Some Red Guard Questions of My Own [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-28-2005, 10:00 AM
Hi everyone,
My husband and I are total newbies at tiling, so we are very glad to have discovered your forum. We had planned just to retile our bathroom floor and replace our fixtures, but apparently we are also retiling our tub surround. When we removed our old bathtub, we discovered the previous tile experts had tiled directly onto sheetrock, which needless to say was rotten all the way through. We stripped everything down to the studs and put up hardibacker -- no moisture barrier because a former contractor said we didn't need one... After reading here, I went out and bought Red Guard. My questions are:
1. When mortaring and taping the joints, do we put the tape into the wet mortar or put it on after it dries? (permission to laugh at the newbie :) ) If after, do we have to wait a full 24 hours?
2. How long after taping and mortaring the joints can we apply Red Guard?
3. What do you use to measure the thickness of the Red Guard?
4. It says on it that it contains chemicals known by the state of California to cause cancer... I know California is extra-careful, but I'm assuming exposure to these chemicals is just during application? i.e. it's not going to in any way affect my baby when she's in the bath tub once tiling is done?
Thanks again for offering all this great advice to us amateurs!

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01-28-2005, 12:18 PM
Here's what we found after removing the previous tile job... The sheet rock crumbled away pretty easily and we even had to remove some moldy insulation behind it.
Did I mention this is the only shower in the house? Help!

01-28-2005, 04:14 PM
Thought I'd reply because Redguard seems similar to the method I use here in NZ.

1. Recommend bedding the tape like plasterers do. Apply the thinset into the joint with a broadknife or trowel slightly wider than the joint/recess. Bed the tape using the broadknife pushing it down into the joint. Apply another coat of thinset and then smooth off by running the broadknife down the joint. Make sure you've got another trowel or similar handy to keep regularly cleaning the gunk off your broadknife.

2. Follow the manufacturers recommendations - do they have a toll free number?.

3. As above. If redguard is similar to the paint on membrane I use, the finished thickness should be 2 to 3 mm (just under 1/8 inch) If Redguard is a thick paste-like consistency just try not to spread it out too much, like you would when painting, let it flow off the brush or roller. Just means frequent dipping of the brush/roller into the Redguard.

4. Just about everything causes cancer nowadays!. Seriously doubt you'd have any concerns once the membrane has cured. I'm no scientist but once it's solidified there shouldn't be any issue with chemicals leaching from it. Greatest risk would be during application without adequate ventilation.

One last thing - I assume the internal corners are being taped and thinset too, not just where the cementboard sheets adjoin each other?

01-28-2005, 05:13 PM
About the cancer risk: After the RedGard is dry, and is tiled over, the risk it poses to your daughter is less than that of a meteorite dropping into her bath. Even asbestos or lead would pose no danger behind a layer of tile.

So go finish your bath and have fun playing with her in the tub. :)

01-28-2005, 06:59 PM
Thanks, guys!
We're taping/mortaring all corners and where the backerboard meets other backerboard. Do we do the same where the backerboard meets the drywall at the top? From other posts, I gather that we should caulk rather than mortar and tape where the backerboard meets the tub -- did I understand that correctly -- 1/4" seems like a large space to caulk?
Thanks for all your help!

01-28-2005, 07:31 PM
You can let the bottom row of tile overhang the bottom of the backerboard a but to make the joint narrower. Fill the tub with water before caulking as it may drop a bit from the weight. Leave the tub full until the caulk cures.

01-28-2005, 08:18 PM

I understand about adding water might stretch the caulk, but there won't be any problem when the water is drained? Sorry, but in my business I deal with elasticity and I am curious as can be! :)


04-21-2010, 07:50 PM
I've been under the assumption that I should caulking all joint where there is a change of plane including where backer board walls meet eachother or the floor as oposed to using morter and tape. Do I have some thing wrong? if not, is it ok to put redgaurd over a corner that has filled with clear silicone caulk? Should I then embed mesh tape into the corner with the redgaurd?

04-21-2010, 08:00 PM
For steam showers we caulk the board but for regular showers with Redgard over them just tape and thinset,then redgard with membrane.