As I stated in a previous blog post, Polyurethane Leak Seal in Cold Weather, twin streaming can be an effective way to ensure that water reactive resin sets up quickly and thoroughly after injection. In that post I only mentioned twin streaming briefly. Here are some more details:
Twin streaming is a technique in which you use a high pressure F-valve to inject resin AND water at the same time. As you can see in the photo, the F-valve has two supply connections - one for water and one for resin. The water and resin come into contact right before they exit the nozzle.
1. Ensures there is enough water for the resin to react with.
2. Starts the reaction immediately.
3. Allows you to inject in cold water.
When working on jobs that require void filling behind walls, also known as curtain grouting, it is imperative that you are prepared for any obstacles that may occur. If the voids are large and dry, resin may not have enough water to react with when injected in the conventional manner. In this case injecting water behind the wall prior to injection might not be sufficient (especially if the void is open or filled with gravel, giving the water an easy path to escape). With twin streaming you are guaranteed there is enough water for the resin to fully react and fill the voids.
Twin streaming also works well if you find yourself having to inject into a cold, underwater environment. You can inject warm water along with the resin to jump start the reaction process before the cold water gets a chance to slow down the process.
The ratio of water to resin can be controlled by opening the valves at different angles. Some products such as AP Fill 700 and Spetec H100 only need a little water to react with (10:1 resin to water is plenty). In this case, you would crack the water valve slightly, then open the resin valve all the way. Other products such as AP Seal 500 and Spetec GT350 need more water. A 2:1 or 1:1 ratio of resin to water both work well. In this case, you may want to open both valves all the way.