I am called to inspect probably twenty to thirty solid hardwood floors every year that after several weeks or months have started gapping. A quick reminder: solid hardwood floor planks are each one piece of wood, whereas engineered wood planks are several different layers of wood glued together-very much like plywood. Once-in-a-while I’ll see an engineered wood with gapping. In either case, it is a serious and very expensive problem. If you will take the time to read the rest of this article, you can be sure this won’t happen to you, I promise.

“Moisture levels” are very important with solid hardwood flooring. All wood has moisture of some amount. When a solid wood floor has been installed, especially if nailed/stapled in, and then starts gapping at the seams so that there is space between adjacent boards, it is because they have shrunk. The only other possibility is that your house has expanded, but I’m pretty confident that has never happened and never will. So, why did the boards shrink? Because they lost moisture since being installed. When wood dries out, it shrinks, when it gets wetter, it expands. Okay, now we’re getting to the very important part.

Most people are familiar with the term “acclimation”. Most people know that wood flooring, even laminates (like Pergo) is to be acclimated before being installed. Usually the instructions say to acclimate for 48 hours, or 3 days, or whatever, then install. THAT IS NOT CORRECT. If you acclimate the product as outlined by the manufacturer for the proper time, then install it, and then it gaps, it will not be warrantied or replaced by the manufacturer. The small print on flooring installation is this: when the installer installs the flooring, he/she accepts that the flooring and subfloor are suitable for installation. The problem is, sometimes the wood flooring is showing up at the house to be acclimated at 15% moisture level, and is to be installed in a home with the subfloor having 6% to 9% moisture level. There is no way that flooring can acclimate to those conditions in a few days. It will still be too wet. And after it is installed, it will shrink-causing gapping. And the worst part, the flooring will have to be pulled up and thrown away. It is not a correctable situation.

I need to interject one small point here. “Some” gapping on solid hardwood flooring is very normal, especially if you live in an area with real seasonal changes like I do eastern Washington. Our homes here will invariably be drier in the winter and wetter in the summer, causing some minor gapping and is perfectly normal. One sure way to know if the gapping is normal is if it pretty much disappears each year during the wetter time. But the gapping I’m talking about is not like this. One lady showed me how some spaghetti that had fallen on the floor had rolled into the gaps. Or if your missing one or more of your favorite pets-that is also a clue.

THE SOLUTION So before this horrible scenario happens, make sure the following is done before your new floor is installed. The flooring needs to be moisture checked with a wood meter. There are pin meters (invasive) and magnetic (non-invasive), either of which will work. However, these run $200 to $300 or more. Insist that the installer have the moisture checked, especially as it will be the installers BIG problem if later you have gapping. Because you know what will happen? The manufacturer will send me to look at the floor, I’ll make a lot of measurements of dimensions and moisture levels, and using the Wood Handbook’s coefficient of dimensional change tables, I’ll be able to determine what the actual moisture level of the wood was at the time of installation. I’ll find that it was too high (or WAY too high), and the finding will be that the wood floor was not acclimated to the home’s normal environment before being installed. OUCH! That will cost somebody a lot of money, and will cost you at least a lot of hassle with the issue of replacement, etc. You don’t want that, and neither do I.

By the way, engineered wood should definitely be acclimated as well, although some of the manufacturers do not want the cartons opened for acclimation and some do, so pay attention to that. Also, laminates (which are real layers of wood similar to engineered except for the top layer which is melamine (aluminum oxide or similar) are also to be acclimated but I’ve never seen a claim rejected because the floor wasn’t acclimated. Typically laminates and a lot of the engineered woods are “floating” which means they connect together and become one unit. Any dimensional change does not normally cause gapping but rather a change of the amount of clearance (perimeter expansion space) at the walls. Some of these issues I’ll cover in another article.

TO SUMMARIZE: With any kind of wood flooring, but especially with solid hardwood, be sure that the moisture levels of the wood is within 2% to 4% of the subfloor the flooring is going on top of. In my part of the country where the relative humidity of homes is usually between 25% and 40%, the flooring should be between 6% and 9% before being installed. That leads to one of my favorite phrases, “IMAGINE NO GAPPING!”.

Source by Steven Kohl