Greetings,

I need to know what my best underlayment option is for ceramic tile based on
MY PERSONAL CRITERIA. Please help. I have tried to outline all the
information below. If some going back and forth is required I will be glad
to clarify or answer any questions you might have.

A special note:

The Tile Council of America doesn't have my personal criteria in mind. The
Tile Council of America has emphasis on quality beyond economic sanity. I
have to run my business as a business so I am seeking your help instead of
just doing what the Tile Council of America tells me.

A made up example: = this example is fictional

Tile Council of America would never suggest tiling once knowing it will
crack in 10 years. Even if tiling over the cracked layer again will produce
a lasting product. (The first layer of tile in addition to the underlayment
will prevent the second layer from ever cracking.) If the money saved from
the corner cutting in the first tiling invested for 10 years would more than
pay for the second tiling then the Tile Council of America isn't making
economic sense.

Economics:

If I am not looking for "the best" tile job what am I looking for? I am NOT
LOOKING FOR THE CHEAPEST JOB. I am looking for the most economical tile job
IN THE LONG RUN. For instance, I wouldn't want to install tile only to have
to replace it in three years. I would also not want to pay an extra 10% to
extend the life of the tile from 50 to 300 years because I'll be dead. If I
can cut the cost of the job by $1000.00 but I'll have to spend $30.00 fixing
popped tiles every year it is worth it. If I cut the cost by $1000.00 but I
have to spend $250.00 replacing cracked and popped tile every year it is
not.

The Goal:

I would like to tile the first floor of several rental properties to reduce
future costs.

Facts:

The tile:

Type: Ceramic

Size: 6x6 and 12x12

Amount: roughly 5000 sq. ft.

Note: I already purchased the tile, in bulk. It cannot be returned.

The houses:

Brick Row homes

Built in late 1800's

Floor spans: 12-15 ft

Joist spacing: 16 inches on center

Joist size: 2x10 (some 2x8)

Basement present: Yes, on all

Current floor: painted and unpainted floor boards 1x6 and 1x4 (3/4" thick)

Labor costs:

Low

First question:

How do I determine the amount of weight the floor will safely support?

Second question:

What underlayment should I use? Below are several choices under
consideration.

PLAN A

=================

Use 1/2" wonderboard and thinset

Cost: $3300.00 + latex modifed thinset

PLAN B

=================

Put down 15 lb felt and pour as thick a mud bed as the floor will support.
If metal lath is absolutely required that would probably price the mud bed
option out. If no metal lath is required this might be the cheapest option.
A 1 part Portland, 6 part sand mud bed costs $60 per cubic yard. If I added
$10 worth of fiber reinforcement per yard a 2 inch thick mud bed would still
cost less than 45 cents per square foot or $2250.00 for the whole project. A
1 1/4 inch mud bed would cost about $1400. The problem is that I think it
might be too heavy and I don't know if I could increase the strength of the
floors for the money I would be saving over Wonderboard. I also don't know
if fiber cement is going to allow me to not use steel reinforcement and
lath.

PLAN C

==================

Pour a thin layer of "high performance" mortar. If I could match the
properties of Wonderboard somehow that would be ideal. Does anyone know what
I need to do to make a similar product? How many parts sand / lime / cement?
Is that fiberglass matting and how could I obtain it? Does Wonderboard use
some special magical ingredient that I do not know about? At $430.00 per
cubic yard Wonderboard is phenomenally expensive concrete. Sand is only $30
per cubic yard. Pure Portland cement is about $175 per cubic yard. That
leaves a lot of extra money to purchase fiberglass matting and still come
out ahead. I also like this option over Wonderboard because some rooms on t
he first floor are 1/8th inch higher or lower than ajoining rooms and could
easily be "made level" during the process.

PLAN D

==================

Put down plywood / OSB over the floorboards and then tile directly onto the
plywood. The cost, of course, depends on how thick a sheet of plywood used.
I imagine the cost is probably slightly less than Wonderboard. Since I have
reason to believe the floor may be exposed to moisture from time to time I
would opt for Wonderboard

PLAN E

==================

Put down 1 / 4 inch Luan and tile over. Cost, around $1720. This is the
cheapest option other than a mud bed which might weigh too much for the
floor.

A final note:

Please don't say: "do this, do that". Explain WHY and where possible use
numbers.

Thank you all very much for your help,

William