Before you get started on any concrete coating job, the first thing you will need to determine is the moisture content of the floor. Concrete coatings are not breathable or moisture tolerant. What that means is that the coating does not like to have any moisture underneath of it, and because it is unbreathable it will not allow moisture to escape up through the coating. If too much moisture ends up getting trapped underneath a coating, the moisture pressure in the slab could become to high and the coating will start to lose its bond with the slab and delaminate. The same thing can happen if an excess of moisture collects underneath the concrete slab. Therefore, testing for moisture before you install a coating is incredibly important. While there is nothing you can do about moisture getting underneath the slab due to improper drainage after the coating is installed, a simple moisture test prior to installation can certainly avoid the problem before it ever starts.
There are a few different ways to test moisture in concrete-
Plastic Test-Start with a 2'x2' piece of 6mil plastic and tape it to the concrete floor. Make sure that it is laying flat on the floor and make so that all the edges are sealed off with the tape. You do not want any potential moisture to escape. After 24-48 hours, peel the plastic back up and see what it looks like. Does it have any condensation on it or not? Does the concrete look wet where the plastic had been placed? If everything looks to be completely dry, you should be good to go. If that is not the case and there does seem to be some condensation on the plastic and/or concrete, we know that we could potentially have a moisture problem. The plastic test is great for letting you know if there is or is not moisture present. One of the downsides however is that it does not give any measurable information on how bad the problem really is. The other downsides of plastic test are that it is slow (24-48hr) and can be time consuming if you want to test more than one or two spots of the floor.
Calcium Chloride Test- A calcium chloride test will require a few more items then the plastic test. You will need a calcium chloride moisture vapor kit, a postal scale, and a grinder with a cup wheel. Grind a spot on the floor slightly bigger than the test kit, follow the directions in the test kit for weighting the calcium chloride and placing the test kit box. After 72 hours, remove the test kit box and follow the instructions for re-weighing the calcium and calculating the reading. This test will give you a very accurate reading, the downside is having to grind the test spots on the floor, and it will take even longer than the plastic test. This test would also require a test kit for every spot you want to test.
Moisture Meter- There are some great electronic moisture meters that make testing moisture a lot faster and easier. The Tramex CME5 will give you an instant reading of the moisture content on as many spots of the floor as you want. Just make sure the meter is turned on, set it on the floor and push it down until it bottoms out. Hold it down until the needle stops moving, and you have your reading in under 5 seconds. Make sure you take readings from multiple spots on the floor especially along the exterior walls and around the drains. No concrete coating should be applied to a slab of concrete with a moisture content greater than 5% without taking the precautions needed to ensure long-term adhesion of the coating.
Moisture mitigation products like Moisture Shield Primer can be a great option on those floors that have an average reading of just over 5% and no spot on the floor is above 5-1/2. If the overall problem is worse than that or if there are spots on the floor where the needle on the meter pegs all the way to the right, more extensive measures will need to be taken. Just putting a moisture mitigation product that has excessively high moisture content will not guarantee long-term, adhesion. Most coating contractures don't have to deal with floors like this very often, but when it does happen it is important to have a plan for what to do next. The that you have tested for this and know about the problem before you've even started the job is key, at this point you have options and it would be better to not even do the job then to deal with coating delamination down the road. The first thing to do is start asking you customer some questions. How long has it been since the concrete was poured? Sometimes the slab just has not had enough time to cure out. The general rule is 28 days, but i have seen floors in certain situation that took well over 60 days for the moisture content to get down to 5%. Is there any busted drainage pipes or down spouts that are clogged? Most of the time if the moisture problem is concentrated in on corner of the floor along an exterior wall, there is usually a reason for the problem. It is better to focus on fixing that problem first, then let moisture content in get down below 5% and continue on with the project.
Please feel free to send us an email with any questions you might have about moisture testing or any other topic relating to decorative concrete. Jeff@deco-cretesupply.com