# Lightweight concrete alternative in a condo



## DanFreysinger (Nov 12, 2012)

I have spent the last couple of months trying to find a solution to my condo floor problem in a small bathroom. I found a slow leak from my wax seal ruined the underlayment. After ripping out the vinyl, I found that the underlayment was cracked and soft. Because there had been a leak, I wanted to see the condition of the subfloor so I ripped out the lightweight concrete topping. It was poured over a foam sheet, so it was easy to remove.

I now have a 6.5' x 8' area that is ready for replacement underlayment and vinyl. The previous underlayment was 1.5" thick. The local levelrock contractor wants $15 sq ft to install just the underlayment. Unfortunately, we don't have any other installers that I can find in Colorado Springs, CO. From my research it appears that this stuff is inexpensive to install on big jobs but requires a decent sized crew which is why it is so expensive for a small install.

Finally, to my question. Is there an alternative underlayment that would provide similar sound deadening and fire resistive characteristics? The final floor covering is going to be vinyl installed full spread. Our condo association has given me the approval to replace it with a product of similar characteristics as long as I am installing a soft floor covering. Basically, our board isn't real construction savy, and we don't have specifics in our documents.

Thanks ahead of time for the advice. I ran out of hair to pull out. If there happens to be any Colorado Springs, CO contractors reading this that are interested in the job, just speak up.

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One solution I have come up with is two layers of 1/2" backer board over a 6mm cork underlayment. The cork would provide a decoupling while the backer board provides the mass and fire resistance. Because I wouldn't want to penetrate the cork, I assume I would have to glue down the cork, then glue down the backer board to the cork then with staggered joints glue down the next layer of backer board. I know, it sounds hokey, but I am at a loss here. 

The main problem I see with my solution is everything I read says backer board is not for vinyl and I assume stapling underlay to cement board would be out of the question.

As a floor guy, I make a good electrician.


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## GO Remodeling (Apr 5, 2005)

you could use a mudbed like in a shower. A piece of 6 mil plastic over the subfloor is all the decoupling you need. You could pour a final layer of self leveling concrete to make a smooth finish. 

You could use your method gluing the first cementboard to the subfloor with a high latex thinset like Laticrete Platinuim or Keralastic/Kerabond. A few concrete nails or weight down the board.The next layer could be cemented together with a sound control thinset (Laticrete or Mapei).

A final self leveler or skim coat with Armstrong embosser might be enough to get you to your require height.



The gypcrete might still be less costly but will require a sealer coat that the gyp guys should supply.


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## DanFreysinger (Nov 12, 2012)

*Follow up question to olzo*

If I were to screw down down the first layer of backer board using the appropriate screws, would the laticrete 125 be an appropriate thinset for the first layer? Just thinking I would have a lot of waste buying two separate products. Since there would be a sound isolation layer between the two layers of backer board I wouldn't be as concerned about not attaching the first layer to the subfloor.

I forgot to add thanks for the help.


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## Inner10 (Mar 12, 2009)

DanFreysinger said:


> If I were to screw down down the first layer of backer board using the appropriate screws, would the laticrete 125 be an appropriate thinset for the first layer? Just thinking I would have a lot of waste buying two separate products. Since there would be a sound isolation layer between the two layers of backer board I wouldn't be as concerned about not attaching the first layer to the subfloor.
> 
> I forgot to add thanks for the help.


You choked at $15/sq for levelrock but you are going to use 125 S&C? :laughing:


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## DanFreysinger (Nov 12, 2012)

*My reasoning*

8 sheets of hardie backer will run me about $100. Not sure of the coverage of the 125, but I am thinking no more than two bags to set the 8 sheets of hardie. That would run less than half of covering the same area with levelrock and the $15 sq ft doesn't cover the sound isolation mat.

Am I off track here somewhere?

I guess it is only necessary between the two layers so I could save a bit by using a cheaper thinset under the hardie that is screwed down.


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## Inner10 (Mar 12, 2009)

DanFreysinger said:


> 8 sheets of hardie backer will run me about $100. Not sure of the coverage of the 125, but I am thinking no more than two bags to set the 8 sheets of hardie. That would run less than half of covering the same area with levelrock and the $15 sq ft doesn't cover the sound isolation mat.
> 
> Am I off track here somewhere?
> 
> I guess it is only necessary between the two layers so I could save a bit by using a cheaper thinset under the hardie that is screwed down.


125 comes in 25 pound bags and costs an arm and a leg...get pricing and perform calculations first because those little bags add up fast.


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## DanFreysinger (Nov 12, 2012)

*Thanks for the advice*

I have a floor guy coming buy this week to give me an estimate. I will run the idea past him and see what he thinks. 

Thanks for the advice


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## slowsol (Aug 27, 2005)

You don't have any gypcrete installers in Colorado?


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## DanFreysinger (Nov 12, 2012)

*Gypcrete Installers*

The Maxxon guys are up in Denver. The trip cost to get them to drive an hour south is more than the total price of the job. If I were doing the whole condo it would be much easier to deal with.


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## slowsol (Aug 27, 2005)

Gypsum Poured Floors 
2330 Waynoka Road, Colorado Springs, CO
(719) 203-7535 ‎


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## DanFreysinger (Nov 12, 2012)

That is the company that I got the $15 sq ft quote from. The guy who gave me the quote was actually surprised at how expensive it was when he did the calculations. I am sure it is just a problem of it being such a small job. If it comes down to no other reasonable choice I will just have to bite the bullet, but I was hoping to get away with a grand for the underlayment and vinyl.


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## griz (Nov 26, 2009)

You need maybe a yard +....

Try this route....


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## GO Remodeling (Apr 5, 2005)

Needs approximately 800 lbs of material. But stills needs the sound control


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## DanFreysinger (Nov 12, 2012)

*Sound control*

The sound control I am concerned about is footfall type sound. From everything I have read, it appears that the density of the underlayment will take care of the STC for airborne sound but there needs to be some type of decoupling to provide a decent IIC. 

I am no pro, just going on what I have been able to learn from soundproofing and flooring forums. 

The whole reason I am here is to learn so I understand at least a little when I talk to the contractor bidding the job.


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## DanFreysinger (Nov 12, 2012)

*Question for Griz*

Would a lightweight mortar like that Sakrete be ok for installing at 1 1/4 to 1 1/2 inches?

If it comes down to paying the price of a self-leveling product vs paying a local tradesman to put down a lightweight mud bed, I would rather pay the tradesman. 

I appreciate the input. This is definately something I will discuss with the floor guy.


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## DanFreysinger (Nov 12, 2012)

If the floor is done with deck mud, would there be a problem with replacing some of the sand with perlite to get a lighter mix?


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## GO Remodeling (Apr 5, 2005)

Don't over think this. Is the unit going to collapse because of an extra 100lbs?


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## DanFreysinger (Nov 12, 2012)

*Overthinking*

Good point. I carry 200 lbs in there on a regular basis. Thanks for the reality check.


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