Straight in drilling. Why it's better!

[Rod Johnson]

When injecting tight cracks in un-reinforced concrete, we have found high success rates by drilling straight into the crack to a depth of 2/3 the thickness of the wall (always measure and tape your drill bit for depth). High pressures can be maintained with virtually no spalding blow-outs (as opposed to angle drilling) and excellent grout penetration. Space the packers every 2.5 - 3 inches and a depth of 5 inches for an 8 inch thick residential wall. Use a low viscosity resin or heat up your grout in a tub of hot water (Lowers viscosity significantly, i.e. 600 cps down to 200 cps) to assure 100% penetration. This procedure will work for reinforced structures as well, if you can get deep enough into the concrete and you seal the surface crack tightly enough to generate pressure to move the grout back into the depths of the crack.
Technically speaking, the straight in drilling technique increases the surface area of possible grout penetration into the crack, within the wall. When angle drilling, you can expect grout penetration to occur at the point the drill hole intersects the crack. The exposed injectable surface area is just slightly more than the diameter of the drill bit used. Let's say a 3/8" drill bit produces a 1-3/16" (d=3.14 x r) of penetration point per drill hole. However, the straight in method will create a 10-3/8" penetration point in a 5" deep hole. This is almost a 900% increase in usable penetration point. When it is possible to use this method with the correct grout selection, you can lower pressures and achieve superior results in a shorter time. Our inexpensive hammer-in plastic packer won't cost you much for the extra packers used up by this process.
Also, apply a small amount of the polyurethane injection resin to the outer surface just prior to inserting the packer in the drill hole and hammering it in. The grout will set in a very short time providing an excellent seal. Packers can always be used without the "coat" method.
See more on this here: http://leak-proof.com/catalog/plastic-hammer-packers-p-1332.html

[CrackMan]

Hi Rod

Still cant my head around the math.  Dont mean to be a pain, but I am a stickler for understanding.  Could you walk me through how you determined the difference in the percentage.  I need to understand so I can relay this info to customers on why the method we are using  is better.

Thanks

[Rod Johnson]

When you drill on a 45 degree angle and intersect the crack at the midpoint of the wall, your intersection point creates a ring around the drill hole. This is where the grout will enter the crack. It is the circumference of the circle that was made by the 3/8" diameter bit or 1.1775". So your grout must be forced into the crack through that 1.2 inches available at the drill hole/crack intersection. If your pressure is too high, you can pop that piece of concrete off the wall.
Now if you drill straight into the crack 5 inches deep, you contact the crack for 5" along the top of the drill hole, 3/8" along the back of the drill hole and another 5 inches along the bottom of the drill hole. Added up, that is 10.375 inches you can use to force grout into the crack. That is 8.64 times (864%) more exposed crack face than drilling on a 45 degree angle.

Now because you are moving the same volume of grout per stroke from your pump (or grease gun) into the drill hole, you don't need the same pressure, or time to move the volume into the crack because it is entering the crack from the drill hole at a much higher rate.