Putting turf on a basement or garage concrete floor

Dry slab first, turf second

You can lay turf on a basement or garage slab for a putting area or a home gym. What decides whether it lasts is the concrete underneath. If moisture keeps reaching the underside of the turf, it has nowhere to go. A damp, dark layer pressed against the floor is where mold gets started.

So the order matters:

1. Find and fix any water.
2. Test the slab.
3. Choose the turf, pad and attachment to suit the result.

Two ways a slab gets turf wet

EPA’s basement remodeling guidance names two problems with carpet laid over a slab:

• From below. Liquid water or water vapor can come up through the slab. EPA says that causes chronic dampness in the carpet, leading to mold growth.
• From the air. A slab is often cooler than the room above it. Moisture in the air can condense on it, and EPA notes this is more likely under carpet, which insulates the slab and makes it colder still.

EPA wrote that about carpet. Turf goes down on a slab in much the same way: a backing, sometimes with a pad, lying directly on the concrete. The same two questions apply.

Outdoors, water that gets through the turf drains into a compacted stone base. Our article on what goes under artificial turf walks through those layers. Indoors there is no base to take the water, so the slab has to be dry to begin with.

Why a dry-looking floor is not a test

A slab can look and feel dry and still hold water. EPA’s Moisture Control Guidance, published in December 2013, describes concrete floor slabs as very porous and able to hold a great deal of water. It says concrete must be thoroughly dry before it is covered by water-sensitive materials such as carpeting.

The same guide makes two more points worth knowing before you buy anything:

• Manufacturers set limits. Floor covering makers specify the most water vapor a slab may give off before their product goes on it. Covering a slab above that rate can make the covering fail and promote mold growth.
• Old slabs count too. EPA recommends measuring the slab before a covering is installed, even when that happens long after the building went up.

The moisture tests, in plain terms

EPA’s guide notes that an ASTM guide lists eight ways to test a concrete floor, and it names the two most common. A third, quicker check also exists.

Relative humidity probes (ASTM F2170). A hole is drilled partway into the slab, and a probe measures the humidity of the air inside that hole. ASTM’s summary of F2170 says too much moisture in a slab after a floor covering goes down can make the covering fail. It adds that manufacturers generally require moisture testing before installing on concrete.

Calcium chloride (ASTM F1869). A canister of calcium chloride is weighed, set on the slab under an airtight plastic dome for 60 to 72 hours, then weighed again. The result is pounds of water vapor from 1,000 square feet over 24 hours. ASTM’s summary of F1869 gives two limits:

• The result reflects the floor surface on the day of the test, and may not indicate later conditions.
• It is not for gypsum concrete or floors made with lightweight aggregate.

The plastic sheet method (ASTM D4263). This practice indicates whether capillary moisture is present in concrete, and ASTM frames it as a check before coatings go on. It tells you moisture is there. It does not give you the reading that F2170 or F1869 produce.

Which test you need is not a matter of taste. Use the method the turf and pad instructions name, and compare your result with the limit those instructions set.

Fix the water before you test

Testing a slab in a room that still leaks tells you what you already know. EPA’s remodeling page puts moisture first: deal with it up front, and look for leaks or other signs of a moisture problem before a basement becomes living space.

Start with the room:

• Humidity. EPA’s guide to mold and moisture says to keep indoor humidity below 60 percent, ideally between 30 and 50 percent. NC State Extension’s mold and moisture checklist suggests a dehumidifier if it reads over 60 percent.
• Cracks. The same checklist says to inspect the floor for foundation cracks, and to check outside as well, because they may lead to the exterior.
• Outside water. EPA lists missing gutters and water flowing toward the house among the causes of water in a basement.

Then test, once the fix is in place. A calcium chloride result describes the day it was taken, so a reading from before the repair says little about the floor after it.

Pouring a new slab, for an addition or a new basement? EPA’s design guidance calls for a vapor retarder sheet directly under a basement floor slab, to stop water vapor coming up through the floor. Under an existing slab, that choice was made the day it was poured. Testing is how you find out what it means now.

Basement putting greens and garage gyms

The floor question is the same in either room. A garage floor is a concrete slab too, and EPA’s point that slabs are porous and hold water is not limited to basements.

What changes is what goes on top. A putting green and a training floor with sled lanes ask different things of the turf and pad. For indoor turf, we check the existing floor, the transitions to other flooring and the attachment method before a system is chosen.

When water gets on it later

A slab that tested dry can still meet a spill, a leaking water heater or a burst pipe.

EPA’s guide says to dry water-damaged areas and items within 24 to 48 hours. If wet materials are dried in that window, in most cases mold will not grow. It also warns that porous materials such as carpet may have to be thrown away once they are moldy.

For turf on a slab, that means asking a question before it goes down: if this ever gets soaked, how would you dry the concrete underneath in time?

Before turf goes on your concrete

1. Look for leaks, stains and cracks in the floor, and check the outside of the wall too.
2. Measure the room’s humidity. Keep it below 60 percent.
3. Fix water and humidity problems first.
4. Test the slab with the method the turf and pad instructions name, such as ASTM F2170 or F1869.
5. Compare the result with the limit in those instructions, and keep the report.
6. Plan how you would dry the floor within 24 to 48 hours if water ever gets under the turf.

On the free visit we measure the room and look at the floor with you. Then we draw a custom layout for you to approve before any work starts. Call 303-349-2368.