I have this small corner of floor next to the tub in my bathroom where water got in at one point (very long ago it seems), so I’ve peeled back the VCT and vinyl floor layers to reveal that the top layer of the wooden subfloor had crumbled due to the water. There is a very solid base under that top layer.

How should I repair this? Could I just patch it with something like this product? I have done large areas of subfloor patching for a flooring installation so I know that for certain products there are very strict requirements for the condition of the subfloor for it to take the patch so I’m wondering if there’s something that works for this type of situation.

(This is a follow up of my previous post here)


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I would suggest cleaning out all the rotted material back to sound material, which will most likely mean going down to the subfloor level. If one or two layers of the underlayment veneer are left in place that are "sound", then that layer won't be stable enough to hold the filler since the plywood underlayment needs more layers to keep it from moving once the moisture from the leveler is introduced to it.

I would find a way to score the old underlayment so it cuts to the subfloor, but not into it, at least not by much, maybe a 1/32" or 1/16" or so. and remove the rotted underlayment. A circular saw set to depth will work for most of it, and an oscillating tool would cut the corners quite handily, but if you do not have access to an oscillating saw//tool then a sharp chisel will do the trick too. Screw down the fresh cut perimeter of the old floor since there is no way to know where the other fasteners are that may or may not be holding the cut edge down. Then after the depth is measured you can get a 2X2 piece of the proper thickness of plywood to fill the area you cut out after it is cut to size. Big box stores has small pieces for repairs like this. Screw this in place. Using the flash patch/filler, level any discrepancies to the surrounding area.


I think you will be ok patching if it is still solid underfoot, as you say it is.

I would use a hard-setting plaster patch (sometimes called by trade names like Fixall, Fix-It All or Water Putty) after removing all crumbly unsound material. It can be difficult to get setting plaster smooth and level, so what I would do is use it as a base for regular floor-leveler, which can be troweled perfectly level and smooth for blend with surrounding floor. Then install your LVT on top.

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