cloth, while trapped air over the Covered cloth fills with water vapor and nearly stops evaporation.
Water evaporates when molecules at the wet surface escape into the air. The layer of air touching a wet surface quickly becomes humid, and evaporation slows once that air is close to saturated. The fan keeps replacing it with drier room air, and spreading the cloth flat exposes more surface. The Covered cloth is folded, so less of it is exposed, and the small pocket of air under the container becomes humid within minutes and stays that way. Accept any answer that links the drying rate to air movement, humidity next to the surface, or exposed surface area.
Answer: Hidden materials stay wet long enough for mold to grow out of sight, so they must be removed or opened up to protect the residents' health.
Strong answers cite data, such as the pilot Covered cloth holding 0.975 of its water after 40 minutes while the Fan cloth held about 0.41, or their own Covered cloth still holding most of its water after 24 hours while its top felt only damp. They explain that mold needs moisture, that a surface check cannot show what is happening inside a pad or wall, and that mold growing unseen releases spores into the air people breathe. They connect this to health: mold can set off allergy symptoms and asthma attacks, and people with asthma, young children, older adults, and people with weakened immune systems face the most risk. Accept answers that make the moisture, mold, and health links with at least one piece of evidence from the data.
Answer: Accept any real difference with a correct direction.
Examples: real carpet pad and drywall are much thicker than a washcloth, which makes drying slower; a flooded apartment's air is already humid, which slows evaporation; a building's lower floor may be cooler, which slows evaporation; a real cleanup crew may use several fans and dehumidifiers, which makes drying faster; water from a flood or sewer backup can carry germs, which changes what must be thrown away even when a material can be dried.

Differentiation

Support

Give these students Table 2 with the subtraction and division already set up as formulas in a spreadsheet, so their work is entering masses and reading the results. Work the first ratio in question 4 together, and let students answer question 6 by building a table of 80 × 0.8^n for n = 1 through 12 and finding where it first drops below 8 grams, instead of using logarithms.

Extension

Have students enter their own Fan cloth data into a graphing calculator or spreadsheet, fit both a linear and an exponential regression, and compare the residual plots to decide which model fits better. A second option is to add a fourth condition, such as a folded bath towel in front of the fan, and explain how thickness changes the fitted ratio.

ELL supports

Pre-teach "evaporate," "humid," "porous," "mold spores," and "ratio" with a labeled photo of each setup. Post a word bank with "dries faster," "dries slower," "stays wet," and "traps moisture," and provide sentence frames for question 10: "The Covered cloth still held ___ of its water after ___, so a carpet pad under a rug would ___. This matters for health because ___."

Extensions

Students can connect this lab to leak prevention. Household leaks waste an average of about 180 gallons of water per week, and many of them are slow drips under sinks and behind appliances that also soak cabinets and flooring out of sight. Groups can write a one-page checklist for tenants in the Ellisfield building that covers finding a leak early, drying the area, and knowing when to call the building manager. A building maintenance worker or a water damage restoration technician can be invited to show how a moisture meter detects water inside a wall that looks dry from the outside.