how to prepare for new underlayment


Old 07-16-04, 10:07 AM
Thread Starter
Join Date: Jun 2004
Posts: 34
Question how to prepare for new underlayment

Hi all,

I need to lay new underlayment in my kitchen and bathroom. I think we will be going with 1/4" plywood in the kitchen for vinyl or linoleum floor and backerboard for tile in the bathroom.
I want to go with 1/4" so the step-up is not too noticeable as you come into the kitchen from the dining room (which has the original fir floors.) This might be too thin, though...
The kitchen and bath both have some old asbestos tile in places, which I don't want to mess other places (like under where the cabinets used to be) it's just the fir flooring, so there is a slight height difference between the two).
If I lay the 1/4" ply down, will this difference be noticeable?
What if I go up to 1/2"?
Do I need to level the surfaces with a leveling compound before laying the underlayment?
If so, what is a good compound to do this with?
Thanks for your help!!!!
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Old 07-16-04, 12:06 PM
Join Date: Jul 2004
Location: Chester, IL
Posts: 285
For the kitchen, unless you have some pretty big bumps/valleys/etc you shouldn't need leveling compound. Where the cabinets used to be you can lay in some plywood of equal thickness as the asbestos tile to take that space up. However, if you are going to use compound then why not just lay the tile/vinyl over that without using underlayment. If you're worried about the tile not sticking (as in with the self sticking 12x12 tile you can get), you can get a bucket of floor adhesive (check the bucket label for whatever type of floor you are using) and use that. But if you use underlayment 1/4" should be fine, and a regular offsetting threshold should cover the step pretty well.

Now for the bathroom, or anytime you are putting down ceramic tile, you will need to use concrete board (I assume that's what you meant by "backerboard"), but I think, unless your sub-floor is VERY sound, I would go with at least a 1/2", any flex in this at all, after the tile are set, will cause the grout to crack at very least, and could possibly crack the tile itself. If you use 1/2", that will create a 7/8" (1/2" concrete + 3/8" tile)step from one room to the other (assuming the rooms are level now). I'm not sure about a threshold for this, I personally have never seen one with that much offset, but that doesn't mean they don't exist.

1. What room is adjacent to the bathroom? Is it a large room or a small hallway? and what tpe of flooring is in it?
2. How thick are the asbestos tile?
3. Are the asbestos tile in good shape? (which would somewhat indicate if the subfloor needs concrete board at all) I know that's contradictory to what I said up there, but if the tile are in good shape, the subfloor is probably in good shape and you MAY not need to back the ceramic tiles, which would make a smaller step-up.
4. Are the 2 rooms and their respective adjacent rooms level in their present state? or how much offset is there, and which room is higher?

P.S. - the problem with removing asbestos is the dust it creates when broken not the material itself, so if you could remove it(if you need to) without alot of breaking, it wouldn't be such a bad thing.

Anyone more familiar with asbestos tile please jump in about the subfloor requirements.
Old 07-16-04, 01:37 PM
Thread Starter
Join Date: Jun 2004
Posts: 34
wow, thanks for the quick response!

To answer your questions

1. Outside the bathroom is a small hallway off of the kitchen, which means it will be getting the same 1/4" subfloor treatment as the kitchen.
2. The asbestos tile are very thin, 1/8" or so, but there are also some dips where the original fir floor has some dry rot (under where the fridge used to sit, which will now be covered with cabinets). Is there such a thing as 1/8" plywood? Or 3/8"? if so I could use 3/8" where there is no tile and 1/4" where there is and they should match.
3. I should clarify, I think it is the adhesive that is asbestos, not necessarily the tile. It is black and fibrous looking. The tile is under where we pulled up the existing subfloor. The floors are pretty rough and I feel like new underlayment would make a big difference.
4. The 2 rooms are adjacent and are at the same height the difference between the two would be ~5/8" with tile in the bathroom and plywood/vinyl in the kitchen/hallway...

Old 07-16-04, 03:46 PM
Join Date: Jul 2004
Location: Chester, IL
Posts: 285
OK...if those are the only 2 floors involved, and u say that the difference when finished would be 5/8"...I'm assuming you mean the kitchen would be lower than the bathroom...if this is the case, just use..say ....3/4" plywood in the kitchen and reduce the step to 1/8", easily taken up by a regular offset threshold....also if you use 3/4", you won't need to fill the space where there is no tile (under the original cabinets)...3/4" is plenty strong to hold close enough you would never notice it, or you could find a 1/8" strip of some kind and just put it all the way against the wall(longways)...nothing fancy or well fitting, just something to hold the edge of the 3/4" up a little, and maybe another about mid-way in the gap, and the rest will hold up by it's own strength.

I don't know what area you're in, but if 3/4" is expensive, compare the price of the other close sizes....sometimes true 3/4" is reallllllly high, but nominal 3/4" (which is, I think, 23/32") isn't so bad, and the extra 1/32" will still be covered quite easily by a regular offset threshold.

Just a few thoughts, post back any more questions or let us know how it's going as you proceed.
Old 07-19-04, 08:50 AM
Thread Starter
Join Date: Jun 2004
Posts: 34
Well, seems like I was worried for no good reason.
The plumber was in this weekend and needed the subfloor down.
So I went plywood shopping (Yeah, it is REALLY expensive!)
Got 1/2 inch and it nailed down perfectly!
No leveling compund, nothing.
I went back and forth between 3/4 and 1/2", but the miser in me won out and I decided it was worth it to save $50.
Thanks for all the help and thoughtful reponses

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