Prime Practices

Prime Practices

Activated Oakum Technique

Call: 1-800-321-7212

Scope of Work: Prime Resins’ oakum is a fibrous twisted jute rope. It is used in conjunction with Prime Flex resins to seal leaking joints, pipe penetrations and conduits. Prime Resins’ oakum is dry and unoiled to ensure maximum absorption of Prime Flex.


Problem: Wide gaps or high hydrostatic pressure can make it difficult to stop leaks.


Solution: Chemical grouts are used to seal active leaks in concrete or brick structures to help control groundwater infiltration. By slowing the leak with the activated oakum technique, you allow the chemical grout more time to react with water and seal the defect.

This method can also be used to form a primary seal at the surface of wide joints or pipe penetrations in order to fill the space within the joint or around the pipe with chemical grout. The primary activated oakum seal acts to contain the expanding chemical grout within the joint or pipe penetration and to promote a dense cell structure in the cured foam.



Make sure the oakum stays dry until used or its absorption of resin will be diminished. Do not place a box of it on a wet surface. Transfer it to pails or trash bins in preparation for use in a wet space.

  1. Clean the area in the joint. Dust, laitance, dirt, grease and any chemical contamination must be removed. Be sure to remove any unsound concrete. (Cut an inverted “V” joint around the pipe if there is not enough room to insert the oakum when sealing around a pipe.)

  2. Cut the oakum (open-cell foam or burlap may be substituted) into sections that are the proper size for the job and put it into the pail or plastic bag. Unwind the oakum to a loose consistency for maximum absorption.

  3. Pour enough Prime Flex 900 XLV, Prime Flex 920 or Hydro Gel SX onto the oakum to cover it up entirely (approximately 1.75 gallons for every 10 feet of oakum). Let it soak up as much Prime Flex as possible. You may want to dunk or prod the oakum in the resin to ensure it gets completely soaked with resin. Wear chemical resistant gloves while handling the activated oakum. Avoid breathing urethane vapors and use adequate ventilation.

  4. If the joint is dry, spray it with water before inserting the activated oakum.

  5. Take the Prime Flex-saturated oakum out of the pail or bag, strip off excess resin with a gloved hand and

  6. submerse it in water for 5-10 seconds, or

  7. if you need more time to place the oakum before it is activated — such as in a hard to reach place or when covering a large area — you can wet the surface to be treated with a pressure sprayer of water, place the resin-soaked oakum, then thoroughly wet the oakum with the water-filled pressure sprayer to activate the resin. If applying multiple layers or an extremely thick layer, wet each layer as you go to ensure good reaction of the grout.

  8. Remove the oakum from the water and force it into the joint or between the pipe and concrete.

  9. The Prime Flex will expand and bite into the wet concrete to achieve a tenacious bond. This will prevent further water infiltration at the joint or around the pipe. As the chemical grout expands, the oakum plug may protrude from the joint. Continue to work the surface flush with the joint during this phase for a more aesthetic appearance.

  10. Tight joints or pipe penetrations can be V-notched with a grinder or chisel to create a gap wide enough to insert the activated oakum.


 Prime Oakum and Prime Flex Grout Volume Requirements for Pipe Joints Sized 1” – 1.5”

Pipe I.D. Oakum in feet Prime Flex in gallons
24” 6.5 .7
30” 8 1.4
36” 9.5 1.7
42” 11 1.9
48” 12.5 2.2
54” 14 2.5
60” 15.5 2.8
66” 17 3.0
72” 19 3.4
84” 22 3.9
96” 25 4.4
108” 28 5.0
120” 31 5.6


It requires approximately 22 gallons of Prime Flex 900 XLV or Prime Flex Hydro Gel SX to saturate one 50 lb. box of Prime Resins unoiled oakum.


Safety Considerations:

  • Always wear protective clothing, chemical resistant gloves and safety goggles at all times when handling resins. Blowouts can occur when injecting resins at high pressure.
  • Polyurethane resins contain isocyanates, which can cause respiratory irritation. Use mechanical ventilation in confined spaces.
  • Be careful of electrocution when working with power equipment in wet environments. Keep water off of electrical cords and equipment.
  • Carefully read MSDS prior to handling any chemical.
  • Keep first aid kit (eye wash, bandages, etc.) present on site with easy access.


Materials List:

  1. Prime Flex 900 XLV, Prime Flex 920 or Hydro Gel SX
  2. Oil-free oakum


Equipment List:

  • Clean, dry pails
  • Plastic bags
  • Chemical resistant gloves
  • Safety goggles
  • Screwdriver
  • Hammer