Gypcrete vs. Mud [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-07-2007, 12:34 AM
I have read through alot of the threads here and have done research online. I'm in the process of getting bids on some flooring work and I am getting conflicting advice. I have done hydronic radiant in two rooms in my house and now want to continue through out. The one room I did was a bathroom and i ripped pieces of backer board into sleeper strips and filled with sand mix and ran the 3/8 tubing in between. I installed marble over it using flex bond and it worked out well so far. The other room I did was a complete mud job without any sleepers over 1/2 tubing. Luckily I put laminate/pergo flooring over it because as a newbie i didn't float it too level.

Now I'm ready to do the rest of the house. Two rooms will have laminate, one bathroom will have travertine and the rest (600 sq ft) will have porcelain. The floor that is being replaced with porcelain tile has a "pillow" tile now with a mud job of about 1". I'm planning on putting tar paper down, lath, 1/2" tubing and then flooring.

The question I have is the gypcrete/gypspan pumped in vs. mud. I'm concerned about weight and height. The house was built in the late 80s and all the joists are 2x10s with very large center beams (very open floor plan - sprawling ranch) Most spans are 12' and under. Some guys recommend mud base of as close to 1 1/2" as i can get without raising my front door entry (I have about 1 5/8" from subfloor to bottom of door) The subfloor is 5/8" plywood with a 1/4" luan. Other guys recommend a lightweight mix pumped in. The tile now is missing grout and is crunchy when you walk over it. I believe it is an inferior mud job at construction. There is lath in the mud but no vapor barrier. I'm hoping its not deflection.

The other question i have is that some people say to use plastic sheeting instead of tar paper because when you start heating the floor you smell tar. Any one have any experience with that?

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03-07-2007, 06:35 AM
Hello jager, I would stay away from gypcrete, they should call it JIPcrete.

I had a bad experience a couple years ago with a builder that had his guys pour a gypcrete bed 1 1/2" thick with copper heating tubes imbeded. The tile cracked all to heck.

The builders I work with these days install pecs plastic tubing under the subfloor in the joist pockets, seems to work fine.

I am not an expert in heating mudbeds, but it seems to me that placing 3/8" to 1/2" tubing in a mudbed less than 1 1/2" is asking for trouble.

You may want to consider an electric heating system, John has a link to a manufacturer/distributer to your right. ------>

03-07-2007, 08:57 AM
Hi Jager,

I'm working on the same project as you - radiant install in a bathroom over wood subfloor. See my thread...
Jeff's Master Bath (
So far I have learned that you want to use a decoupling membrane such as Ditra between the mud and the tile. This isolates any cracks in the mud base from reaching the tile. Regarding the tar paper, I've also read that the paper will off-gas when heated. I question whether any barrier is needed. If using mud, I'd imagine it will be on the dry side (3 parts sand,1 part portland?) and could probably be put right on the plywood or plywood with lathe attached. This link shows several install options depending on the subfloor. Watts Radiant ( Note that Watts Radiant does not show the use of tar paper or lathe when going over wood. For that matter, they do not show a decoupling membrane but I would not skip that step.

Hopefully we can get a pro over here to provide more insight.

I'm interested in learning more about your experience with using strips of backer board with samd mix between vs. doing a full mud job.

03-07-2007, 12:13 PM
Everyone I speak with recommends a barrier when doing mud.

The Gyp-span guys (gypsum-nework) don't use/need any barrier or lath. The other pump-in person I spoke with uses 3/8 grit portland pump mix with fibermesh over barrier and lath. He is starting to look at gypsum products because of there advancement over the years to increase its psi at a thin application.

I'm leaning towards a full mud job at this point since the price is about the same and I have confidence in the team that will work with me on both the radiant and mud application. Anyone on the forum have a going rate for costs per square? The prices I'm getting are consistent and the gyp-span runs about $3.20 a square and the pumped-in portland mix and mud job runs about $1 less a square.

Also I found that under 2" the weight of both products is neglible. I was told that the gypsum product is about 1 lb per sq ft lighter.

I have 2x10 joists with no more than 12' span so i should be good with deflection. I can go higher than 1 1/2" mud since I'm replacing most of the doors in the house as well but my tile guy seems to think that 1 1/2" should be enough.

To answer question regarding the sleepers -- it worked great. My buddy put cement siding on his home and had scraps left over so i ripped them in half on a table saw and made sleepers (glued them together with PL). It gave me a great guide to push sandmix in between. The other larger room I did without sleepers was tough. Luckily I put pergo/laminate in the other room because I found it extremely difficult to get it level.

03-07-2007, 02:59 PM
i find gypcrete conducts heat better than a mud pack, packing mud around somewhat loose tubing is not easy. you can not pack it as firmly.

i prefer to use 3/8 tubing, but your loops need to be shorter.

also,i used ditra over the gypcrete

03-07-2007, 03:17 PM
Yeah, I'd put a membrane over Gyp.