Page 39 - QR CIMAR LASER SCREED

SCREEDING OPERATIONS

TAKING A BENCHMARK

Perhaps the most critical task in all of screed preparations is taking a benchmark. A benchmark is a
precise measurement of the distance between the finished floor elevation and the height of the laser
beam. The benchmark is used to set the same distance between the screed head and the
mast-mounted laser receivers. It’s also used to double check that the laser beam is running exactly
parallel to the non-grade reference points all around the placement.

Before you begin, remember to work carefully throughout this procedure. Making an error at this point
could cause the entire floor to be placed above or below grade - and that’s an expensive mistake to
correct after the fact.

To start with, attach the hand-held receiver to the screed grade rod. Press the on/off button once to turn
the receiver on.

The receiver has three (3) sensitivity settings, make sure that the receiver is in the fine mode. Use the
button to select between them. Set the audio level. There are three settings. Choose an audio level that
can be heard easily over the general noise of the job site.

Next ask your supervisor or foreman to point you to the grade reference point on the job site that is
closest to your transmitter. This grade reference should be used to take your benchmark. Once you find
the grade reference, extend the grade stick is sitting on the grade reference. Hold the grade stick over
the grade reference point and high enough so that the receiver is above the transmitter’s reference
beam.

Then, holding the grade stick vertically, slowly lower the receiver until you hear the tone that indicates
that it has found the laser beam. During this initial adjustment to the grade reference point, when setting
the screed head, and throughout the process of checking the height of the finished concrete, it is
absolutely imperative that you always start high and lower the receiver into the transmitter’s reference
beam. That’s because the receiver has what is called a dead band.

In fine mode, this dead band is approximately 1/8th of an inch. Therefore, if you do not consistently
bring the receiver into the laser beam from one direction, you may inadvertently introduce a 1/8th of an
inch error in your finished grade level. It should also be noted that in coarse mode, the dead band is
larger, so never use the hand-held receiver in coarse mode.

Now make sure the screed Grade Rode is locked and mark the rod with a pencil. During the course of
the day, it’s a good idea to check this pencil mark periodically to assure yourself that the stick has not
slipped in one direction or another.

Now that the screed Grade Rod has been set against the grade reference point, you should walk the
screed Grade Rod around the placement area, checking that all forms and other grade reference have
been properly set.

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