SFA: What's the Answer?
Slope on Outdoor Countertop
JGCSTONE
Good morning! I’m looking for recourses on installing outdoor stone, specifically the slope needed for areas that will get lots of direct exposer to rain and snow. I couldn’t find anything from MIA about outdoor areas. What’s the industry standard? What are installers normally doing?
We installed a large (120” x 50”) granite outdoor island, with a T-shaped seam (3 pieces, 2 seams) to fit around posts. We live in a cold, wet-weather state and the location of the post was close to where the two seams intersected, so I intentionally set the tops sloping towards the edges slightly. The maximum lippage on the seam was ~1/32 in the center, and flush on the ends. My concern is that the freeze/thaw cycle will be brutal on the seam, so I tried to slope it away from the posts, to keep water from pooling and leaking around the post. I was not given a base that was built with a slope going all one way, and maxed out on shimming just to get it as close as we did. All my outdoor install experience says this was the correct approach, but builder is disagreeing, and says that the seam is unacceptable and needs to be completely flat. Could use any advice you have.
Dave.Scott Premium Member
I do not know of any requirement for slope on an outdoor countertop. I do understand your thought process on it but it takes a bunch of slope (1/4”/ft) to get much flow of water off of the top. Using silicone for the seams is a good move because it will allow for the movement that will occur.
I'd make the GC happy, make it flat, and have him sign off on it. David Scott Architectural Stone of Montana / Slabworks of Montana Bozeman, Mont. 406-522-9001 "What we leave behind is not what is engraved in stone monuments, what is woven into the lives of others" - Pericles
JGCSGTONE
Thanks Dave, I appreciate the input. That’s basically the answer I got from a couple other tradesmen I spoke with since posting. We have some tilesetters who install our quartz shower benches, and they said industry standard is ~1/4”, but it’s somewhat of an unwritten guideline. I was hoping for something definitive like the MIA for indoor granite, but I guess as long as the builder signs off, it’s his decision.
Do you follow a different seam lippage tolerance for silicone soft seams?
Thanks again!
Dave.Scott Premium Member
No, we always try to keep lippage as close to zero as possible.
Mark Meriaux
Natural Stone Institute's DSDM Chapter 16 - Wet Areas calls for 1/4" per foot slope for waterproofing. Outdoor installations aren't necessarily regarded as "Wet Areas" even though they may occasionally get wet. Additional concern should be taken to consider potential absorption of the stone being used, as well as the number of freeze/thaw cycles in your area/climate. There is no standard that I know of for a countertop application. Seams should be made to fail before the stone - they can be re-joined easily if needed. Mark Meriaux Accreditation & Technical Manager Natural Stone Institute 440-250-9222 mark@naturalstoneinstitute.org