Silicone based waterproofing material having low volatile organic chemicals

An improved silicone rubber waterproofing composition having a low volatile organic chemicals content is the subject of the present invention. The composition comprises an RTV silicone rubber, a small but effective quantity of amyl acetate, and a solvent comprising mineral spirits and trichloroethane or its equivalent. The composition is highly penetrable, has a long residual life and is not subject to UV degradation. It meets the most stringent environmental regulations but is still economical to manufacture and exhibits low combustibility after curing.

BACKGROUND OF THE INVENTION 
This invention relates generally to waterproofing compositions and, more 
particularly, to an improved silicone rubber coating composition 
characterized by a relatively low percentage of volatile organic 
chemicals. 
Silicone rubbers are known as useful in various types of protective coating 
compositions. Typical compositions of the prior art are found in U.S. Pat. 
Nos. 2,751,314; 2,934,464; 2,979,420; 4,144,216; and 4,105,617. 
Prior art formulations incorporating silicone rubbers are known to be 
expensive to manufacture and are characterized by a high percentage of 
volatile organic chemicals to which there is presently considerable 
environmental objection. The present invention overcomes the limitations 
of many of the prior art formulations by providing a composition which is 
economical to manufacture and has a relatively low volatile organic 
content. 
It is therefore a primary object of the present invention to provide a 
silicone based water composition which is highly penetrable, has long 
residual life, is economical to manufacture and produces little 
environmental pollution upon use. 
An object of this invention is also to provide a silicone waterproofing 
composition which meets the object set forth above and is not subject to 
sunlight degradation, particularly by ultra-violet rays. 
Still another one of the objects of my invention is to provide a silicone 
rubber based waterproofing composition which is economical to manufacture, 
has a low volatile organic chemical content and can be safely applied by 
operators without the need for special equipment. 
An aim of this invention is to provide a silicone waterproofing composition 
meeting by objectives set forth previously which can be used on masonry, 
wood and asphalt substrates. 
Another object of this invention is to provide a silicone rubber base 
waterproofing composition meeting the objects set forth above which, after 
curing, exhibits very low combustibility and thus may be safely applied to 
wood and other combustible materials utilized in building construction 
without presenting a fire hazard.

Other aims and objects of this invention will be made clear or become 
apparent from the following description and claims. 
The process for the manufacture of silicone rubber is well known to those 
skilled in the art and is described in expired U.S. Pat. No. 2,380,955. 
The term "silicone rubber" as used throughout this specification and the 
attendant claims is intended to include any polysiloxane which has been 
crosslinked. Most silicone rubbers are predominantly methyl polysiloxane 
but the polymer may also contain other organic group substituents on the 
polymer chain such as phenyl or vinyl. Typical crosslinking agents for 
silicone rubbers are organic peroxides, especially benzoyl peroxide and 
its derivatives. A particularly useful silicone rubber is dimethyl 
polysiloxane having a molecular weight of about 500,000. The silicone 
rubber which is employed should be a room temperature vulcanizing (RTV) 
silicone so that it will crosslink at room temperature either through the 
addition of a catalyst or by moisture in the air. 
The silicone polymer which is a component of the composition according to 
the invention is dissolved in a nonreactive organic solvent which may 
comprise from 67 to 96 percent by weight of the final composition. The 
solvent may comprise one or more of the following compounds: 
trichloroethane, methylene chloride, trichlorofluoromethane, 
dichlorodifluoromethane, chlorodifluoromethane, dichlorotetrafluoroethane, 
trifluoromethane, chloropentafluoroethane and trichlorotrifluoroethane. 
For economic reasons, it is preferable for the solvent to also comprise up 
to forty percent by weight mineral spirits, preferably thirty to forty 
percent, and most preferably approximately 38 percent (by weight). The 
silicone rubber may comprise from three to thirty percent by weight of the 
final composition and preferably about five to ten percent by weight. 
It has been discovered that utilizing a relatively small percentage of amyl 
acetate in the composition greatly enhances its performance as a 
waterproofing material. The quantity of amyl acetate is at least one 
percent by weight but not more than about three percent by weight. While 
the exact mechanism by which the amyl acetate and the organic solvent for 
the silicone work in a synergistic manner is not fully understood, it is 
believed that the amyl acetate breaks the silicone polymer into smaller 
units so as to substantially increase its penetrability without 
deleterious side effects. If, however, the quantity of amyl acetate 
exceeds about three percent by weight, the silicone rubber is broken down 
to an extent that it no longer serves as an effective waterproofing 
barrier. 
The mineral spirits utilized in the preferred formulation should have a low 
naphtha content and virtually negligible quantities of sulphur. The total 
aromatic composition of the mineral spirits should be less than about two 
percent by weight. 
A general formula for the composition according to the invention is: 
3-30 percent by weight RTV silicone rubber 
1-3 percent amyl acetate 
67-96 percent by weight of one or more of the following: trichloroethane, 
methylene chloride, trichlorofluoromethane, dichlorodifluoromethane, 
chlorodifluoromethane, dichlorotetrafluoroethane, trifluoromethane, 
chloropentafluoroethane and trichlorotrifluoroethane. 
As previously indicated, the composition may include up to forty percent by 
weight mineral spirits of the type described as one of the components of 
the solvent. 
A preferred composition formulation according to the invention is as 
follows: 
5-10 percent by weight RTV silicone, acetic acid cure. 
1 percent by weight amyl acetate. 
30-40 percent by weight mineral spirits of the type described. 
49-64 percent by weight 1,1,1-trichloroethane. 
As indicated previously, methylene chloride, trichlorofluoromethane, 
dichlorodifluoromethane, chlorodifluoromethane, dichlorotetrafluoroethane, 
trifluoromethane, chloropentafluoroethane, and trichlorotrifluoroethane 
may be substituted for the 1,1,1-trichloroethane. 
The composition is prepared by first mixing the mineral spirits and the 
trichloroethane and then adding the RTV silicone and amyl acetate to this 
solvent mixture with mixing. The composition may be applied as a 
waterproofing material by brushing or spraying, although spraying is the 
preferred application technique. The application rate can vary widely, but 
a preferred rate is one gallon per 200 square feet. 
A particular advantage of the composition according to the invention is 
that it has a relatively low volatile organic chemical content and, 
accordingly, can meet the most stringent environmental regulations. These 
advantages in terms of environmental impact have been achieved without 
detracting from the effectiveness of the composition. It is, however, 
important that the relative percentages of the components of the 
composition be maintained as set forth herein to achieve the desired 
results. 
As previously indicated, the composition according to the invention is 
useful in waterproofing any material which is capable of absorbing the 
composition but it is particularly well adapted for use on masonry and 
concrete surfaces. Its high penetrability and good adhesion provide for 
superior waterproofing properties. 
It is to be understood that the foregoing description of the invention and 
the uses to which it may be put are only exemplary in nature. The scope of 
the invention is intended to be limited only by the appended claims.