Deck Mud that won't harden [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-25-2008, 05:27 PM
Hi all, I am in the final or thought I was in the final stages of building my Kerdi shower...

However I am now trying to get the "Deck Mud" as John Bridge calls it to be firm enough to lay the kerdi membrane down.. the mixture for the Mud was one 47lb bag of portland cement and five 50lb bags of playsand. I followed Johns "mud instructions" to the "T".

Problem: It seems that there was not enough water in the mix. After 24hrs of set time walking on it leaves "scuffs,dents, and deformities" to the pan profile. Now if this is normal I am real heasitant to use the very expensive rocks, as i feel that while standing on the floor will cause the mud to bust up.


1. have I waited long enough for the mud to set?

2. did I get the wrong mixture?

It is no big deal at this point as this is a test pan at the same dimensions that the shower is.

6'6" 350lbs

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06-25-2008, 06:00 PM
Hi King, that's not the right mix if you used 47 lbs of portland with 50 lbs of sand. It should have been about 5 sand to 1 portland, maybe 4 1/2 sand to 1 portland. That would be about 50 lbs of sand to 10 lbs of portland. Mix it dry first, then slowly add water while mixing until it's about like sand castle sand. Just moist enough to make a ball in your hand when to squeeze it.

You didn't add enough water because with a batch that rich, it would have been hard as a rock and would have been very hard to work with. :)

Rd Tile
06-25-2008, 06:05 PM
Davy, he said 5 50lb. bags of sand.:)

Probably not enough water and didn't pack it well enough, not sure.:)

06-25-2008, 06:11 PM
After 24hrs of set time walking on it leaves "scuffs, dents, and deformities" to the pan profile.another hard did you pack it ?
I have seen some homeowners and tile setters not pack a floor hard enough
and the unpacked softness can be seen as still soft and not cured.

06-25-2008, 06:13 PM
Hi King
47bs to 5 50 lb bags of sand is about right. Deckmud can take a while to harden up. Next morning I can make a dent with my thumb sometimes. If it's really denting maybe you didn't compact it enough when you formed the pan. Easily scuffed is routine for deckmud. You can coat it with a loose thinset to put a hard shell on it any time now. It could take a few days to harden up enough not to dent.

Course at 6'6'' and 350 you might need to wait a couple months. :)

06-25-2008, 06:23 PM
Okay, my goof, been a long day. :) Yep, the mix sounds about right, probably not enough packing and a little too dry. :)

06-25-2008, 06:40 PM
Well you are in "the mud box". You probably didn't mix the cement and sand together well and didn't use enough water. you really have to chop it up good, Just bust it out and try it again. It will work if mixed correctly.

06-25-2008, 06:43 PM
You might try taking a spray bottle with water and wetting the bed well, then leave it for another day to see if that helps. If there is enough water in the mix already, it won't hurt, but if there isn't, it might help.

06-25-2008, 06:51 PM
Okay, my goof, been a long day.

You call that a goof? Today I gotta laugh outta that statement.

I had a goof today Davy.
The kinda goof where I needed a hammer and pry bar :lol1:

Don't ask

06-25-2008, 10:36 PM
I grabbed the broom and swept the loose stuff off of the shower pan and wow to my suprise the area that pops packed was uneaven. the area that I packed was a bit better and the area that had a small bit more moisture looked pretty good. I think that I will spend another 30 bucks and mud another test bed.
Thanks a bunch fellas, I appreciate it