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Plaster Filler - Whirlpool Tub Installation

Plaster Filler - Whirlpool Tub Installation


Old 06-07-05, 10:36 PM
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Plaster Filler - Whirlpool Tub Installation

We are in the process of installing a drop-in Jacuzzi bathtub. The cement board was installed (as per installation instructions) directly above the flange. It shows to fill the 1/4" gap between the cement board and the top of the tub with plaster filler. Is there another name for this? We have not been able to find anything with that name. We are concerned about making it a waterproof seal. We did find some expoxy type fiberglass material used for boat repairs. Is this what they're talking about?


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Old 06-07-05, 10:50 PM
Doug Aleshire's Avatar
Join Date: Feb 2002
Location: United States
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Here is a prewritten item I did awhile back.


Studs should be spaced a maximum of 16" o.c. (Edges/ends of backerboard parallel to framing should be continuously supported. Provide additional blocking when necessary to permit proper backerboard attachment.) INSTALL ¼” FURRING STRIPS TO ALL STUDS BEFORE INSTALLING BACKERBOARD. Do not install backerboard directly over protrusions from stud plane such as heavy brackets or fastener heads.

Moisture Barrier: While cement boards are unaffected by moisture, a moisture barrier must be installed to protect the wall cavity for wet area installations. Nail or staple 15 lb. roofing felt or 4 mil. to 6 mil. Polyethylene sheeting to the studs.

Installation: Precut the cement panels and make necessary cutouts. Install backerboard leaving a 1/8" - 3/16" space at all joints and corners. Stagger board joints with those of adjacent rows. Fasten backerboard every 8" o.c. along studs. At all joints and corners prefill gap with polymer-modified mortar, then embed 2" alkali-resistant fiberglass mesh tape and smooth material over joint and corner.

Any shelf, ledge or horizontal surface subjected to water exposure needs to have a slight downward slope for water run-off. These areas also require proper waterproofing. Apply RedGard or Trowel & Seal Waterproofing and Anti-Fracture Membrane.

When installing the backerboard, leave an 1/8” – ¼” space along the area where the wall meets the top of a tub (nailing flange) or shower base (nailing flange). This area will be caulked later with silicon caulk. Caulk is flexible enough to allow movement—settling or expansion and contraction—without cracking.

Hope this helps!
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