Marble Floor

We are getting ready to redo our Master bath on the second floor and want to put Marble down and have two questions.
1. The subfloor is not level (by about 1/2" over 5'), I know we need to level it, my question is what is the best way?
2. We have concerns over the amount of weight the joists can safely support and have been trying to research. The joists are southern pine 2x10, 12 in on center with a 13' span. I have been able to find some tables that give max wieght, but now need to determine what the wieght of the marble floor, cement board, mastick will be. The marble is 3/8 thick 12x12. If we need to stregthen the joist what is the best way? We were thinking of sistering?

Thanks,
K

 

Consider talking to a engineer, and DON'T use mastic!!Marble substrates need to meet l/720 deflection requirments .

 

Thanks,
Not sure what the adhesive is for Marble. We are planning on using one designed for marble (I noticed a home depot specific adhesives for marble), just don't know the name of them.
K

 

There are several out there . It should be something you mix yourself with either water or liquid latex..In most cases it will say meets ANSI 118.4 when mix w/????

 

I have seen both the "mix yourself" and pre-mixed. I was thinking of buying the pre-mixed (just cuz it's easier). Have you seen any significant difference between the two types?

Also, any suggestions on leveling the floor? I have seen alot of information on self-leveling agents, but am concerned that they will add alot of weight and with that already being a concern....
K

 

I'm pretty sure that anything premixed is mastic. I could be wrong tho'. To check if you have enough strength in you joists you could go to http://www.johnbridge.com/vbulletin/deflecto.pl and put in you joist info. They will tell you if you have too much deflection.

 

I agree. According to my experience, if it is premixed, it's not thinset mortar (even if it says "thinset" on the container). The problem is that once you add the water, you can't stop true thinset mortar from setting up even in a sealed container.

 

Does this pre mixed stuff meet ansi 118.4???

 

I can't think of the manufacturer of the so-called pre-mixed thinset off hand, but the stuff is utter garbage. Furthermore, I believe the company is defrauding the public. Thin set mortar is always made from portland cement, and as has been stated, it cannot be pre-mixed and then stored in a container. Real thin set will set up in an airtight container. It will set up under water.

The stuff in the container is nothing but junk mastic. I can't think of even one good use for it. It's garbage.

 

So what are you saing John? use it or not?

 

he does talk in riddles alot.Dont hold back john tell us exactly what you think and stop beating around the bush. heh heh!

 

I know many good uses for the pail, though.

 

I think the packaging probably says "thinset" rather than "thinset mortar". It's not their fault if you inferred the word "mortar" (which is what the marketing department would say in court).

 

dont put any weight on what they say at those box stores.More importantly whay type of marble were you thinking of putting in?

 

Everyone,
Thanks for all the information!!!
That web site was exactly what I needed. The floor is not rated for stone, so instead of getting a engineer in and looking at how to reinforce, we are going to go with ceramic tile on the second floor bathroom.

K