Daily soaking for one hour in dilute H₂SO₃, H₂SO₄, or HNO₃ (pH 2.0, 2.5, 3.0, 3. 5, and 4. 0) during accelerated weathering increases the rate of erosion of specimens of <i>Thuja plicata</i>. A new gravimetric procedure is described for assessing erosion during accelerated weathering. Treatment with H₂SO₃ caused the fastest rate of erosion, followed by H₂SO₄, then HNO₃. Rate of erosion increased linearly with pH below pH 3.5. None of the acids affected erosion at or above pH 3.5. Sugar analysis of residues from the acids used to soak the wood indicated degradation of polysaccharides during increased erosion.