Kitchen Subfloor repair

Hello Folks,

Bought a house 2 years ago in which the kitchen was subject to a slow but constant leak at the main water line. So, the subfloor got damaged and in order to repair it I removed big chunks of the subfloor and replaced it with two layers of plywood: ¾ plywood sheet with ½ higher grade plywood on top of it. All the rest of the subfloor seems to be solid and good with the exception of the fact that back then in my stupid rush to dry the subloor I removed some of the plys of the good plywood as shown below:



I plan on using thinset mortar and cement board throughout this small kitchen to then install ceramic tiles there. So, I was wondering whether or not simply filling the plywood with missing plys would suffice?

Another issue that is not easily seen on the pic above is that I used a circular saw to cut and trim the cut of the old plywood subfloor bad portion and unfortuantely I am not good at making precise cuts without much of a reference and with obstacles along the way, as a result it was left with gaps of close to to ½” in some spots. 2X4 lumber was also attached to the joist as extra brace wherever and whereon the edges of the new plywood would lack proper support.

Any insights on how to approach this repair would be welcome.

What you didn't tell us is that the top sheet is bigger than the bottom sheet so the joints are over lapped.
For the gaps between sheets, the trick would be to lay a 6" strip over the crack and mark out a new cut line on old and new plywood and set the saw depth. then a patch will fit nicely.
Screws holding sheets together and longer screws into the joists.

nealtw said:

What you didn't tell us is that the top sheet is bigger than the bottom sheet so the joints are over lapped.
For the gaps between sheets, the trick would be to lay a 6" strip over the crack and mark out a new cut line on old and new plywood and set the saw depth. then a patch will fit nicely.
Screws holding sheets together and longer screws into the joists.

Click to expand...

The top and bottom sheet are about the same size. The main difference is that the top sheet is a single sheet whereas the bottom one are two sheets (one sheet halved).

Shouldn't I use large screws (3") to join the bottom sheet to the joists and then use smaller screws to join the top sheet to the bottom on (instead of aiming upon at joining the top sheet to the joist). On top that there will be cemenet board too.

Maybe the gaps are not so large, I will try to take a pic with close up view.




thks

Instead of me asking a bunch of questions Lets go with what would have done and you can see how close you are to that.
Plywood sub floor are tongue and grove so when you walk on one board it does not bend independent of the next sheet.
You stated you added 2x4 to catch the end of the sheet, good but for the side where there is no T&G we would add 2x4 blocks under the joints length ways on the flat between the joists, don't have to be tight to the joists just screwed into from above. With 1/34" screws and longer when screwing thru 2 sheets
I would screw the first sheet to the joist first with 1 3/4" screws .
And then screw down the second sheet with same screws with a 8" by 8" pattern and if the rest of the floor has 2 sheets screw that together with the same pattern.
Keep in mind the screws or nails that just miss a joist is a great source for squeaks later so anything that is questionable when you drive into joists should be removed.

nealtw said:

Instead of me asking a bunch of questions Lets go with what would have done and you can see how close you are to that.
Plywood sub floor are tongue and grove so when you walk on one board it does not bend independent of the next sheet.
You stated you added 2x4 to catch the end of the sheet, good but for the side where there is no T&G we would add 2x4 blocks under the joints length ways on the flat between the joists, don't have to be tight to the joists just screwed into from above. With 1/34" screws and longer when screwing thru 2 sheets
I would screw the first sheet to the joist first with 1 3/4" screws .
And then screw down the second sheet with same screws with a 8" by 8" pattern and if the rest of the floor has 2 sheets screw that together with the same pattern.
Keep in mind the screws or nails that just miss a joist is a great source for squeaks later so anything that is questionable when you drive into joists should be removed.

Click to expand...

I am not using tongue and groove plywood, instead I am using plain and flat plywood boards.

"Keep in mind the screws or nails that just miss a joist is a great source for squeaks later so anything that is questionable when you drive into joists should be removed
"
Yeah, I will keep that in mind. And normally I trace and number the spots where the screws will go, so the next layer of screws will not coincide or conflict with the lower layer. Also, I use a straight edge to determine where the screw will go. Then to double check, I send a drone to the crawlspace to make sure there has been no screw missing in action. :nono:

I used 2x4 or 2x6 blocks in all joints to increase the support even when there enough support present by the joist itself.

Some older pics showing the bracing added:



Ok, I will switch to smaller screws, 3" seems to much in this case. The idea of a pattern is important to avoid the screws from meeting each other.

thks

The blocking I was talking about is the space between you black arrow and the other joist and from the pink level to the other joist and so on

I added some blocks perpendicular (and some boxes made out of 2x4s) to the joist in a spot where it seemed needed, but then simply adding block parallel to the joists (as shown in the pic) seemed to significantly increase the surface area to screw the subfloor boards.

In some case, I did not add any blocking like the following:


since the plywood boards were almost perfectly aligned with the joists, but in hindsight I should add extra blocking anyways.

Isn't that enough blocking?

If you second sheet was going to overlap the first joint you would likely be fine.
What you are trying to do is make the floor one big sheet that moves and bends as one.
In this photo see where this guy added to the joist but also added 2x? on flat to join the sheets on all sides

nealtw said:

If you second sheet was going to overlap the first joint you would likely be fine.
What you are trying to do is make the floor one big sheet that moves and bends as one.
In this photo see where this guy added to the joist but also added 2x? on flat to join the sheets on all sides

Click to expand...

Yeah, I see. But in this case it is a small piece that would lack support on its edges in case it lacked a box surrounding it. All the edges of my boards end in joists, and there are joists in between the edges adding more support. I assume you mean to add blocks to the lateral edges of the board (all the way around); is it really necessary? The previous subfloor did not have this extra support either.

I add a similar box in some situation too, but that was because the board would smaller, the following:

really necessary not sure, I don't think there is way to know for sure. I doubt you will get much flex with plywood 1 1/4 think but if you are going over this with cement board make sure you have no joints any where near these.

I think your job so far looks pretty good. all you can do is work with what you got and add blocking as required. Any patching I do without T&G edges I make sure I have support all the way around as you did and at least 16” OC in between. If it’s 17” I might skip it but if it was 24” I would add one in the middle. IMO once you get into patching all you can do is look at each area as a new problem and add in as much as you think you need and then add more. Lastly before I button it up and call it good I stand on it and give it the jump test. It should feel as sturdy as anyplace else in the floor you haven’t touched.

You should be good that’s a nice thick layer of plywood. When you have multi layers as best you can never have the seams line up and when it can’t be avoided use plenty of screws.

Having a minion in the basement directing the fire is a nice idea also.
:thbup:

bud16415 said:

I think your job so far looks pretty good. all you can do is work with what you got and add blocking as required. Any patching I do without T&G edges I make surel I have support al the way around as you did and at least 16” OC in between. If it’s 17” I might skip it but if it was 24” I would add one in the middle. IMO once you get into patching all you can do is look at each area as a new problem and add in as much as you think you need and then add more. Lastly before I button it up and call it good I stand on it and give it the jump test. It should feel as sturdy as anyplace else in the floor you haven’t touched.

You should be good that’s a nice thick layer of plywood. When you have multi layers as best you can never have the seams line up and when it can’t be avoided use plenty of screws.

Having a minion in the basement directing the fire is a nice idea also.
:thbup:

Click to expand...

Thanks! I will peruse large screws to make it more solid and avoid future squeaks. I see so many new constructions whose floor is already in a state of squeaking all over: it seems that they are always polarized by cost and time and use a nail gun all over.

The joists in this floor are 16" apart, and the two layers (3/4" lower layer + 1/2" upper laywer) have the upper layer halved but the lower layer is a single uniform piece of about the same two halves above.

Yeah, I planning on adding some small pieces of 1/4" plywood wherever there is more than 1/4" of plys missing (but it is really minimal), other than that I will simply even it out with thinset mortar and then lay the cement boards.

Slowly I am also building new kitchen bottom cabinets, and it seems that most of the time installer do not put cement board and flooring on the spots where the cabinets will be present. But it seems to me that I want to change cabinets or its position in the future having a proper floor under the cabinetry would be a good idea.

I will have to deploy a drone down in the basement to be a vigilant against fires and whatnot :rofl:

IMO glue and screw = no squeaks.

I put my flooring under the cabinets also. Has worked out ok so far.