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use of silicate admixtures for slab moisture mitigation

use of silicate admixtures for slab moisture mitigation

use of silicate admixtures for slab moisture mitigation

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?

RE: use of silicate admixtures for slab moisture mitigation

Interesting... does the slab still 'wick' water from a damp subgrade... if it does, then the product may not work as required.


RE: use of silicate admixtures for slab moisture mitigation

i would imagine that if the product is batched homogeneous, it would have the same properties throughout which would prevent wicking too. One of the questions i have is concerning reliability. concrete is a statistical product and a concrete pour isn't necessarily homogeneous. i don't accept the existence of a manufacturer willing to warranty their product as reliability evidence. A warranty is better than nothing, but there is plenty of independent construction info on proper preparation of a slab for finishes.

RE: use of silicate admixtures for slab moisture mitigation

The easy way out would be to accept the warranty and if anything goes wrong, you wave the warranty. Whether or not you get the manufacturer to honor it or pay for damages is another story. I am skeptical of the warranty.

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

i'm with you on 2nd point motorcity. i find lots of internet chatter about this particular manufacturer using escape hatches to avoid the warranty. Another thing i don't like about using this is there isn't industry standards for the Owner to QA test to see if the product works. Basically, you pay for it.... cylinders are shipped off to the manufacturer and they do their testing (ASTM D5084). Then they issue the warranty. But, there isn't really a way for the owner to check the work for themselves.

RE: use of silicate admixtures for slab moisture mitigation

I think I'll pass on this product... and, stick with the PEVB... it works...


RE: use of silicate admixtures for slab moisture mitigation

FYI Dik, it's not a substitution for vapor barrier. The product doesn't warranty slabs without VB. it's for the leftover water in a slab to get vapor rates under control so finishes can be applied. PEVB definitely works but contractors have to get control of their buildings. There are lots of benefits to getting a building dried in with humidity control for many of the finishes and other materials (joint compound, paints, sheet rock...)

RE: use of silicate admixtures for slab moisture mitigation

Let's see... I've had no problem with finishes using PEVB, and by using this product, I'll have no problem with finishes...


RE: use of silicate admixtures for slab moisture mitigation

dsg....kind of reminds me of roof warranties....not so good!

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

i was wondering when i might drag you out Ron. thanks to dik and motorcity for jumping in too.

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

Quote (Ron)

Silicate hardeners have been around a long time.

I remember them from 'way back when' and they were topically applied... had forgotten all about that until your post.
Roofing warrantees have more holes than a leaky roof... almost have to be installed in August, on a Sunday afternoon...


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.


RE: use of silicate admixtures for slab moisture mitigation

i'm not sure i follow. the Arch/SE firm i work for doesn't specify using this admixture ever. Sometimes contractors want to include this admixture in their submittals because it is favorable to the project schedule. Those contractors would like to have the flooring people released to work by relying on a moisture warranty that lets them bypass the traditional time-tested slab drying and QC testing approach.

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

Here is a Technical Brief on ALKALI SILICATE-BASED ADMIXTURES by Simpson-Gumpertz & Heger. They appear to be against the us of these admixtures. One thing they note is that these admixtures can result in elevated pH at the surface. Most flooring & adhesive manufactures state the concrete should have a pH of 9, which is already really low for new concrete. Link

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

If the admix was not in your design documents, the GC should not have bid the project assuming it would get approved. Also, your seal = your design......contractor's seal = contractor's design

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

Quote (Epoxybot)

Most flooring & adhesive manufactures state the concrete should have a pH of 9, which is already really low for new concrete.

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.


RE: use of silicate admixtures for slab moisture mitigation

dik - I know. I couldn't believe it when I read it. My childhood best friend owns a flooring bsiness and I read his literature when we sit around wasting each others time. A manufacturer's spec of pH 9 is very common. I think it is intentional. It may have slipped into installation bulletins back in the late 80's & 90's when flooring manufacturers were first moving towards water-based adhesives.

RE: use of silicate admixtures for slab moisture mitigation

at least snake oil works with a pH of 12...


RE: use of silicate admixtures for slab moisture mitigation

I would trust the SGH evaluation more than the manufacturer's warranty.

RE: use of silicate admixtures for slab moisture mitigation

dsg...your dilemma goes back to a contractor and his sales ability. They are usually better at telling people crap that sounds good than we are with explaining problems and repercussions through facts and logic. No one wants to hear the downside, but we often have to tell them those things.

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

Thanks for comments. The SGH evaluation epoxybot linked to is the kind of stuff i'm looking for. bullet points 2 and 4 of that document are two of the concerns i have had for years... but it brings up additional concerns to point to. i find points 3 and 6 particularly interesting. My client, the Owner, is losing a lot of money because of delayed occupancy so i'm going to keep building the strongest argument and will check out those paths. Ron, i'm going to use that quote about experience until i'm dead.... here's a star for it.

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

Quote (OP)

Ron, i'm going to use that quote about experience until i'm dead.... here's a star for it.

I preferred his 'junkyard dog that chews concrete'... much better, but, inappropriate for this thread.


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