use of silicate admixtures for slab moisture mitigation
use of silicate admixtures for slab moisture mitigation
(OP)
More and more we're having contractors who want to use this admixture (at additional cost) for slabs-on-grade. A little background first for curious people less familiar... The product in the region is called Barrier 1 and it gets batched into the concrete. the concrete tester takes a photo of the vapor barrier and collects the cylinders and mails them to the admixtures lab. Then the contractor gets a nice warranty from the admixture provider that says the slab is under warranty regardless of any MVER or RH testing results. So with that warranty in hand the contractor can install their finishes (carpet, vct, etc...) without waiting for the slab to dry which is the warranty condition of the finishes that are being placed. The way the admixture is supposed to work is to make the concrete less porous in the hopes that the water that is trapped eventually emits out at such a lower rate that doesn't damage flooring materials.
Ok. So my position on this product is that i'm more interested in removing the water from the slab than i am having a manufacturer warranty that the slab will trap water well enough that we won't have problems. I'm bumping heads with contractors who want to consider this admixture the "industry standard"... even to the point that denying the product is considered a delay. Since most of the technical literature about construction materials are generated by manufacturers, it is hard to find references to cite about concerns over one product or another. So to the tip... i'm interested in independent studies and references that might support (or refute) my concerns. Anybody have any links?
Ok. So my position on this product is that i'm more interested in removing the water from the slab than i am having a manufacturer warranty that the slab will trap water well enough that we won't have problems. I'm bumping heads with contractors who want to consider this admixture the "industry standard"... even to the point that denying the product is considered a delay. Since most of the technical literature about construction materials are generated by manufacturers, it is hard to find references to cite about concerns over one product or another. So to the tip... i'm interested in independent studies and references that might support (or refute) my concerns. Anybody have any links?





RE: use of silicate admixtures for slab moisture mitigation
Dik
RE: use of silicate admixtures for slab moisture mitigation
RE: use of silicate admixtures for slab moisture mitigation
The overall performance of the slab depends on several other factors besides whether or not the product is mixed homogenously throughout the mix. In other words, there are several opportunities for something to go wrong......mixing, placing, finishing, curing, etc. If any one or more of those steps did not go perfectly, the admixture manufacturer would probably hang his hat on that as a loophole to get out of his warranty. He cannot warranty performance of a slab that depends on things he has no control over.
RE: use of silicate admixtures for slab moisture mitigation
RE: use of silicate admixtures for slab moisture mitigation
Dik
RE: use of silicate admixtures for slab moisture mitigation
RE: use of silicate admixtures for slab moisture mitigation
Dik
RE: use of silicate admixtures for slab moisture mitigation
Silicate hardeners have been around a long time. They do react and fill pore spaces...a reaction that can be a bit unpredictable both in its completeness and its effect on durability. In fact, most placements on hardened concrete warn that the concrete should be cured to strength before application so that the expansion that takes place during the reaction doesn't cause the surface to scale or crack. As an admixture the same or similar reaction has to take place and it does so during the curing and hydration process....lots of room for problems there!
In short, I'm not a fan of snake oil that tries to compensate for poor design and construction. Contractors love it because it might get them past their warranty period.
Keep in mind that warranties are much more about risk management than they are about quality. Well consolidated concrete with a low water cement ratio, coupled with proper placement, finishing and curing techniques will do more for the slab than an admixture or surface treatment.
Develop good specs and enforce them. That works!
RE: use of silicate admixtures for slab moisture mitigation
The big thing i'm concerned about is what to do when sticking to well-written specs just isn't good enough. if the Owner and Contractor are both looking at the designer who is sticking to their guns and seeing the designer as the problem... what recourse does the designer have to demonstrate that this was the right decision. Especially since slab admixtures is an early decision and it will likely have already been made when delays are the hot topic and the contractor is desperate to find excuses. The contractor will have all the manufacturer's product literature from the questionable material and the owner might not have the years of construction experience to understand that this isn't industry standard and there is a real gamble involved. A gamble that wasn't in the contract or the design. When a project is delayed, owners might not be sympathetic to designers who can't back up their guns with independent research, industry guidance documents, or industry articles that provide commentary.
since this is an open forum that people come to for tips... a little more background on the subject. everyone commenting so far are on the same page SOG on VB is good structural design, practicing SE's probably won't have to deal with the finishes or delays in the schedule to install finishes. This isn't about having 1 extra admixture, it is about adding a product that allows the contractor to completely remove the quality control programs in place that protect those finishes. Properly drying the slab per spec and installing a VB is what protects the finishes. Slab vapor comes in 2 forms: transmission & drying. The transmission from the soil to the building is dealt with by doing a good job with the VB, but trapped water in the slab dries out and this usually only starts once the air above the slab becomes conditioned. Slab vapor is in the architectural specs for the flooring materials. ASTM F710 gets referenced often and google it to read more. Almost every flooring material out there has a slab dryness criteria that needs at least 3 weeks of climate control to have a chance of reaching. The specs usually put the burden on the flooring installer to test and accept their slab before they put the finishes down. The test is real simple and cheap so contractors do it and don't share the info unless they are pressed for it. Flooring installers won't mobilize to a job and lay floor. They will send one of their project managers who will come and test the slab, and if it passes... they lay floor.... and if it doesn't they explain it to the GC and it gets talked about at the next Owner/Arch/Contractor meeting. Since finishes are appropriately named and happen last... delayed projects are usually already on critical path by that point so additional delays make drama. This power-point is a good thorough primer on the subject matter. https://www.sportsbuilders.org/events/presentation...
RE: use of silicate admixtures for slab moisture mitigation
I remember them from 'way back when' and they were topically applied... had forgotten all about that until your post.
[Added]
Roofing warrantees have more holes than a leaky roof... almost have to be installed in August, on a Sunday afternoon...
OP:
You need the EoR to issue a notice of change to remove this item... else, you bought the baby. Look for a credit <G>. The Owner may have some suasion in this matter... and, if you're not careful, either you or the Owner may have bought this. Snake Oil works as an admixture, as well.
Dik
RE: use of silicate admixtures for slab moisture mitigation
The question is really about what does the design team do if they deny this to a contractor who routinely gets this allowed on other jobs and perhaps even relied on this schedule relief in their bid. Sometimes the response 'We didn't specify it' isn't good for anybody else, including the client. When there is a lot of money in lost schedule involved, people want to know WHY.
RE: use of silicate admixtures for slab moisture mitigation
Chemical Admixtures for Concrete, Third Edition by Noel P. Mailvaganam, M.R. Rixom has some cautionary words as well. Link
RE: use of silicate admixtures for slab moisture mitigation
Not very popular approaches with GC's, but we as design professionals are constantly being forced to compromise our level of comfort, and most of the time it offers little benefit or compensation in return. I suppose its an age old battle that will always be there.
For substitutions, we have notes that indicate that they may be allowed after EOR review and approval, but they WILL NOT be considered without the contractor's engineer PE seal (this is typically the approach for alternate steel connection design, but it may also work in this case). The contractor needs to have some skin in the game if he is going to benefit from compressing the schedule
RE: use of silicate admixtures for slab moisture mitigation
Any concrete I've encountered with a pH of 9 is so badly carbonated that the rebar is starting to corrode. Most concrete pH is in the order of 12.
Dik
RE: use of silicate admixtures for slab moisture mitigation
RE: use of silicate admixtures for slab moisture mitigation
Dik
RE: use of silicate admixtures for slab moisture mitigation
RE: use of silicate admixtures for slab moisture mitigation
The other issue is that we live with projects and issues for the long term...and through the problems the contractors create. It goes back to experience....instead of 20 years of experience, contractors often have one year of experience, 20 times!
RE: use of silicate admixtures for slab moisture mitigation
The pH <9 requirement is about the concrete surface itself, not the concrete. You can take a pH pencil to a slab and find that the pH is 8 or 9, but if you take your keys and make a tiny scratch to the surface you just tested, the scratch is dark purple with a pH of 13 to 14. The point of good pre-finish preparation is to reduce the transmission of vapor through the slab or vapor from the drying process because those vapors bring alkaline salts with them and those salts don't work well with adhesives.
RE: use of silicate admixtures for slab moisture mitigation
You are correct about the surface pH. That's why when we check for carbonation (usually 1/8" or less), we have to use a freshly broken piece of concrete (not cored or sawcut) to treat with phenolphthalein to check for depth of carbonation.
Agree with the SGH evaluation. They are top notch. I have consulted with them, for them and against them!
RE: use of silicate admixtures for slab moisture mitigation
I preferred his 'junkyard dog that chews concrete'... much better, but, inappropriate for this thread.
Dik