use plastic sheet before putting down gravel ?
 

I cleared an area 12' x 20' where I will have a metal RV port installed for my truck camper. I outlined the area with pressure treated 4x6 lumber that the frame work of the car port will sit on top of and will be spiked through it. My goal is the fill the area with 3 inches of gravel. Is there any value to lay down a couple layers of plastic before putting in the gravel ? This is going to be an open car port so just a roof no sides if that matters.

Yes.

Keeps the moisture from rising up, if it doesn't become a swimming pool.

I would think geo cloth would be a better choice. It lets water drain down thru but keeps weeds from growing up. Then the gravel would keep the moisture below the surface.

I never use plastic under anything except impermeable surfaces. Not sure what the standards are in your area, water table depth and drainage considerations might make plastic right for your area.

If it were in my backyard a couple layers of typar or another construction/geo fabric would be the right thing to do. Not the landscape fabric from home depot, unless you want to use 4+ layers (the gravel will eat that).

For your gravel I would suggest a crushed/angular product, not a rounded aggregate like pea gravel or something used in a drain field.

I think it is called "mulch wrap" you lay it down to prevent grass and such from growing through the gravel but it allows water to pass.

+100 much heavier and won't deteriorate over time.

Oh yeah, if you're worried about weeds go down and get a chemical that is used for a bare ground treatment and, following label directions, apply it under the geo cloth.

Visqueen is quick, easy to install and cheap.

He's putting down gravel. Visqueen is not going to hold up for the long haul in gravel.

I assume the idea is to prevent moisture from the earth from rising up through the gravel and rusting the underside of your camper. I would put plastic down, but I would also make sure the soil under the plastic was carefully graded so water that falls on the gravel runs off to the sides instead of pooling on top of the plastic.

:d

If you use a crushed aggregate, weeds will grow regardless of what you put underneath it.

JR

How much for a concrete slab?

My idea will run you in between what a gravel parking area and what a concrete slab would run you. Go to Lowes etc.. and get you a five gallon bucket of cold process roof patch. Mix this 50/50 with diesel and use a cheap garden sprayer to spray the whole area with this mixture. Check locally with your local asphalt company or dump truck owner and tell them that you would like 3-4yds of COLD process asphalt delivered to your place. This is basically the same type of driveway patch that they sell in the 80lb bags at the hardware store. But if you try to buy it a bag at a time it will cost way too much to do the job. Most asphalt companies will have bulk cold process and it will be cheaper. If this option is still too expensive, they do sell the waste HOT process material that you can use to do the same thing, but you will have to break up the larger pieces with a hoe/sledge hammer. It is still new material, just the left overs that have hardened. I have built many a parking area using both of these materials. Best of all you can do the work yourself. Packing the material you can run the vehicles back and forth on it after you spread it out and level it or you can rent a vibratory compacter for a day.

Sorry to not have been more specific... Crushed gravel with no fines. Not sure of your standards/product nomenclature but around here I use 3/8 clear crushed limestone.

Not understanding you guys being stuck on the plastic thing here, do you have water swelling from the ground? I am NOT suggesting the cheap weed barrier material or plastic with holes. Filter cloth will allow the ground below to dry, will allow blown precipitation to drain and will hold up to the gravel for many years. Plastic will not do any of those things. Typar is the brand that I use, I'll try to get some pics of it in action later today.

A lot of good input here. One of the major problems will be durability of the cloth/vapour barrier (especially with crush), with vehicles driving over it. If you place some sand over top between the crush and the cloth/plastic it would afford some protection for the barrier. If you choose plastic, ensure that it doesn't have places where water will pool otherwise the concern of water vapour coming up from the ground is guaranteed, even with the plastic. Cheers

yeah, that landscape cloth stuff might be better

The whole idea of the geo cloth or geotextile is to keep the gravel from sinking into the ground once it's softened by rain. The gravel floats on the cloth. You simply grade your surface, stake the geo cloth to the ground with 6" metal staples every few feet and level your aggregate on the cloth. If there are any drainage issues, sink a drain tiles under the pad.

nothing looks as bad as an area that the gravel is wearing thin, and the plastic is showing.

i would skip the plastic. i would then buy stock in some weed killer company :D