Round Eucalyptus wood treatment in sequential stages with inorganic borates and metal salts (zinc sulfate and boric acid+borax) was studied; the aims were to form an insoluble precipitate of zinc borate inside wood and to reduce treatment costs by performing the first treatment by simple ascent and diffusion of the preservative, at the same time as it was sought to impregnate the heartwood. The second preservative was applied by pressure and non-pressure methods, and the effectiveness and retention achieved were compared. This paper presents the results of treatments effectiveness after five years of field trial. The degree of deterioration was rated for different treatments and the deterioration index was added. It was determined the average life time of the test pieces. B and Zn remaining in wood after 5 years were quantified in the aerial and buried parts of test pieces The determinations of Zn and B in a sample taken from the aerial part and another near the ground line of the test specimens with equal treatment, yield the same results in both points. The concentration of zinc could be determined in no case, because it is less than 1 μg / ml, boron could be determined, which indicates a longer permanence in the wood even in those specimens without second treatment. Untreated controls had a deterioration index (DI) of 100 after five years, while the treatment with best performance had a DI of 25. The highest deterioration rates are observed in the wood subjected to simple ascent of any of the salts (boron or zinc). At the same time treatments that begin with simple ascent of boron show a superior performance compared to those that use zinc salts, whereas the one which applies Zn in the second treatment by the Bethell method, shows the greater durability. The treatment in stages of Eucalyptus grandis round wood, shows greater effectiveness when the first stage applies boron salts and the second salts of zinc by Bethell's method. Zinc borate may be formed in situ under the treatment conditions.

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