Archive through December 14, 2009

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Author Message (Unregistered Guest) Unregistered guest Posted on Friday, December 04, 2009 - 06:00 pm:    A client has indicated on their drawings the use of cementitious waterproofing under terrazzo tiles on an exterior patio. The patio is located on an existing roof deck, which is a structural concrete flat-slab. Due to elevation limitations, the thinnest possible system is desired. The patio is covered and has a brick masonry low wall around the perimeter. My question, is regarding the use of cementitious waterproofing in this application: is cementitious waterproofing a suitable substrate for terrazzo tiles? TCNA doesn't get specific on waterproof membranes, so any experience with thin-set exterior tile applications over waterproofing would be appreciated? Ron Beard CCS Senior Member Username: rm_beard_ccs Post Number: 318 Registered: 10-2002 Posted on Monday, December 07, 2009 - 12:17 am:    Guest: Based on your description, is it correct to assume that the scenerio is an existing structural deck with a existing roof membrane that is being removed to receive a new tile patio over a new cementitous setting bed .... hence the desire for a "cementitious waterproofing"? There are several questions that need clarification: 1) is there any roof drains in the patio, 2) is there any insulation that needs to be placed under the patio, and 3) is the existing roof membrane still under warranty?. First of all, cementitious anything will not be waterproof, save for perhaps the old-time metallic waterproofing [which should never be used under tile]. A reinforced "mud-set" installation using fully grouted joints will shed water quickly to the nearest roof drain. But the entire system should be placed over a waterproof membrane [preferably a fluid-applied type] directly to the concrete structure below with your thermal installation applied over the new membrane. Terrazzo, or any other tile designed for an exterior application, can be placed on the "mud-set" setting bed. Today most "mud-set" applications are actually a new concrete topping sloped to drains and the tile units applied using a thin-set method over the new cured topping. Roof drain placement needs to be coordinated with the referenced brick wall. If the existing roof membrane is not at the concrete deck level then the brick wall will be needed to separate the two roof systems. "Fast is good, but accurate is better." ....Wyatt Earp (Unregistered Guest) Unregistered guest Posted on Monday, December 07, 2009 - 10:35 am:    You are correct in your assumptions. There are no roof drains and no insulation to deal with. I know that metal oxide cementitious waterproofing membranes are not appropriate for this application, but I was looking at the non-metal varieties, such as crystalline and polymer modified. Ron Beard CCS Senior Member Username: rm_beard_ccs Post Number: 319 Registered: 10-2002 Posted on Monday, December 07, 2009 - 01:00 pm:    Crystallines and additives don't work if there is a crack in the cementitious substrate [crystallines can bridge small cracks but try to explain to the jury that you were only concerned about the small cracks]. Your most important goal is to keep the structure dry and warm. "Fast is good, but accurate is better." .............Wyatt Earp David Stutzman Senior Member Username: david_stutzman Post Number: 59 Registered: 07-2002 Posted on Sunday, December 13, 2009 - 10:53 am:    Tile setting manufacturers such as Mapei offer cement based waterproofing materials. The tile can be thin set over the waterproofing. You mentioned that the patio is covered. Typically tile setting waterproofing is not sold as a primary weather barrier. Dale Hurttgam, NCARB, AIA,LEED AP, CSI Senior Member Username: dwhurttgam Post Number: 52 Registered: 10-2005 Posted on Monday, December 14, 2009 - 01:59 pm:    We have a project of a different type - interior toilet/shower rooms where we had specified fluid applied membrane waterproofing, and the contractor is proposing a latex modified portland cement waterproofing product. I did not feel very comfortable with the proposed substitution - perferred our std. material which essentially becomes an elastomeric rubber membrane. One of the details that we found was that the fluid applied membrane will bridge up to 1/8" cracks whereas the latex modified portland cement will only bridge 1/16" unless it is totally reinforced in which case it indicates that it will also handle 1/8". Just did not feel as comfortable with the flexibility of a "portland cement" based product. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 240 Registered: 10-2007 Posted on Monday, December 14, 2009 - 03:26 pm:    Typically well reinforced concrete should have cracks less than 1/16". The one place where I would be concerned has to do with concrete on metal deck. In many instances there is minimal reinforcing in the concrete, often limited to wire mesh sitting on the deck. I typically see significant cracks in these slabs. These cracks do not impact strength and are typicall not noticable when covered with flooring. This is one place where I would not be comfortable with a cement based waterproofing system.