Background

All brands of expansive demolition grouts are susceptible to “blowouts” if the wrong version of product is used or other user errors occur.

Avoiding blowouts is of utmost importance to:

• ensure safety of personnel

• complete projects successfully, on-time, on-budget

• avoid legal liability for any injuries or property damage

• prevent damage to trust and reputation

What is a Blowout

If the reaction occurs too quickly, the heat of hydration can reach 150°C and boils the mixture’s free water before it has fully combined with the powder. Typically this heat is dissipated by the surrounding material, if it isn’t or other user errors have occurred, a blowout may occur.

A blowout occurs when an expansive grout, under pressure within the confined holes, is ejected with sudden force. A blowout creates a loud pop sound with a sudden geyser-like powder being shot into the air.

*** see the videos below***

What Factors can Cause Expansive Grout to Blowout

1. Using the wrong version of expansive grout.
2. Purchasing the version of product based on the air temperature or weather forecast. Select the correct product based on the internal, core temperature of the rock or concrete.
3. Pouring grout mixture into hot holes.
4. Hole diameter is too large. Possibility of blowouts increases when hole diameter is greater than 1-3/4” (44 mm).
5. Leaving unused product sitting in mixing bucket.
6. Water temperature is too warm.
7. Not measuring water = wrong water to Dexpan ratio.
8. No open face or insufficient expansion room for material to expand, crack and break apart.
9. Water in the drilled holes.
10. Distance between holes is too large.
11. Dexpan and water is not fully mixed. Be sure to scrape bottom and sides of bucket.
12. Mixing more than 1 bag of expansive grout at a time resulting in #12 below.
13. Mixing expansive grout by hand vs. using electric hand drill with mixing paddle attachment resulting in #12 below.
14. Too much time passing between beginning to mix and pouring into holes. Ensure mixed grout is poured into holes within 5-10 minutes of adding, mixing with water.
15. Adding expansive grout and water to leftover mixture remaining from previously mixed batch.
16. Grout sitting in sunlight or warm conditions before being mixed with water.
17. Filled holes exposed to hot direct sunshine.
18. Using well water. Some well water taps into ground water with high mineralization which affects the chemistry of the product.
19. Filling holes incorrectly. Always fill row of holes closest to your open face first, pouring left to right; next row, back to the start, pour left to right.

See the videos below for two examples of Dexpan blowouts:
1. inside borehole when the wrong product version was used for the conditions
2. when surplus mixture is left sitting in mixing bucket / pitcher

Video Credit: Premcrete UK