s 
 
 MEMORANDUM 
 
 THE TREATMENT OE SAWDUST INSULATION FOR 
 
 PROTECTION AGAINST DECAY, INSECTS, 
 
 ANIMALS AND FIRE 
 
 January 1944 
 
 
 No. R1C92 
 
 UN! IY OF FLLRIOA 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 
 FOREST SERVICE 
 
 FOREST PRODUCTS LABORATORY 
 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wisconsin 
 
MEMORAimUM 
 
 THE TR5AT:SITT CF SAWDUST DTSULATIOiT FCR PROTEC TION ASAI'/ST 
 DSC AY, INSECTS, ANIMALS, ABB FIRE- 
 
 fot for fjslicatioit 
 
 Dry sawdust or planer shavings properly packed in the walls and attics of 
 "buildings afford excellent heat insulation. They have long "been used for 
 the purpose although apparently not very extensively. The Forest Products 
 Laboratory is frequently asked "by prospective users of such insulation, to 
 suggest methods of treatment to prevent it being used as a nesting place for 
 rats, mice, and insects, or to increase its resistance to decay or fire. So 
 far as known, no experiments have "been published to supply the answers to the 
 questions about rodents and insects hut a few experiments on the effective- 
 ness of fire-retarding chemicals in sawdust have "been reported—. 
 
 From a consideration of the character of the insulation and the habits of 
 mice, rats, and insects, it seems improbable that a wall packed with either 
 sawdust or planer shavings would prove more attractive than hollow walla to 
 any of these pests, but it is known that they will nest in insulated walls 
 if other conditions are favorable. Although termites could build their 
 runways through insulated walls and use the sawdust and shavings for food 
 if they so desired, they probably prefer solid wood, The presence of the 
 insulation in the walls should be of no advantage to them. Similarly it does 
 not seem probable that sawdust or shavings in a wall would offer any 
 attraction to bedbugs, cockroaches, silver fish, ants, or other household 
 insects or provide any more favorable conditions for them than are provided 
 by hollow walls. For these reasons it is believed that sawdust or planer 
 shavings need no treatment for protection against insects and vermin. If 
 the walls of a building remain damp for any considerable period of time they 
 may decay and if they remain dry they will not decay, whether or not they are 
 filled with sawdust. 
 
 -This memorandum is not for publication. It has been prepared in order 
 to answer the numerous requests of corresvondents for information 
 about the subjects discussed, It is subject to revision from bime 
 to time as new information is obtained, 
 
 2 
 
 -"Decreasing the Combustibility cf Sawdust," by Joseph L. McCart 
 
 Ind. and Eng. Chem. , Vol. 32, p. 1^-96 • ( :Tov - 19 u 0). 
 
 R1092 -1- 
 
Condensation may develop in walls during cold weather and the more efficient 
 the insulation the more likely condensation is to occur. Most building 
 materials, such as plaster, wood, brick, and concrete, are permeable to 
 vapor. Condensation takes place when outside temperatures are below the 
 dewpoint of the inside atmosphere and the moisture passing as vapor through 
 the plaster and insulation reaches some surface that is below the dewpoint. 
 The same principles of vapor movement apply to unventilated attics. The 
 relative humidity in a house of normal occupancy and without air condition- 
 ing will average about 20 percent when the outside temperature is zero. The 
 dewpoint for 70° F. and 20 percent humidity is 2g° F., and laboratory tests 
 on insulated walls show that the inside face of the sheathing will be con- 
 siderably below 2g° during periods of zero weather and possibly even with 
 temperatures as high as 15° above. Conditions are then favorable for con- 
 densation. Obviously, the higher the inside humidity the higher the dewpoint 
 temperature, and the greater the amount of water that will condense in the 
 wall in cold weather. 
 
 Attics can usually be protected against condensation by ample ventilation. 
 Protection against condensation in side walls is obtained by increasing the 
 resistance of inner wall surfaces to vapor transmission. For new houses, 
 the use of asphalt -coated sheathing paper applied ever the inside face of 
 the studs before plastering is recommended. For buildings already con- 
 structed, suitable paint coatings on the plaster or interior finish should 
 give ample protection for most cases. Aluminum paint followed by other 
 finishing paints gives excellent protection over plaster. Primer and sealer 
 paints also make good base coats, due size, kalsomine, and cold water 
 paints offer practically no protection. For further details on the subject, 
 see the publication "Condensation Problems in modern Buildings," which may 
 be obtained from the Forest Products Laboratory upon request. 
 
 If a wall containing sawdust or shaving insulation became thoroughly damp 
 it would take a long time for it to dry out, and considerable trouble might 
 result. The insulation should, of course, be thoroughly dry when place! in 
 the walls, the walls should be dry and the construction should be such that 
 they will remain dry. If this can be accomplished no disadvantage from the 
 standpoint of decay should result from the use of untreated sawdust or 
 planer shaving insulation. 
 
 A wall properly filled with sawdust or planer shavings is more resistant to 
 flame spread up through the wall space than a similar hollow wall, for the 
 insulation prevents drafts and thus retards the spread of flames. A 
 smouldering fire in a sawdust-filled wall might be difficult to get at and 
 extinguish but this disadvantage should be more than offset by the very slow 
 rate of burning which should allow plenty of time for extinguishing. If one 
 side is burned, away from a sawdust-filled wall, of course, loose sawdust 
 will run out. 
 
 For the foregoing reasons given, treatment of the insulating material does 
 not seem very important. Nevertheless, it is possible by suitable treatment 
 to increase the resistance of planer shavings and sawdust to fire, decay, 
 and insects. The following treatments are suggested for the benefit of 
 
 R1092 _2_ 
 
those who may be willing to undergo the expense and inconvenience of treat- 
 ment for the additional insurance of satisfactory performance that treatment 
 will : co lie. It is not known that these treatments will have any effect on 
 rats and mice, but they include chemicals known to be highly effective against 
 decay, insects, and fire. 
 
 Treatment A 
 
 For Decay and Insects 
 
 To each 100 pounds of air-dry sawdust or planer shavings add 3 pounds of 
 sodium fluoride. The addition may be made by spreading the sawdust on a 
 floor, spreading the sodium fluoride over it, and then mixing the t;/o to- 
 gether by repeated shoveling and stirring. A concrete mixer could be used 
 if available. Sodium fluoride is a. fine white powder that is poisonous to 
 human and animal life. Care should be taken to avoid breathing or swallowing 
 the dust. Since sodium fluroide resembles sugar, table salt, and baking soda 
 so closely that it may be mistaken for them, it is best not to have any left 
 over after the treating job is done. Dampening the sawdust with water before 
 spreading the fluoride on it should avoid dusting troubles. A still better 
 method Of application is to dissolve the sodium, fluoride in 12 to 1R gallons 
 of hot water and mix the water with the sawdust. 
 
 After the chemical is mixed with the wood, the mixture should be dried very 
 thoroughly before putting it into the walls of a building. 
 
 Treatment B 
 
 For Fire proofing 
 
 With 100 pounds of dry sawdust mix thoroughly (by sprinkling and stirring) 
 • vater solution containing 5 pounds of monoammonium phosphate and 5 pounds 
 of bor- ( Lb out 12 to 15 gallons of water should be sufficient). If insect 
 and eoaj resistance are desired as well as fir*e proofing, both Treatment A 
 and Treatment 3 can be given at the same time, dissolving all the chemicals 
 in the same water. 
 
 No specific information as to cost can be given, for labor and chemicals 
 costs vary widely in different localities. Both transportation charges and 
 quantity purchased have an important bearing on the cost of the chemicals. 
 Current wholesale quotations in trade journals (July V)kh) for considerable 
 quantities are as follows: sodium fluoride, 3 cents per round, monoammonium 
 phosphate, £ to o-l/2 cents per pound; borax, 3 "to H- cento per pound. Retail 
 , ;h would include shipping costs, might be considerably higher. 
 
 92 -3- 
 
Special Treatment Against Rat s 
 
 The following is quoted from a memorandum from the Fish and Wildlife Service 
 
 (formerly Bureau of Biological Survey): 
 
 "It is found that rats are prone to nest in available 
 walls filled with sawdust or wood shavings, T>rovided, of course, 
 the nearby environment is otherwise favorable. It has rec<= b] 
 been learned that it may be possible to prevent this disturbance 
 to sawdust to a considerable extent by blending with it powdered 
 copper carbonate, using 12 pounds in each 100-pound mixture. 
 
 "This preparation may be mixed with treatment A when it 
 is either wet or dry. It may mix more uniformly, however, 
 following the drying process." 
 
 Attention is called to Farmers' Bulletin 163S, "Hat Proofing Building and 
 Premises," and Conservation Bulletin S, "Rat Control," which can be btained 
 for 5 cents each from the Superintendent of Documents, Government Frinting 
 Office, Washington, D. C. (stamps not accepted). 
 
 R109?- 
 
 
 Date Due 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 85 
 
 
 
 
UNIVERSITY OF FLORIDA 
 lllll III! I 
 
 3 1262 08927 9102