The situation: a heliport on the 8th floor of a hospital with occupied space below. We will have 10 inches of concrete, a waterproofing system, and 4 inches of concrete as a topping. I’m proposing the use of Ashford Formula to seal the top concrete.
My question: What the heck is the best solution for the waterproofing system between? We’ve discussed bentonite, drainage pan, hot mopped asphalt, PVC membrane, etc., without being able to reach a decision. We need to be certain that no liquid will penetrate this system and that includes jet fuel A.
Ideas?
Hot rubberized asphalt will be eaten by jet fuel. However what is the likelyhood of a spill? PVC may be stable but I’m not sure. Will the chopper be refuled at the hospital? I doubt that would be the case. If there was a fuel leak significant enough to penetrate through a 4" slab then I think you greater safety issues than waterproofing.
On airport work we have done, we have used CPE (Hypalon) for roofing because it is resistant to jet fuel. I have not used this product for waterproofing and don’t know if it is suitable for this purpose.
You might consider a coal tar pitch based system; if I recall correctly, its non-petroleum-based chemistry makes it resistant to deterioration from petroleum products. (It’s used on roofs in petroleum refineries, which produce asphalt.) I heard years ago that the coal-tar pitch roof of the Houston’s art deco landmark Gulf (Oil Co.) Building, a membrane sandwiched in between a concrete roof slab and topping slab, had lasted over 50 years without any problems. (Of course, coal tar BUR components today aren’t quite the same as they were back then.)
(If this is an occupied existing hospital, instead of new construction, disregard my previous message; coal tar would be inappropriate due to fumes, even from the low-fuming variety.) (Not bentonite, either; even below grade it can be problematic…)
This should be a new thread, I suppose, but what are the problems with bentonite below grade?
The problem with putting any just any material over top of a roofing membrane is that one runs the risk of voiding the roof warranty. It would be wise to stay with a material acceptable to the roof system manufacturer.
I suggest roofing the concrete structural deck with fluid-applied modified bitumen system and installing 6" of 100-psi StryoFoam [an acceptable roofing material]. A concrete topping can be placed over the StryoFoam. The 100-psi StyroFoam is manufacturered for the highway industry (usually not shown in the StryoFoam’s Architectural catalog) but it is available. I’ve used this system successfully over fluid-applied membranes under excessively heavy rooftop planters and over an ambulance driveway over a vaulted boiler room in a hospital.
I’ve used the Ashford Formula sealer over concrete garage slabs and it appears to work well with petroleum products. I assume a special roof drain would be required to drain the heliport pad with special filters to clean the water before reaching the storm system.
There is an intregal concrete waterproofing additive the should work fine for your application..The product is C-1000 by the XYPEX corp. advantages are..
Resists extreme hydrostatic pressure from either positive or negative surface of the concrete
Becomes an integral part of the substrate
Highly resistant to aggressive chemicals
Can seal hairline cracks up to 0.4 mm
Allows concrete to breathe>Non-toxic
Less costly to apply than most other methods
Permanent
Ashform Formula has no waterproofing capability and is a clear sealer ONLY..It will not bridge any future cracking.
The link for the Xypex product is
http://www.xypex.com/products/admix1_desc.html