Checking the Site and Doing it Right
By Tom Inglesby
Contractors are well advised to hire professionals in the specialized fields that are required to establish a job site and construct a building. But sometimes, a little do-it-yourself work to augment those professionals not only gives you a better sense of what is going on, it gives you a greater confidence ? and legal backing ? during the job itself.
One area that many mason contractors overlook is in establishing the actual versus planned job site layout. Did the previous trades, such as grading and foundation, hit their marks? When you start to lay your first courses, will they be exactly where the plans call for them to be? Taking time before you start work to survey the job site and lay down your own coordinates could save you from problems later. If nothing else, those efforts will give you better peace of mind, letting you know where things are as well as where they are supposed to be according to plans.
Over the past decade, tools that were designed for and used by surveyors have migrated into the construction market. It used to be that only construction surveyors and engineers used these tools, but as the instrumentation has become easier to use, these tools have become appropriate for contractors to use. According to Lawrence Smith, business manager at Trimble's Construction Instruments Division, Sunnyvale, Calif., these new instruments "allow better productivity and lower cost. Trimble alone provides a wide portfolio of survey-type products and solutions for building construction and site preparation applications."
Depending on the application involved, the appropriate surveying tool will vary. Smith says, "The two Trimble technologies that are most appropriate for a masonry contractor are the construction total stations and LaserStation products. The construction total station is an optical product that measures angles and distances. An example would be the Spectra Precision Optical TS305 total station from Trimble. This uses survey technology to provide simple layout or as-built checking capability for the contractor."
The TS305 can be used to layout or check as-built structures in relation to the blueprint. The LaserStation product line, on the other hand, uses two, unique laser transmitters to provide 3-D positioning on the job site. This technology was developed specifically for contractors and allows the contractor to layout or check as-built positions based on the blueprint.
Matthew Delano, a Registered Land Surveyor and product manager in the Surveying Department, Nikon Instruments, Melville N.Y. admits, "Normally when you see one of these instruments, it appears to be high tech and probably difficult to use. Many contractors feel they are outside the range of what someone who lays out walls would want to use. These workers generally want to stick with tapes and snap lines. However, technology has made these instruments a lot easier to use. Instead of just being an instrument that reads angles and distances and requires a lot of calculations to use, the instruments now have onboard systems that are menu driven and also have the ability to collect data or take electronic data from plans and load them into the instrument to use for layout."
These instruments are pretty flexible. Delano explains a typical operation by saying, "The flow works like this: your architectural or structural plans typically show all the masonry walls, structural walls, whether they be block, brick, whatever the case may be. The plans are prepared in CAD (computer-aided design) by the designing engineer or architect. If these plans can be made available in electronic format to the contractor, they can be imported into a software package called Stake It. Once the data is imported, they'll be able to browse or zoom and pan around the CAD drawing, identify the points they wish to layout, and simply drop point entities on them.
"For example," he continues, "I bring up the plans and see that there are a several interior or structural walls I need to layout. I can indicate that, on this intersection, I want a point, and along this wall I want a point, and on this building corner I want a point. You can place a series of points all over the drawing wherever you feel you'll need one to do layout. Once all of these points are established and you have everything you think you'll need for layout, that information can be transferred through a cable or, depending on the instrument, though a data card to the total station."
That instrument then goes out into the field to the person who is actually going to do the layout. All that is needed is to set it up and operate a very simple onboard interface that basically says, "My instrument is set up on this point, I am initializing by lining up my instrument in this reference direction, and I'm going to layout these points."
Looking through the viewfinder, the instrument will tell you, "Turn the instrument to the right 7 degrees, 12 minutes, 14 seconds, and go out 47 feet." You can then take a measurement to someone at that approximate location and the instrument will indicate you're close but you need to go to the right two inches and you need to come closer to the instrument by four inches.
Rather than rolling out a set of plans on a concrete deck in the wind and rain, and trying to find everything you need, you simply set the instrument up and tell it what points you want to layout and the instrument tells you where to go and how far to go to do it.
So, when and how can you use these instruments? Smith comments, "Masonry applications for survey products would be associated with checking layout and making sure forms are poured according to blueprints and that the foundations are level before starting construction. This will save the mason from any rework and other costs associated with incorrectly poured foundations, for example."
The key for a mason contractor looking at buying or renting a surveying solution is to select the right tool for their application and to invest in a high-quality, accurate and durable solution that will withstand jobsite conditions. Applications include layout and checking positions from the building axis, alignment along a building line, 90-degree layout from anywhere on the job site, as-built checking, checking plumb, and measuring distances.
Delano adds, "The total station is a raw measuring device. It measures horizontal and vertical angles and distances. In other words, from any known point that you place the instrument on, you can measure and get a three dimensional position on another point. The rest of it is all intelligence on the instrument. If I know where the wall corner is supposed to be, I can take a measurement to someplace close to that and it will tell me how close I am. It can compare the measured point with the theoretical point and tell me where I need to go to get to the theoretical point."
Bob Bailey, manager of the Surveying Department at Nikon, notes, "These instruments use a digital display and, basically, the only requirement is that you have to be able to read. The old transits were difficult to read and required a special education. The new technology ? especially with the advent of computers ? has made all of this a lot easier to use and because of that, we have many more contractors getting involved with surveying."
Half a century ago, when I was doing jobsite layout with a level and transit, to read a horizontal angle you needed a magnifying glass and the ability to read a vernier scale. Even to turn a 90-degree angle, you had to be able to work with that type of instrument. Today, you turn on an instrument and the numbers just appear on the display.
"It's gone way beyond the ability to digitally read angles and distances," explains Delano. "Now, rather than worrying about what the angle or distance is, all you need to worry about is what point you want to layout and it will tell you where to go. It will tell you as soon as you start taking check shots ? it will tell you where you are now, where you're supposed to be and how to get there. It's pretty straight forward."
With the older surveying instruments, you needed someone to hold the rod ? sometimes called a stick ? that was used as the target for the instrument. Today, there are some instruments that enable you to do non-prism measurement whereby you can take a measurement to any object without having to have a "rod man" but it's still a good idea to have a two-person team doing the work.
"To be honest, for layout applications, it's not practical to try and do it with one person," admits Delano. "To take a measurement and then run up there and make an adjustment and run back and take another measurement, it's really non-productive. We do not promote non-prism or one-man systems for that type of application."
There are other options to the standard rod. There are small targets that can be clipped on your belt or stuck in your tool apron. Another option is to use stick-on targets that can be placed on a wall or column near the point you are shooting. That would still require a lot of back and forth as you zero in on the measurements so having that second person saves time and exercise. If you use another of today's technologies ? the cell phone ? you don't even need to shout back and forth.
Inside a building, when doing interior walls, for example, you're typically within a range of one to two hundred feet of the instrument. "You can carry what we call a peanut prism," says Delano. "We have small reflector type targets that are just as accurate, if not more so, than using the rod with a big piece of glass."
He goes on to demonstrate how the small targets can benefit both the worker, who doesn't have to carry that rod around, and the accuracy of the survey. "When I'm working on a deck, I don't want to plumb a pole with a big glass prism on the top, four or five feet above that deck. I want to get down on my knee at deck level, where the instrument man can observe right down to the deck so I don't have any plumbing error. I want to see the deck and make my mark on the deck and be able to put my target down on the deck and measure to that. These are the simple accessories that make all that possible and enable you to achieve very accurate results with these instruments."
Total stations and other surveying gear are available through rental agencies, as well as for purchase. Depending on your workload and how often you need that extra assurance of accuracy on the jobsite, you might find owning an instrument to be a logical step. With the tax benefits for depreciation and equipment write off, it might not be so expensive in the long term.
In that regard, Smith of Trimble cautions, "The first and most important thing is to source your equipment from a supplier that understands your needs as a contractor, and can offer you training and support. While learning to use the equipment is straight forward, the most important thing that you can do to guarantee your work is to make regular instrument checks. This means regularly checking a few known positions, and doing simple things like checking diagonals ? a simple task with such tools."
Using a total station provides a complete layout solution that eliminates the need for using measuring tapes, plumb bobs, theodolites, or separate distance measuring equipment to give the mason contractor more control and better accuracy when checking layout on the jobsite. Give one a try.
About the Author
Tom Inglesby is a San Diego-based freelance writer whose work has appeared in numerous online and print publications. He is the winner of the Construction Writers Association's 2002 Boger Award for Special Reports.