Monthly Archives: September 2016

A layman’s guide to concrete moisture and it’s relation to floor covering. This is a revised and updated version.

A layman’s guide to concrete moisture and it’s relation to floor covering.
As most of you know concrete is a mixture of aggregates, cement and water. As the concrete dries, moisture moves to the surface through capillary action.
This process continues for the life of the concrete. Even when the slab is “dry” the pores in the concrete retain moisture.
The moisture content varies due to quite a few factors.
Here’s the big ones:
1. The original concrete mix, known as the water to cement ratio (W/C)
2. The porosity of the concrete (the more water in the mix, the larger the pores in the concrete).
3. A low perm vapor retarder (or lack of) beneath the slab. When the vapor retarder is placed below the slab and a sand base, it is called a “blotter layer”.
4. Intrusion from outside influences like irrigation systems and/or water runoff from landscaping or terrain.
So how does this effect flooring? Yesterday’s solvent based adhesives have been replaced by today’s “eco-friendlier” latex based ones.
The prior adhesives were inherently resistant to liquid moisture (think oil and water).
Latex itself is water based and can actually draw moisture from concrete. Today’s flooring adhesives, when exposed to high moisture levels in concrete, don’t cure properly and
provide the bond required.
What types of flooring are affected by concrete vapor emission?
Almost all commercial and residential products with the possible exception of “action back” (latex mesh-backed) broadloom carpet.
Of course the materials vary in their reaction to moisture. Here are examples from most sensitive products to least:
1. Heat-welded resilient sheet vinyl or linoleum.
2. Rubber sheet or tile.
3. Cork sheet or tile.
4. “Vinyl back” broadloom carpet (typically 6’ wide).
5. Modular carpet
6. Luxury vinyl tile and plank
7. Hardwood flooring
8. VCT (vinyl composition tile).
There’s plenty more but you get the idea.
Prior to installation, flooring and adhesive manufacturers require that the concrete be tested for moisture.
Believe it or not, some contractors skip this vital step. Why?
1. The existing flooring looks fine and doesn’t show any signs of a moisture problem.
2. The testing is too expensive based on the size of the job.
3. “I’ve been installing flooring for 30 years and never had a problem”.
4. If the test results come back “high” there will be a battle between client and contractor to assign fault and
determine who’s financially responsible for “the fix“.
Let’s assume that proper protocol was followed and the decision is made to test.
What kind of testing is used? For commercial carpet and hard surface flooring two methods are typically used:
1. ASTM F1869 the CaCl (Calcium Chloride) method which measures emission in lbs. per square foot.
A reading under 3 lbs. is acceptable for most resilient flooring, a reading under 5 lbs. is acceptable for most carpet.
2. ASTM F2160 In-situ Relative Humidity testing (RH). This system measures moisture in percentages.
For example, a reading under 75% is acceptable for most flooring, sometimes under 85% for some carpet.
Which method is the more accurate, or the more reliable? Most floor covering manufacturers recognize one or the other (sometimes both) in relation to warranties.
The flooring industry is moving more toward ASTM F2170 RH testing because it measures concrete moisture deeper into the substrate and is less affected my external
(or ambient) conditions.The RH method has the option of single use versus reusable sensors.
Single use sensors are factory calibrated and certified for a one time installation.
Reusable sensors require periodic calibration to remain accurate as well as sufficient equilabration time at the job site.
One more thing, There are very strict testing standards issued by the American Society for Testing and Materials.
These standards cover proper testing methods, locations, quantities and job-site conditions.
If the testing does not comply with ASTM standards the test results are null and void.
So, we’ve gone by the book, done proper testing and the results are not in compliance with the manufacturer’s requirements.
Don’t be surprised. Many concrete slabs don’t comply. The reasons are the same as stated in the first papragraph:
1. A wetter mix (higher W/C ratio) made the concrete easier to place.
2. Water was added to the surface of the slab to aid in the finishing and curing process.
3. The lack of a proper low perm vapor retarder placed directly beneath the slab.
4. Water intrusion from lanscape irrigation or terrain (on or below grade).
5. Weather, (i.e. rain, fog and even high humidity for long periods).
OK, the concrete moisture level is too high, what are the options?
Here they are listed by worst idea to best:
1. Ignore the results, install the floor and hope for the best.
2. Apply the least expensive “concrete sealer“ available and roll the dice.
3. Contact the manufacturer for their recommendation on an approved moisture resistant adhesive.
4. Apply a proven and warranted moisture control system.
From a warranty standpoint $3 and #4 are really the only options. Let’s look at some budget numbers:
Manufacturer approved moisture resistant adhesives can cost as little as .50 to $1.00 per sq. ft.
If there are no special adhesives available for the specified product (often times there are not) the option is #4.
OK, what’s that going to cost? Anywhere from $4.00 to $6.00 per sq. ft. depending on the system and warranty.
Does that seem like a lot of money? Not so fast…Think of a couple of things:
1. The life-cycle cost per the life of the flooring material (typically 10 years minimum).
Your average cost to protect/insure your expensive floor covering is minimal compared to repair or replacement of damaged flooring.
2. Replacement cost of your flooring if and when a failure occurs.
This varies quite a bit depending on the flooring and the application but take into consideration these factors:
Removal and replacement of furniture, computers, office equipment, etc.
Then add demo of the flooring and adhesive, installing a vapor control system (we didn’t the first time), then add material and labor costs for new flooring.
All this work will probably be phased/after hours (at an additional cost) to create minimal chaos and keep your business operating.
It’s safe to say that this could easily cost 4 to 5 times the original price of the flooring.
Ready for some good news?
Architects, design professionals, construction managers and contractors can be proactive and pre-budget concrete moisture control solutions into the project pricing.
Typically floor covering is pretty far down the list cost-wise on a project.
By accounting for the additional cost up front, the impact is minimal and there are no surprises or delays to the project.
Here’s something else. These are contingency costs. If a concrete moisture control system is not needed, the money goes back to the owner!
Hopefully this article has given you some insight into the world of concrete moisture and it’s relation to floor covering.
There’s many more details and nuances to the actual testing, reporting, installation and warranty aspects of this subject.
Brewer Contract Consulting can assist you with your questions, concerns, etc.
Please contact us. We’ll be happy to assist you with your project.