Sealing OSB subfloor from moisture? Patching small gouges?


What are some methods that can be used to seal an OSB subfloor from moisture? And patch small gouges (quarter sized)?

Background: Small Bathroom remodel. Tile came up with finger pressure, underneath was Gypsum Concrete (Gyp-Crete or Pyrofill). It was crumbled, mildewed and in loose chunks two foot around the tub, and a foot around toilet and vanity. Removed it all to the door threshold to set new tiles. OSB is in great shape, but there is a tiny bit of mildew on the surface in a few spots and some small gouges where the Gyp-Crete took up a quarter-sized strand. Will either go with HardieBacker 500 or self-leveling concrete to raise floor up to height to tile. To remove the mildew, I've done light sanding and sprayed bleach solution and spread it with a rag. I plan to fill the gouges with epoxy (unless there is a cheaper recommendation. Epoxy is a bit on the pricey side). I'd like to moisture seal the OSB also since moisture has found it's way down there in the...

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Love it or despise it, OSB is here to stay. But how well suited is OSB for flooring or subflooring? Are there any better options available?

OSB Defined

OSB stands for oriented strand board. OSB has the appearance of giant cornflakes pressed together to form structural panels in sizes similar to plywood, such as 4' x 8' x 5/8".

OSB: Floor Covering vs. Subfloor

Floor covering (or finish floor) is the term for the topmost, eventual floor--the floor that you walk on and see.

Laminate, luxury vinyl, and ceramic tile are examples of floor coverings.

OSB is generally unsuited as a floor covering:

Appearance: OSB is not attractive enough to serve as a floor covering. Not only is the chip-board appearance unattractive, the surface is often marked with grid lines and manufacturer markings. Moisture: OSB, when exposed to the weather, will eventually swell and bubble up. Minor instances of bubbling can be sanded, but for the most part the OSB...
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Posted in Builders, Dealers, DIY, Framers on June 7, 2017

Knowing the moisture content of your OSB sub-floor panel is an important indicator on whether to proceed with other stages of the build, especially if hardwood flooring is the next step. You need to know that using a moisture meter doesn’t give very accurate measurements with OSB or other glued products.

The problem with using moisture meters with OSB is that the adhesives/binders and waxes skew the readings, making the use of specific gravity as the calibrations basis unreliable.

One option that can help meters work better with OSB is to first calibrate the meter by checking a piece of the same OSB that is known to be “dry” (OSB from northern mills is typically Aspen while southern mills it’s Southern Yellow Pine). Then, with the meter properly adjusted to the “dry” OSB, check the sub-floor that may have an elevated moisture content. Always take numerous readings in different areas in order to provide...

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An OSB subfloor is a subfloor made from oriented strand board (OSB), a manufactured wood product. OSB is often used for sheathing in floors and walls, and in some regions, it is the building material of choice. As with other engineered wood products, OSB comes in a range of thicknesses and styles, and it is important to make sure that the appropriate product is used.

A subfloor is a rough floor made from sheathing which is attached to the joists of the floor. Other flooring such as tile, carpet, wood, or stone is fixed on top of the subfloor. The subfloor needs to be durable and strong, as it is part of the system which supports and distributes the weight of the house, but it does not need to be particularly attractive, because no one is going to see it. OSB subfloors may not look pretty, but they certainly do the job.

At first glance, a sheet of OSB looks sort of like someone took a bunch of wood chips, glued them together, and compressed them into a sheet. That's...

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