Document k9Kvz91vNRvGNkekXVKwMQEZn

* mu TD CCs S* Graces, lab, W. F. Singleton, hab, M. J. McDowell3 lab. Indexed #*.. v9 Marshall laboratory February 11, 1952 MEMORANDUM REPORT #425 k ,-V-rtb C W&i NOI Hi CliCilillii BACK PRIMING QF HOUSE SIDING It ha been shown that the water vapor passing through the wall and thence through the clapboard siding is responsible to a large degree for paint blistering and peeling. To prevent this, on suggested corrective measure was back priming or the clapboards with aluminum paint. Aluminum paint lays doim a film that by itself :Lf highly impermeable. This idea is now undergoing a field trial at Syracuse, New fork by Mr, Paul Schoeek, house builder. Presented here are the results of several experiments whereby measurements were made of the moisture passing through aluminum-backed, red cedar clapboards. The aluminum paint used in this experiment is 354-751, a mixture of a phenolic resin and aluminum paste, . The back priming of house siding with one coat of aluminum paint is not an effective moisture 'barrier. This is due in part to the roughness and irregularity of the unfinished side of the clap board causing a discontinuous film of paint and partly to the = porosity of the wood itself. With two coats of paint a more nearly continuous film of paint is laid down.. The permeability of the two coat system is low enough to meet the FHA Specification for a vapor barrier. Experimental Details? In Experiment #1, the aluminum paint was applied at two different spreading rates over the backs of red cedar clapboards. N35437 ~2~ > When dried th panels ware shaved down to approximately 1f$ inch thickness. Fro selected spot on the board,, small pieces were out. These were sealed onto a small glass cup containing water* Also, run along with these were two unpainted sections of clap board. These cups were then placed in a desiccator in the constant temperature room. Gups were weighed accurately peri odicully, When loss of water reached a constant rate, the tests were terminated. Results from this experiment show that a single coat of aluminum paint does not make the wood less permeable. These results were somewhat surprising, so to reeehck them, we had the builder at Syracuse send us some or his clapboards that have been back-primed on the job. , In Experiment #2 parts of the builder's boards were given another coat of aluminum paint so that the effect of two coats could be checked. Also included in this test were uncoated section of the builder's boards and sections from the boards used In the previous experiment. Panels were shaved to about one-eight inch thickness and selected sections cut out to be sealed over glass cups. This time the desiccant was placed inside the glass cup and the wood sealed on.top. All,the cups were then placed in the constant temper ature room and a fan blew air over the cups at th rate of 500 ft. per minute. These particular conditions are specified by the FHA in the manual on moisture barriers. Cups were weighed periodically and tests terminated when a constant rate was observed. In this set, the rate of .mositur passing through the aluminum film was considerably less than in the first experiment, but the c.onclusions are the same. The amount f moisture passing through the panels with two coat was approximately on fifth of the amount going through bare wood or on coat. Table 1 attached, ^Details can be found in notebooks 3B0X & 3#19 2H/A6S/J5h2fte ATTACH % MARSHALL LABORATORY H. ' AA , SOHMWJSTLTLIEMMSif DUP030003325 &b & la 3 4 5 6 M1 MWLA M**2 .M-2A 1 2 3 4 5 5A 6 6A SUM iiiaii Bar Wood n ir Fainted 268 sq.nft./galnlon Painted 312 sq.ft../gallon Oraias/Sq.ft/Br./in 3*84 10.10 5.76 3.12 7.40 9.60 Bar Wood One coat.{268 sq. ft./gal.) One coat (312 sq. ft./gal.) Overall ate. for 1 ct. kuaum 6.97 444 8.50 6.43 MPKS1MEMT #2 Pfat nel #n3 is!n Enxp. #1rc 2 ct. Panel #4 in Exp. #1 .88? .225 .719 ss n it n 2 ct. .2,35 Bae re (Syr a cuse pasns el) 1.630 .800 1 3c8 t. p* a33int 3"3 33 83 St Mt' Si .743 1.319 2.490 2 eta. 18 " tf .287 1 ct. fS 33 2 ct. 13 ts 53 1.053 .240 lab. panels 1 ct. 0 " 2 ct .80 .23 Bare wood 1.2:2 Syracuse panel 1 ct. 1.40 Syracuse panel 2 cts. .26 DUP030003326