Question about plastic and gravel under new shop

[Marty Walsh]

Ok, Birth of a shop offshoot thread #3 so far...

I'm getting ready to have the concrete piers poured in my Birth of a Shop thread (http://www.sawmillcreek.org/showthread.php?t=36894). Once that's done, I had planned to put down plastic and gravel. I have a few questions before I proceed.

Is there some sort of 'rule-of-thumb' as to how deep I should put the gravel? Frank, in your shop thread you said you put down 37 very full wheelbarrows worth. (There's that wheelbarrow again!! :o ) How deep was it with that many?

I'm asking since I just did the math on how many tons 2 inches deep is versus 4 inches deep for my shop. I've also called a few places to get prices. Sheesh, it's just crushed rock! :eek:

And second, what exact purpose do the two layers serve? I'm assuming the plastic serves as a vapor barrier of sorts, with the gravel holding the barrier in place, as well as provide better drainage. Correct...?

Thanks...
- Marty -

[Ben Grunow]

I don't think you need plastic, maybe just the fabric that keeps the weeds down. Plastic (poly sheeting) is usually used under slabs in enclosed basements and crawls to control moisture. Under an open structure we usually only place gravel (decks mainly) to keep weeds down and avoid mud should you have to go under there. I would just put 2" of gravel in over the weed stopping fabric. The plastic might cause problems if the area under the shop is the low point in the surrounding grade (no cross pitch to the ground to allow run off). Then it might cause puddling (and that would cause ice which might damage your piers and the water would foster mosquitoes in the warm season).

BTW, after looking at the plans for the shop (great space-I'm jealous) it occurs to me that you should have some diagonal bracing going both ways on the legs of the shop. I don't recall what the legs were made of but if they are PT 4x4 or 6x6 they should be braced with long 2x6's bolted through, IMHO. Just a thought. Good luck.

[Jeff Horton]

......I've also called a few places to get prices. Sheesh, it's just crushed rock! :eek:

The stone is just a few dollars, literally. It's the trucking you are paying for.

[Marty Walsh]

I don't think you need plastic, maybe just the fabric that keeps the weeds down. Plastic (poly sheeting) is usually used under slabs in enclosed basements and crawls to control moisture. Under an open structure we usually only place gravel (decks mainly) to keep weeds down and avoid mud should you have to go under there. I would just put 2" of gravel in over the weed stopping fabric. The plastic might cause problems if the area under the shop is the low point in the surrounding grade (no cross pitch to the ground to allow run off). Then it might cause puddling (and that would cause ice which might damage your piers and the water would foster mosquitoes in the warm season).

BTW, after looking at the plans for the shop (great space-I'm jealous) it occurs to me that you should have some diagonal bracing going both ways on the legs of the shop. I don't recall what the legs were made of but if they are PT 4x4 or 6x6 they should be braced with long 2x6's bolted through, IMHO. Just a thought. Good luck.

Well, I'm not sure the weed stopping fabric would be cheaper than the price I've gotten on the plastic, and both would server the same purpose. I like the idea of just 2" since we're talking TONS of gravel!!!

As for diagonal bracing for the posts, have a look at my plans and you'll see that the 'legs' are in fact 12" concrete rebar reinforced piers. I don't think bracing is required or possible. But thanks for thinking.

- Marty -

[Marty Walsh]

The stone is just a few dollars, literally. It's the trucking you are paying for.

Actually Jeff, I found a place that only charges $50 for trucking it to my site. The stone is the real cost...$29/ton!!! And I need A LOT of tons!!!

Still waiting to hear peoples opinions on how thick I need to have the gravel...

- Marty -

[Ian Barley]

Well, I'm not sure the weed stopping fabric would be cheaper than the price I've gotten on the plastic, and both would server the same purpose....

- Marty -
Not really Marty - if you put plastic down it will trap moisture both ways. If your site is a bit low you will get a moat around your shop from the pond underneath it. The landscape fabric is water permeable and avoids any potential problem in this way. For me - landscape fabric and 2" gravel.

[Frank Pellow]

I used the plastic to retard weeds. I could have used cloth to let the water through and would have done so if drainage away from my building site posed a problem.

There is an average depth of about 10 centimetres (4 inches) of crushed stone under my deck and shop.

[Marty Walsh]

I used the plastic to retard weeds. I could have used cloth to let the water through and would have done so if drainage away from my building site posed a problem.

There is an average depth of about 10 centimetres (4 inches) of crushed stone under my deck and shop.

Thanks for the update Frank. The slope on my site is very good for drainage so I think I'll stick with the original plan to use plastic. But, I'm not sure I can deal with 4" of stone. I'll have to look into that from a cost perspective.

- Marty -

[Peter Mc Mahon]

$29 a ton? It must be getting shipped an awfully long way. I recently bought 60 tones [3-20ton dumptrucks] for $525 delivered and dumped in the right spots.

[Cliff Rohrabacher]

I'd not lay plastic unless it was on a slope or a mound of earth either must extend well beyond the building.

[John Gregory]

I poured a slab, so I used plastic as a moisture barrier. However if I were to build on piers, I would use weed block fabric. It seems to me the frabic lasts longer. You don't need a moisture barrier, just a barrier to keep the soil from migrating up through the gravel. Concerning weed control. you will get some shallow rooted weeds because the wind will deposit some soil in the gravel. But they will die quickly due to limited soil and limited sunlight under a building. If you have a Sam's club nearby they sometimes have the fabric at a good cost.

[tod evans]

marty, after giving this some thought why even gravel it? let alone fabric or plastic. just enclose it with the material of your choice, no sunlight, no critters, no wind and far less costly unless you opt for marble...02 tod

[Marty Walsh]

marty, after giving this some thought why even gravel it? let alone fabric or plastic. just enclose it with the material of your choice, no sunlight, no critters, no wind and far less costly unless you opt for marble...02 tod

Enclose it? What sort of material were you thinking about? I'll probably run lattice around the base after the buildings done, but I hadn't planned on ANY enclosure. Enclosing implies a crawl space, and that's something I want to avoid for several reasons.

BTW, I spoke with a contractor in the area and he said he always does the plastic and gravel thing, even in crawl spaces. Says it helps with weeds and bugs. Although I don't understand the bug thing. They can still crawl.

- Marty -

[tod evans]

how `bout anything from dry stacked block to mobile home skirting, the pvc fake rock siding companies sell ect.? any of these are easily removable, will block sunlight- no weeds, still offer the benifits of being "above grade" but eliminate the cost and hassle of rock and fabric. just thinking outloud....02 tod

[Marty Walsh]

how `bout anything from dry stacked block to mobile home skirting, the pvc fake rock siding companies sell ect.? any of these are easily removable, will block sunlight- no weeds, still offer the benifits of being "above grade" but eliminate the cost and hassle of rock and fabric. just thinking outloud....02 tod

Tod,

Interesting ideas. I'll do a little poking around and see what cost around here is for that sort of stuff. I'm not sure I'd like the look, but it's worth looking into. Saving me labor is worth LOADS right about now!!!!

I'm still leaning heavily towards plastic and rock. It's not gonna blow around or get damaged, and it pretty much helps me grade the exterior perimeter. And since our deck has lattice work around it, matching that on the shop might be the way to go. I'm trying what I can, within reason, to have the shop match the house and surroundings.

Your "thinking out loud" is exactly why I post these questions. Thanks for the input...and don't ever hesitate to offer your opinion! ;)

- Marty -

[Don Baer]

I'm with Todd on this one. Use the money you would spend on plastic and gravel to enclose it to keep the critters out. Otherwise you'll have every Cat, coon and other critter making nests under there. When one of em crawls under there and die's you'll be the first one to know about it..:eek:

[tod evans]

marty, how `bout black vinyl behind lattice? .02 tod

[Marty Walsh]

Well, asthetics wins out in the end. Denise and I decided that the shop exterior HAS to match the house, so we're going with lattice work around the bottom. That means that it's going to be plastic sheeting and gravel.

Although Tod, I almost won her over with your idea, especially after I explained the labor and money savings. But in the end, looks is what won out. Thanks for sharing the ideas...

- Marty -

[tod evans]

no problem ya` know ideas and opinions are like.........everybodies got `em..02 tod

[Jim Andrew]

Thickness of rock under slab. Seems to me it depends on how high you
want the elevation of your slab. If you need drainage, you should shoot
grade on the site, and figure out from that . Do not understand why you
do not use fill sand under the slab? Is fairly inexpensive, and will do the
same as rock under a slab, and that is raise the grade. If you fill significantly, say 4", you should use a plate compactor so the concrete
sets on a solid base. And do not fill up to the edge with sand, unless
you fill up with dirt equally on the outside, to keep the sand from working
out from under the slab. I usually dig the sand out along the edge and make the concrete thicker on the perimeter and the concrete keeps the
fill from working out. Jim

[Marty Walsh]

Thickness of rock under slab. Seems to me it depends on how high you
want the elevation of your slab. If you need drainage, you should shoot
grade on the site, and figure out from that . Do not understand why you
do not use fill sand under the slab? Is fairly inexpensive, and will do the
same as rock under a slab, and that is raise the grade. If you fill significantly, say 4", you should use a plate compactor so the concrete
sets on a solid base. And do not fill up to the edge with sand, unless
you fill up with dirt equally on the outside, to keep the sand from working
out from under the slab. I usually dig the sand out along the edge and make the concrete thicker on the perimeter and the concrete keeps the
fill from working out. Jim

Jim,

Thanks for the update, but if you read my "Birth of a Shop" thread that's linked at the start of this thread, you'll see that I'm building on piers, not a slab. I wanted wooden floors and didn't want to have to deal with sleepers on top of a slab. Also, I'm doing ALL the work myself, and I know I'm not capable of laying a slab as big as my shop will be!!

The plastic and gravel I'm putting down isn't for leveling. more for weed control.

And for what it's worth, we're going with between 2-3 inches throughout on top of the plastic.

Thanks...
- Marty -

[Rob Russell]

Ya know, if you have a fairly level area with plastic that's going to hold water, that's a good place for mosquitos to breed even with the gravel. I'd put the landscape fabric down. The whole point of the gravel is so you have something that will drain and the plastic will kill that.

On your lattice work around the base of the shop - to keep small critters out, put dark stainless steel mesh on the back of it before you install the lattice work. That will keep the small rodents and bees from using that nice dry area under the shop as breeding grounds.

[Harry Goodwin]

My shop has a plastic vapor barrier necessary for code and sand. I have had little trouble with rust as long as I hang tools and don't put in a closed box. My dad used plastic under his little metal shop and also had little trouble with moisture. I would not want to live without that cheap plastic. Harry

[Marty Walsh]

Ya know, if you have a fairly level area with plastic that's going to hold water, that's a good place for mosquitos to breed even with the gravel. I'd put the landscape fabric down. The whole point of the gravel is so you have something that will drain and the plastic will kill that.

On your lattice work around the base of the shop - to keep small critters out, put dark stainless steel mesh on the back of it before you install the lattice work. That will keep the small rodents and bees from using that nice dry area under the shop as breeding grounds.

Rob,

The area slopes away from the shop pretty well, to the point that I don't think any water will pool. And the way Denise leveled the site, it's a nice even slope across the entire site.

The plastic's already down, and it's pretty easy to see the vabor barrier effect. There's all sorts of water UNDER the plastic, and not a drop above it. We made a point of overlapping the sheets quite a bit before we started laying the gravel. I think it's going to be fine...

By the way, there's a stream running about 150' behind the shop site, and our pond is a few hundred yards away. We already have plenty of breeding ground for skeeters. Luckily, we have a pretty healthy population of purple martins, dragon flies and geckos.

I like your idea of mesh behind the lattice. I wonder if window screening would suffice...? That's got to be way cheaper than stainless mesh. I have seven 100' rolls of galvanized coming to create a barrier under the joists. I know how PRICEY that is. Having to buy even more isn't a pleasant thought...

The more I think about this though, unless I bury the lattice, there's going to be some small gaps around the bottom of it where it meets the ground. We have the lattice under our deck now, and we haven't had any problems at all with critters. And there's NOTHING we can do to get rid of bees, wasps and other buzzy things around here.

I have quite a bit of time before I get to the lattice. I guess I'll think some more about in the interim.

Thanks for your input...
- Marty -

[Rob Russell]

Marty,

If you're talking about the plastic or fiberglass window mesh, I wouldn't use that - the Georgia sun will kill it in a couple of years. I'd use the metal window mesh - it might be galvanized or just stainless - dunno. If you go with galvanized or stainless and PT lattice (which you want to use anyway because of the ground contact), you can bury the lattice a few inches and keep the critters out. Yeah, something that really wants to dig can get under, but if you go with metal mesh that won't rust and PT lattice that won't rot with ground contact, you can bury the lattice/mesh 6" all around and that'll discourage all but the most determined diggers.

Rob

[Marty Walsh]

Marty,

If you're talking about the plastic or fiberglass window mesh, I wouldn't use that - the Georgia sun will kill it in a couple of years. I'd use the metal window mesh - it might be galvanized or just stainless - dunno. If you go with galvanized or stainless and PT lattice (which you want to use anyway because of the ground contact), you can bury the lattice a few inches and keep the critters out. Yeah, something that really wants to dig can get under, but if you go with metal mesh that won't rust and PT lattice that won't rot with ground contact, you can bury the lattice/mesh 6" all around and that'll discourage all but the most determined diggers.

Rob

Rob,

I plan to use PT lattice for sure, same as I did on the deck I built recently. Burying it might not be a bad idea.

I wasn't thinking plastic or fiberglass screening. I was thinking the old fashioned metal stuff. I guess I'll look around and see what's available, and affordable.

Thanks again...
- Marty -