Q&A on using 900 XLV cartridges

By Michael Vargo, senior technical consultant

I recently had an email conversation with a customer about crack injection leak sealing with Quick Mix cartridges of Prime Flex 900 XLV that I think would be helpful for others to see.

Nick asks:

Q: “I have recently used your 900 XLV in 2:1 cartridges for residential foundation crack repairs. I have experienced failures in the past using hydrophobic grouts from lack of flexibility, especially in newer homes that have moved a bit more due to initial settlement. First, let me say, this product is amazing and is exactly what I was looking for in its density and flexibility.

“I am having issues with partially used cartridges reacting in the tube after completion, resulting in the loss/waste. It seems to be when injecting tighter cracks, creating a bit of back pressure upon release of the pressure on the gun, water is being pushed back into resin side. Any suggestions?

Thanks in advance,

I understand why Nick did not have success with hydrophobic materials in the past. They are not well suited to crack injection because they do not form a tight bond with the concrete like hydrophilic materials do. Prime Flex 900 XLV is a hydrophilic polyurethane that seeks out water and forms a tenacious bond to concrete. (Read more about hydrophilic vs hydrophobic materials.)

Here’s my response to Nick:

A: “Are you using the flow restrictors — the black disc with holes in it — that are supplied with the cartridges? This should help with the issue. Also keep in mind that cartridges are best suited for cracks that are wider than 1/16” so material flows in easier and quicker. If the material sits too long in the nozzle, it can cause it to set up, creating waste. Also, using cold water will slow down the reaction time thus giving you more time to get the material into the crack.”

Q: “What is the reason for so much water on the “B” side? For example, if the crack is not actively leaking and after prep and porting the crack is flushed with water from top to bottom, could it be injected with the 900 straight? How much water does it need for proper reaction? Could the material be injected neat and activated by pre-injection flush or even a shot of water in each port after injection? I prep most of my cracks from the front face with drill-in ports and surface seal since most are dry at time of repair.”

This is a great question that gets at the heart of the best way to tackle a narrow crack. Here’s what I said:

A: “The ratio of resin to water is 2:1 (resin : water) in the Quick Mix cartridges to ensure having enough water to fully activate the resin in a dry crack if necessary. If the crack is actively leaking, then yes you CAN inject the 900 XLV into the crack without filling the empty barrel with water.

“We recommend that you flush the crack with water FIRST, then the resin rather than the other way around so you do not push the resin out of the crack with the water if you inject water after the resin. Also, the resin prefers a wet substrate to help draw the resin into the pores and micro-fractures of the concrete (the resin has a water scavenger in it to help with bonding to the wet surface).”

In Nick’s case, if the cracks he is injecting are quite tight, less than 1/16”, it would be better to pump the 900 XLV using a pump such as a Titan 540. If they are wide enough, pre-wetting the crack, using cold water and using the flow restrictor should solve his problem.

For a step-by-step procedure on injecting cracks with Quick Mix cartridges, go to our Prime Practices page, complete the form and select “Injecting wet cracks with Quick Mix cartridges and Bang-In ports” (also relevant if you are using mechanical ports). Here is a video of crack injection of Prime Flex 900 XLV using a pump.

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