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Question DetailsAsked on 10/13/2016

can you put lime on dirt in crawl space and put plastic over it this is my question

crawl space what type of plastic to put over dirt

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2 Answers

Voted Best Answer

PS - VB should be installed with some slack so it has freedom to depress into the soil a bit under loads and walking without pulling on the perimeter seal - commonly about a quarter to a half foot of slack all around the perimeter.

Answered 3 years ago by LCD


Not sure why you are putting lime down - if you had a sewage leak or stagnant water under there, that needs cleanup/remediation first, and yuou don't want to "trap" it under plastic - cleanup of the bulk, lime treatment of the rest, then THOROUGH drying out before putting down a vapor barrier.

More on lime treatment in this previous questions with answer -

Also - if you have high groundwater or foundation water infiltration issues (crawlspace gets wet seasonally) a vapor barrier (VB) without sump pump and drain pipe system can result in constantly wet conditions right under the VB leading to odor and wet foundation walls deteriorating.

As for the vapor barrier - in crawlspaces where access for pipe or electrical repair is NOT likely, usually 6 mil or preferably 10 mil polyethylene is used - typically comes in rolls 6, 10, 12, and 20 feet wide and lengths from 20 to 100 feet - running about 6-10 ¢/SF (material only) depending on whether reinforced or not. Best to use a single sheet without any splices for better moisture control, though there is special adhesive sealant to join sheets (use vapor barrier tape as well to hold till sealant cures). Where access for utility repair in the future (wiring and pipes running through floor joists) it is recommended to use 20 mil reinforced poly at about $0.20-0.30/SF for the material. In cases where light storage or possible frequent access is needed 40-80 mil HDPE or Hypalon-type reinforced PVC pond liner is recommended (rare for single family residences), at ballpark $0.50-0.60/SF.

The liner, to be effective in preventing moisture issues in the crawlspace, has to be tightly sealed at any seams and securely and airtight fastened to the foundation - commonly with a compatible sealant on the foundation a couple of inches above the soil level (though higher in some cases where external moisture is coming through foundation wall as well), then the vapor barrier placed over that, and secured and compressing it against the foundation with battens - treated wood best (to minimize rot or insect damage) in 2x2 or 2x4 dimensions all around the perimeter. It should NOT overlap the wood sill plate on top of the foundation - should stop against concrete.

In termite areas a termiticide should be applied to the ground before putting the vapor barrier down, and if possible there should be a foot or more of exposed concrete/stone wall above the top of the plastic before you hit any wood.

With thin (6 or 10 mil) VB, unless the soil is very fine grained (rounded sand or silt) the ground should be smoothed off (not necessarily level) and all protruding rocks/sticks removed, then 1/4" of rounded sand put down first as padding to prevent VB punctures if any maintenance work has to be done in there. 40+ mil VB the rock and stick removal is needed, but sand padding is necessary only if storing materials on top of it (which should be placed on pre-placed pallets or additional layer of 40+ mil liner) to minimize the risk of puncture, and to give it good air circulation all around pallets work well) or if frequent access will occur (like access to HVAC equipment for periodic servicing - it can handle normal occasional worker movement in the area. If a large crawlspace and access for appliance servicing is needed you can also provide a separate strip access for that with heavier material like 60 mil liner plastic, with untrafficked areas using the thinner product. In termite zones NOT recommended to store anything wood or paper or fabric in unfinished areas - metal or plastic pipe or such OK.

If appliances are in there, adhere to fire code on clearances from the appliance to the plastic - and be liberal on clearance, because the plastic sheet burns aggressively and hot and almost always with very nasty poisonous smoke generation. Generally, the appliance itself will have to be on a fireproof platform (concrete usually) over the vapor barrier (or VB sealed around its edges if already in place) - and I would ensure that fireproof base extends at least a full foot beyond the perimeter of the firebox footprint. I recommend 6 feet in the event of oil fired appliances because when they have problems they sometimes spray oil around the appliance for a few feet.

You should check code requirements in your area on plastic barrier use - especially if this crawlspace connects to living space without a fireproof (concrete/concrete block/mortared stone) wall between them - in many areas if exposed to living spaces (like a half-crawlspace connecting directly to basement) the vapor barrier has to be fire-retardant, which about doubles the cost of the material itself. Some areas also have specified minimum thickness of the barrier.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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