Should I be concerned about moisture with installing an Engineered Wood flooring over a concrete slab (on-grade)? We have been living in the house for 10+ years with carpet flooring and I don’t recall the carpet ever being moist (except for spills of course). However the room does feel a bit humid on a rainy Summer day. Should I be concerned about moisture affecting my installation?

This is the product I am considering installing: SolidPlus® engineered Flooring by Somerset Floors


You have to put something between the concrete and the engineered flooring. Whether this is a thermal barrier or plywood depends on what type of engineered flooring you put in and how much moisture the floor has.

All concrete floors have moisture. This might be next to nothing or a considerable amount, even in an unnoticeable way. To make matters worse the engineered flooring you are getting might be pretty closed system or rather breathable it is really hard to tell. Also with an on-grade install the moisture levels of the concrete can vary by season or year. Heavy rains for a month might cause a slight issue after 5 years of no moisture at all.

I have two pieces of advice:

  1. If putting engineered on an on-grade slab make sure the backing of the flooring is a real wood - in a hard plywood form. No mdf/mush/particle-board type of back - period. They will warp on you. I mention this because most stuff that is a decent price at most local stores will be made out of crap backing (don't care if it has padding or not). These products are only for the simplest of installs - on commercial type concrete or in a residential above grade. An easy test is take samples and put them in a bucket of water for a few hours, let them dry and see how they look. The other option is getting pure vinyl click lock which is getting pretty damn close to engineered in the way it looks. You have to look pretty close to tell its not a wood product for the good ones - which can also mimic tile.

  2. Follow the manufacturers instructions - call them if you need to. Not the store's instructions, the manufacturer's. If they tell you, you can install it directly on the floor but they suggest a 1/2" plywood - do the plywood. I personally haven't heard of many manufacturers of engineered flooring that will OK direct concrete install that is on-grade but who knows. Got to hit their website and call them. 20 mins of research can save you time and headache.

  • This is what I am thinking about installing, it is not cheap and they say it can be used below grade even. somersetfloors.com/pages/specialty.html#../images/collections/… Apr 4 '17 at 21:38
  • I looked at some vinyl floors and according to this link americasfloorsource.com/… they only last 10 - 20 years. That is not long enough in my opinion. Apr 5 '17 at 12:14
  • The specs on that look really good. You have 3/4" thick which to me is the perfect thickness for engineered (I buy only 5/8-3/4") and you have the 8 plies. I am gathering from the 8 plies it is a pine or birch layered plywood. I would be more than happy with what you have picked.
    – DMoore
    Apr 5 '17 at 14:54

The difference is that carpet breathes, and padding doesn't (as much), so you wouldn't have noticed moisture beneath the padding.

One good test is to securely tape down a sheet of plastic, say two feet square, and leave it for a few days. See how much vapor accumulates under it.

  • You can buy breathable padding now. There is padding specifically designed for engineered that will probably be the norm in 10 years. Even if you aren't install on slab if you have traditional padding and it doesn't breath , liquid from a spill from above can also take days to dry. There is a lot of stuff out now, just not at big box yet.
    – DMoore
    Apr 13 '17 at 16:02

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