We purchased a house that is 105 years old about 5 years ago. Twelve years before we purchased the house the house was remodeled with new electric, plumbing, and subfloor… We have been remodeling since we purchase the house. I am now looking to remodeling the guest bathroom. I am removing all the appliances, stripping the walls down to the studs and, replacing the subfloor.

The subfloor has two layers. The original tong and groove floor and ¾“ particle board. As you might expect, over the years the particle board has gotten wet and has swollen up in areas. I am going to remove particle board and replace it with ½” BC exterior grade plywood.

Because it is a 110 year old house the bathroom floor is not completely level and has one area that is about ½” below the average grade of the floor. I am considering using a self leveling product on top of the tong and grove floor, then covering the floor with 15 pound felt and then installing ½” plywood screwed down on a 6” grid pattern. I will then float out the screw heads and seams and lay DuraCeramic floor tile with 1/8” grout spacing.

My questions are:
1. Is this a good plan? If not, suggestions would be greatly appreciated.
2. What self leveling product would you recommend? In selecting the self leveling compound, weight is a consideration.

Thanks in advance for your assistance.

Lonny

Hi Lonny...

I've been remodeling bathrooms for over 20 years now, but I am not a tile/floor guru by any means. I can say with pride, however, that I learned from some of the best when I was a kid and I have tried to keep up with the latest and the greatest.. SO...

In my opinion, remove the particle board (as you suggested), and if you want the best tile job, remove the tongue & groove flooring as well. T&G flooring will inevitably cause a buckling to the flooring you install and could be a costly mistake.

I would then install a 3/4" tongue and groove plywood (I just like this stuff for many reasons) or a 3/4" exterior grade plywood and then install a 1/2" cement board in a layer of thinset (using 1/4" trowel). Tape all the joints using an alkali-resistant tape and use alkali-resistant screws as well.

This should make the floating of that 1/2" unnecessary if you are lucky. I would definitely not lay any tile over plywood... ;)

Let us know if you want to discuss more...

Finally, please wait to see what some of the other pros think...just to be 100% on this...O.K.?? Every state seems to have a different method. You need to choose best for you.

MARK

PS: If the old T&G flooring is a true 7/8" or larger, let me know...O.K.??

When I take the toilet out I'll measure the T&G and let you know.

Lonny

Quote:

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Originally Posted by Our_Old_House

The original tong and groove floor

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Is the sub floor really tongue and groove or just 1X boards running on a diagonal?

Harold,

The floor was the original floor laid 110 years ago. It is completely covered by a second layer. I assumed it was T&G but have not been able to see an end section to determine the depth or structure. From the crawl space each 3 1/2 " board is very tight together with no visible space between the boards. That led me to believe it was T&G. I'm not sure about the exact width measurement of the boards. I will check it next time under. When I remove the toilet and toilet flange it will give me a good view of a end section of the boards and I can determine the depth and structure of the boards.

Lonny

The use of any self leveling product would be used over the top layer of plywood, not between the layers. Trying to drive nails or screws through it would tear it apart and really make a mess for you.

You specifically mention "duraceramic" as your floor covering, which is a vinyl composite floor covering and as such, the rules governing a ceramic install don't apply, but if you use some ceramic prep materials, the rules for those materials would apply.

Keep in mind that your floor covering will in 99% of situations, no care one bit about level. It will care about flat, so even if a room dips to one side, as long as it's flat, then most often, OK.

You could install a layer of 1/2" plywood over the plank subfloor, bc or better plywood, long edge crossed the joists, and the short edge lands 2-4" past the joist, not on it. Fasten it every 6" around the perimeter and every 8" within the field, using corrosion resistant deck screws, only to the subfloor and not to the joist. You need a 1/8" gap between panels and a 1/4" perimeter gap.

Over top of that, you could pour self leveling cement. On plywood, the minimum depth is usually no less than 3/8" with diamond lath first stapled to the plywood and the appropriate manufacturers primer used as well. SLC will find every spot where it can run through the floor to the space below and you also need to maintain the perimeter gap with the self leveling cement. Foam tape, used for weather striping works well for that.

You could then use the correct vinyl adhesive to bond the duraceramic.

The other option is more labor intensive but more cost effective and that would be to install 1/4" cement board in thinset to the underlayment plywood. With that, you can prime the cement board and pour the slc to a feather edge. It saves you about 1/8" in floor height and no lath to install and much less slc to mix and pour.

(1/8" height saved assumes 3/8" thick pour over plywood with lath vs 1/4" cement board with feather edged slc)

I am continuing the remodeling of our six foot by 8 foot hall bathroom. I have just removed the MDF subfloor that is over the original 3” wide and ¾” deep tong and groove (T&G) subfloor. This MDF floor was swollen due to water leakage and I could not get a good idea of the level of the floor until it was removed. The floor has a low point of ½”. I considered attempting to adjust the height of the piers but this would only make the kitchen unlevel. Using a rotary level, I have included a chart showing the floor. Zero is the high spot and the other numbers are the inches below the zero reference. Because of the age of the house and foundation I think the best approach is to use cement backer board. However because of the variance in the floor I am concerned about voids under the backer board if I put it directly on top of the T&G and then us a self leveling compound to level the floor. The T&G floor is in good shape and solid, however there are some gaps between a few of the boards and holes in the floor due to removal of the bath tub, toilet and sink. Is there some way to use a self leveling compound to level the floor before installing ¼” backer board?

Thanks in advance for you help.

Lonny

Floor Level Chart attached

Hi Lonny...

Is this true T&G flooring? If so, then I don't think you'll like to hear this, but in my opinion, the best job will result from you ripping out the T&G subfloor and then ripping some studs down to make up for the uneven floor. Use adhesive to join the new ripped studs to the joists and nail them to the joists. When you no longer have any 0 points you would then lay down a new 3/4" plywood subfloor (I like the 3/4" T&G plywood) screwed and adhered to the joists.

Then you would spread some thinset mortar with a notched trowel and install the hardibacker into that and screw to the plywood using the alkali-resistant screws every 6-8". Don't forget to tape the seams using alkali-resistant tape at all seams.

Give blackjack or others a chance to chime in on this though... may have other ideas... ;)

Let me know what you think...

MARK

Hi Mark,

Thanks for the prompt response.

Removing the T&G sub-floor is problematic. If you look at the diagram, the pantry wall was added in an earlier remodeling. This wall is non-stress bearing and does not sit on a floor joist. The T&G boards run under this wall. The floor joist runs about 12” from the pantry wall. To remove the T&G board the pantry wall would have to be braced and new support added for T&G plywood along the pantry wall. Yuck!

The finished floor in the bathroom will be 16” x 16” x 0.160” Congoleum DuraCermaic vinyl composite tiles installed with a 1/8” grout line. This product is rated for installation over plywood. I've been vacillating between plywood and cement backer board. Plywood would be an easier installation than backer board and it is really my preferred method. I believe the floor would be stable with the addition of ¾“ plywood over the ¾” T&G boards. I'm concerned about placing backer board or plywood over the uneven T&G flooring and then using a self leveling product because of possible voids between the T&G and backer board or plywood. I have read other posting of people that have had similar problems and they recommended adding ¼” plywood to cover any cracks or holes, then self leveling compound and then ½” plywood. However, blackjack says the self leveling compound must be on top of the plywood because of a breakup problem when screwing down the top layer, which makes sense. Maybe I'm over thinking this issue of voids and should just install the backer board or plywood and the use the self leveling compound.

I have not heard anything from blackjack as of yet. I am looking for additional suggestions and recommendations.

As always all suggestions and recommendations are greatly appreciated.

Lonny

Hi Oldhouse:

I am not familiar with duraceramic so should not really advise here. Check out this link:

Congoleum Duraceramic Tile Floors - Cheap Duraceramic Prices

On the first page at the bottom of the first paragraph is the INSTALLATION INFO. You may find helpful. Click on INSTALLATION INFO. and it will bring you to a large PDF file... hopefully has some useful info.

Finally, my gut tells me that this stuff is pretty darn flexible and that you could probably get away with feathering out the edges with a self leveler (over tar paper) and then install plywood or cement board as instructions indicate.

Let me know if you want to discuss more... OK?

MARK