Capillary-Free granular base for moisture barrier/retarder
Capillary-Free granular base for moisture barrier/retarder
(OP)
Can anyone guide me to a helpful source for a gradation of AB material that is "capillary-free"? I have worked with moisture and vapor barriers in the past, but never one that is made of AB material.





RE: Capillary-Free granular base for moisture barrier/retarder
RE: Capillary-Free granular base for moisture barrier/retarder
RE: Capillary-Free granular base for moisture barrier/retarder
One reason that we like dense-graded aggregates is that they are much better during construction. A subbase (base) of dense-graded aggregate will shed off rainfall, which in turn allows for better site control following rain. Open-graded aggregates, while less likely to facilitiate capillary rise, allow for 100 percent infiltraiton of rainwater. If the roof is not on the building and you have a gully washer, where does all this infiltrating water end up - on subgrade. This perched water within open-graded aggregates has led to numerous subgrade failures, rutting from trucks and highly variable slabs on grade.
Just some things to consider.
p.s., I did a bench test on a dense-graded aggregate (VDOT No. 21A) and recorded well in excess of 2 ft of capillary rise. Textbook calculation, based on the D10 (or is it D20) size would suggest a dense-graded could have up to 40 inches of capillary rise. If you are worried about this use a vapor barrier.
f-d
¡papá gordo ain’t no madre flaca!
RE: Capillary-Free granular base for moisture barrier/retarder
Here are my random thoughts on the subject.
I think that owners are getting conflicting info and current specs sometimes show this.
Owners who have dealt with there floor coverings not sticking are willing to spend money on vapor barriers. As a result I have seen upgraded vapor barrier to 10-15 mil taped together and taped off penetrations placed above 6 “ of crushed 57 stone (I worry that the vapor barrier will be cut or ripped during concrete placement). Open graded natural moves too much during placement. The other increasing problem I see is the (clay) pad is built then by the time the plumber, electrician, computer cables etc are placed more than 50% of the pad is disturbed and maybe replaced with sand, stone? each contractor uses a different material? Wouldn’t 2 feet of medium clean sand be a good replacement for the 6” of crushed stone? Better protection of the vapor barrier can be reused in the trench backfill, gives some resistance to capillary rise. Medium clean sand seem to be hard to write specs to be used in multiple states.
My last random thought!
I still like the vapor barrier buried in 4 to 6 inches of sand.
RE: Capillary-Free granular base for moisture barrier/retarder
RE: Capillary-Free granular base for moisture barrier/retarder
Anyway back to the original question about the AB vapor barrier. Didn't the old BOCA code allow AB instead of visqueen with approval form an engineer?
RE: Capillary-Free granular base for moisture barrier/retarder
I assume by AB you mean aggregate base. In general I believe that aggregate base describes a specific material associated with asphalt or concrete pavements that has specific strength and quality properties.
Given that, if a site is free-draining, such that moisture cannot migrate upward beneath the slab from either internal (broken pipes) or external (landscape, groundwater, etc.), then the gradation of the material supporting the pad shouldn't really be restricted, other than by the ability to construct on top of it without creating depressions resulting in thin and thick spots in the slab.
If there is no potential for water development beneath the slab, then the vapor barrier actually refered to by ACI 302.2R-06 and ACI 360R-06 as a "vapor barrier/retarder") would in my opinion not be necessary.
Check out ACI 302.2R-06 Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials for more information and guidance.
RE: Capillary-Free granular base for moisture barrier/retarder
RE: Capillary-Free granular base for moisture barrier/retarder
f-d
¡papá gordo ain't no madre flaca!
RE: Capillary-Free granular base for moisture barrier/retarder
Remember water vapor can travel upward nicely through free draining material.
I have done most of my work in the Midwest so I have never seen a site that has no potential for water development under the slab.
The new flooring glues are much more environmentally friendly but a little bit of water vapor and the don't stick.
I would say that ACI has been behind the times on this issue over the last 10 years or so.