What is moisture pressure?

[Inventive1]

In reading some of the prior posts on this forum, I've seen references to moisture pressure. Based on the context, I'm guessing this is refering to pressure under a concrete slab which forces moisture up through the concrete. If this is correct, what creates this pressure and how is it measured?

 

[Edger]

I am no expert on this subject, but I understood that most of the time water wicks up through the slab rather than being forced up. You do not see it on the surface because it is evaporating all the time unless you place a piece of plastic on the floor and tape the edges for 24 hrs. When you return and lift the plastic it will be wet.

A very high pressure however is developed when a water soaked slab gets hot sun on it because the trapped water gets so hot it turns to steam and cannot get out fast enough until the steam blows a piece of concrete off the surface, usually round in shape about an inch diameter and about one eighth inch thick in the middle. This usually happens in several locations and will continue until it is fixed or until most of the harder surface concrete has spalled away.

 

[LegacyIndustrial]

The same way fuel moves through a lanterns wick is exactly what happens to water beneath a concrete slab.

It gets sucked up beneath, travels through the slab and leaves the substrate as water vapor. Some tell tale signs are white minerals left on the slab (called efflorescence) , wet spots beneath items left on the floor (rugs, boxes, etc...).

Epoxies have a good molecular lock. The water vapor cannot pass through most epoxy and the result is a pressure build-up and then perhaps the epoxy releases and fails. Urethanes are worse as they have a VERY tight molecular lock (this is what makes them so chemical resistant).

In addition to the pressure of the water building beneath the epoxy, the water brings salts and minerals with it. These combine to attack the epoxy also helping with the release/failure.

This is why all of us (epoxy people) stress a water vapor test prior to coating. If you do have water-vapor all is not lost. If it's not too bad you can apply a water based epoxy coating (one coat) or an acrylic sealer. These products have a looser lock and will allow water vapor to pass through them.


Other solutions to this issue:
vapor barrier beneath the slab, curtain drain, sump-pump, drain tiles, etc..

 

[knight]

I did a water vapor test recently (taped down a plastic bag). My climate is dry in summer and humid in winter. Is the test still valid if done during the dry season?

 

[Edger]

Only a test in winter will tell. Normally water vapour is not a problem unless the soil underneath is wet due to a natural water table, a broken water/drain pipe beside or under the slab, or from water entering the end if it meets wet soil or if water gets down a joint at the end when it rains.

 

[MrMark]

What paint can you use if you fail this test. I am sure I will fail as I have seen this issue in the winter only in the past.

 

[LegacyIndustrial]

Our HD-015 would likely survive.

 

[Edger]

Have you seen the waterproofing products you can put down under a coating to stop the water?
http://www.aquron.com/our-products/concrete-protection-and-waterproofing/aquron-cpt-2000/
http://www.protecrete.com/Densifier.htm

 

[thegarageguy]

Have you seen the waterproofing products you can put down under a coating to stop the water?
http://www.aquron.com/our-products/concrete-protection-and-waterproofing/aquron-cpt-2000/
http://www.protecrete.com/Densifier.htm

from a quick glance, these are densifiers and I didn't see anything about how many lbs. of vapor emissions it resists.

There are a few Companies who make moisture vapor primers....matter of fact, most major manufacturers now offer them. Some to withstand from 5% to 20% in one coat.

 

[MrMark]

Can you say who these companies are? Thanks.

 

[MrMark]

Our HD-015 would likely survive.

Is the HD -015 a 50 percent solids paint? Would the moisture move right through it. One coat or two on this product?

 

[thegarageguy]

Duraflex, Dexotex and Ardex to name a few.....there are others but I haven't used them so I won't comment on those.

 

[AlphaGarage]

If you have very high hydrostatic pressure another company to look into is Barrier-1. They have both an add mix for new construction and a topical application for existing concrete. They offer a very strong guaranty, I think one of their reps needs to be onsite during the application to qualify for the guaranty.

 

[Edger]

from a quick glance, these are densifiers and I didn't see anything about how many lbs. of vapor emissions it resists.

There are a few Companies who make moisture vapor primers....matter of fact, most major manufacturers now offer them. Some to withstand from 5% to 20% in one coat.

The whole purpose of these products is to stop all water transmission through the slab, not just at the top of the slab, the densifier part is a byproduct of the process. They penetrate 6 inches into the concrete which is all explained in their data sheets. I used Aquron in Australia many times with 100% success.

One job was a garage epoxy coat with lawn butting to the end of the slab. Water from lawn watering soaked through the end and the sun spalled the top of the concrete at that end. I ground off the epoxy, applied a fine spray of Aquron, next day filled the holes, ground smooth and reapplied the two coats of epoxy again. No more problems. The Aquron penetrated through the slab so no water got into it again.

 

[thegarageguy]

The whole purpose of these products is to stop all water transmission through the slab

With all due respect, the pds you linked, under attributes on the top right says, "allows necessary vapor transmission"

Now, I'm not a chemist or engineer, I'm just a dumb flooring contractor that's been installing seamless floors since 2002.....but when I read that, it leads me to understand that the use of this product still allows the concrete to breathe and allows an X amount of "necessary" vapor transmission. Necessary for what? How much does it allow? How much does it block? What is it's limitation?

So, according to the pds is does not completely block vapor transmission, therefore rendering it useless in a moisture problem slab when a film forming coating will be applied.

If I had to apply a coating over a moisture slab where an epoxy chip or quartz is a finish, I would not use this product. I wouldn't be able to warranty it.

Show me where I'm wrong

 

[Edger]

If I had to apply a coating over a moisture slab where an epoxy chip or quartz is a finish, I would not use this product. I wouldn't be able to warranty it.

Show me where I'm wrong

You can ask for their warranty. Apparently, which you can ring up and check to be sure is that it allows vapor to pass, but water molecules are too big to get through. It is the water that is the problem so the slab breathes, but no water gets through. I am a past licenced applicator of Aquron in Australia, it would be better to make a call directly with the companies who produce the products for more technical information.

 

[thegarageguy]

Sorry my friend, it's vapor transmission and efflorescence that wreaks havoc on coatings. Vapor accumulates under a non permeable coating and creates a water blister, like so..

I've also seen extreme efflorescence develop under a concrete coating, which is breathable, like so...

If there is an obvious moisture issue, then it's best to use a product dedicated to the system that you will be using or at least compatible. Not sure this product is correct for a high build coating system over a moisture problem concrete. I could be wrong, but I doubt it.

like you said, contact the manufacturer and get their warranty in writing...don't ever take their word for it. Remember, they are all salesmen.

 

[Edger]

I used Aquron under polyurethane and 100% solids epoxy coatings in industrial environments where fork trucks tear around all day with no problems.

The two product links I put on this forum are specifically designed to stop the problems you have shown in your pics. You can only get efflorescence if you have water transmission because the water carries salts with it.

As I suggested, contact the manufacturers and get some data. I know Aquron have decades of successful work behind them in many "impossible" concrete situations from marine to basements. I am not trying to sell them, I only want to bring them to the attention of garage owners as a solution to a problem.

As to the definition of vapor I am unsure, but I do know that the conditions in your pics were created by water soaking through. You cannot see it normally because when the water gets to the surface it evaporates. Perhaps that is why some people think it is water vapor coming through rather than water.

 

[CamarosRus]

Other than AQURON what other specific brand names have YOU had good results from ?

I'm trying to reach a conclusion as to which/what products are the best value as some of the below are very expensive and can only be purchased and applied by certified installers

such as:

KOSTER
AQUA FIN
ARDEX
MOPEI
BASF MASTER TOP
Sherwin Williams
AZ POLYMERS Vapor Solv

and the list goes on and on

 

[pauls340]

There's a new product line that just started in Australia called Vapor Lock. They are also carried by construction supply distributors throughout US and Canada. This product not only waterproofs concrete but it vapor proofs it. 5 & 10 year warranties are available. We've done over 2million sqft of VL20/20 with zero dry shrinkage cracks and no slab curl. It'd be worth it to look into it. I put it on my garage floor three yrs ago and zero moisture, anywhere on the floor.