Product warranty

[Swizzle]

I work for a ready mix concrete producer and have to provide a written warranty for some concrete delivered to a job site. Does anyone have a generic form letter or know where I can download one?

 

[civilperson]

Bad idea. Instead limit your responsibility by listing all the ways your good mix can be ruined by on-site practices. (Delay of off loading, adding water, over vibration and free fall, lack of cure, etc.) Warrantee the ingredients instead, i.e. Certs for aggregate, water, admixtures and cement. Supply a series of thirty sample cylinder breaks for the mix design per ACI.

 

[eea]

Isn't all of that langauge already on the back of your load ticket?

 

[Swizzle]

Perhaps I should have explained the situation better. The concrete in question has already been placed. The project's testing lab made cylinders which did not come up to strength. A second testing lab went in and shot Windsor probes. All these passed with flying colors. The concrete can remain , but the Engineer wants some sort of written warranty for a 5 year period.

 

[jartgo]

I'd get help from your attorney. Five years is a long time.

 

[concretemasonry]

Very bad idea. You can only warantee certain things.

You can guarantee the materials you used and submit test reports to verify mix designs. - That is about as far as a supplier of materials can go except for verifying the mixing and delivery times.

Once the concrete is placed, you have no responsibility for the in-place quality and performance. You cannot warantee that it was placed timely and properly without anything added. You cannot guarantee the finishing. You cannot guarantee the curing conditions. - Those are probably the biggest problems providing the cylinders met specifications and that is stretching things depending on who made the cylinders, how they were cured and very importantly how they were transported. - That is why you have inspection and testing.

 

[Zambo]

The problem may be that "Engineers" tend to bully Contactors by withholding payment. The issue here seems to be that the project laboratory has recorded failures in thecylinder strengths. No doubt the Engineer is only dertifiying partial payment. The Contractor will try to pass on the responsibility to the supplier by withholding his payment.

Just my opinion, but this sort of thing causes a dilemna.

 

[jartgo]

concretemasonry, I don't think I follow your logic. It is my understanding that the cylinders did not meet specifications, "The project's testing lab made cylinders which did not come up to strength." That's an issue with the concrete supplier, right?

Assuming of course that the spec details the testing methods that should be used and the results required from that testing method. I understand the engineer's concern, but also would be weary if I were the concrete supplier. There's so many things that would effect the performance of the concrete once it's placed, other than the raw materials.

However, the alternative would be to dig it up now and replace it with material that passes the specs. Wouldn't be the first time that happened. In light of that, the engineer is giving the concrete supplier an oppurtunity to save himself from that burden. Of course I'm assuming again the the cylinders were out of spec to the point that the specs call for replacement, in which case I wouldn't allow any warranty period...I'd insist on replacing it because in my somewhat limited concrete experience, to be in "replacement" criteria, concrete is generally way out of spec. Otherwise it would be a scaled pay factor situation.

I think if I were a concrete supplier and faced the options of 1) replace it now or 2) replace it IF it fails within five years...I'd be inclined to take the five year option.

Of course we probably don't know all the details.

Zambo, I agree...but keep in mind that the Owner is in charge...and sometimes the Engineer is just the messenger of that "bullying."

 

[DarthSoilsGuy]

swiz, could you give more detail about the use of the concrete in the structure, ~ yardage, and about how bad the breaks were.

the windsor probe test is an indicator and technically has to be considered supplemental to the laboratory cured specimen.

if you were to have had a representative sample of cored in-place concrete strength tests, they could have served for acceptance testing on their own merits regardless of the lab-cured cylinders. This may not be practical depending on the dimensions of the structure. It is also considerably more expensive.

i don't think there are enough concrete companies willing to concede this for it to have some standardized form to it.
i think there are some generic forms for trashing the testing company out there or it certainly seems that way ;-) Concrete companies need to tackle this on a case-by-case and push their strengths. Whatever the case, i would push hard to limit any warranty to providing free concrete only as your concession.

 

[concretemasonry]

jthompson -

You are missing a very big point. Cylinders are not the ultimate in determining the quality of a construction project. They are just one measure of the quality of a structure. With a cylinder, you are attempting to create a measure of the optimum in-place concrete strength.

I am not trashing testing laboratories, but pointing out a situation.

When you look at the reliability trail for cylinders, there are critical points that have to be identified, especially when subsequent testing produces conflicting results. It is ironic that people only worry when the initial results were low and never question higher than anticipated results.

1. A second test was selected. The provider of the testing was probably mutually agreed on. Because it was a check/verification, more care was taken by the new testing firm and the results were probably more closely monitored and reviewed before the report was issued. Because of this, it may carry more weight than a routine "garden variety" test if the new procedure yeilds more applicable results.

2. Cylinder tests are very necessary procedure as a check on the potential quality of a structure. It is very difficult to make an error (except in calculation) that would produce a result too high, but there are many possibilites to produce erroreous lower results.

If a cylinder is made from properly samples material, prepared as specified, site cured as specified, transported and handled properly, capped properly, positioned properly and tested at the proper rate with an adequate machine, the results can be relied upon. There are a few common pitfalls in the sequence.

One of the problems is that cylinders can be treated as a commodity and unrocognized errors can be made easily. Too often, cylinder testing costs are used a criteria in the selection of a testing laboratory.

Based on working in testing in concrete inspection and testing while an engineering student and 30 years as a professional engineer doing design and supervising a construction site testing lab, I have some recognition of the problems that can effect the results of cylinders.

Since construction is usually somewhat seasonal, many temporary employees are hired to do many tasks with short training programs (an unfortunate situation). The lab curing, sample preparation and compression are usually reasonably supervised. During the construction season, much of this work is done by seasonal employees ("grunts" like me) and take the regulars out of the mainstream. Even experiencd employees can have problems. Much of the cylinder chain has more variables.

Sampling time may be controlled by the contractor depending on the unloading situation (early, middle ot late in the load). If the technician is not well trained or does not have power complex, the sampling can be bad, because the immediacy of the job site conditions seem to control.

The cylinder preparation can be adversely affected by sloppy placement and rodding. Most engineering students recognize the affects of sugar and rabars in cyliders, so the preparation is good. Complicating the the situation is the site curing conditions and timing (a lot of concrete is poured on Thursdays and Fridays) and cylinders can get "lost".

Transporting fragile heavy cylinders can be a challenge. All to often, uneducated (like me with only 2 years of engineering education) or untrained people pick up the cylinders, toss them around and unload them at the lab a few hours later. I never saw a cylinder that gained strength in handling, but many suffered unreported dropping or banging that would reduce the strength.

The point is that concrete cylinders were seen as the utopia for the measure of concrete in a structure, but that can be misleading.

Fortunately, with the advent of vertical integration of the international cement industry, the major ready-mix/transit-mix suppliers have an increased availability/requirement to quality control. The emphasis on technology and quality has taken a step upward. It will take a few years to "trickle down" to the smaller suppliers. I really do not know how the change can bsr be accomplished through the link to job site preformance of concrete on BOTH large and small projects. - In place methods were and will be recognized to provide a measure of the concrete, when there is a need for the determination of the real in place concrete properties.

 

[jartgo]

Concretemasonry, I respectfully disagree. I didn't miss any of the points you described. I acknowledge that those items you point out are certainly very real possibilities. I attempted to cover those (without listing them) under this statement, "There's so many things that would effect the performance of the concrete once it's placed, other than the raw materials."

I was merely pointing out that the testing required in accordance with the specifications are part of the contract, that presumably the supplier agreed to in advance of beginning the work. If so, then he was aware of the risks involved with the type of testing specified and the results required, or he missed a very big point.

 

[concretemasonry]

If there is a proper contracrt in effect, why is an additional warantee needed? Any properly written, executed and enforced contract should be adequate.

I was just pointing out the problens of relying only on cylinder tests. The subsequent specific testing that showed the adequacy of the material, so why would any additional warantees be required? It sounds like a "cover all possible bases" situation.

 

[jartgo]

That's correct, as I understand it, the concrete failed the cylinder tests, which I assume was required in accordance with the specifications. So, instead of requiring replacement of the already placed concrete, the engineer has given the contractor the option of providing a five year warranty.

 

[Swizzle]

I work for a ready mix concrete producer which does a good deal of business in the decorative concrete area. We use the Davis integral color system (Chameleon). I was asked by a stamping contractor to look at some pool deck concrete he poured this summer. His customer notified him early February (once the snow had melted) that there was a problem. The deck has severe scaling on about 50% of the area. Short of replacing the concrete, does anyone have any experience with polymer modified overlays? If so, can you recommend a product?