[oldhouse49]

trying to bring up two slabs to the same height. one slab is about 1 inch lower than the other. I've put down 1/2 inch osb (screwed down with concrete screws), then I put 1/2 inch wonderboard on top (using Rock-On screws). But I noticed when I walk on the wonderboard near the edge, it gives a little up/down play, not significant deflection, is this okay?

thanks.

 

[JazMan]

NO!

Rip it all out and we can help you do it right.

Jaz

 

[joecaption]

Any plywood or OSB in direct contact with a slab is going to rot out.
What I have done and it worked out great is used a 6 mil. vapor barrier, 1/2 foam then A/C plywood over that with Tap Con Screws to hold it down.
It adds a thermal break and it does not flex at all.

 

[oldhouse49]

Any plywood or OSB in direct contact with a slab is going to rot out.
What I have done and it worked out great is used a 6 mil. vapor barrier, 1/2 foam then A/C plywood over that with Tap Con Screws to hold it down.
It adds a thermal break and it does not flex at all.

yeah, I did install a layer of vapor barrier before the osb. Looks like what I need to do is take out the backer, apply thinset then re-install the backer, then tape and thinset all the joins.

 

[oldhouse49]

yeah, I did install a layer of vapor barrier before the osb. Looks like what I need to do is take out the backer, apply thinset then re-install the backer, then tape and thinset all the joins.

Any plywood or OSB in direct contact with a slab is going to rot out.
What I have done and it worked out great is used a 6 mil. vapor barrier, 1/2 foam then A/C plywood over that with Tap Con Screws to hold it down.
It adds a thermal break and it does not flex at all.

will this work ?

 

[joecaption]

What's the finished flooring going to be?

 

[oldhouse49]

What's the finished flooring going to be?

tiles

 

[rusty baker]

tiles

Ceramic? If so, I will leave it for Jaz.

 

[JazMan]

The best way to proceed is to bond deck mud to the slab then install the tiles. This gives you a permanent base that will be flat and level. Problem is many homeowners may not be able to do the work themselves and so in an attempt to save money come up with all kinds of alternative methods. The good news is that some of these alternatives will work, but many will not work well or may create a science experiments that may not be discovered for years.

Placing plastic on a concrete floor can only work well if there's very little moisture under the slab, AND if it can evaporate faster than it can collect. What happens to the moisture that is trapped by the plastic under the osb/ply or foam panels? You need to be very careful and only use an approved system after proper testing.

Most people when asked, will tell us their slab is dry. Well sure, it may look dry cuz it's bare and there's nothing to trap excess moisture. Install something over it and everything can change.

Jaz

 

[oldhouse49]

The best way to proceed is to bond deck mud to the slab then install the tiles. This gives you a permanent base that will be flat and level. Problem is many homeowners may not be able to do the work themselves and so in an attempt to save money come up with all kinds of alternative methods. The good news is that some of these alternatives will work, but many will not work well or may create a science experiments that may not be discovered for years.

Placing plastic on a concrete floor can only work well if there's very little moisture under the slab, AND if it can evaporate faster than it can collect. What happens to the moisture that is trapped by the plastic under the osb/ply or foam panels? You need to be very careful and only use an approved system after proper testing.

Most people when asked, will tell us their slab is dry. Well sure, it may look dry cuz it's bare and there's nothing to trap excess moisture. Install something over it and everything can change.

Jaz

Thanks for the great advice. I felt quite unsure about the vaporbarrie/osb/backer myself, went to homedepot, luckily talked to the right guy and he told me to use deck mud. So I hired a guy to rip out everything and will be doing deck mud later.

thanks again.

 

[JazMan]

..........went to homedepot, luckily talked to the right guy and he told me to use deck mud.

What? :surprise:By golly there's hope that occasionally the big boxes will give a good answer.:smile:

Jaz

 

[oldhouse49]

What? :surprise:By golly there's hope that occasionally the big boxes will give a good answer.:smile:

Jaz

how long do I have to wait before I can put tiles on the mud ?

 

[JazMan]

When it's done by a pro and it's not a large area, we install the tiles immediately while the mud is still plastic. Otherwise you should wait 3 days or longer.

Jaz

 

[oldhouse49]

When it's done by a pro and it's not a large area, we install the tiles immediately while the mud is still plastic. Otherwise you should wait 3 days or longer.

Jaz

any reason why it can be either immediate or 3 days ? My area is 8' by 8', can I tile it right away?

 

[JazMan]

You can tile it right away if you have the experience and know how. Since you're asking, I'll assume you do not have the experience to pull the mud and install the tiles while it's still plastic.

So, it's best to wait a few days, however if you're careful and protect the floor while tiling, you could tile the next day if you had to. It's just that the mud will not be very strong and may break.

Do you know how to mix and instal deck mud?

Jaz

 

[oldhouse49]

You can tile it right away if you have the experience and know how. Since you're asking, I'll assume you do not have the experience to pull the mud and install the tiles while it's still plastic.

So, it's best to wait a few days, however if you're careful and protect the floor while tiling, you could tile the next day if you had to. It's just that the mud will not be very strong and may break.

Do you know how to mix and instal deck mud?

Jaz

I've seen it done. The guy that took out my plywood/backerboard also did the mud for me (another 8 x 8 section). But I think he mixed a little too dry, there're random spots where there're loose sands on the surface. Majority of the area is hard, I tap it with a wood handle and it sounds solid and I can't drill in with a screw driver.

The bag says no more than 3.5 liter of water per 50 bag (I'm going with quickrete premix), so that's the guideline I'll be using. Mix well, make a sand ball with it and it shouldn't crumble. Pack it tight with a rubber trowel then go over with a steel trowel. Is this a sound procedure?

 

[JazMan]

Is this what you're planning to use? I don't think so. http://www.quikrete.com/PDFs/DATA_SHEET-Sand-Topping Mix 1103.pdf Since the water ratio isn't right and the correct product doesn't come in #50 bag. What were you thinking of using? What's Quikrete premix?

This is what we use for deck mud, but we modify it a bit. The product is 3:1, for shower floors ideal is 4:1, standard mix is 5:1. So add enough sand to modify as noted. http://www.quikrete.com/PDFs/DATA_SHEET-Sand-Topping Mix 1103.pdf Be sure to bond it to the slab with thinset.

There's no rubber trowel used in deck mud installation. And yes, it's supposed to be dry.

Jaz

 

[oldhouse49]

Is this what you're planning to use? I don't think so. http://www.quikrete.com/PDFs/DATA_SHEET-Sand-Topping Mix 1103.pdf Since the water ratio isn't right and the correct product doesn't come in #50 bag. What were you thinking of using? What's Quikrete premix?

This is what we use for deck mud, but we modify it a bit. The product is 3:1, for shower floors ideal is 4:1, standard mix is 5:1. So add enough sand to modify as noted. http://www.quikrete.com/PDFs/DATA_SHEET-Sand-Topping Mix 1103.pdf Be sure to bond it to the slab with thinset.

There's no rubber trowel used in deck mud installation. And yes, it's supposed to be dry.

Jaz

this is what I'm using. see attached. $4 something at Home Depot.

How do I bond the mud to the slab with thinset? Do I apply a thin coat of thinset, wait until is dry and hard, then install the mud?

 

[JazMan]

Ok good. Most stores do not stock that item, but since yours does, that's what you should use.

You had me worried when you called this "premix". This is not premixed, it's pre-blended.

For 1" thickness you have 2 choices if you follow Quikrete's directions. Either scarify the concrete and also use their Fortifier #8610 as directed, or Bond to the concrete with Adhesive #9902.

The "tile" industry does not generally do it this way. For a 1" fill you can spread thinset as you go and place the deck mud over the fresh thinset so it will all dry together. Do not let the thinset dry cuz there's no bond after it dries. Again, experience and the skill to do it is the key. Did you read their directions in the "Admixtures" paragraph?

You might be better off doing it as Quikrete suggests.

Jaz

 

[oldhouse49]

Ok good. Most stores do not stock that item, but since yours does, that's what you should use.

You had me worried when you called this "premix". This is not premixed, it's pre-blended.

For 1" thickness you have 2 choices if you follow Quikrete's directions. Either scarify the concrete and also use their Fortifier #8610 as directed, or Bond to the concrete with Adhesive #9902.

The "tile" industry does not generally do it this way. For a 1" fill you can spread thinset as you go and place the deck mud over the fresh thinset so it will all dry together. Do not let the thinset dry cuz there's no bond after it dries. Again, experience and the skill to do it is the key. Did you read their directions in the "Admixtures" paragraph?

You might be better off doing it as Quikrete suggests.

Jaz

Just looked into the 9902 bonding agent,
http://www.homedepot.com/p/Quikrete-1-Gal-Concrete-Bonding-Adhesive-990201/100318465

Seems to be the best way to go and it's quite economic too. under $12/gal. which is more than plenty. I just roll it on then install the mud while it's still wet, right ?