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Kerdi Questions and Answers


Is Kerdi better than cement board?

As you can see, KERDI-BOARD is easier to lift and cut versus cement board. Plus it’s warrantied by Schluter…and that should give you peace of mind.


Can you Redgard over Kerdi?

No, it won’t interfere with the performance or adversely effect it. RedGuard is not harder to adhere to. There is no reason to use both products although it can be easier to use the RedGuard in corners and niches without the build up you can get with kerdi.

Do I need a vapor barrier behind Kerdi?


Kerdi is the vapor barrier, there is no need for anything behind it. Kerdi can even be installed over drywall. Cement board and grout are not water proof, if there’s Kerdi no moisture is ever going to be able to get behind it.


Does Kerdi board go over drywall?

Yes,Kerdi can be installed on drywall or cement board. However if installed on drywall it is only protecting one side. The back side of the drywall fails and it is just as bad or worse than if it had an issue on the tile side. All shower/tub areas should have concrete board (I prefer hardiboard).

Is Kerdi board strong enough?

It has to be pulled straight off or sheared off up or down. Neither would be strong enough to pull the kerdi off. A real world test is to build a test board to simulate your wall condition- Drywall, mortar, Kerdi, mortar, tile, grout.


Is Kerdi fix waterproof?

Schluter®-KERDI-FIX is a single component, waterproof sealing and bonding compound with a silane-modified polymer base. … KERDIBOARD can be adhered with KERDI-FIX in various applications, such as countert ops, partitions, and other building elements. Bonding KERDI membrane.

Can you use Kerdi over plywood?

It is suitable for use over exterior grade plywood.

Can you use Kerdi board on ceiling?

You can install KERDI-BOARD directly to an existing ceiling using thin-set mortar, or fasten directly to the stud frame structure if no ceiling is currently in place. The KERDI-BOARD will protect the ceiling from both water and vapor penetration.

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How long does Kerdi have to dry?

24 hours

Wait 24 hours after the membrane (i.e., Schluter®-KERDI-BAND and Schluter®-KERDI) installation is complete to allow for the final set of the mortar and to ensure waterproof performance of the assembly at seams and connections before water testing.

Is Kerdi band necessary?

Since the matting is made of waterproof polypropylene, the only extra step necessary is to seal the seams and floor/wall connections. … The result is a waterproof installation that will not suffer damage in the event of an unexpected water leak.

How long does Kerdi fix take to cure?


Colour: Grey/brilliant white

Elongation at failure        approx. 200%

Skinning               about 10 minutes

Curing   3 mm per 24 hours

Permissible total movement       about 20 %

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What happens if you use modified thinset on Kerdi?

Modified thinset mortars aren’t recommended for use with Kerdi. They must dry out to gain strength,the membrane inhibits drying, which can lead to unpredictable results. For example, if a shower is used before the mortar has cured properly, leaks and polymer leaching can occur.


Can you plaster over Kerdi board?

Cover Schlüter-KERDI-BOARD with a spackling compound or plaster, if partial areas will not be tiled.


Can you remove tile from Kerdi membrane?

In the worst case, it’s OK to cut the Kerdi, remove the damaged section, scrape up the thinset from the areas, and set a new piece of Kerdi. A pain, yes, but the installation won’t suffer performance-wise. Only took 45 minutes or so to remove the 9 tiles.

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