There needs to be a 1/4" gap next to all walls to allow the flooring room to expand.
This gap should be covered with trim of some sort. The problem with baseboard alone, is that most baseboard is 3/8" thick, leaving only an 1/8" of an inch for the wood to contract without exposing the edge. This also assumes that the flooring is laid with tremendous precision, which it is likely not.
So your options are:
- Find thicker baseboards. Door and window casing comes in 3/4" thickness and can be used.
- Use quarter round or shoe molding to thicken the baseboard.
- Use door stop in the same way you would use shoe molding.
- Undercut the drywall so the flooring can expand underneath and use regular baseboard (thanks Matthew)
I had the 3rd option done in my basement, and it turned out pretty nicely.
I would also recommend the caulk. It makes everything look nicer.
@iLikeDirt covered a lot of important information, but I'd like to add something since the majority of the information assumes that there is a problem of excess moisture due to the concrete, while the expert assessment says it is actually dry cupping that is the problem.
Dry cupping implies that the interior humidity is dropping below the average frequently enough that the wood surface dries out. It sounds like they are suggesting that the vapor barrier between the slab and floor is probably doing its job correctly.
One way to help prevent this is to bring the wood into house and allow it to be exposed to the air within the home so the moisture content is similar to that within the home (acclimation). I like to assume this is standard practice and this was already done, but if you're using a special reclaimed antique pine wood, then maybe a longer period would have been desirable. Major seasonal humidity variation can still have an impact.
Do you know if there is a period during the year where it seems more prominent, or has it not been long enough? If I had to guess, it could be during the summer when the AC/dehumidifier is running more frequently. I'm not as familiar with the climate there, but in parts with cold winters you are more likely to encounter dry air issues during the cold months.
One thing that could be happening is that the glue on the underside of the wood is acting as a seal on just that side, inhibiting the wood from 'breathing' underneath. The only surface area for moisture to leave the wood is on top. A solution that allows the wood to better breath on the bottom, or simply avoids using glue or too much glue, might help. But then you need make sure the vapor barrier is doing its job or you will end up back where you started with too much moisture underneath, the expert seems to imply you no longer have that issue though.
You can still end up with this problem with engineered floors. It could still be a problem with an unknown source of moisture throwing things out of balance as well. I'd see what the neighbors are doing as a solution for your area and if they have similar problems before I spend more money.
Best Answer
I would have either
removed the door trims, trim as necessary then refitted after,
cut the door trims in-situ so that the new floor would slide under.
Have used both methods in the past - often depends on how hard it would be to remove the old door trim (sometimes they are so old they split), but cutting in-situ can be difficult - have used just a blade held in a rag as one solution.