wedi vs kerdi system

Discussion in 'Shower & Bathtub Forum & Blog' started by sue4072, Apr 21, 2010.

  1. sue4072

    sue4072 Reporter

    Messages:
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    Location:
    new york
    My husband and i are trying to renovate our old standing shower from seventies. we have been shopping around and came across Wedi and Kerdi shower system. Wedi system looks easy to install. anyone has used Wedi system before? Any pros or cons of either?
    thanks in advance for your response.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    They each have their advantages. Wedi may be faster to get done, but in some ways isn't as flexible (in what you can do). In some ways, you can do stuff with Wedi you really couldn't do any other way, so it depends. For example, if you wanted a high fashion, scroll shaped, free-standing shower, it would be a pain to build conventionally or with Kerdi. But, you can buy a kit, glue it together, and be tiling it in less than a day with Wedi.

    Kerdi is more flexible if you want a custom shaped shower pan. You can use their preformed pans (as you can with Wedi), modify them slightly (if it do it extensively, you'll have problems with asthetics, not operation because the bottom row won't be even if you cut things), but with Kerdi, you can save some money and make your pan out of the traditional deck mud (very inexpensive - mostly sand with enough portland cement to hold it together). With Kerdi, you can finish the walls with regular drywall, since the membrane is totally waterproof, the drywall is perfectly fine behind it. With Wedi, you can screw the panels directly to the studs.

    With Wedi, the seams rely on you getting a good bead of their special urethane glue/caulk, and you have to seal the screw holes as well. Do a good job, and it's fine. Wedi also adds some insulation, so the walls/floor warm up quicker (same is true if you use the Kerdi foam pan). With Kerdi, it relies on you getting the proper overlap. Putting up Kerdi is sort of like putting up wallpaper, except there's no pattern to match, and you need the edges to overlap. You can get the overlap with either the full sheets, or (easier) use the thinner Kerdi-band material.

    Cost wise, if you don't use the Kerdi pan, and 'roll your own', it would end up less expensive. If you use the Kerdi pan, Kerdi and Wedi are probably close to the same costs. Kerdi material is more widely available, so you have a chance of some price competition. Wedi is not well represented in this country, so your choices of supply may be more limited (depends on where you live). If you use their pan, it's about the same as Wedi. I think the Kerdi drain is more flexible and easier to use - it's more adjustable.

    I've used Kerdi twice, and found it to work quite well. I considered Wedi on one project, but in that instance, Kerdi worked out easier. They had a demo near me on Wedi, but I couldn't get away from work to attend. I did get a chance to attend a school on Kerdi...very informative. If I'm lucky, they may do the Wedi thing again now that I'm retired, and I'll get a chance to see it first hand rather than in a video.

    If you want a shower without the need for any caulk, Schluter also makes some neat expansion joints for the corners/floor seams. But, if your walls aren't very plumb, it can be a pain to use them.

    Check out www.johnbridge.com for help and advice on tiling. And, both the www.schluter.com and www.wedi.de sites have a lot of info on their products. I think both of them have videos you can view to see their stuff being installed.
  3. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    I've used Kerdi to re-do my shower. I found on the old one that water had been seeping behind tiles, with no visibile clues. The shower was wonderboard over greenboard. The wonderboard was soaked, greenboard was moldy mush, and the wood frame of the house was completely destroyed. A few studs were literally gone from the floor up to about 4-1/2 feet up the wall. Sub floor was rotting. Even though only the shower area was bad, I gutted the entire room down to the dirt, re-framed and rebuilt it, because I wanted to get rid of all traces of mold. There are treatments for mold but the best one of all is to put the material in a dumpster and put up all-new. At least that was what me feel safe. In other words, IMO you're doing the right thing looking at on of these waterproofing technologies. I wish the person that I bought my home from had done that!

    To put up the Kerdi, use an unmodified thinset (per the manufacturer's specs). On the John Bridge tile forum they claim you can use Versabond successfully, but Schluter will not warranty the installation. Mix the thinset up fairly soupy - pancake batter - or you end up with lumps in the Kerdi, which you don't want. The very wet thinset also helps the Kerdi stick. It will take a few days for the thinset to really grip strongly, so don't pick at or peel the Kerdi. It's translucent - if you can see the uniform grey color of the thinset through the Kerdi it will be fine. If it looks splotchy you need to press your Kerdi down into the thinset better. You'll get a feel for it instantly. Even though the thinset takes a long time to fully dry, you don't have to wait more than a day to set the tile. Don't use greenboard under the Kerdi, it won't stick well to greenboard. Use regular white sheetrock (Kerdi prevents ALL the water from getting to the sheetrock so it's fine). Some of the guys on John Bridge forum use cement board, but the most experienced users just use sheetrock. The only problem I noticed was buildup where sheets of Kerdi overlap. It wasn't a problem for me but might be if you are using very small tiles or use too thick a layer of thinset to hang the Kerdi and end up with a very large bump. I used the kerdifix sealant to seal up all the Kerdi around the penetrations. Kerdifix is expensive - over $20 for a tube - but seems to work. It's a bit messy, and it's not water cleanup, you use mineral spirits. Be very careful to follow the Kerdi instructions EXACTLY and do seal up every possible spot where moisture can get through the Kerdi.

    Can't comment on the Wedi, as I haven't seen or used it. From the website it does seem like it would be less work to build a shower, although Kerdi is IMO easier than a traditional shower if you use the Kerdi pan and drain.

    Again, good job researching these more modern waterproof installation methods. After my experience, I will NEVER rely on a traditional installation, when you can have the advantage of a Kerdi kind of deal for a little more money and probably less work. Many tile guys claim that the old methods can last a good long time and they may be right if the job is done expertly... but why risk it?
    Last edited: Apr 21, 2010
  4. sue4072

    sue4072 Reporter

    Messages:
    11
    Location:
    new york
    thanks tweak and jadnashua for your insight on the project. we have found a distributor near us who carries wedi and schulter systems. we ar egoing to go check it out in person. until then.
  5. I've used both. There is a massive amount of marketing pressure to get the orange membrane to be talked about highly. It is given away as free product to the oldtimers at one famous and friendly tilesetting advice forum. There are many other ways of creating buzz and pressure to make it appear to be the best thing to use. There are many ways to make you fear "trying" any other way. Faced with this, the alternative (foam boards faced with fiberglas mesh and gray concrete) is an amateur in terms of modern guerilla warfare and it's a wonder that company is still standing. I've used both. Wedi is numbskull simple, saves time, adds no complications, and gives you straight walls. Kerdi is not this. But, Kerdi is successfully marketed.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    If your walls are straight, when you screw the drywall for use with Kerdi, or screwing down Wedi panels, the system will be straight. If the walls are not straight, neither will give you a straight wall unless you fix it first (shims, sisters, or whatever it takes). Wedi panels can be cut, and inbetween sizes created, just like drywall. WIth Wedi, you need to cut a new rabbit joint to seat the panel in. I think the Kerdi membrane is sturdier than the covering on the Wedi panel, but if it is intact before you tile it, both are fine. Wedi panels need to be sealed properly along with the screws. Kerdi is hydrophobic, so it repels water even if you do have a less than perfect seam. Wedi doesn't. I think you have more flexibility with Kerdi. Given the right circumstances, I'd be happy using either.
  7. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    Why the venom regarding kerdi? Irrespective of their marketing efforts, I found it to be a quality product, and very, very easy to use.

    In using Kerdi, I learned that it works much better if you mix your thinset quite loose. It wets the Kerdi better and you don't get lumps. If you're capable of tiling a shower, you certainly will have no problem hanging sheets of kerdi, 4 inch minimum overlap, etc. But do think, "loose thinset"!

    I imagine Wedi is fine, too - I just can't swear to it since I haven't used it. I also think that some of the liquid membranes may do a fine job, although I think these likely take more skill. For example, I have used RedGuard, and getting the required film thickness to achieve waterproofing (read their instructions) requires more material than the coverage data on the instructions indicates (unless they've updated their instructions in the past couple of years). If you're not paying attention you might get in trouble! In comparison, Kerdi is pretty goof-proof. Hang it, overlap seams, kerdifix the raw edges... etc. Good stuff, IMO. Too expensive, but isn't everything?
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    Since the Wedi panels are somewhat flexible, how straight they are depends on the studs they are attached to. Same thing with Kerdi over drywall...if the wall isn't straight, neither will be straight. You seemed to indicate Wedi would be superior. That has no basis in fact.

    If you think this is venom, you need to re-read what I said. Both systems are good, and in my opinion, superior to a conventional shower with liner and cbu. There are other systems that work well, too. Latticrete has a nice surface membrane, and others. Redgard is a good product, but the variability of how it is applied means it takes some skill to get perfect coverage and the required thickness. Most people don't have a film thickness gauge, or know how to use one. You can have problems if it is too thick or too thin, and especially if you have pinholes. Take any two people painting something on, and they will have different results on how thick and consistent the painted film ends up. With Redgard, it is critical to have it fairly consistent and within the specified range of film thickness.

    With a surface waterproofing system, the whole shower dries out much faster (which is more important in a hot/humid environment or high use shower) which helps to prevent mildew. In a conventional shower, the walls and pan can and will absorb some moisture and may not dry out in between uses. This can lead to a buildup of moisture.

    As with anything, there is some skill involved in installation. Mixing the thinset for use with Kerdi is the bigger issue with it. Getting a good seal at the joints and penetrations of the screws with Wedi is it's weak point, as is generating a good rabbit joint if you need to cut it to fit. Neither is a horrible limitation and a typical moderately skilled homeowner can do it successfully. I think the Kerdi film scares some people, and they don't believe it could work at keeping out moisture on the seams. Wedi seems like it should be more reliable since the seams are sealed with a urethane adhesive. But, tests have proven that in a proper Kerdi seam, water under pressure (i.e. submerged, which isn't normal in a shower), that moisture only penetrates about 1/4", and they specify at least a 2" overlap (800% margin). With Wedi, you do not have anywhere near that margin. Again, both are quite good, and not hard to use. They each have their strengths and weaknesses. At one class I attended, they had a cardboard box covered with thinset applied Kerdi that had been in use as a drink cooler for months. The cardboard was getting soft, not from moisture, but from the constant flexing from the ice turning to liquid and the rummaging in it to find the desired cold drink. If you take a hunk of Kerdi, roll it into a funnel, and fill it with water, even with the pointy end, it will hold water because of its hygrophobic properties. Now, make the joint at least 2" wide and hold it together with thinset, and it is waterproof under pressure (which you don't normally have in a shower). Kerdi works...Wedi works...Redgard works. Understand the system, install it correctly, and you'll have a successful installation.
  9. TWEAK

    TWEAK New Member

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    Location:
    Bay Area CA
    Jim, my "venom" comment was directed at "geniescience". IMO he seems to have some sort of issue with Kerdi and/or Schluter. I guess I should have quoted him in my post, but I don't like to do that unnecessarily as it makes the threads s o l o n g.

    My comment was *NOT* aimed at you in any way, shape or form. I detect no "venom" at all in anything you said!

    In fact, you said nothing that I disagree with at all or that I thought was anything less than an objective assessment.

    Please re-read what I have posted. I use and like Kerdi, and agree with your comments about it and how to use it. I have used (successfully) Redguard, but you do have to get the film thickness right, as, again, you mentioned. I have NOT used WEDI, and since I haven't, I don't feel qualified to comment other than to say to me it *looks* like it would work fine and be fairly easy.

    BTW, I did 25 years in defense/aerospace engineering (mechanical-UCLA 1979). I'm currently consulting. Where did you work?
  10. All three work. Liquid membranes, Wedi and kerdi.

    The first post was from a husband and wife team, to whom I recommend Wedi as being an excellent choice for a DIY (for reasons Jim pointed out), and to whom the caveat is watch out for bias at a famous "friendly" tilesetter's discussion forum. It's a sponsored bias.
  11. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    Sorry if I took it wrong, , it seemed like you were railing against Kerdi a bit much.

    Kerdi is awfully easy for anyone to do. As I mentioned and Jim mentioned, mixing the thinset is probably the biggest issue. You need it thin, and most folks are used to mixing it to tile-setting consistency. Other than that, it is more or less similar to hanging wallpaper. It's hard to imagine this being a challenge for any DIYer that is comfportable enough to undertake a shower's worth of tiles. To be sure, Wedi seems pretty easy too, but it seems easier to me to hang light pieces of Kerdi, with a relatively sloppy tolerance for the overlap (just stay above the minimum), than it would be to deal with the Wedi. But neither should really be a challenge.

    Regarding the "other" forum, I don't see Kerdi as a problem there. In fact many there are many of the guys that still promote traditional showers (for reasons I will never understand). But I do notice that they overuse Ditra. It's another good product, definitely a good hedge for isolation...but it really adds to the cost of a flooring job. I don't use it unless there is no alternative, and don't ever get any cracked tiles. So in the Ditra case I do see the "over-promotion" you're describing.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
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    Off topic...

    Installation of a tiled floor is, if not a big expense, at least a big effort in time...anything you can do to improve the odds that it will survive has its merits. With that in mind, I prefer Ditra over humping heavy cbu sheets, and dealing with large quantities of expensive screws (I don't own a nail gun, and finding proper hot-dipped galvanized roofing nails is tough, too) and worrying about the panel jacking up when screwing it in place from the surface underneath. The cub dust (if you cut it) is horrendous and toxic, and scribed cuts are nasty, especially if trying to cut a small amount off. Most people don't own the shears that can cut it. Ditra is easily cut with a good pair of shears or a sharp knife, and you can carry a roll big enough for a large room up on your shoulder...so, to me, anyway, it is worth it. When you account for the cbu panels, the tape, and the screws, the cost isn't all that different between the two. If you are paying for labor, Ditra is likely to be the same or cheaper because it is faster to install, although tilemen that are not familiar with it may charge more; those that do use it, it's often on par with cbu, and you get a better warranty, plus the height penalty is less.

    Unless dealing with all new subflooring (and even then), the ability to get a good install directly on two layers of pristine ply is tough, expensive (ply is almost as expensive as the cbu), and the required high-flex/strength mortar required costs considerably more than that you can use with Ditra or a cbu install (but you only need one layer). If noise is an issue, I think a tiled floor on Ditra is a little quieter than one on cbu or directly to the ply...probably not much, and it may be just me, but it seems that way.
  13. TWEAK

    TWEAK New Member

    Messages:
    86
    Location:
    Bay Area CA
    An interesting perspective, Jim. I hadn't really thought about the noise issue.

    I almost always tear out whatever underlayment is there, as it's seldom good enough anyway. I like to piut down a 6 mil poly sheet, then sanded 3/4 ACX, which is obscenely expensive -- but it's more or less all the same thickness. With a jillion deck screws, as you note. Then, the cheap(est) thinset / Wonderboard / a jillion more CBU screws. Then I like Versabond for the tile. Yes it is time consuming.... but not terribly expensive. As it happens I'm in the middle of a big tile flooor job at my house right now - 1600 sq feet - and yes it really is a grind.

    As for dealing with the CBU, the 1/4 inch is fine for floors and not that heavy. I use the carbide scoring tool for big pieces, and a diamond dry blade on an angle grinder for the problematic slim cuts. A dust mask is a must. But it's not that bad when you get in the groove.

    I know Ditra is a good product and I have used it when called for... and like using it.... but I am far too much of a cheapskate to use that pricey stuff on everything! I will go to 1" ply, or add structure in the crawl space if I'm worried about the deflection of the floor... never had a single floor tile crack (yet!)

    Thanks for your comments, I will definitely keep them in mind for next time.
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