Sanding the Hardiebacker mortar before redguard & tile?

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Old 08-22-15, 10:51 AM
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Sanding the Hardiebacker mortar before redguard & tile?

Here is where I am at with my shower remodel... I have put up the Hardiebacker concrete boards on the wall. And I have also just finished taping and mortar floating the Hardiebacker seams.

Before I paint on the Redguard waterproofing membrane and start tiling... Should I sand down the mortar a little bit so that I have a perfectly flat surface on which I can then apply Redguard and then thinset mortar & tile?
 
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Old 08-22-15, 01:26 PM
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Using the right width knife and holding at the right angle it should already be smooth enough.
How rough is it?
 
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Old 08-22-15, 07:00 PM
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...and tonic's reply is........?

Jaz
 
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Old 08-23-15, 04:25 AM
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Don't know what you would "sand" it down with, it is a cement based product. You can lightly scrape any high spots off with your putty knife to make it a little more smooth. Keep in mind that the notches on your trowel will provide you with some relief to float over minor imperfections. If on the other hand, you "went to town" with the mortar at the joints, you may want to consider starting over and being a little more frugal with the application of the mortar.
 
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Old 08-23-15, 08:37 AM
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Tonic,

Try not to sand as there's bad stuff in both the thinset and Hardie. Silica is not good for your lungs although a brief encounter may not be harmful. Why chance it?

We often see people make speed bumps while taping the joints. It's bad technique. Next time use a min. 6" wide flex knife and make the thinset a bit looser than normal. Or, tape as you tile so it doesn't harden.

Jaz
 
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Old 08-23-15, 08:44 AM
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Silica is not good for your lungs although a brief encounter may not be harmful. Why chance it
This is why dust masks were invented.
 
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Old 08-23-15, 03:45 PM
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This is why dust masks were invented.
Yes, I know, but a simple dust mask is not good protection plus the dust also gets on clothing, floors, etc., then people sweep it and guess what? You really need an approved mask/respirator and most people don't have one sitting around.

I'm guilty of just doing as you say, but it's not the right thing to recommend to others. Heck, most pros don't even use a mask unless it's a large area to sand/sweep.

Jaz
 
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Old 08-25-15, 10:06 AM
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Thanks guys. I actually did go aitt bit overboard with the taping and mortaring in a few spots because I'm paranoid of water leaks. I ended up buying something called a rub brick in the cement aisle at Home Depot. It took down the high spots of mortar ok. In fact, I probably took down a little bit too much and ended up with an area where the Hardiebacker screws are showing through. Oops! I didn't actually notice that till after I started painting the Redgard waterproofing membrane on.
 
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Old 08-25-15, 11:02 AM
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No problem with the screws. Remember, two good coats of the red stuff.

Jaz
 
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Old 08-28-15, 11:49 AM
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Thanks Jaz. And thanks everybody for the advice. I have it all pretty decently smooth and flat for the most part and onwards to painting on the waterproof membrane Redgard.
 
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