When laminating floors, is fixing plywoods necessary?
Yes. It is necessary to replace rotten floor boards when applying laminate. If you have carpet now the little dips in any warped boards is not noticeable. Laminate will not stick properly to the wood if it has a lot of rough spots or knotholes. Also, depending on the age of your house you may want to consider having it leveled before putting in new floors. To tell if your house needs leveling is very simple. If your doors swing open or close by themselves is an easy way to tell. Or if your doors are hard to open or close.
I’m assuming you mean when installing laminate floors? Yes it is important to have a sound and level subfloor. Are you gluing down or floating the floor? Here is a site which tells all about installing laminate flooring and includes instructions on how to do it yourself. http://www.findanyfloor.com/InstallationGuides/InstallingLaminateFlooring.
