770.10 Linseed Oil Treatment

All bridges with a concrete deck receive an initial application of a linseed oil mixture by the contractor at the time of construction. An additional application will be made by maintenance forces one year later. No further application will be made except as determined by the visual observation of scaling during the annual bridge inspection. Refer to the planning guidelines for linseed oil treament for more information.

Linseed Oil Treatment Methods

All concrete surfaces of bridges exposed to chemical solutions shall be treated with the linseed oil mixture. These surfaces include the decks, curbs, medians, sidewalks, parapet walls and end handrail posts. The tops of the parapet walls and the outside faces of the floor, curbs and parapet walls need not be treated.

The surfaces to be treated shall be dry and cleaned thoroughly to remove any materials that will prevent the mixture from penetrating the concrete. It is desirable to remove any dust remaining on the bridge with compressed air just prior to the application of the linseed oil mixture.

The mixture, consisting of 50% boiled linseed oil and 50% mineral spirits, shall be applied at a normal rate of 0.04 gallons per square yard for regular B-1 concrete decks, 0.03 gallons per square yard for B-2 concrete decks and 0.02 gallons per square yard for decks having low slump concrete overlays. This normal rate should be varied depending on the condition of the surface to be treated and the supervisor in charge of the work should determine the specific rate to be used. No linseed oil treatment is to be applied to decks having latex mortar overlays.

The mixture may be applied using a pick-up mounted herbicide sprayer and special spray bar equipped with oil distributor nozzles spaced at approximately 12 in. centers and mounted at bumper height. A hydraulic disconnect can be mounted at the pump and a hand sprayer attached to spray curbs. A solenoid valve operated from the cab allows more control in application. Typical speeds are about seven M.P.H. This method requires substantially less cleaning time than using a distributor.

The mixture may be applied with a distributor equipped with special nozzles (#S 36-116) spaced on 8 in. centers (alternate holes plugged) with the spray bar set at a height of about 16 in. The distributor must be clean and in good condition to prevent leakage of the material and shall be calibrated to provide the desired application rate. The linseed oil-mineral spirits mixture has a low flash point and care must be exercised to prevent ignition of the mixture on the treated surfaces by exhaust sparks, open flame or other means and in no case shall the mixture be heated in the distributor. A small sprayer may be used for areas which cannot be sprayed using the distributor.

The mixture is to be applied to one-half of the bridge at a time and traffic must be maintained. As this mixture causes the deck to be slippery, the treated portion must be barricaded to traffic until it is dry. After allowing a reasonable time for penetration and drying, puddles should be squeezed to assist drying or blotted and the deck sanded. Traffic may be allowed only after sufficient drying to ensure traffic does not pick up linseed oil. Time will depend on application rate, temperature, humidity, sunshine and wind velocity. After the deck is completely dry, the excess sand shall be removed.

When applying this mixture on windy days or over lower roadways, measures must be taken to protect the traffic from drifting sprays, etc.

This work is best accomplished during hot dry weather and preferably during the months July of August.