I just retiled my bath tub wall, unfortunately I used green board and
so to compensate for its lack of waterproofing I used REDGUARD
(waterproofing membrane) and applied the mastic directly onto this.
The tiles I am using are 12 by 20 inch and I used a 1/4 inch trowel to
spread the glue. After 2 weeks I grouted the tiles, but when I noticed
one that was cracked I removed it, and to my surprise the glue was
Will the glue eventually dry? The tiles seem to be on pretty solid, no
moving, will this change when I start to shower due to humidity? Will
the tiles fall off or will they stay stuck due to suction?
Green board is water resistant and the correct product to use in a bathroom.
I do not know what redguard is nor how to install it.
When ever I do bathrooms I use a fan to circulate the air.
Can not see the installation so I can not comment on the other questions.
I keep reading how Green board should not be used in a tiled bath tub
area. Since my walls were already up I asked at HD and was told to use
a waterproofing membrane to protect the wall ( I painted on this
membrane with a roller which leaves a rubbery film on the wall, thus
making the wall waterproof). My fear was that it was due to this
waterproofing barier that the mastic was not able to dry (through the
wall) as air could not pass through this barrier to dry the glue under
The tiles seem pretty secure now, but was wondering how long this could
last if the mastic never dried. From a previous post it seems that it
is normal for mastic to take a long time to dry and sometimes does not
dry and still keeps the tile stuck to the wall.
I will put a fan near the plumbing hole so as to let air get behind the
tile walls and hope this helps.
For now, unless I am told that all the tiles will come crashing down, I
will live with this and wait it out.
We put a waterproof membrane behind a concrete backer board and the
tile is installed to the backer board. I am unfamiliar with the system
that you used.
But - I have seen tile installed over other tile, over Formica, and
over metal and there was never any problem with the mastic setting in
a reasonable time frame - by that I mean within 24 hours.
I can't help but wonder if there might be a problem with the mastic
or a chemical issue between the mastic and the rubber film. A few
years back one of my tile subs had a bad batch of mastic. He said that
after 24 hours that you could still pull the tile off the wall with
He had to remove the tile, clean it, scrape down the walls and clean
them, the he re-installed the tile. It was a mess. Fortunately it was
not one of my jobs.
I doubt the problem was the mastic, but rather the user of the mastic.
I believe 2 factors are contributing to the mastic not drying:
First, I must have used way too much glue (it was my first ever tile
job and I wanted to make sure the tiles would not fall off, well I must
have over done it).
Second, the size of the tiles being 20 by 13 is not allowing in any air
to dry the mastic.
For such big tiles I should have used a thinset mortar that does not
require air to dry or I should not have used a waterproofing membrane
so that the mastic could dry through the wall.
Oh well, if you never try you can never learn :-(
Did you put the tile on with a notched trial? 20 x 13 inches? Or are
you in the metric part of the planet?
You most likely should have used thinset mortar instead of mastic,
but it might not have adhered the rubber membrane.
I am theoretically from metric Canada, but we still use imperial for
almost all measurments, go figure. So yes, 20 by 13 inch tiles.
For one wall I used a 1/4 inch square notched trowel, but when I
realized that I was almost through my mastic which was supposed to be
more than enough for the whole job according to the tile store guy, I
changed to a 3/16 inch V shaped trowel for the other 2 walls.
The tiles seem pretty secure now as I already grouted, (thinking after
2 weeks the mastic would be dry), and the tiles did not budge during
My main concern is, if the mastic never dries will the tiles stay on?
My second concern is, if the mastic never dries will mildew develop?
I figure if they are up now, why would they fall? and if there is no
air to dry the mastic, there should not be any air for mildew to form.
My choices: Start over now, or wait and see what happens. I'm opting
for wait and see
Your problem is that the tile-store guy was an idiot for selling
you mastic to install such large tiles, and the HD person was
an idiot for for selling you that "membrane". But don't feel
bad...it happens everywhere- everyday.
Ideally you should have used cementboard or hardibacker board,
but "greenboard" or otherwise called MR drywall should be OK for
many years. With a large tile over 8x8, you should have used
multi-purpose thinset. "Greenboard", or MR drywall, has a
moisture resistant paper on the surface, which is what you were
trying to achieve with the membrane. I've tore out hundreds of
rotted tubs and showers made with it, so it isn't a first choice.
Membrane or not, the mastic needs to air dry and cannot.
It has probably dried around the perimeter of the tiles enough
to hold them, and if no water gets behind them, they probably
would never fall off. Suction will hold them, but if moisture ever
gets back there the mastic will turn to mush, so I hope you did
a solid grout job.
The mystery is this "membrane", and whether mastic will stick
to it. Multi-purpose mastic is pretty sticky stuff, and probably
you will be OK. I wouldn't take it apart at this point. Get a
box fan or something and keep a fan on it for several weeks.
My guess is by knocking on it, you can tell where it is bonded
and where it is not. For now the moisture will have to escape
out through the joints, so having a fan on, or A/C on, will dry
out the bathroom air and draw the moisture out.
But......it will take a long time.
Mastic will dry in a sealed bucket if you give it enough time. Tile
is porous and most mastics use solvents that will eventually
dissipate. Depending on the mastic, it may take some time. My guess is
that it really does not take all that much mastic to hold a tile in
I think that you will be ok.
Thanks guys, I am feeling much better about this problem. I really
appreciate your comments.
Now I want the mastic to dry and at the same time not let water get
I guess I should wait before using a sealer on the grout so some air
can get through, then again, if even vitrous (glazed) tiles are porous,
the mastic will eventually dry through the tile.
I've kept a fan on through a plumbing hole to help dry from the back of
the walls, I will turn on my ventillator in the bathroom to help draw
out moisture. (With temperatures dipping down to 5 degrees (-15
celsius), I don't want to turn on the air conditioner)
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