Subslab Distribution When Short-Rodding

During a two-year period, a series of studies was conducted to determine the lateral distribution of fluorescent dye under slabs when using vertical treatments with different pressures and dispersion tips (Frishman and St. Cyr, 1988, 1989).

Since short rodding for termite control is common in some parts of the country and in some situations necessary if imbedded pipes are present or if the homeowner does not want the surface of a floor marked, it was decided to include this study on subslab distribution when short rodding. It examines how effective current short rodding techniques are n applying termiticides under slabs.

Procedure. Six 4-foot by 8-foot pieces of ½-inch plywood served as slabs. The plywood slab covered a wooden frame 1-foot high divided into four 2-foot by 4-foot compartments and filled equally with sand that was then compacted prior to placing the slab over the soil. Treatment holes were drilled laterally through the sides of the boxes.

The following parameters were studies:

• Four-way tip versus straight tip. In some cases, a slab injector was also tested.
• Horizontal rodding (0 degree angle), 22.5 degree angle and 45 degree angle.
• Rodding laterally 2 inches versus 8 inches below the slab. In some cases, 5 inches below the slab was also tested.

Most tests were replicated three times, using 25 psi at the nozzle. Some ancillary tests were done one to two times as the opportunity arose. Applications were made with a Hypro electric roller pup N4001C and 100 feet of hose. A 4-foot by ½-inch diameter rod was sued with interchangeable tops. The rod and tips were provided by R.E. Chapin manufacturing Works Inc. of Batavia, N.Y.

To determine the distribution patterns produced, a fluorescent dye (Pylam D & C Green #8) was added to the termite tank at a rate of 0.5 pounds per 50 gallons of water. No termiticides were used to avid having to dispose of treated soil.

A special ultra violet light and bulb (B-100 A UV lamp and 100 watt UV floor bulb) were used after dark to best show the fluorescent dye. Photographs were taken with ASA-200 Ektachrome film. Before photographing, a number was applied to the soil using a paint brush and the dye. This allowed easy identification of the photographs taken. A video was also taken for future reference.

Following Dursban TC volume rates it was determined that 0.8 gallons of finished material was needed per injection hole. This represented 24-inch hole spacings along a foundation wall under a slab. A stop watch was used four different times to determine the average time it took to fill a 1-gallon container. The average value was multiplied by 80 percent to calibrate the number of seconds needed to apply the 0.8 gallons. These values were determined as 26 seconds for the 4-way tip and 25 seconds for the straight tip.

When applying the material through the 4-way tip, the handlebars of the injector were held in the same position each time to insure the holes on the four-way tip were oriented the same direction each time. The handle bars were kept parallel to the ground so that the four jets were straight p and down and horizontally left and right.

To insure that the 22.5 degrees and 45 degree angles were accurate a protractor was used each time. Results were photographed and videotaped at night to get the maximum effect of the fluorescent dye. If present, the dimensions of the dye were measured and recorded. Once recorded, a side panel was removed to observe the vertical distribution just behind the vertical board which would assimilate the edge of the slab. This was possible because the boxes were constructed using wood screws instead of nails. In most cases the soil stayed intact because it had been tightly compacted. A flat shovel was used to vertically shear off fine layers of the soil. This procedure was done several times until the soil was reached at the point where the tip of the injector terminated. This was at a depth of 6 inches.

After looking at the results when treating 2 and 8 inches below the slab and seeing a significant difference in terms of dye appearing in the surface of the soil just below the slab, it was determined to do additional injection sites 5 inches below the soil. This was done for both the straight tip (2 replicates) and the 4-way tip (3 replicates) using a horizontal treatment.

A1/2-inch straight tip slab injector with a coned rubber tip was tested when inserted laterally 5 inches below the slab and 2 inches below the slab. Material was injected for 26 seconds in these tests.

Results. The study’s findings included:

• Drilling angle. Tips were inserted 6 inches below the slab gave no coverage on the surface of the soil regardless of the type of tip used. Applications made 5 inches below the slab gave no coverage on the surface of the soil when a straight tip or slab injector was used. A four-way tip did result in 9-inch average coverage on the soil surface. Treating horizontally only 2 inches below the slab injector gave about 14 inches of coverage, while a 4-way tip gave over 19 inches of coverage.

Drilling just 3 inches too far below the slab can greatly reduce the effectiveness of the treatment. When short rodding, a technician must drill immediately below the slab for best results.

• Drilling angle. Tips were inserted 6 inches into the soil at a distance of 2 inches below the slab. At a 45-degree angle, the ends of the tips were too far below the surface to have any effect. At a 22.5 degree angle, only one of the three replicates using a straight tip resulted in termiticide on the surface, but that one was only a 6-inch patch. All three replicates of the four-way tip gave coverage at the surface. The average coverage was over 9 inches. The best coverage was provided by horizontal drilling.

Straight tips and slab injectors gave an average of 14 inches coverage beneath the slab. The four-way tips have an average of over 19 inches of coverage.

• Type of tip. In all situations, the four-way tips gave better coverage beneath the slab than straight tips or a slab injector. The four-way tip was the only one to reach the surface at a treating depth of 5 inches below the slab. At a treating depth of only 2 inches, the average was high (19.5 inches), but variability was great with a range from only 12-1/2 to 24 inches. Two-foot drill spacings would not always result in adequate coverage, but 1-foot drill spacing would if you drill close enough below the slab. It is important when using four-way tips to keep one hole facing straight up.

• Penetration into the soil. Six-inch penetration resulted in many replicates that had gaps between the "foundation wall" and the dye patch. For instance, replicate #8 resulted in a 6-inch patch of dye on the soil surface, but this patch was 3 inches from the edge of the box. Similarly, replicate #2 provided a 13.75 inch spread of dye on the surface, but there was a 1-inch untreated gap between the edge of the dye and the edge of the box.

Unfortunately, when tips were inserted only 2 inches into the boxes, the dye splashed back out If this occurred in a cinder block wall, and the tip extended only 2 inches beyond the block, the termiticide would flow back into the block. No termiticide would be placed where it was needed and the technician would be unaware of what was happening. If treating a solid or poured wall, the termiticide would flow back out and run down the wall. Fortunately, if this occurred inside a structure, all of today’s termiticides could be cleaned up with detergent and water.

It appears that technicians should try for about a 4-inch penetration beyond the foundation wall. If drilling through an 8-inch block wall, total penetration would have to be at least 12 inches.

Discussion. Short rodding provides inconsistent and often times inadequate coverage beneath a slab. Drilling and treating from above will result in a better distribution of termiticide beneath a slab (Frishman & St. Cyr, 1988,19890. Short rodding from the side should be considered only as a last resort.

Short rodding at an angle is least effective in getting adequate coverage under a slab. Every effort must be made to keep the rodding angle as horizontal as possible.

The distance of the drill hole below the slab is also important. A miscalculation of only 3 inches can result in very poor to zero coverage under the slab.

Four-way tips appear to be most effective in providing coverage beneath the slab. This is due to the one hole that faces straight up. A three-way tip (eliminating the hole facing down) might provide even better results.

Rods should be inserted 2 to 6 inches beyond the foundation’s wall. If not inserted far enough, termiticide will splash back or flow into the hollow block. If inserted too far, an untreated gap will occur between the foundation wall and the treated site.

With four experienced people watching the procedures and carefully doing the work, one hole was drilled but not treated during the study. This was not discovered until the slabs were lifted to collect data. Upon checking the soil it became evident no dye had been applied. This replicate was then repeated to provide the necessary data. This embarrassing situation demonstrates how easily gaps could happen during a regular treatment. Technicians must be very careful to insure that each and ever hole is treated.

The greater repellency of pyrethroid termiticides compared to the organophosphates the chance of termites moving to another area to reach a structure. The complete and even dispersion of the termiticide in the soil is more critical than ever. This and previous studies show how easy it is to have gaps in a treatment. Short rodding under a slab using current tips leaves much to be desired. The key to successful termite control is to use the correct equipment, use the correct techniques, keep drill holes close together and, finally, to use the proper volumes.

___ Austin F. Frishsman and Alfred St. Cyr