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point indentation, it is acceptable to proceed with the first
test installation. Use of a powder‑actuated system is not
recommended if the following occurs during the center
punch test:
•
The fastener point has been blunted. This indicates that
the base material is too hard (Fig. F).
•
The base material cracks or shatters. This indicates that
the base material is too brittle (Fig. G).
•
When using an average hammer blow, the fastener
penetrates the base material easily. This indicates that
the base material is too soft (Fig. H).
Fig. F
Fig. G
Fig. H
Fastener sinks in with
average hammer blow
Functioning in Concrete (Fig. I, J)
The performance of a powder‑actuated fastener when
installed into concrete or masonry base materials is based
on the following factors:
•
Strength of the base material
•
Hardness and concentration of the aggregate
•
Shank diameter of the fastener
•
Depth of embedment into the base material
•
Fastener spacing and edge distance
In addition to these factors, installation tool accessories such
as a stop spall which reduces the tendency of the concrete
Point flattens
no indent
surface shatters
Material cracks
surface to spall during the driving action can increase the
performance of the fastener.
When a powder‑actuated fastener is driven into concrete,
it displaces the volume of concrete around the embedded
area of the fastener shank. As this occurs, the concrete
directly surrounding the fastener is compressed and in turn
presses back against the shank of the fastener. Additionally,
the driving action generates heat which causes particles
within the concrete to fuse to the shank of the fastener. This
combination of compression and fusion holds the fastener
in the concrete base material. A similar action occurs when
fastening into block masonry.
Fig. I
Generally, the performance of the fastener in a given
concrete strength will increase with greater embedment
depths in a certain range. Depending on the fastener style
and base material strength, embedment depths range from
5/8" (16 mm) to 1‑1/2" (38 mm). For depths greater than
this range, there is the possibility of fastener bending or
fishhooking which may decrease expected load capacities
and create a safety hazard.
During the driving action, some localized surface spalling
of the concrete may occur. Normally, this is a surface effect
which does not effect the performance of the fastener.
However, it may pose an aesthetic problem for exposed
applications where a fixture is not used. In cases such as
this, two methods can be used to improve the appearance
of the fastening. A stop spall adapter mounted on the
powder‑actuated tool can help to reduce surface spalling.
Another method used is to drive the fastener through a
steel washer to improve the appearance of the application.
Fig. J
stop spall
Fastener Installation Requirements
It is important to understand the required minimum base
material thickness requirements along with the minimum
spacing and edge distance requirements. Failure to follow
these requirements can result in an unsuccessful fastening
and create a safety hazard.
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