"floor" for garage

[patrick_g]

Eddie, I'm not going to write a 20 page thesis on concrete. Be assured I understand about water in concrete and how some of it goes into chemical reactions and is no longer available as water and the excess (added to make handling the concrete easier and to control cure speed, cracking, etc) humidifies the space above the pour during cure.

The chart we were given the link to agrees with all my previous learning. More or less standard mixes reach about 90% of the final strength in about 28 days. In theory concrete never finishes curing but instead asymptotically approaches a final value (also visible in the referenced chart.)

The test I described (vapor barrier taped to the concrete) can be used as you describe to judge the rate at which concrete is losing water during initial cure but it can also be used on 50 or 100 year old concrete too and if the test shows too much water you don't but certain kinds of floor coverings down. Among those that aren't suggested for wet locations is porcelain tile because it is like glass and doesn't pass the water, allowing the vapor pressure to loosen the tile. There are other coverings that don't "like" water as well.

Excess water indicated by the afore mentioned test applied to old slabs is NOT left over from the initial pour but is transported through the slab. Uncovered floors may not appear wet because the water may evaporate as fast as supplied. Your shirt sleeve may not appear wet on a low RH day even when you are working but that isn't because you are not perspiring at all it is because it is evaporating fast enough to not feel wet.

Now for your supporting cast who are hung up on water going uphill. Can you say capillarity? stick a rag in a glass of water and, over time, the rag gets wet way above the water level. Can you find a wick for an oil lanp or Tiki torch? Put one end in water and support the other end STRAIGHT UP INTO THE AIR. Water will make it STRAIGHT UPHILL to the top of the wick. Concrete does this too, just not as good. Now I know we have all heard the term heart wood but surely no one thinks a tree has a heart that pumps water up to the top of the tree. How do you suppose it gets there? (See also capillary action.)

I'm sorry we ended up on opposite sides of this discussion as you have quite a following on this site and I am not getting any points for taking up a contrary position but I feel the need to support the side of science and engineering on this one.

Pat

 

[gemini5362]

This is good a nice topic with two different sides to the discussion.

1. Eddie I use laminate floor quite a bit. I have started reflooring all my rental houses in laminate to get away from carpeting. The instructions for laminate flooring tell you to put a vapor barrier down. All the brands I have used tell you tape the vapor barrier with a cloth tape with agressive adhesion capbilities. I interpret that to mean duct tape. I have not seen any that advocate just masking tape. I know some people do that but it is contrary to the instructions and in my opinion negates the vapor barrier. The instructions in the laminate flooring I have been using tell you to do a test to see if moisture is coming through the concrete. Prior to installing the laminate

2. A friend of mine and I were in OKC and went to visit patrick g. I have worked with engineers for years. I have been a field engineer and have worked a lot with design engineers. I can tell you beyond any shadow of a doubt that Pats house just screams out " I was designed by an engineer. " His house has so much overkill that I cannot imagine him not knowing or at least researching every facet of the material that went into the building of it. I would include the concrete floors in that. I agree with him 100 per cent about the wicking action of concrete.

 

[woodchuckie]

Is there a moisture barrier I can apply on top of the concrete in the floor of my shop. It use to be the third bay of a three car carport till I walled it up and insulated it. Anything not cromed or painted will rust in no time. When the temp and humity is right, water pools inside the shop just like outside on the carport.

 

[Red55]

JUST a thought could you both be right? Personally I would never pour a slab without a vapor barrier. . . But something has to be said about field conditions. (ie hot dry Texas vs damp & wet north?) My understanding of vapor barriers down south are on the exterior vs on the interior up north, with regards to wall insulation. And homes are conditioned spaces either heat or A/C which will remove the moisture out of the air and dry out the concrete slab ED

 

[Builder]

Is there a moisture barrier I can apply on top of the concrete in the floor of my shop. It use to be the third bay of a three car carport till I walled it up and insulated it. Anything not cromed or painted will rust in no time. When the temp and humity is right, water pools inside the shop just like outside on the carport.

I have seen this happen in other buildings.

Try ventilating the garage with a ridge vent in the roof or gable end wall vents at the peaks or just crack a window or two if possible. If none of those are possible, run a fan to help dry out the air.

You can check out the garage floor paints that are made to be applied over concrete garage floors. Read the label first to make sure it will work in your conditions.

 

[EddieWalker]

I live in East Texas. We get around four feet of rain per year and it's extremly lush and almost tropical with the extreme humidity and moisture. Saying that it's drying in Texas might be accurate, but not so for East Texas. Imagine Louisiana if you're not familiar with this part of Texas.

Yes, I understand capilary action and realize that to some degree, this is possible. What I fail to grasp is why gravity doesn't have the same effect on concrete, and why capilary action only happens inside a shop, not the living area of a house?

If it works in one area, it should be a universal occurance all throughout a slab foundation. Why isn't there moisture on the concrete in the areas of a home that have AC and Heat? I'd think that if this was true, then around all the plumbing drain lines, there should be wet areas. Has anybody ever come across this? Capilary action would sure work allot better with a seam then through solid concrete.

I'm not aware of aged concrete not being suitable for floorings. I've never come across this, nor heard of it happening. I don't know enough to say it's not true, just that it must be very rare and one of those exceptions to the rule type of situations.

I've also never heard of concrete being too wet for tile. Once concrete has cured, it will hold tile. I've never heard of it being tested before putting down tile, nor heard of it failing because of wet conditions. Swimming pools, tubs, fountains and patios all hold tile without any problems when properly installed. What could be wetter then a swimming pool?

Laminate flooring is the main one that I'm aware of that you have to be concerned about with moisture content in the slab. Once you can leave the plastic down for 24 hours and not get any wet areas, then it's safe to install. If capilary action, wicking, or any other method for moisture to work it's way up through solid concrete was in effect, then it should be reasonable to expect that plastic test to fail forever in some areas. For those of you who live in what you consider wet locations, does this happen? Here, with the worse raines of the last fifty years, concrete dried without any problems and floors passed the test to install laminate flooring. With all that rain and moisture, this shouldn't happen under those conditions if I'm wrong.

I'm not trying to disregard science or the experts here. These are just my observations and opinions based on what I consider to be common sense. Swimming pools never gain water when empty from the ground, and water doesn't leave a pool in the oposite manner. I don't know if concrete is water proof, but it sure does a great job of keeping water in a tank for livestock, or a septic, or just about anything it's used to store water. It's not different concrete that's used, so how come it lets moisture travel one way through it, against gravity on slabs in shops, but not the other direction with gravity, or in any other application that it's used?

Eddie

 

[Lynkage]

Lynkage - not sure if they have the recycled asphalt around here. How tiny do they grind it?

It is usually about 1/2" to 3/4". It is also best if you can do it on a hot day with a plate compactor. It will sort of melt together again. You should be able to find it where you can find crushed concrete (road base). Most of the ready mix companies will have a sand and gravel pit.

 

[jimmysisson]

As someone posted this may a ground-conditions difference. Here in the northeast, our soils are fairly damp. Vehicles parked over grass rust. Cars and pickups parked in dirt-floor garages rust, if the doors are closed. Open sheds, cars don't rust. Tractors are mostly painted underneath (at least when new) and rust less.
We typically put 1" of foam under garage slabs and 2" under house slabs, this with a full frost wall (4' below grade per code). In the garage, that lets the slab maintain temp closer to atmospheric, and reduces sweating, which is wicked in early - mid summer. Insulated slabs barely sweat. In a house, the 2" breaks the capillary action, and keeps the slab closer to house temp.

Per the OP, around Mass you'd scrape off the topsoil maybe 12" and replace with pervious material - whatever's best/cheapest in your area, over landscape fabric to keep the under-soil from pumping, if it's wet or clay. Recycled asphalt must have something else for binder or it won't pack, in my experience. But, many materials will pack and not wick. If you later want concrete, scrape out enough to get your slab where you want it, plus 1" foam. You won't regret it.

 

[Builder]

I use crushed concrete. If it gets damp and compacted, it makes an amazingly tight, compact surface.

 

[daTeacha]

After reading all the various opinions and positions on the moisture topic, may I offer a simple suggestion?

Check with your local building code. If local conditions are such that water vapor from the ground is a problem there will be a requirement for a vapor barrier beneath occupied structures. If the conditions do cause such a problem, there will not likely be such a requirement.

This, of course, presupposes that you have a local code rather than adhering to national standards or perhaps like some counties around here, have none at all.

Water can travel in all directions through soil, up, down, laterally, or whatever combination of the above you wish. Same for concrete. Whether it shows up as condensation above the floor will depend on the temperature of the object in question, the temperature of the air, the relative humidity, and the dew point.

Regarding trees, Pat, water moves up through a combination of factors such as capillarity, transpiration pull, and root pressure. The latter is essentially caused by osmotic pressure as water moves through the semi-permeable membranes of the root hair cells from the relatively low salt/nutrient concentrations of the soil water into the higher solute (and thus lower water) concentrations of the interior of the cells. The cells also undertake active transport of the water, expending energy to bring it into the cells and increasing the pressure inside the root. This is why a stump will "bleed" when a tree is cut down.

Eddie, regarding the movement of water in concrete, the direction of net motion is dependent on simple osmosis. Concrete is slightly permeable to water. Given time, water will move through it in whatever direction the balance of forces acting on it direct. Like soil, it can be up, down, sideways, or whatever combination works for you. Like soil, whether you see the result of that movement will depend on the conditions extant at the end of the journey. Quite often it will enter the air as vapor, which can then condense on cold objects like tractor steel, the inside walls of a building, etc. Sometimes, it will simply stay in the air as a vapor (not fog, an invisible gaseous form of water) and leave the room with a change of air.

The whole business of whether or not you will get condensation in a building of a particular design is highly dependent on local conditions, which include soil as well as air.

 

[patrick_g]

Rich, I wish I could have said what I know about the flow of liquids in trees as succinctly as you did. Yes, all that is true but not the point I was making. I was offering an example of water flowing UPHILL without a mechanical pump or head of pressure from an elevation. How it did it, although interesting and well stated by you, was not a required part of the example.

Wicking, or osmosis, will move water in any direction and is much stronger than gravity so it will flow water uphill.

We have no code requirements regarding the use of vapor barriers where I am so you are left to the experience/knowledge of your contractor/sub team or other inputs such as my personal requirements based on many factors including standard practices from areas were slip joint pliers aren't considered high tech and other sources.

My basement floor is 5-7 feet below the water table. It and the walls are unsealed concrete. They are so dry that vapor barrier taped to several wall and floor locations for 10 days does not even discolor the concrete much less show any droplets of water as is often the case.

The only time I got water in the basement was when I was using a 2 inch engine driven pump to make a slurry of the sand backfill and some of the embedded snap-ties leaked a little liquid when a few feet of head was applied. Since then, even this year, the wettest year on record, The walls and floor are quite dry. I have no sump or pump. I have porcelain tile on abouit 1/2 the floor and it is non permeable and will pop if it gets much water vapor coming through the slab. The rest is glued down carpet and likewse has no problems.

There is a vapor barrier under the floor and the seams are taped with a special tape sold for that purpose. There is 2 inches of rigid foam under the vapor barrier and 16 inches of washed septic gravel under the insulation.

I excavated the original grade about 12 feet to have a walkout basement and had to allow for drainage as the hole wanted to be a swimming pool. About 10 feet from the basement wall on the walkout side there is a stand of cat tails growing in the yard beside the patio slab. They are naturally occuring, I did not plant them. They flourished during last year's RECORD DROUGHT.

Pat

 

[AndyMA]

Don't know where in CT you live, around this northeast area, most use Amrec,, This is a combination of asphalt millings, broken up concrete Jersey barriers, 1/2 " stone, and on ocassion you will find new shingles that didn't make the grade, ground up and all this concoction has binder put in., I have most of my 1600 ft driveway in Amrec, most municipalities Ct and lower Massachusetts use Amrec to go over gravel and or dirt roads. Once a rain hits it, it binds right up tight and is hard as concrete.

Amrec is the company name of a company in Charlton Mass that reclaims many materials and turns them into a usable product. Here is there web site.

..:: Amrec ::..

Andy

 

[daTeacha]

DanG, Pat! I thought I had a chance to educate you a little. I figured your engineering background left you a little light in the biology area. Oh, well.

Your basement sounds like the barnstone wall I just had put in -- my dX29 will not pick up and move sandstone blocks measuring 5' x 2.5' x 2.5', no matter how nice I talk to it, so I hired it done. Anyways, the stones are two courses thick, holding back a hillside. The lower course is on pea gravel and carefully tamped with the bucket of a track hoe to level the tops of them. The area behind this course, which backs into a layer of broken shale in the hillside, has a perforated drain surrounded by more pea gravel and is about 2 feet front to back. The gravel layer was brought up level with the top of the first course, then crusher run was laid on top of that to serve as a platform for the second course. More pea gravel was laid in to within about 3 inches of the top, then finished with dirt. I don't think there will be any problem with frost heaving in my wall.

Subgrade construction around here usually involves laying in a subfloor and peripheral drain system as yours must be, plus a vapor barrier on exterior surfaces. I'm on the glacial moraine and the soils in my county are all mixed up, ranging from broken shale to gravel, muck to clay, and lots of good loams for farming with plenty of glacial drift rocks thrown in for good measure, plus a little swamp (15,000 acres) here and there, the occasional bog, and some artesian wells and springs. The building code needs to be pretty comprehensive and any septic system must be specifically designed for the site and approved by the health department before any work can start. And yet, a few miles away and across county line, anything goes since there is no code!

Do you have Radon in your area? The common solution around here is to install a section of perforated pipe through the basement floor and connect that to a vacuum pump so you are constantly removing the air from the soil beneath the floor and pumping it outside. I don't have a condensation or moisture problem, but can't help but think something like the Radon system would help alleviate it if I did.

 

[patrick_g]

Rich, My favorite aunt was a highschool biology teacher for almost 40 years and ALWAYS lectured about everything we saw hunting and fishing together or just nature walking. She never cleaned fish or dressed a rabbit or turtle, they were dissected (with lecture) then cooked and eaten.

Radon: My take on handling a potential radon problem in my basement was to bury a 4 inch perf drain pipe under the basement floor within the 16 inches of washed septic gravel. I have a super good vapor barrier on top of the gravel and 2 inches of rigid foam insulation. The barrier plastic (Stego Wrap) is taped at all seams and penetrations with an expensive "super tape" for that purpose (NOT masking or duct tape.) The perf pipe is reduced to 2 inch for the vertical run to the house top away from windows.

I don't know if I have radon, the "FIX" was so simple I did it instead of testing. This is not a particularly HOT zone for radon but better safe that irradiated. One of the worst offenders in radon is shower water. Well water often has radon and it is released in your shower. I have an exhaust vent in the ceiling of my tile shower and it is exhausting air 24-7 but at varying rates as controlled by a humidistat.

I have two French drains at the elevation of my foundation (2 ft below the top of the floor.) One is all the way around the basement on the outside of the foundation and the other on the inside. This gives you 4 ends. Each is run underground to a backyard pond independently. Should a pipe plug the water in the French drain will get an inch deeper and drain out the other end.

I also have an intercepting trench parallel to the front of the house (the uphill side) but about 8 ft away. It too has a French drain in it which has its own run to the pond. All 5 of these drain lines have been running a small but fairly steady stream of clear water sine they were installed. After all they are installed below the water table on a slope so the high water level of the pond is about 5 ft below the French drains.

All the French drains are 4 inch perf pipe embedded in washed septic gravel and that all wrapped in geotextile and backfilled with gravel for the first few feet and then a layer of geotextile and then sand.

This drain system (and the foundation) was designed in collaboration with a consulting soils engineer who brought out a drilling rig and operators to drill a bore hole and take soil samples every 6 inches till we hit solid rock in the middle of the basement site prior to excavation. I like the results. This is the wettest year on record in Oklahoma and the floor and walls of the basement are quite dry as tested with plastic coverings left on for a week.

Pat

 

[daTeacha]

Radon around here is very spotty, depending on which mix of glacial till your house is on. One guy I teach with had to have 3 radon vents put into his house (AFTER he had bought it!) to alleviate the problem, while another house about 300 feet away had no radon showing up at all.

My place was built in '88. The radon test was marginal when we bought it, so the seller installed the system and it now tests out just fine. I hadn't heard about the shower water situation although it makes sense. I suspect that might vary quite a lot, too depending on how deep your well is and what the materials surrounding it are.

Is there some test that you know of for shower radon? The common house test involves having the detector sitting in the basement for several days. It just might be fun to tell the local health department about the shower water thing so they can add even more to their already lengthy list of conditions for buildings around here. Even more important, it might keep some houses from being built and ruining more farmland and open space.

 

[patrick_g]

http://www.nicholas.duke.edu/radon/presentationssummary.pdf

Health Risks | Radon | Indoor Air Quality | Air | US EPA

The second greatest cause of lung cancer (after smoking which is first) is radon. The #3 cause of lung cancer is second hand smoke. Lots of folks worry about second hand smoke and are blissfully ignorant of a greater danger. partially because radon is invisible and odorless.

Radon in solution when consumed with water is not as health threatening as breathing it. That is why the shower is such a radon danger. There is lots of well water which has radon in it and it is available to breath in higher concentration in the shower.

There have been worse things. How about the concrete blocks which were made from sand that was the tailings of uranium mining and were used to build a nice new grade school.

So much for the idea that we don't need no stinking EPA.

Pat

 

[gemini5362]

http://www.nicholas.duke.edu/radon/presentationssummary.pdf

Health Risks | Radon | Indoor Air Quality | Air | US EPA

The second greatest cause of lung cancer (after smoking which is first) is radon. The #3 cause of lung cancer is second hand smoke. Lots of folks worry about second hand smoke and are blissfully ignorant of a greater danger. partially because radon is invisible and odorless.

Radon in solution when consumed with water is not as health threatening as breathing it. That is why the shower is such a radon danger. There is lots of well water which has radon in it and it is available to breath in higher concentration in the shower.

There have been worse things. How about the concrete blocks which were made from sand that was the tailings of uranium mining and were used to build a nice new grade school.

So much for the idea that we don't need no stinking EPA.

Pat

Pat I am not sure we need a stinking EPA. Having the EPA might be ok but do they need to stink ?

 

[LarryRB]

Thanks for all the feedback everyone.
Larry - I'm near Enfield. How does Amrec's cost compare to cement (about $100 CU) and who offers it?
?

Amrec is on Rte 20 in Charlton MA.. About 12 miles from my home and I am on 84 right on the MA/CT lines. I pay 375 for a 20 yeard load of Amrec,, You're not too far from me being in Enfield