I am currently specifying a mositure vapor mitagation coating for a renovation project.
What is the best way to have the Contractor bid on this system since the quantity will be unknown until the floor covering is ready to be installed?
Is this for a new slab or an existing slab? If it’s existing, has it been tested for moisture?
In the past I have specified vapor transmission testing requirements in the appropriate floor finish section, specified the mitagation system or method in a seperate section with a unit price article, and added a unit price section to Div 01 and a unit price line item to the bid form.
Sorry I posted without completing the answer:
The actual mitigation work if required due to test failure is handled as a change order.
David,
We do this all the time for a specific client’s TI projects using a Unit Price.
Included a Div 01 Section for Unit Prices + mention of Unit Prices in Part 1 of the appropriate sections.
For example
A. NO. 2 - EPOXY VAPOR RETARDER
- Item: State the price for providing epoxy vapor retarder as specified in Section 071930.
- Unit of Measure: Per square foot.
- Basis for Determination of Price: Base unit prices on the square foot area for resilient flooring and carpet tile indicated on the Drawings.
You could also request an Informational Bid, where the contractor breaks out the cost for this so the Owner knows exactly what it will cost it it has to be used. And if it doesn’t, then the Owner knows how much will be saved.
what is an “Informational Bid?” And where would this be defined in the Contract Documents?
When it comes to excessive moisture vapor emissions from concrete floors, why must the Owner pay to correct defective construction?
Contractors and Construction Managers, in my experience, want a fixed price included in the Contract Sum (allowance) for remediation of excessive moisture vapor emissions. They also want the Architect to determine, in advance of construction, how much that price shall be.
So, a unit price is included in the Contract Sum with an estimated quantity, to be charged against an allowance amount or to be added by Change Order. The Contractor will be sure that the vapor emission is excessive in order to get paid the maximum amount according to the allowance or for the Change Order.
I’ve given up on specifying products, procedures and quantities to correct excessive moisture vapor emissions. Now, I simply specify that concrete floors shall be tested and, if not in compliance with the floor coating or floor covering manufacturer’s criteria, the Contractor shall fix the problem … just like other defective, non-complying construction.
It’s only defined in the Bidding Documents. You provide places on the Bid Form to list costs for roofing, or concrete, or lab furnishings, or lockers, or whatever. I’ve also seen it used by Division - what’s the cost for all the work in Division 05, etc. It’s used when an owner wants to know the costs for certain items or scopes of work within a project. I used it in public work, mostly, but have used it in private work, too. I don’t think it’s a “sanctioned” practice, but it can be useful.
I agree with John.
Concrete slabs with floor finish is not the only locations for potential excessive moisture problems in relation to subsequent finishes. Paint or high performance coatings on any concrete surface, waterproofing or roofing on concrete slabs, etc. Why the special exception for floor finish on concrete slabs other than it is todays hot button?
We can divide the potential causes for excessive concrete slab moisture into two basic categories:
- Design.
- Construction means and methods.
As for all other elements of a project, the Design Professional is responsible for an appropriate design and performance requirements such as:
- Appropriate concrete design mix.
- In terms of slabs-on-grade, total assembly appropriate for the site conditions and in compliance with soil report recommendations.
- Requirements for appropriate testing to ensure there is not excessive moisture at time of floor finish installation. The requirement has to be in accordance with the requirements of the floor finish provider. The testing requirements establish the performance requirement for the Contractor.
The Contractor is responsible for construction means and methods for such things as not adding excessive water to concrete mix, proper protection in terms of weather exposure, proper curing time, etc.
If the design is appropriate, why should the Owner pay additional costs for moisture mitigation when the probable cause was the Contractors means and methods? As in any situation, the Contractor always has the right to claim that the design was at fault, but in addition to criticisms of the design he will also have to explain why he didnt document something about that before the slabs were installed. If the Contractor doesnt believe he can meet the performance requirement (test results), then he is obligated to state that before he starts that element of the construction.
Of course dealing with floor finish on an existing concrete slab is a different situation.
At this point in a conversation about slab moisture issues I like to add the following about the first time I personally experienced a finish floor on concrete fail during the restoration of a historic “grand” hotel in San Francisco:
1908: The ground level (over 2 basement levels) concrete floor was originally constructed. Yes, 08, in a re-build following the San Francisco earthquake of 1906
1988: Hotel closed for restoration (listed landmark).
1989: Roof over floor area in question removed to facilitate installation of long span beams to frame a column-free large convention space/grand ball room.
1989: New grand ball room closed in about 3 months later.
1991: Pirelli rubber flooring installed in service corridors from the kitchen.
1991: Re-opening about 3 months later.
1992: Call back to witness blister like bubbles, about 8-inches in diameter and several inches high. Pirelli rubber replaced with low pile carpet.
Sometimes these things are hard to predict. Here a concrete floor had an enclosed service life of 80 years, got rained on for a couple months, had a couple years to dry out, and we still had a perfect FAIL.
It has been suggested that if the design is appropriate that it will never be necessary to apply a coating to the slab. This is not necessarily true. When the engineer specifies the concrete and curing for the slab he may not be in a position to ensure that the slab will dry out in a specific duration. He has other considerations that may trump concerns about floor treatments.
The drying of the slab is influenced by the concrete mix requirements, the specified curing, and the weather and thus the Contractor may not be able to control the situation to eliminate the need for a coating. Further it is my understanding that different manufacturers may have different acceptance criteria.
Suggest that you go to your structural engineer and tell him the moisture test values that must be met, the time of year the work will be done, and how long after pouring the slab the flooring will be installed and ask him if he can assure you that the values can be obtained without the moisture coating. My guess is that if the engineer says he can do so he is either God or he doesnt know what he is talking about.
In a situation like this if you insist on making the contractor responsible for the coating if needed, then you will be costing your client more money.
Mark: “It has been suggested that if the design is appropriate that it will never be necessary to apply a coating to the slab.”
I don’t believe anyone said that. The question is why was there a moisture problem, who is responsible for it, and who should pay for remediation such as applying a coating to the slab.
Robert
You state that If the design is appropriate, why should the Owner pay additional costs for moisture mitigation when the probable cause was the Contractors means and methods? This implies that if the Contractor does everything right that moisture mitigation is not needed and if this is not the case then the design was not appropriate.
As a structural engineer who has read more than a few articles on this subject I do not know what is the magic formula that will guarantee that moisture mitigation is not needed. I know to reduce
I do not believe that there is a methodology that if followed will essentially guarantee that moisture mitigation is not needed. Can you provide me with references to experimental studies that show that such a methodology exists and is effective.
I am doubtful that the flooring manufacturers really understand the cause of failure. Based on reports I have seen I am doubtful that the testing methods are meaningful and accurate.
Concrete requires water and naturally has a high ph. Concrete must be cured if it is to obtain the required strength. Curing reduces the loss of water. The weather, over which we have little control, can have a significant impact on moisture in the concrete.
Bottom line is that either there is no guarantee the design will be adequate or that the Contractor will have sufficient control to prevent the need for moisture mitigation.
Ultimately it is the Owner that pays the cost of making the slab suitable for the flooring. The question is how do we minimize the cost to the Owner.
If you assign total responsibility to the contractor when he is not able to control the work to prevent the need for moisture mitigation he may not have any option other than include the price of the floor treatment. In such situations he if the contractor gets lucky he will keep the cost of the floor coating as profit. If the floor treatment is considered an alternate then the Owner can potentially save some money.
I am suspicious that the problem exists because the manufacturer of the floor covering is selling a system that is not naturally suited for concrete floors.
Mark
I would agree that the cause of excessive moisture may be a mystery. The design may have been appropriate and the Contractor may have used good means and methods. There may have been some other circumstances that were beyond the control of either the Design Professional or the Contractor. If that is the result of an investigation, then it is appropriate for the Owner to pay the additional costs. If however that is not the case, then the Design Professional or the Contractor may be responsible for some of the problem.
My problem is with just assuming that both the design and the Contractor’s means and methods were proper and the Owner pays any additional costs for moisture mitigation. We don’t do that with other design/construction situations, why is it suddenly the thing to do with concrete slab/floor finish moisture problems?
In order for there to be an investigation to determine whether the problem was beyond the control of the contractor we need to have objective evidence that establishes what the contractor should have done. Can you provide me the studies that establish what the Contractor needs to do along with evidence that if this is done there will be no problems?
I will suggest that the reason that this is typically not an issue for other situations is because this situation is not based on good science. Further I do not see that the flooring manufacturer is motivated to find a solution since in the current situation he can blame the problem on another party and deny liability.
To me, this problem is easy to resolve.
The flooring installer performs the moisture test that is required by the flooring manufacturer: calcium chloride or in-situ RH probe (or both). If the test results do not exceed the manufacturer’s maximums and the installer installs the flooring, then the flooring installer has accepted the slab and can no longer blame another entity.
If the test results exceed the flooring manufacturer’s maximums, then there are three things to look at immediately:
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Was a vapor retarder installed on the project? If yes (and hopefully it was installed properly), then look at No. 2. If not, then the owner pays for remediation (and the architect may have some liability, too).
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Check the results of slump and cylinder compression tests. If the results indicate marginal passing of required minimums, that could indicate added water. Thus, a contractor problem and the contractor should pay for remediation. If test results don’t show evidence of added water, then go to No. 3.
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If the slab became wet from weather (and the contractor could not have protected the slab), then the owner has two options: a) allow the slab to dry out if schedule is not a problem; but, if schedule is a problem, then b) use remediation and owner pays for it.
I know this is probably over-simplification, but it is a guide to follow. There are only three sources of moisture in a slab: from the ground, from the concrete mix, or from the concrete when wetted after curing. The designer controls the first (unless improperly installed), the contractor has significant control of the second, and, depending on the circumstances, the contractor may have control over the third.
I have been moving in the direction of agreeing with Mr. Johnson. I have been told by structural engineers in this area that only about 1/2 of the water in a concrete mix needs to be there to hydrate the cement even with a .45 water/cement ratio. The water that is not required for hydration needs to go somewhere. With the use of heavier under-slab vapor retarders (15 mils thick, less than 0.1 permeance), the only place for the water to go is up and out through evaporation. In the Gulf Coast area, the rate of evaporation may slowed by the higher humidity during much of the year. Having said that, overly damp slabs have been a problem in less than 10 of the 250 to 300 projects that I have written specs for over the last ten years. In one of those cases, the Owner did not want to run the A/C system so that the slab would dry out.
While I do understand that water vapor moving up through the ground can cause flooring problems, it seems to me that when problems arise for new construction, it is most likely the result of residual moisture in the concrete itself, possibly compounded by the slab’s exposure to wet weather. Because these project conditions are well known to experienced contractors, it would be my position that a competent contractor would allow for this in the construction schedule. I come down on the side of considering this a “means and methods” item in providing (or conveying) a substrate that will be acceptable to the subcontractor who has to install something over it.
Ronald:
Given the common use of admixtures there is not always a correlation of slump with water content. Further you would need to be able to define marginal passing.
The contractor probably has less control over the water than you assume. Many engineers specify water cement ratios of 0.40 or 0.45. It may not be practical to go much lower.
Here again we are assuming that we know what needs to be done and if this is done there should be an expectation that the coating will not be needed. I am not convinced that this is the case. Show me the reports that document the experiments that prove this assumption.
Ron:
There is a fourth thing to look for: cleaning of the floor slab in preparation for coating and floor covering. Water used during cleaning can make the reading sky-high. A colleague reported a new concrete slab on grade, that had been baking in the desert sun, tested with excessive moisture vapor emissions because of over-zealous cleaning a few days before floor coverings were to be installed.
The (General) Contractor is responsible for sequencing and scheduling the work. Actions by the Contractor by closing-in the building and inhibiting drying of the concrete need to be considered against the need to dry the concrete sufficiently for the subsequent application of finish coatings and floor coverings. That’s the Contractor’s responsibility and not the design professionals’.
It comes down to means, methods, techniques and sequencing (scheduling) of construction which are the Contractor’s responsibilities (and why the Contractor is paid a markup on all the work).
A competent Contractor would consider curing and drying of the concrete and jobsite conditions, and provide ventilation and heating as necessary … or use one of the moisture vapor sealer products in order to meet the completion schedule and ensure acceptable moisture vapor emissions. Supposedly the Contractor is a builder and not merely a construction subcontract broker (except, of course, in public works construction).
By the way, where’s the Construction Manager in this? S/He is hired for having more superior knowledge of construction than architects and engineers. Oh, that’s right. CMs are only responsible for “on time” and “in budget.” Quality ain’t their problem