October. 19%
ISDC;)'TRIA/I A-ISD ENGIAVEERING C H E M I S T R Y
1091
The Painting of Treated Wood' By M. E. Dunlap FOREST PRODL-CIS L A B O R ~ T O~RI Y A D I S O X \VI$ .
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F TREATED n ood were available to builders there would be little reason for decay in houses. .Is it is now, the most durable woods are the only ones suitable for uae in parts of the structure subject to the attack of fungi. Even the durable woods often fail to give the most satisfactory results because pieces containing sapwood have not been cullrld out. Sapwood, in general, is not resistant to decay. *Imong building parts particularly subject to decay are factory roofs, porch woodwork. water tables, nnd sills laid at or near grade level. The wood-preserving industry has made remarkable progress in the treatment of railway ties, posts. poles, and bridge timbers, but it has never developed the field of treated lumber in retail yards and mills. The treatment of building lumber would solve the decay problem with which the builder is often confronted. On the other hand, it offers new problems which must be taken into account a t once. The success of this new development depends upon our ability to master, not only the successful penetration of the wood with preservatives, but also, in many cases, the painting of such material. It is well known that creosote is exceedingly difficult t o paint over satisfactorily, but water-soluble preservatives present more attractive possibilities. Lack of accurate information on this subject has been one of the chief obstaclw to the adoption of treated lumber in house construction. The Forest Prodiicts Laboratory has started a series of painting tests of woods treated with the following preservatires. creosote, mixtures of creosote and 1Iontan wax, gas oil, pine oil, sugar. borax, zinc chloride, sodium fluoride, Triolith, mercuric chloride, and Ac-Zol. The last seven materials are water-soluble. The absorptions of the various preservatives and the strengths of the solutions or mixtures used in treating the wood are shown in the accompanying table. Satisfactory trmtments usually require from 10 to 15 pounds of preservat i r e oils or half a pound of dry salt per cubic foot of wood. Xercuric chloride does not require so great an absorption as other salts. Two sets of panels were made up from the treated material-one set painted white for exposure on a test fence, each specimen composed of three boards measuring 7/$ by 6 by 36 inches, and one set consisting of boards 5/s by 4 by S inches, for color test exposure on a roof and indoors. The latter specimens were coated with white, gray, blue, and chrome green paint, and with spar varnish. All the paints except the chrome green have a white lead base. Three coats of paint were applied to the panels, as recommended b y the National Lead Company.
It was impossible to do satisfactory painting directly over creosote with white lead paint. The paint rapidly turned brown and was exceedingly slow in drying. Sealers especially designed for covering bitumens were tried. Although the painting properties were improved somewhat, there was still an undesirable yellowing of the paint film. Mixtures of Montan wax and creosote provided better painting surfacw and the bleeding of creosote was materially reduced. Staining still occurred, however, in proportion to the quantity of creosote in the mixture. Gas oil produced a yellowing of the paint in spots. Pine oil, while it did not discolor the pailit, broke through the coating of one board a t a number of points. Sugar, borax, zinc chloride, sodium fluoride, Triolith, mercuric chloride, and h - z o l produced no discoloration of the paint. Chrome green paint (Brewster green) can be satisfactorily applied over creosote but is slow in drying. Varnish can be applied satisfactorily over any of these preservative\. It is rather slow in drying over creosote, but is much better in this respect than oil paint. .4verage A b s o r p t i o n s of Preservatives by S p e c i m e n s for P a i n t i n g Tests TREATIWG M I X T U R E S AVERAGE ABSORPTIO\S -PER CENT-LES PERCU.FT Paint Small Dissolved Creo- Monfence test preserva- sote tan Treatinc material Water tive or oil wax specimens specimens 20 80 20.7 a 16.2 Montan wax-creosote 40 60 26.7 a 8 , Montan wax-creosote 14.x 15.9 a IO0 Creosote 1 5 . .i 100 28.7 Gas oil 13.7 i.0 100 Pine oil 3 5 0.53h 0.iS Sugar 97.3 0.90 1.26h Borax 94.0 6 0 0.77 3 0 0.646 Zinc chloride 97.0 0.53h 0.80 Sodium fluoride 97.0 3 0 0.426 0.6:3 Triolith 97.0 3 0 0.13b 0.10 Mercuric chloride 99.0 193 1.32~ hc-Zol 92.5 a Oil absorbed I Dry weight of water-soluble materials c Weight of solution absorbed a s furnished by maker
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Presented before the Midwest Regional Meeting and the Section of Paint and Varnish Chemistry of the American Chemical Society Madison, \Vis, May 27 to 29, 1926.
After three months' outdoor exposure the panels on the fence and on the roof show similar effects. Those treated with creosote and coated with sealers are in bad condition from bleeding and checking. The Montan wax-creosote treated paneIs are showing a tendency to peel near checks. Staining has increased on the gas oil-treated panels. The pine oil-treated panel is in very bad shape because of bleeding. KOapparent change has taken place in the panels treated with sugar, borax, zinc chloride, sodium fluoride, Triolith, mercuric chloride, and Ac-Zol. The panels exposed indoors show no change as yet. So far as the tests have gone it can be said that all the oil preservatives tried are difficult to paint over successfully, because they discolor the coating and sometimes come through. Coatings over the wood treated with water-soluble preservatives show no change attributable to the treatment, and continued exposure is necessary to determine whether any of these preservatives are detrimental t o the coatings
Hevea Rubber in Florida-Many trees and plants that produce rubber are thriving in Florida, but it has not been known t h a t the principal rubber-producing tree-that cultivated extensively in the East Indies-could survive the winters and grow t o maturity in Florida. Recently a small tree of Hevea brasiliensis was found growing a t Palm Beach. It has stood in the open for nearly twenty-five years, under unfavorable
conditions, showing that Hevea is much hardier than has been supposed. The survival of a single tree does not prove that commercial production of Hevea rubber in Florida is feasible, but there are large areas in Florida where conditions may prove more favorable for Hevea than where this tree has survived. Experiments will be required t o determine the full extent of hardiness in Florida or elsewhere.
