Sealer for hydrostatic pressure [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-12-2017, 05:22 PM
We recently discovered we have moisture problems with our slab. We started to remove some of our flooring and discovered mold. Apparently one of the previous owners must have glued down wood and when they ripped it up, they did not clean up the glue. They put plastic down and then laminate. Turns out we have moisture wicking up and mold formed on the glue. We had it remediated and now just have bare concrete. We did a calcium chloride test and it came back with 20 pounds of pressure. Our neighborhood has high water table and I have been told some of the homes were built without vapor barriers. We plan to put down tile, but don't know if we should seal the floors first, put down a membrane or if there is another solution. Most of the sealers that have been recommended to me by various flooring companies say not to use with hydrostatic pressure. We live in Florida, slab above grade. Please help - We are at a loss. Thanks in advance!

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03-12-2017, 07:48 PM
Welcome, Chris. :)

We live in Florida, slab above grade.I'm a bit confused here. If your slab is above grade, how can you be suffering from hydrostatic pressure? :scratch:

03-13-2017, 07:01 AM
We live in the FeatherSound neighborhood near Clearwater, FL., which was/is a very low lying, marshy area.

Either our homes vapor barrier is failing, or there wasn't one used at all.

We've done several calcium chloride tests, with results ranging between 18-20lb psi.

Thanks for any suggestions to help solve our problem.

03-13-2017, 08:49 AM
It'll help if you'll add that geographic location to your User Profile, Chris.

And can you answer the question in Post #2?

03-13-2017, 08:59 AM
Location updated. I'm not sure how to answer your question in the second post.

03-13-2017, 09:16 AM
Chris, if your slab were "above grade" as you indicate in your first post, there would be no way for you to be experiencing hydrostatic pressure. If, on the other hand, your slab is actually on grade (on the ground), that would be a different story.

03-13-2017, 09:25 AM
So it must be on grade.

Typical residential home construction for a single level ranch style concrete and stucco home in Florida.

03-13-2017, 09:49 AM
Lotta Slab On Grade construction in that area, Chris, so I'm gonna guess that's what you have. But I just hate guessing when trying to answer questions here. :)

If your Calcium Chloride test was properly conducted with the environment in the room to be tiled at the same conditions as it would be in normal use and you have MVER of 20 or more, you may have a problem with some types of tile installation. Most tile installation product manufacturers have some method they will consider useful in those conditions, but you really need to talk with a representative before proceeding.

If you actually have a negative hydrostatic problem at some times, you have a different issue. And there will be no doubt, you'll be seeing liquid water on the surface of your slab under normal room environmental conditions and you'd need no moisture vapor test to tell you there's a problem.
We did a calcium chloride test and it came back with 20 pounds of pressure.

There is some argument in the construction industry over whether the Calcium Chloride test really tells you what you need to know and that a slab relative humidity test is more accurate, but at 20 pounds on the Calcium Chloride test, there is no question that you have a bit of a problem there. That is not a measure of pressure, by the way, that's a measure of the quantity of moisture in a given area in a given time.

That amount of moisture vapor emission is even beyond the maximum level recommended by Schluter ( for their Ditra, I do believe and they advertise that product for MVER control under ceramic tile installations. You might talk with them about your situation, though. And find what thinset mortar manufacturers' products are available in your area and call them to see what recommendations they'll make. MAPEI across the state in Deerfield Beach ( be my first contact down there.

My opinion; worth price charged.

03-13-2017, 09:54 AM
Thanks for the info CX. I have reached out to Mapei through their contact page on their website.

What do you know about this:

Knowing our situation, do you believe a sealer that actually goes into the pores of the concrete and bonds is better than a two part epoxy that simply covers the top?

03-13-2017, 10:05 AM
What about this product?

03-13-2017, 10:36 AM
It's discontinued.

03-13-2017, 10:44 AM
They have another one called TechMVC Moisture Vapor and Alkalinity Barrier. Spec sheet attached.

03-13-2017, 12:45 PM
There's another product that has replaced it. Spec sheet attached.

03-13-2017, 12:53 PM
Chris, if you've read that PDF you know as much as do I about that product. It sounds as though it would suit your situation (presuming your slab is in good condition and your calcium chloride test results are accurate. It also sounds like it is gonna be a tricky installation for an inexperienced user, but I don't know your capabilities.

Let me see if I can get you a better opinion on that.

Steve Taylor
03-13-2017, 02:10 PM
As CX said, Tech MVC would be a good choice to stop moisture vapor transmission, assuming we are not dealing with hydrostatic pressure. Hydrostatic pressure is generally evident when there is visible water on the slab surface or the slab is dark, wet looking. Moisture vapor emission is not evident except through testing.

With this high Calcium Chloride result, you will need a product like Custom Tech MVC. I do recommend that you have a professional install the MVC and you will need a primer to install tile to the MVC. I suggest that you talk to someone on our Tech Service line to help with the products needed, 800-282-8786.

MAPEI - Product Support
03-13-2017, 03:13 PM
I have reached out to Mapei...

MAPEI has two moisture reduction barriers called PLANISEAL VS and PLANISEAL VS FAST.

These are alkali-resistant, two-component, 100%-solids epoxy coatings that effectively stop moisture-related problems over concrete with floor coverings. In addition, PLANISEAL VS and PLANISEAL VS FAST expedite floor-covering installations by eliminating the traditional wait time required for new concrete slabs to reach moisture levels suitable for installations.

Before using either one of these products, however, the concrete slab must have a CSP profile of 2 or 3. This is typically achieved by “light shotblasting” or “grinding”.

Once the moisture reduction barrier is dry, we recommend applying our ECO PRIM GRIP primer over the top of it. After the primer has dried, a polymer-modified thinset must be used to set the tile.