Floors and Sub-floors
A bathroom on the main floor or upstairs bath generally will have a plywood sub floor so for the sake of this discussion let’s just assume that this is the case.
Bathrooms not located in the basement generally will have better ventilation but this does not mean that they are immune from mold and mildew.
This can be a problem anywhere there is a source of water and mold can literally destroy a room.
It can eat up a sub floor and down into the room below. It can eat up drywall and grow on fiberglass insulation behind walls.
When renovating an upstairs bathroom floor the same principle holds true as in the basement bath.
Getting all the old flooring material removed is the safest and wisest thing to do in order to avoid future problems. Water leaks are frequently found around the tub or shower, especially on the floor at the front and back walls of the tub or around shower doors.
People often assume water leaked in these areas just dries up. Surely some does, but if any goes down cracks or floor seams, into the sub floor huge problems can result.
Assume you’ve got all the old flooring material pulled up and the old adhesives cleaned up.
By the way, dealing with old adhesive, whether in a basement on a slab floor, or elsewhere on a plywood sub floor you may have residue that you just can’t get removed.
The solution here is to cover it up. There are a couple of ways to do this. The easiest and least expensive is to use a highly pigmented solvent based primer such as Kills or Bulls Eye.
I’m recommending solvent based primer vs latex because the solvent base stuff penetrates both the wood and even concrete as well as the solvent itself.
The latex primers will cover the adhesive but they may bleed through later.
The other product to cover old adhesive are waterproof elastomeric coatings.
These go on like thick paint and leave a thin waterproof coat wherever applied.
At first thought it may seem like a great idea to paint the entire bathroom sub floor with this stuff, providing you can afford it. That’s probably not a good idea.
Keep in mind that its waterproof going both ways. If water gets underneath whatever you install as new flooring and sits on top of the elastomeric coat, some deal. The water has no where to go.
Another factor to be aware of with an electrometric coating is that although adhesive, and mortar will bond to it, they won’t penetrate it.
So whatever you glue or cement to it, is essentially floating on a very thin plastic film.
In the next post, I will talk about testing and patching the old sub floor, the use of underlayment products and water resistant bathroom walls.