| Author |
Message |
Steven Baker (Unregistered Guest)
Unregistered guest
| | Posted on Tuesday, March 09, 2010 - 05:35 pm: |    |
A contractor is about to start work on re-caulking all of the expansion joints in the concrete pavement (sidewalk and plaza areas) for an office campus where I work. At the last minute they mentioned they would not be using a closed cell foam backer rod, instead they will be using torpedo sand.
I am concerned about the angular properties of "torpedo" sand, and how it may comprimise the ability of the expansion joint to expand.
Torpedo sand (comprised of angular, sub-angular, round and sub-round particles) is used inside of the interlocking paver joints - and I think it may act the same way in an concrete expansion joint.
I did a little research and discovered *most* expansion joint sealant manufacturer's recommend using backer rod - but I did find one manufacturer who at least mentioned the use of sand.
Has anyone ever used sand in this application? Specifically, these pavement sections contain 1X4 Redwood headers that had a rip-strip removed. The orginal contractor applied the caulk right on the header, all the way to the level of the pavement. In time, the caulk sagged and looks terrible. To complicate matters, vultures are removing the caulk also - but that is another issue altogether.
I feel like the sand will interlock with the pavement sections and restrict the expansion.
I appreciate any information anyone may have.
...Steve |
George A. Everding, AIA, CSI, CCS, CCCA
Senior Member
Username: geverding
Post Number: 514
Registered: 11-2004
| | Posted on Wednesday, March 10, 2010 - 10:42 am: | |
Another benefit of backer rods is that the round profile provides the perfect hourglass shape for tooled sealants. I am not sure how important this is on pavement sealants, but it is critical for building sealants. ASTM C 1193 provides good information, including this: "A sealant backing for a building joint application can have three primary purposes. First, it is used to control the depth and shape of the sealant in the joint opening. Secondly, it assists in attaining full wetting of the substrate when the sealant is tooled. Lastly, depending on type, it allows movement of the backside of the sealant between substrates."
George A. Everding AIA CSI CCS CCCA
Cannon Design - St. Louis, MO |
Steven Baker, LEED AP BD+C
New member
Username: qualitymanager
Post Number: 1
Registered: 03-2010
| | Posted on Wednesday, March 10, 2010 - 11:12 am: | |
Thanks, Mr. Everding, excellent points.
I have done a little more research and discovered these points from the New York State Department of Transportation:
"Backer Rod Material: Backer rod material for Silicone Joint Sealant shall be closed cell polyethylene foam rod. Backer rod material for ASTM D6690 sealant shall be any backer rod from the Department's Approved List titled "Backer Rod for Hot Pour Joint Sealants."
Backer rod diameter shall be a minimum of 25% larger than the joint width, it shall: support the sealant at its proper depth, prevent the sealant from leaking around and underneath it, and allow the sealant to deform freely when the joint expands and contracts."
Given these desired characteristics, the use of sand instead of backer rod is difficult to support.
Steven Baker, LEED AP BD+C |
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 330
Registered: 08-2005
| | Posted on Wednesday, March 10, 2010 - 11:47 am: | |
The use of the backer rod is pretty common and effective. I would reccommend keeping it, for the reasons George listed above. The shape of the sealant bond joint deterimes its effectiveness, and backrod allows that shape.
However, a "sanded" urethane caulk is a topical application of sand after the caulk has been freshly laid down. Sanded caulk's look good and last a long time, and are very common in decorative concrete work around here in SoCal. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1177
Registered: 03-2002
| | Posted on Wednesday, March 10, 2010 - 01:54 pm: | |
I would expect a compressible filler in the full deptht of the joint, not sand. This serves a bit of a different pupose than backer rod. As you correctly point out, sand could restrict the movement of the joint in expansion. It also could cause a ratcheting action in climates with wide temperature ranges--joint expands in cold weather, sand settles, joint contracts in warm weather and is restricted by the sand. Repeat. |
Dave Metzger
Senior Member
Username: davemetzger
Post Number: 347
Registered: 07-2001
| | Posted on Wednesday, March 10, 2010 - 02:07 pm: | |
The backer rod will still be needed in addition to the compressible filler. Expanding on George's last sentence above, a backer rod prevents 3-sided bonding of the sealant; bonding of the sealant to the backing material could result in cohesive failure and tearing of the sealant. |
Jo Drummond
Senior Member
Username: jo_drummond_fcsi
Post Number: 44
Registered: 06-2007
| | Posted on Wednesday, March 10, 2010 - 07:15 pm: | |
Regarding the vultures:
When I worked at Wells Fargo, we built a data center which had exterior walls of lightweight concrete panels with 3/4 to 1 inch joints sealed with silicone. That was the only water barrier. I was the facilities manager, not the designer! We had large pine trees around the campus, in which crows nested and lived. The crows quickly learned that silicone sealant tasted good, and I guess it was nutritious because they thrived in the trees. They ate it down into the backing and sometimes the backing also. We had to reseal large areas of the building, specially parapet tops and walls where they could easily reach from perching on some part of the building.
So I can empathize with your vulture problem. See if you can seal with something besides silicone. I think that is the only one they like. Urethane might be tasty. I'm sure polysulphide isn't, but that can't take much movement. |
Gerard Sanchis
Advanced Member
Username: gerard_sanchis
Post Number: 5
Registered: 10-2009
| | Posted on Thursday, March 18, 2010 - 07:58 am: | |
I would suggest that you specify a joint backup material that cannot be pierced by stiletto heels. A cork insert works well. Remember that the backing is there only to provide the proper shape for the sealant. Although the sealant will not have the hourglass shape, it should work fine.
We had a case where a shoe got stuck in the expansion joint when the heel became embedded in the joint, all the way thru the backing rod. The shoe wearer was slightly injured.
I would not use sand either. |
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