I plan to use Durock backer board as underlayment for tile (in
conjunction with plywood). My preference is to use 1/2". However, I
downloaded Durock's install guide and got confused. It sounded as if
they made two kinds, one for walls and one specifically for
underlayment. They call the 1/2" and 5/8" board their "Standard Board"
while the "Underlayment" version comes only in 5/16". Is there
anything that makes the 1/2" board unsuitable for underlayment or is
this just a matter of advertising the 5/16" as underlayment because
it's thinner and will not raise the floor as much?

Secondly, convention suggests a gap of 1/8" between boards. However I
can't seem to get a straight answer regarding the space that should be
left between the backer board and the wall. 1/8"? 1/4"?

Help is a appreciated!

Mak Wilson wrote:
I plan to use Durock backer board as underlayment for tile (in
conjunction with plywood). My preference is to use 1/2". However, I
downloaded Durock's install guide and got confused. It sounded as if
they made two kinds, one for walls and one specifically for
underlayment. They call the 1/2" and 5/8" board their "Standard Board"
while the "Underlayment" version comes only in 5/16". Is there
anything that makes the 1/2" board unsuitable for underlayment or is
this just a matter of advertising the 5/16" as underlayment because
it's thinner and will not raise the floor as much?

The Durock is bonded to the subfloor with thinset. It does not need
the strength of the thicker board used for wall installations as there
is no span, and as you noted the thinner board doesn't raise the floor
as much. You can use the thicker board on the floor if you'd like -
there's no harm in it.

Secondly, convention suggests a gap of 1/8" between boards. However I
can't seem to get a straight answer regarding the space that should be
left between the backer board and the wall. 1/8"? 1/4"?

You don't need a big gap. Whether it's new or old that you're butting
up against, all joints between different wall and floor surfaces should
be caulked. Don't try to grout it.

R

Thanks for the help Rico. As a reward for your assistance, I pile on a
few more questions....

Regarding not needing a "big" gap between the wall and the cement
board, I was hoping for a more concrete answer (no pun intended). I
know with plywood you have have to allow for expansion. Is that the
same thinking here with the cement board?

Regarding caulking the wall-to-backer board gaps, is it best to use
100% Silicone or is a tub/tile silicone better? (To be clear, I use
thinset on the backerboard-to-backerboard gaps).

Finally, in true amature form, I don't know the difference between
modified and non-modified thinset, but from what I've read I'm to use
non-modified thinset to bond the backerboard to the plywood. Another
source said to just use constructive adhesive. Any thoughts on that?

Thanks again for any help you can offer!

Mak Wilson wrote:
Thanks for the help Rico. As a reward for your assistance, I pile on a
few more questions....

Lucky me.

Regarding not needing a "big" gap between the wall and the cement
board, I was hoping for a more concrete answer (no pun intended). I
know with plywood you have have to allow for expansion. Is that the
same thinking here with the cement board?

There will be very little movement - nowhere near 1/4". You should
think of it as more of flexing between different wall and floor planes.
In a mud job they'd reinforce the corners with metal lathing and just
continue up the wall. Since backerboard isn't as bulletproof as a mud
job, you should allow for that little bit of movement.

Regarding caulking the wall-to-backer board gaps, is it best to use
100% Silicone or is a tub/tile silicone better? (To be clear, I use
thinset on the backerboard-to-backerboard gaps).

I think you misunderstood me. The only place that needs to be caulked
is the floor tile to wall joint...unless you're looking for a
waterproof installation and then I'd go a totally different way

Finally, in true amature form, I don't know the difference between
modified and non-modified thinset, but from what I've read I'm to use
non-modified thinset to bond the backerboard to the plywood. Another
source said to just use constructive adhesive. Any thoughts on that?

Modified thinset has latex additives. It allows for the materials to
flex more - a good thing. I use it exclusively.

Thanks again for any help you can offer!

You're welcome.

R

The only place that needs to be caulked
is the floor tile to wall joint...unless you're looking for a
waterproof installation and then I'd go a totally different way

I'm trying not to go too far off topic here, but the backer board is
going over my entire bathroom floor in preparation for ceramic tile. I
also plan to put the baker board under the tub primarily because it's
the easiest way to keep the tub level with the rest of the bathroom.
(Tub is new install). I assume you mean waterproof as in what you'd do
with a shower floor or something like that, so no, there isn't a need
to water proof. I'll leave a slight gap between backer board and wall
1/8"-1/16". I hadn't considered the reason for the gap is for the
expansion of the wood wall studs. That was a good insight.

Oh, when the time comes shouldn't I also caulk where the tile meets the
tub?


Finally, in true amature form, I don't know the difference between
modified and non-modified thinset, but from what I've read I'm to use
non-modified thinset to bond the backerboard to the plywood. Another
source said to just use constructive adhesive. Any thoughts on that?

Modified thinset has latex additives. It allows for the materials to
flex more - a good thing. I use it exclusively.

I'll probably go with modified then. Although, if you google on
"modified" and "backer board" you might be surprised to find that
there's some debate on this. I don't have the knowledge or field
experience to sort it out.

I guess I'm ready to move forward from here. Thanks again. I really
appreciate people like you taking the time to help out newbies like me.

Mak Wilson wrote:
The only place that needs to be caulked
is the floor tile to wall joint...unless you're looking for a
waterproof installation and then I'd go a totally different way

I'm trying not to go too far off topic here, but the backer board is
going over my entire bathroom floor in preparation for ceramic tile. I
also plan to put the baker board under the tub primarily because it's
the easiest way to keep the tub level with the rest of the bathroom.
(Tub is new install).

When you say keep the tub level with the rest of the bathroom, what
does that mean? The backerboard can be done either way - either under
the tub or butting up to it. Doesn't really make a difference other
than you don't have to worry about a precision cut for the backerboard
if it extends under the edge of the tub.

I assume you mean waterproof as in what you'd do
with a shower floor or something like that, so no, there isn't a need
to water proof. I'll leave a slight gap between backer board and wall
1/8"-1/16". I hadn't considered the reason for the gap is for the
expansion of the wood wall studs. That was a good insight.

Oh, when the time comes shouldn't I also caulk where the tile meets the
tub?

Absolutely. Caulk all changes in wall planes, wall to floor
transitions, around all edges of the tub inside and out of the wet
area, etc.

Finally, in true amature form, I don't know the difference between
modified and non-modified thinset, but from what I've read I'm to use
non-modified thinset to bond the backerboard to the plywood. Another
source said to just use constructive adhesive. Any thoughts on that?

Modified thinset has latex additives. It allows for the materials to
flex more - a good thing. I use it exclusively.

I'll probably go with modified then. Although, if you google on
"modified" and "backer board" you might be surprised to find that
there's some debate on this. I don't have the knowledge or field
experience to sort it out.

There's debate on everything, but having a little leeway with flex
between the floor and the backerboard can't hurt. The converse is not
true. It also simplifies your job by not having to keep switching
materials. If you're only doing one bathroom it's not a big deal.

The John Bridge Forums are another good place to get tiling
information.

I guess I'm ready to move forward from here. Thanks again. I really
appreciate people like you taking the time to help out newbies like me.

People like me? People like me?! Crap - here I thought I was unique.

We were all newbies at one point. Answering questions here is my way
of trying to pass on some of the help and instruction I've received
over the years.

Do a good job and have some fun with it.

R

No new questions this time around. I think you got me where I need to
be...

When you say keep the tub level with the rest of the bathroom, what
does that mean?

Just means that when I tile the bathroom floor for the tile I'll go
ahead and raise the tub floor too (as opposed to having the tub be a
1/2" lower which really wouldn't have bothered me that much but that's
not the way I'm going with it). Put another way, the floor is already
level across the stretch of the room including the floor that's under
the tub (or rather were the tub was before I took it out).

The backerboard can be done either way - either under
the tub or butting up to it. Doesn't really make a difference other
than you don't have to worry about a precision cut for the backerboard
if it extends under the edge of the tub

Right. The tub itself rests on 4 evenly spaced square mounts so those
are the important points to cover. Even so, I'll just put the BB under
the entire tub. The board will extend out beyond the tub a half a foot
before meeting up with another BB.

I assume you mean waterproof as in what you'd do
with a shower floor or something like that, so no, there isn't a need
to water proof. I'll leave a slight gap between backer board and wall
1/8"-1/16". I hadn't considered the reason for the gap is for the
expansion of the wood wall studs. That was a good insight.

Oh, when the time comes shouldn't I also caulk where the tile meets the
tub?

Absolutely. Caulk all changes in wall planes, wall to floor
transitions, around all edges of the tub inside and out of the wet
area, etc.

I figured as much and was just being clear. That's one of the reasons
they call it TUB & TILE caulk.

I'll probably go with modified then. Although, if you google on
"modified" and "backer board" you might be surprised to find that
there's some debate on this. I don't have the knowledge or field
experience to sort it out.

There's debate on everything, but having a little leeway with flex
between the floor and the backerboard can't hurt. The converse is not
true. It also simplifies your job by not having to keep switching
materials. If you're only doing one bathroom it's not a big deal.

The John Bridge Forums are another good place to get tiling
information.

That's one of the places they were debating the issue. I must say I
wasn't really clear on the points of the arguement, but I'm satsified
to go with the modified thinset. Thanks for helping me get off the
fence.

I guess I'm ready to move forward from here. Thanks again. I really
appreciate people like you taking the time to help out newbies like me.

People like me? People like me?! Crap - here I thought I was unique.

We were all newbies at one point. Answering questions here is my way
of trying to pass on some of the help and instruction I've received
over the years.

Do a good job and have some fun with it.

That's what it's all about (not to mention saving a couple bucks and
getting some time away from from my beloved wife). Thanks again.

Durock is fine but just to complicate the issue look through the
Schluter site. Ditra is perhaps a better material if you anticipate
floor movement. I've used both in my home and have been happy with
both. Home Depot has some Schluter products and can order the others.

Don't use construction adhesive to put Durock down, use a modified
thinset mortar.

Boden

http://www.schluter.com/english/prod...toverview.html



Mak Wilson wrote:
I plan to use Durock backer board as underlayment for tile (in
conjunction with plywood). My preference is to use 1/2". However, I
downloaded Durock's install guide and got confused. It sounded as if
they made two kinds, one for walls and one specifically for
underlayment. They call the 1/2" and 5/8" board their "Standard Board"
while the "Underlayment" version comes only in 5/16". Is there
anything that makes the 1/2" board unsuitable for underlayment or is
this just a matter of advertising the 5/16" as underlayment because
it's thinner and will not raise the floor as much?

Secondly, convention suggests a gap of 1/8" between boards. However I
can't seem to get a straight answer regarding the space that should be
left between the backer board and the wall. 1/8"? 1/4"?

Help is a appreciated!

I don't anticipate floor movement and I've already got the backer board
on hand, so I'll pass on the Ditra for now, but thanks for the thought.

Don't use construction adhesive to put Durock down, use a modified
thinset mortar.

Agreed. The constructive adhesive is only for securing the tub itself
to the (soon to be) Durock floor.

Mak Wilson wrote:
I don't anticipate floor movement and I've already got the backer board
on hand, so I'll pass on the Ditra for now, but thanks for the thought.

Don't use construction adhesive to put Durock down, use a modified
thinset mortar.

Agreed. The constructive adhesive is only for securing the tub itself
to the (soon to be) Durock floor.

That's usually not necessary. Once it's all plumbed and tiled in, it's
not going anywhere. If it's an acylic tub are you planning on using
something under the floor of the tub to help take the weight?

R

Agreed. The constructive adhesive is only for securing the tub itself
to the (soon to be) Durock floor.

That's usually not necessary. Once it's all plumbed and tiled in, it's
not going anywhere. If it's an acylic tub are you planning on using
something under the floor of the tub to help take the weight?

No, I hadn't planned on it. The previous tub was cast iron and much
much heavier and there was never an issue so I think the acyrlic should
be okay. The construction adhesive is mentioned in the tub install
specs as an alternative to a cement bed. It's not much trouble and I
figure it can't hurt, although it won't be as much fun taking the tub
out again should there ever be a need to do so.

Mark-



If it's an acylic tub are you planning on using something under the floor of the tub to help take the weight?

I think that when Rico said this he wasn't concerned about the weight
of the tub or water.

IMO he was concerned about the flexibiblity of the tub bottom.
When a person steps into the tub, unless the tub bottom is well
supported (wood members, well spaced or lots of foam) the tub bottom
will flex downward.

It's a minor annoyance but can also lead to premature flexural failure
of the tub by cracking; cast iron doesn't have this problem.

cheers
Bob

Mark-

That cast iron tub (if it's not trashed) is worth soemthing to someone.


Put it on CraigsList, you might get some $'s for it , help out someone
doing a restoration & dispose of it w/o trashing it.

cheers
Bob

BobK207 wrote:

That cast iron tub (if it's not trashed) is worth something to someone.

Put it on CraigsList, you might get some $'s for it , help out someone
doing a restoration & dispose of it w/o trashing it.

But smacking the crap out of a cast iron tub with a sledgehammer is a
great way to get rid of some of those pent up aggressions!

The craigslist is a good way to get rid of all sorts of stuff. Pulled
doors, windows, sinks, whatever. Let someone else reuse it instead of
landing up in a dump somewhere.

R

Mac,
Learned what I know working with my husband, professional tile
installation, all applications, in Florida.

1) Use mastic, not thinset to set 1/2" durock (permabase). Butt sheets
up, their slight variance will give you all tolerance required.

2) we typically use 1-1/4" coarse thread drywall screws about every 8
-10 inches to further secure the rock.

3) get out of the tech sheets and go to the local dealer who sells to
the pros, (ie: Wholesale tile stores). If you see anyone in an orange
apron RUN!!!

Mark-

That cast iron tub (if it's not trashed) is worth soemthing to someone.


Put it on CraigsList, you might get some $'s for it , help out someone
doing a restoration & dispose of it w/o trashing it.

cheers
Bob

wrote:
Mac,
Learned what I know working with my husband, professional tile
installation, all applications, in Florida.

1) Use mastic, not thinset to set 1/2" durock (permabase). Butt sheets
up, their slight variance will give you all tolerance required.

Why do you feel your way is better than what the manufacturer
recommends? This from National Gypsum's web site:

Can I attach PermaBase directly to my floor or countertop?
No. Using a 1/4" square notched trowel, apply a setting bed of
latex-Portland cement mortar to the subfloor or base and immediately
laminate the PermaBase, leaving a 1/8" space between adjoining pieces.
Make sure you have a minimum of 3/4" exterior plywood/OSB as a subfloor
or base and that the framing members don't exceed 19.2"o.c

2) we typically use 1-1/4" coarse thread drywall screws about every 8
-10 inches to further secure the rock.

Again from the NG web site:
What type of fasteners do I use?

Either a 1 1/2" galvanized roofing nail or 1 1/4" cement backer board
type screw are used with wood framing. If you are attaching the
PermaBase to 20 gauge or heavier metal framing, use 1 5/8" S-12 cement
backer board screws. DO NOT use typical drywall screws.

Notice the capital letters? Drywall screws are definitely not
recommended.

3) get out of the tech sheets and go to the local dealer who sells to
the pros, (ie: Wholesale tile stores). If you see anyone in an orange
apron RUN!!!

I'd agree with you if you said to go to the pros for tile advice
instead of a big box store. Regardless of where you buy the material,
if you follow the manufacturer's installation instructions you'll
rarely go wrong. If not...you're on your own.

R

IMO he was concerned about the flexibiblity of the tub bottom.
When a person steps into the tub, unless the tub bottom is well
supported (wood members, well spaced or lots of foam) the tub bottom
will flex downward.

It's a minor annoyance but can also lead to premature flexural failure
of the tub by cracking; cast iron doesn't have this problem.

I hadn't thought of that, but I think I'm okay. The tub, by design, is
supported by 4 4" squares evenly spaced. The floor itself is very
solid. Either way it's too late now. I already have the BB installed.
Thanks for the feedback just the same. Although I'd say my biggest
aggrivation with projects is over thinking things, it's good to hear
all the considerations.

I busted it up something awful. Even if I had wanted to save it, I
don't know how I would have gotten it down the steps or even through
the door. I put the pieces in 4 or 5 heavy duty garbage bags and the
garbage man refused to take them because they were too heavy. Anyway,
I have another tub in the downstairs bathroom that's exactly the same
but still totally in use. I can't imagine what the cost would be to
ship something like that.

Mak Wilson wrote:
I busted it up something awful. Even if I had wanted to save it, I
don't know how I would have gotten it down the steps or even through
the door. I put the pieces in 4 or 5 heavy duty garbage bags and the
garbage man refused to take them because they were too heavy. Anyway,
I have another tub in the downstairs bathroom that's exactly the same
but still totally in use. I can't imagine what the cost would be to
ship something like that.

Crasigslist - they come get it.

Those cast iron tubs are damn heavy, huh? A 5' one weighs about 300#,
yet one guy brings it up the stairs. It's the easiest way, believe it
or not...just not necessarily the safest! First time I saw that I was
flabbergasted.

R

"Mak Wilson" wrote:

I busted it up something awful. Even if I had wanted to save it, I
don't know how I would have gotten it down the steps or even through
the door. I put the pieces in 4 or 5 heavy duty garbage bags and the
garbage man refused to take them because they were too heavy.

I don't know where you live, but around me, there are "scavengers" who
come around garbage day, and pick up heavy recyclables like metal off to
the scrap yard.

They get paid by the pound, instead of having to pay by the pound.