View Full Version : geofabric or geogrid under patios?
08-15-2002, 06:30 PM
I have used the search feature and have not been able to locate this topic. I am working with an architect that is insisting on me placing geofabric (or grid: he isn't sure which yet) in the base of my patio. He says that it should help prevent settling. His instructions are:
1. Install 3/8 to dust traffic bond in two two inch lifts (compacting in between lifts)
2. Install fabric
3. Install remaining two inches of base and compact.
I really don't think that this will make that much of a difference but figure that it won't hurt. He is also eliminating the thin layer of mason sand that goes between the base and pavers and replacing it with TB dust (finest particles of crushed limestone).
I would appreciate anyones view on these ideas. For the most part I think that architects just throw these things out to feel superior of something. Not all architects just the majority.
Thanks in advance.
08-15-2002, 08:23 PM
If you must use geo textile or geoweb it should go under the dust traffic bond. Do the dig out, place your textile then place and pack your base. The textile will help prevent settling if you have poor soil conditions but is totaly unneeded in most situations and is just overkill.
08-15-2002, 08:34 PM
did this archictect take a soil sample at the site or dig a test pit or something? Not for nothing, but if someone is telling you to use something and doesn't even know what it is he's telling you to use, I'd really question it.
I get the feeling that this is a 'trend' that we may all be going to see in the future......
that is the installation of fabric under all paver installations.
I went to a belgard installation seminar earlier this year, and they were all over the idea of installing fabric under 'ALL' jobs..........and of course, they also strongly suggested using 'belgard' brand fabric.........lol.
I really would not be surprised if over the next couple of years you start seeing all manufactureres recommend fabric......and why not, just another way to cover their ends.
08-15-2002, 09:40 PM
If this architect wants to cover himself, he should look at the current industry standards. Geogrid is for retaining walls. A geofabric is used under the compacted base for pavers. Several months ago I took up a paver job that had failed. That is the pavers had crumbled. Turned out that a thick matted geofabric had been laid under the sand setting bed. The area had been heavily salted during the winters and the salt stayed on top of the fabric (because the pores of the fabric clogged) and corroded away the concrete pavers. Lesson: Put the fabric under the base to prevent the base course from settling into the sub-base.
We have argued the point about the setting course material in earlier threads. Sand is better for creating an interlock that won't break down.
08-15-2002, 09:44 PM
I've only heard of using the geotextile or landscape fabric under paver installs if the soil under it was unstable, like clay . The fabric goes on the soil then your base goes down. What it does is prvent the base from settling or working its way into the soil and causing the overall job to fail.. I have only needed to use it on a few jobs. The GEO GRID on the other hand is completely useless on a paver install... THe whole purpose of this product is primarlly for larger retaining walls. To lock the wall units into the soil and backfill.. Kind of like hi tech dead men.... THey have 3/4" holes in them that would not keep the base of a paver install from failing, just a waste of your time and cust 's money...
More and more engineers are looking at grid to reinforce subsoils, now I don't know what is under your patio. If you have poor unsupported soils that are too deep to remove(read as not cost effecitive) then a grid system might be the ticket, but using it just to use it doesn't mean it will work. on very poor soils we have used it under pavers but we went 3' past the end of the pavers using the roots of the grass to help support the grid. As so you have to use bi-axile grid not uni-axile grid which is much cheaper.
08-15-2002, 11:51 PM
There was an interesting article several months back, I don't recall the magazine, but they discussed a paver project in Miami, where the usual traffic was 80,000# vehicles at the loading docks (not counting the cargo). They installed 3' of base, and actually used grid, not textile. The grid helped to stabilize the base, with larger stones getting trapped within layers of the grid, tightening up the stone interlock.
But back to the task at hand, geotextile a couple inches from the surface seems without value. Install as Dan/Lanelle recommend.
08-16-2002, 06:57 PM
I sort of remember that article and I too cannot remember where. I seem to remember it wasn't really like geogrid but more like a honey comb type of grid about 3" thick. I seem to recall it kept the base from migrating sideways and thus stabilizing every thing. Does that ring a bell? I will look for the article this weekend.
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