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Which Type of Wood Resists Water Absorption the Best in a Natural State and With Surface Coatings

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Purpose

To test a variety of different woods in a natural state for their water absorption rates and again when treated with latex paint and oil stain to see which if either of these surface coatings better reduces the water absorption rates of the various woods tested.

Hypothesis

One of the biggest concerns of homebuilders is the weathering and decay of various woods used in home construction. Water is perhaps the worst enemy of any type of wood. It can cause wood to rot, shrink, and swell, which can change the dimension of the wood, and cause paint to fail to adhere to the wood. Some types of wood may naturally absorb less water than others, and paints and stains have different effects on a wood’s water absorption.

Materials Needed:

  • 15 pieces of commonly used building woods cut to 3x6x½ (consisting of 3 pieces of cedar, redwood, oak, pine, and hemlock)
  • 10 buckets
  • Water
  • Plastic wrap
  • 1-liter graduated cylinder
  • Exterior latex paint
  • Exterior oil-based stain
  • Paintbrushes
  • Paper towels

Experiment

Five pieces of wood typically used for building and construction will be tested in their natural form (untreated) by being submerged into separate buckets containing measured amounts of water for a 7-day period and covered with plastic wrap (to remove the unwanted variable of evaporation from affecting the tests results). Then the wood pieces will be removed and laid to dry on paper towels for later observation. The water remaining in each of the buckets will be measured and subtracted from the original amount of water that was added to the bucket in order to measure the amount of water absorbed by the wood in that bucket. The remaining 10 pieces of wood will be treated with the exterior latex paint and exterior oil-based stain and allowed to dry. The experiment will be repeated on each of the treated wood samples to determine the effects, if any, that the surface coatings have on water absorption by the wood.

Procedure

  1. Measure 1 liter of water into each of five buckets. Carefully place one piece of wood of each type into each bucket. Label each bucket for the type of wood it will contain. Cover each bucket with plastic wrap and leave the buckets at room temperature for seven days.
  2. At the end of the seventh day, carefully remove each piece of wood and allow it to drip back into the bucket for about 15 seconds. Then lay each piece of wood on paper toweling to dry.
  3. Take the water from the first bucket, pour it into the graduated cylinder, and measure the amount of water in the cylinder. Subtract the amount of water that is in the graduated cylinder from the 1 liter that was present in the bucket at the beginning of the experiment. The amount calculated equals the amount of water absorbed by the piece of wood in the first bucket. Repeat this step for the remaining buckets and record your results.
  4. Take the paintbrush and paint one piece of each remaining wood type with a coating of the exterior latex paint. Allow the paint to dry. Paint the remaining pieces of each wood type with the exterior oil-based stain and allow the stain to dry. Once the samples are dry, apply one more coat of each paint or oil to the samples and allow them to dry fully.
  5. Repeat steps 1–3 with the 10 treated wood samples and the 10 buckets (reuse the same 5 buckets that you used for the first group of wood samples tested) and record your results.
  6. After the samples have dried, analyze the condition of all the wood samples after being exposed to the water. Note the overall condition of each piece of wood and examine for rot, shrinkage, or paint flaking, if any. Record your results.

Results

  1. Of all the woods tested in their natural form, which was the most waterabsorbent? Which was the most water-repellent?
  2. Of all the surface coatings, which one appeared to have the most waterrepellent qualities?
  3. Did the most water-absorbent woods become water repellent when treated with the surface coatings?
  4. What was the overall condition of each piece of wood after the experiment? Based on your results, which wood type appears to be the most durable? Is there a correlation between wood durability and water repellency?
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