Selected Answers

From Tim Montgomery of Cooper Hong Inc. on April 22, 2015:
The following response is posted on behalf of Anth ...read more The following response is posted on behalf of Anthony Washington, product manager, Jetstream of Houston, LLP: "High-pressure water blasting does not alter the integrity of the bridge’s surface during the coatings removal process. More specifically, water blasting prevents microfractures in concrete and allows supportive rebar to remain intact. The use of high-pressure water blasting for surface prep has been shown to effectively eliminate rust, old coatings, product residue or even damaged concrete prior to re-pouring. The process also provides a revitalized surface, making it possible for new coatings to adhere without old particles impeding the surface area. Likewise, in certain bridge coatings removal applications, accessibility to the surface area can be a challenge. In those situations, with the proper equipment, water blasting allows the operator to safely tackle any horizontal, vertical or overhead surface preparation or removal task. Water blasting, or waterjetting, is a proven technology that has been in use since the 1970’s. Over time, with the introduction of robotics and automation, the process of waterjetting has become safer and more efficient."

From James Schuster of Painting Service Inspection on March 19, 2015:
I have personally used WJ-1 surface preparation on ...read more I have personally used WJ-1 surface preparation on bridges that have been previously blast-cleaned to create a profile and repainted numerous times. This does work very well, but it really depends on the particular situation.

From Lydia Frenzel of Advisory Council on March 18, 2015:
Waterjetting to remove coatings was originally con ...read more Waterjetting to remove coatings was originally conceived to be used in maintenance, rehabilitation, and repair, not in NEW construction. The issue of making a profile is a false distraction unless you have a bridge that was never abrasive-blasted in the first place. The Federal Highway Research Administration (1999) performed an extensive comparison study between several methods, including abrasive blasting, hand tool cleaning, waterjetting, wet abrasive blasting, and electrostripping. FHWA, DTFH61-97-D-00026 ; SSPC Proceedings 1999. This was available from the Corrpro web site, or may be obtained from Advisorycouncil.org upon request. This report discusses environmental, productivity, and other issues. Robert Kogler in JPCL, Nov., 2005, p. 47, expressed his opinion: "Unlike it has in the marine industry, ultra-high pressure water jetting has not become particularly popular as a tool for highway bridge maintenance painting. There have been a few demonstration projects and state highway authorities have experimented with various pressurized water techniques for surface preparation, but overall, dry abrasive blasting methods continue to dominate for maintenance painting jobs that specify full removal and replacement of the painting system. There are two basic reasons for this – the need for a surface profile and the institutionalization of dry abrasive blasting and containment systems within the bridge contracting community." In other words, in the US, it is not a technical decision, but rather it became a political decision.

From Billy Russell of D&R COATING INSPECTION on March 14, 2015:
UHP is not more environmentally friendly with stri ...read more UHP is not more environmentally friendly with stricter safety measures on bridges. Using it produces no anchor profile, but the coating systems used on bridges require an anchor profile. Choose blasting with a recycling machine, and 1A (REAL 1A) containment system. The specification should include cleaning prior to blasting to remove both visible and non-visible contaminants. This method is head and shoulders above UHP on a bridge.

From Andrew Sedor of AECOM on March 12, 2015:
I would never say never. . . . My question is, wha ...read more I would never say never. . . . My question is, what percentage of bridges have all the surfaces  accessible UHP waterjetting? Water jetting would not be practical on any of the bridges I've worked on.

From ramoo purushothaman of Berken Enterprises pte ltd on March 10, 2015:
A UHP blast has its advantages and disadvantages. ...read more A UHP blast has its advantages and disadvantages. Its main disadvantage is that it does not create a profile; thus, the profile of the blasted surface will be as per the original. I presume this is for a bridge here at Asia; thus, prior salt on the road is never a consideration. Several years ago, we did a cable-stayed bridge deck at Thailand, and we used a mobile autoblast system where steel abrasives were used. This system blasts,  sucks and separates the remnants all automatically. Another method requires covering sections of the bridge and then blasting and priming using a "cocoon system," where all debris is captured. Another method is to use a wet-blast system. This prevents dust, if that is your consideration for opting for UHP, but this method creates a profile because abrasive is added into the system. Lastly, check with the paint manufacturers to learn if they will agree to warrant their materials for the UHP selected, as such jobs usually require warranty. Usually, they do give warranties once they know the scope and whether any inhibitor is used.

From wan mohamad nor wan rahmanVV of ANTAP SEMENANJUNG SDN. BHD. on March 6, 2015:
When we specify UHP waterjetting on a bridge, it i ...read more When we specify UHP waterjetting on a bridge, it is probably because we need a more environmentally friendly painting process and more strict safety measures due to heavy traffic flow at the site.

From Lydia Frenzel of Advisory Council on March 5, 2015:
The general project specifications on bridges shou ...read more The general project specifications on bridges should include WJ1, WJ2, WJ3 or WJ4 in addition to the abrasive blast standards unless the paint to be applied is incompatible with remnants of the existing coating, or the bridge is known to have no profile, i.e., was never blasted when it was constructed. Situations where WJ should be specified include: when there has been road salt placed on the bridge, the bridge is over marine/salt water, lead paint is present, when the bridge design needs a small footprint for equipment,or when the amount of waste needs to be reduced. The NACE- SSPC- ISO standards define the end condition; they do not specify the operating parameters such as pressure washing (LP WC), high pressure waterjetting, or ultra-high pressure waterjetting.