Any seasoned mason contractor realizes there are things they must consider when preparing to grout masonry walls. Here are some of those considerations: whether to mix grout on site or have it delivered by ready mix trucks, processes and equipment to use when mixing on site, and then, how to get the grout into the walls.
The first thing a mason contractor must do is to decide whether to get the grout from the local, ready mix company or to mix it on the jobsite. When you are pouring eight or more yards per pour, as is common when solid filling 12-inch block, it will probably be most efficiently done by using a ready mix company. However, the majority of projects require a large quantity of grout to be installed in a series of smaller pours. This gives the mason contractor the option of mixing on site or having the grout delivered from a ready mix company. How do you decide?
Cost is definitely a factor. When considering the cost of labor to mix on site, grout from ready mix companies is usually cheaper per yard. Ready mix companies in most areas are also cheaper per yard than using silo mixes, such as Spec Mix. So, here's a rule of thumb. If the local ready mix company can deliver the grout at the precise time it is needed without short load charges, then this is generally the best option.
But cost isn't the only factor; there is one more important variable to be considered. Because each pour is usually small (two to eight yards) and grout requires more time to unload than regular concrete, many ready mix companies don't like to deliver grout. They would rather deliver to projects where larger quantities of concrete are being used on pours, such as roads or slabs. Therefore, the mason contractor's crew is often left waiting on ready mix trucks when it is time to grout.
This waiting time costs the mason contractor in lost production. In fact, it can cost much more than the savings the contractor gets by ordering the grout from the ready mix company. To sum it up, if the ready mix company won't deliver grout at the precise time it is needed, then the contractor's best option is to mix grout on site.
Jeff Leonard, Vice President of Bulk Materials at Quikrete, Milwaukee, Wisc., agrees when he says, "It's beneficial for the contractor to consider a Spec Mix system or other bulk system compared to the 'conventional way,' which is the ready mix truck coming to the jobsite. The contractor has more control and can grout as slow or as fast as he needs to when he has a premix grout silo. He has control over that whole process. It's beneficial to use these systems for field mixing, too, just for the saving of the labor factor."
Making the Mix
Leonard discusses what goes into the mix that goes into the silo and then into the mixer. "I would estimate about 40 percent of our bulk material is for grouting, mostly on the commercial side where we're servicing contractors through the bulk systems, such as Spec Mix. We can meet any design specification that is called for but most of what we supply falls under the ASTM C476 specification. We can provide those grouts and if there are some special additives that the contractor needs if they want an accelerator, for example, or perhaps in extremely hot conditions or if they would need to mix it drier for whatever reason, they might want to consider a retarder we are able to supply those and just put them in the dry mix."
He goes on to say, "We work hand in hand with EZ Grout and Spec Mix and in many areas we are a licensee for the Spec Mix system. So we work to create what might be called a packaged deal for grouting."
Quikrete has 70 plants around the U.S. so the mix is never very far from the jobsite. Freight costs to haul dry mix long distances would negate much of the savings. Other factors come into play, based on regional differences in material. Leonard says, "We buy our aggregate from local sand and gravel pits. Based on the gradation of those aggregates and their composition, we come up with a mix design that meets the strength requirements as required by ASTM C476."
He adds, "If I compare my mix design here in Milwaukee with that made in St. Louis, for them to get a certain strength, they need a completely different formula than I would use. I'm in an area of the country where our aggregates are extremely dense and that's very good. More cement is needed with the aggregates that are down South, that have different clays in them. Our aggregates here are sand-based. There's a lot of quartz in it, and that makes for a very dense, strong aggregate. As a result we may or may not need a different sand-to-cement ratio as they do in Atlanta. The formulas are virtually different everywhere to get the same result."
Mixing grout on site
Mixing on site can be accomplished in a variety of ways. Most frequently, drum type concrete mixers or large hydraulic mortar mixers are used. Which option is the best for you?
Drum type mixers roll and tumble the grout instead of cutting through the material. Because of this, tumbling takes extra time to mix the grout and it doesn't give the consistency that can be achieved by using hydraulic mixers that have blades cutting through the grout. Most hydraulic mixers have a large enough space between the blades and the drum to bypass the pea gravel that is usually required in the mix. If these mixers should ever get plugged up, they can simply be reversed to undo the plug in seconds.
The size of the mixer is also an important variable. The larger the mixer the more efficient the grouting process. Using a mixer with a minimum capacity of 12 cubic feet (four bags) keeps your forklifts from having to make extra trips to the mixer for the smaller loads of grout. In contrast, if you use a smaller capacity mixer, the smaller loads require extra time and travel with your forklift. Remember, if the forklift operator has to sit and wait while the laborers mix two or three batches to fill a big mud pan or a Grout Hog, it is also a waste of valuable forklift time.
Several mixer companies now build large hydraulic mixers. EZ Grout Corp. has recently introduced the Mud Hog, a 20-cubic foot, adjustable-height mixer. It is also ergonomically designed so laborers can load materials at a low height and still dump directly into a high mud pan or Grout Hog. (Editorial disclaimer: co-author and mason contractor Damian Lang also owns EZ Grout Corp.)
After you've considered what mixer to use to mix the grout, now it's time to decide how to load the mixer. When mixing grout on site there are two options to get materials into the mixers: mix by hand or use a silo system, such as the Spec Mix system.
Mixing by hand requires laborers shoveling sand and pea gravel, if required, and lifting bags of Portland cement to get the materials into the mixer. With the cost of today's labor force, mixing by hand is usually not economical, especially if your mixer has a small capacity.
If there is a company such as Spec Mix in your area that can supply premixed grout and a silo system, mixing grout can be done much quicker with a fraction of the effort. Although there is an extra cost to getting the premixed grout, that extra cost is minimal compared to the cost of extra labor spent shoveling and lifting. In a high production grout project, two men mixing grout on site have a difficult time keeping up with the process without these silo systems.
"We use 3,000 pound bulk bags to deliver the mix," Stan Harwell, Eastern regional manager for Spec Mix, says. "We'll set a silo out on a job site, and if they're using a Grout Hog, we have some extension legs that will go on the bottom of the silo to facilitate using the Grout Hog. That means you can get your mixer so the Grout Hog will fit underneath it. The contractor will take these 3,000 pound bags and fill that silo up with the dry product using a forklift to lift the bags."
The Spec Mix silo is actually just a holding hopper because the dry mix components are prepared in a factory off site. "We computerize batch all dry products; sand, cement and aggregate if it's a coarse grout," explains Harwell. "There are two types of grout; fine grout and coarse grout. Fine grout is just concrete, sand and Portland cement. Coarse grout is typically 3/8-inch maximum size aggregate rock blended with concrete, sand and the cement.
"With a 10- to 11-inch slump grout mix," continues Harwell, "they'd take our dry material in the hopper and, depending on whether they are using coarse or fine grout, decide what type of mixer they would use. Most contractors today prefer to use fine grout because it's so much easier to get into the cores of the blocks. They go to this fluid mix of concrete, sand and cement and then they reconsolidate it and make sure it's mixed well."
Slump is the fluidity of the mix. Harwell notes, "When I first started in this business they tried to hold us to a slump of about four to five inches, just like you would if you were pouring a curb, gutter or house slab. It wasn't fluid enough to get down in the cavities of the block, past all the rebar. So now they let us use up to 10- or 11-inch slump, a very fluid concrete."
Slump is tested with a cone. The cone is 12-inches tall, the material is put in, and the measure of fluidity is by how much it slumps down when they pull the cone off. A high-tech method it's not.
Placing the grout
After the grout is delivered to the jobsite or mixed on site, there are only a few ways of getting it into the masonry walls. The three most widely used methods are buckets, a grout pump, or a Grout Hog. According to Harwell, "Typically what you do is get so much wall built up, and then come back and grout it. Then they'll pull the masons off and go to another wall while that grout sets. If they are using a pump, they'd pull everybody off, but if they've got a labor crew or they're coming behind it doing low lift grouting, they just take buckets or a Grout Hog and grout right behind the masons as they're working on the wall and then they really don't lose any time, they just don't skip a beat."
Grouting with buckets is the least desirable of the three methods. Using five gallon buckets is labor intensive and time consuming even when grouting in small quantities. This method requires more men and extra energy from each one of them. The energy these men use during the grouting process greatly reduces their production the rest of the day. Studies show that after a person lifts so many pounds in a day's time, production begins to drop. The more weight they handle pouring grout, the greater the drop in production.
Contractors often prefer grout pumps for grouting inside walls or placing large quantities in each pour (generally eight or more yards per pour). Grout pumps work great for these pours. However, grout pumps do require a greater amount of time to clean, and, if not used properly, there is a chance they could plug and stop production.
When grouting in smaller pours (two to eight yards), the Grout Hog introduced in 1999 has become very popular. This system allows grouting to be done with only two laborers while a forklift supports the weight of the grout instead of the weight being on the laborers' backs. The Grout Hog is ideal on any walls that are accessible with a forklift. On larger projects, the savings provided by Grout Hog use allows you the option to have an extra forklift on your jobsite. Once it is used in the grouting process, the forklift is then available to stock block and help increase production.
With the grouting process becoming more and more a factor in masonry projects today, the mason contractor needs to prepare a strategic attack plan to handle the process as efficiently as possible. To do that, consideration must be given to every step of the process from ordering the materials, to method of loading the mix, mixing equipment, and delivery. Cost, efficiency, availability and size of the pours are all important factors to be examined. However, with the right combination, grouting masonry walls can actually become a profit center on your jobsite.
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