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Rick, General Contractor
Category: Home Improvement
Satisfied Customers: 21528
Experience:  Licensed construction supervisor with 35+ yrs. experience.
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Do I have to use 6 inch fiberglass to seal backer board in

Customer Question

Do I have to use 6 inch fiberglass to seal backer board in my shower? Or can I use 2 inch backer board joint tape with thin set to seal it?
Submitted: 1 year ago.
Category: Home Improvement
Expert:  Rick replied 1 year ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can

continue our conversation.

You can use 2" fiberglass mesh tape. You lay a thin layer of thinset over the tape to "seal" the joint. You have to be very careful to keep this layer thin or you'll create a hump which will throw off your tile. The primary reason for the thinset is to keep the tape in place when you lay your setting mud for the tile. You can even do without the layer over the tape if you're careful but it's easy to catch the tape with your notched trowel.

Customer: replied 1 year ago.
Should we be using this waterproofing membrane over the top as well?
Expert:  Rick replied 1 year ago.

If you're using cement board it's not waterproof in that it will let water through. The trowel on membrane is never used for this purpose. If you want a backer that has a water proof surface and is waaaay easier to work with than cement board then take a look at DensShield by GP. It works just like sheetrock.

It's widely available but you may have to look around a bit for it since not everybody carries it. Here in MA/NH most Lowes (they sometimes call it DensGaurd) and Home Depot's carry it.

Customer: replied 1 year ago.
We used hardie backer board 1/2 inch for walls in showers.
Expert:  Rick replied 1 year ago.

HardiBacker is more resistant to water penetration than cement board but it's still difficult to work. Take it from somebody who has remodeled bathrooms for over 40 years, DensShield will make this job a lot easier.

Customer: replied 1 year ago.
The hardibacker is already installed
Customer: replied 1 year ago.
We are concerned with sealing the seams and corners
Expert:  Rick replied 1 year ago.

Ok, then my original answer covered this. No need for trowel on water proofing at the seams. I would caulk the seams with a vinyl caulk like Phenoseal before you apply the mesh tape if you want a tight backer but the water should never get that far anyway.

Customer: replied 1 year ago.
Ok thank you. I am going to leave this open in case we have a question while we are doing it.
Expert:  Rick replied 1 year ago.

You're welcome. This thread never goes away and I'll answer related follow up questions even after you rate me favorably.

Expert:  Rick replied 1 year ago.

Do you have any more questions?