Prior to the installation of any flooring material, the flooring contractor needs to be aware of the factors that may impact the success or failure of the installation.
It is true that the flooring contractor does not need to be (nor should he be) the party to police the construction process. But he does need be able to identify conditions that may lead to potential problems. Awareness can help eliminate problems both before and after the fact; this information is crucial in helping to determine the cause or potential cause for failure.
1. Site Location
- Depth of the water table. Is the water table close enough to the surface to make capillary rise a concern?
- Have you a copy of the soils report? Is the soil fine enough to present a capillary rise concern?
- Is the site an alluvial plain? An alluvial plain is a valley filled with sand and silts carried by water runoff.
- Is the site a hillside lot? A cut into a hillside can present water runoff conditions and expose underwater springs that can impact the concrete slab.
- Has there been a land-use change? Changes from a low density to high density can impact the runoff of water.
- How is the drainage of the area around the site? Is there a swale in landscaping that is impeding the flow of water away from the structure?
2. Beneath the Slab
- Is there a capillary break beneath the concrete slab? A capillary break will serve as a barrier for capillary action from the soil, but will not serve as a barrier for moisture vapor migration.
- Is there a vapor barrier beneath the slab? A vapor barrier needs to be used not only to impede moisture vapor, but other potential vapors such as radon and methane.
- Type of vapor barrier? The type of material used for a vapor barrier is extremely important to the effectiveness of the membrane. A 6-mil Visquene is not a vapor barrier. It can decompose in a short time and is easily compromised during the placement of the slab.
- Thickness? The thickness of the vapor barrier is important to not only its durability, but its permeability as well. A good vapor barrier will be ten times less permeable than Visquene.
- Is there a blotter layer on the vapor barrier? A blotter layer will allow available moisture from a compromised vapor barrier to diffuse throughout the blotter layer
- Sand or granular fill? The finer the fill used in the blotter layer, the faster the moisture will move throughout the blotter layer. In April 2001 the ACI removed the granular fill for concrete slabs to receive moisture-sensitive flooring materials, leaving the slab in direct contact with the vapor retarder.
- Was it wet or dry at time of the concrete pour? The more available moisture in a blotter layer, the more the water/cement ratio of the concrete mix will be changed as a result of the excess water.
3. Concrete Mix Design
- Concrete sack mix. Is the number of sacks of Portland cement too high?
- Was a Fly Ash used to offset the amount of Portland cement? A type “F” fly ash can be used to control the amount of Portland cement in the mix and to increase the compressive strength of the concrete. There is a concern about the bonding once the fly ash reaches 20% to 22%.
- What is the water/cement ratio of the concrete? The lower the water/cement ratio, the higher the compressive strength of the slab, the less porosity of the slab, and the lower the permeability of the slab. ASTM F710 states the w/c ratio should not exceed 0.45, while the flooring industry states it should not exceed 0.50. Either way, the average in North America is 0.58.
- What additives were used in the concrete mix? There are admixtures used in concrete mixes that will impact both bonding and porosity of the concrete’s surface, making the adhesive selection important.
- What were the concrete slump test results? Is the slump at the time of the concrete pour too high for a slab for resilient floor covering? A slump of more than 4 inches is considered too high. If a water-reducing agent was used, you can throw the slump test away.
4. Concrete Slab Placement
- What was the date of slab placement? The time of year is important to the drying of the concrete. A winter-time pour is going to be as much as twice as long to dry as a summer-time pour.
- What were the weather conditions at time of pour? Was the pour of the concrete affected by the weather? Rain can create changes in the water/cement ratio of the concrete mix and dry and windy conditions can impact the curing of the slab. Direct sun can cause cracking.
- How was the concrete finished? The finish of the concrete plays an important role on the bonding of adhesives to the concrete surface. The texture of the concrete should be about the same as 100-grit sandpaper, especially for epoxy adhesives. The burnished or hard trowel finish impacts the drying rate and the bonding ability of the concrete.
- What’s the spacing of control joints? The spacing of the control joints should be 2-feet apart per 1-inch in thickness of the concrete slab for a ¾-minus aggregate, and 2 1/2 feet for ¾-plus aggregate. The control joint is placed in the concrete about 1-inch deep to control the cracking of the slab.
- What’s the spacing of cold joints? Cold joints, also known as expansion joints, are of constant concern to the flooring industry. Resilient manufacturers recommend that the joints be “honored” (able to expand and contract with temperature change) or have an expansion joint cover placed on them.
- Are there signs of concrete cracking? If there is cracking of the concrete, a determination must be made to as to the cause of the cracking. Cracking can occur from drying the concrete too fast, excessive bleed water or control joint spacing too far apart.
- How was the concrete cured? There are two types of concrete curing: wet and chemical. While the trend is turning back to wet curing, the time required for wet curing is sometimes compromised due to the fast-track construction demands. The time required for wet curing is determined by the water/cement ratio. Chemical curing is designed to hold the moisture in the slab while the concrete is curing. In cases of curing compounds that have been applied too heavily, they do not decompose in a timely fashion and the drying of the slab is extended.
5. The Status of the Building
- When was the structure closed-up? The sooner the concrete slab is covered the sooner the effective drying is going to be underway.
- Was there any type of heat used prior to the installation of the HVAC system? If so was the heat a wet or dry heat? Propane and heating oils produce a wet heat that retards the drying of a slab.
- What date was the HVAC system activated? The activation of the HVAC system ensures the stabilization of the concrete slab, the accelerated drying condition and drying of the interior finishes that can affect the flooring installation.
- Sprinkler systems. Are the sprinkler systems too close to the structure or are they spraying on the foundation?
- Vegetation. Is the vegetation too close to the structure? Landscape plants should be a minimum of 4 feet from a foundation to prevent moisture diffusion from entering the structure.
7. Moisture and Alkalinity Testing: Who's Responsible?
- Moisture testing. There are a lot of people who think that moisture testing should be done by a qualified independent testing agency. I agree: moisture testing should be done by an independent agency. Both the general contractor and the flooring contractor have a vested interest in the results.
- Moisture test results need to be documented to show both the high and low readings. Do not average the results. The areas that exceed manufacturer recommendations for moisture vapor emissions need more time to dry. Many of the flooring contractors have gone to the ASTM F2170 with the probes measuring the bottom of the hole at the 40% slab thickness. This is the most accurate method.
- pH test results. The alkalinity of the slab plays a huge role into the success or failure of the installation. The best time to complete an alkalinity test is at the finish of the vapor emissions test.
8. When the Installation Begins
- Temperature at the area of installation. 48 hours prior to the installation the heat is supposed to be on and stabilized. Failure to accomplish this will impact the stabilization of the concrete, handling of the material and open time of the adhesives. I rely on slab temperature rather than ambient temperature as this gives me a better feel for the concrete stability.
- Humidity. Humidity will also impact the materials, adhesives and the drying of patching materials.
- Lighting. The installer needs to be able to see what they are doing. Poor lighting hinders the installer’s ability to see imperfections that will show through the finished floor.
- Floor traffic. Are other trades going to impact the appearance of the finished floor? Many construction trades leave a trail of damage. Things like ladders, pallet jacks and heavy rolling loads destroy a newly installed floor.
9. Maintenance Procedures
- How soon was the maintenance of the floor started? Floor manufacturers recommend the floor maintenance should begin approximately 5 days after the installation. This allows the adhesives to cure to a point that maintenance will not affect the adhesive.
- Was the floor stripped? Manufacturers do not recommend their materials to be stripped. Strippers are high in alkalinity and have a impact upon adhesives.
- Was the floor sealed? New floors should be cleaned and sealed prior to application of polish. The sealer provides a base for which the polish is to be applied.
- How many coats of floor polish should be applied? Manufacturers recommend three to five thin coats of floor polish. A thin coat works better than a thick coat.