Concrete topping slab thickness

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Author Message Anne Whitacre, CCS CSI Senior Member Username: awhitacre Post Number: 186 Registered: 07-2002 Posted on Monday, May 02, 2005 - 08:15 pm:    I've got designers who want to put in a 1" thick concrete topping slab in a high traffic area, and I can't find any "real" criteria that tells them not to do it. I have PLENTY of anecdotal and project experience that tells me that this is a bad idea, but we have the type of contractor where we need an "authority" to be able to reject anything. Can someone point me in the direction of topping slab design criteria? I've done a search and again, can't find a source that will help. Thanks Ronald L. Geren, RA, CSI, CCS, CCCA Senior Member Username: specman Post Number: 130 Registered: 03-2003 Posted on Monday, May 02, 2005 - 08:21 pm:    What's the intended purpose for the topping? Aesthetics, durability, both? In either case, I'd look at something with a high compressive strength (i.e. Ardex). Standard concrete as a topping isn't, in my opinion, the way to go. Anonymous   Posted on Monday, May 02, 2005 - 11:55 pm:    As I remember it the ACI (American Concrete Institute) addresses this issue in its Manual of Practice. Thin topping slabs tend to crack. In order to control the cracking you have to excercise special care with bonding and concrete mix. George A. Everding, AIA, CCS, CSI Senior Member Username: geverding Post Number: 31 Registered: 11-2004 Posted on Tuesday, May 03, 2005 - 01:08 am:    The right way to do it is improve the strength of the concrete, and glue it down, to paraphrase the comments above. Contact the chemists/engineers/technical folks at one of the companies that figured out how to do it right (Euclid, Sika, DeGussa, or another name you trust) and have them provide the ammo you need to convince the contractor that 1” of topping, unmodified and unglued, is the wrong way to do it. Anonymous   Posted on Tuesday, May 03, 2005 - 06:59 pm:    It's possible to use Raeco, Ardex, and the like to get a 1 inch thick "topping" slab and have no worries about cracking or debonding, in installed in accordance with manuf. instructions. Bigger aggregates are added to the self leveling mixes, as I understand it. Di Ann Hassloch (Unregistered Guest) Unregistered guest Posted on Thursday, March 09, 2006 - 11:47 am:    We have a parking garage with a damaged surface where the plan is to use 3/4" of Perma Crete as a decorative finish. Does anyone have any experience with this product, and do you think it will hold up in Biloxi, under traffic? It is listed as 6000 psi, and supposedly is used in numerous horizontal construction renovations. Thank you Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 178 Registered: 12-2002 Posted on Thursday, March 09, 2006 - 01:17 pm:    I think you DO want to encourage this 'topping' approach but change your thinking. The key factors are hydration, bonding, flexibility - NOT compressive strength. A product with compressive strength similar to the substrate will usually perform better in a repair situation. Also, you want a polymer modified product to aid flexibility. Strengthing the bond characteristics is extremely important, so be sure to specify development of a 'profile' to meet the manufacturers recommendations - no more and no less. Select a bonding agent when recommended, and choose a complete system with a technical field person administering the repair. Don't rely solely on a product rep unless you know for certain he/she wasn't selling copiers last week. The classification of useful products might be actually a mortar, not a 'topping'. This is because the product will have the consistency and working characteristics of mortar, not concrete. And if you think about it, a 'mortar' is quite workable and formable when you have an existing slab ready-made as a working surface. Try 'Dura-crete' (L&M); or WR Meadows 'Seal-Tight Meadow-Patch T1'. Be careful to talk with the rep to make sure you get an architectural product as opposed to a civil/industrial product if that's what you're after. Anonymous   Posted on Thursday, March 09, 2006 - 05:43 pm:    It seems that there must be some reason to use a higher compressive strength product since Ardex requires their 6000 psi product when exposed to traffic. I have specified this for pedestrian traffic surfaces for years, and not the lower 4000 psi product, at the recommendation of the manufacturer. Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 180 Registered: 12-2002 Posted on Thursday, March 09, 2006 - 06:43 pm:    I think the distinction that was being made was Di Ann was addressing a parking garage substrate. Most garage slabs are quite flexible (under dynamic loading), in which case high compressive strength products tend to have reduced ductility and increased hardness. Those characteristics are somewhat at odds with the desirable 'thin-ness' and bonding characteristics for that garage application. For what it's worth I am a fan of Ardex's products, although they do have a tendency to do things right (from my experience), hence they've been expensive on my projects, and their stuff works so don't hear me dissing their products that compete with the concept I parroted previously. Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 181 Registered: 12-2002 Posted on Thursday, March 09, 2006 - 06:45 pm:    oops run-on sentence!