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We wish to lay new flooring above our existing chambered edge flooring. The existing floor is nailed to a plywood sub-floor and is completely flat, about 20 years old.

This will make the whole house one even level with no raised sections across all 1st floor rooms, additions, and kitchen without the need to remove perfectly good tiling and engineered hardwood in the existing additions and kitchen.

"OK to do?" I.E. Is it acceptable to edge glue tongue and groove, non locking, engineered hardwood to make floating floor over existing varnished hardwood flooring that has chamfered edges ?

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Yes, you can “edge glue the tongue and groove edge” provided: 1) tight fit between T&G edge, 2) temperature and humidity remains constant, 3) sub-base is stiff enough not to flex

1) The most important element is the “fit” between the tongue and groove. This “fit” must be tight...not snug, but tight. The way to check this is to pick up a board and hold it vertically. Then try to push another board into the groove. If it goes in easy, that is not acceptable. In fact, you’ll probably find that when it’s inserted all the way in, it will slide out (from just its own weight) and fall on the floor. (Don’t just check a few boards...check about 50%)

2) Fluctuations in temperature and humidity will cause the wood to grow and shrink. Obviously bad.

3) If the sub-base is not stiff enough the wood will “flex” and break the bond.

I wouldn’t. I’d install it as per the National Wood Flooring Association (NWFA) intended, by power nailing.

If you glue, you know you’ll still need to sand, right?

  • Thanks Lee, makes sense, appreciate your response. I agree that power nailing is superior in every way. If we went that route, would power nailing into the existing hardwood be taboo from an expert's perspective? We have to resolve this mismatched flooring levels problem and it's just not gonna happen if we have to rip up these chamfered boards which are already a layer too low compared to the rest. It's the main/central floor and the rooms connected to it are all a step up and it's not only an eyesore that can't be hidden but it drives us crazy every time we cross a threshold. – MouthBreather May 9 at 4:29
  • @MouthBreather There are many options to floor systems. My favorite is installing 25/32” or 33/32” thick wood T&G flooring on 1 1/2” thick Sleepers on 1” thick cushioned pads on 6 mil polyethylene vapor barrier. The wood flooring is nailed into the sleepers and the whole floor “floats” on the cushioned pads. If that thickness and system doesn’t work for you, there are others that use plywood, etc. However, never nail into the existing flooring, subfloor, etc. If it’s too low, you could furr the lower area first before you install the new flooring...then everything would be level. – Lee Sam May 9 at 6:10
  • The reason the boards are nailed and not glued is because real wood expands and contracts due to temperature and humidity. If it’s glued, it puts a tremendous stress on all the joints during this expansion and contraction. If it’s nailed,it allows a slight movement between boards (which you’ll never see). I think it’s impossible to keep the room at the same exact temperature and humidity. – Lee Sam May 9 at 6:17
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The original pergo flooring was tongue and groove you glued it and used special straps to pull it together to dry. So it can be done but a thicker tongue and groove may not hold up well because it is not as flexible as the pergo was. At a minimum I would build some straps using 1' cargo ratchet straps as the starting point then a couple of L brackets to hook on the edges to pull them tight together, this is how the original pergo system worked I think I had 4 straps that was enough for large rooms. I might try to assemble an area let it dry and try walking on it just to make sure it dosenot split.

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