Concrete and vapor barrier - Advice please!

[xrdad]

The floor will be poured soon in my 20X20 garage (in Ontario Canada). The concrete will likely be about 4" thick.

I need some advice before they pour:

I read that a vapor barrier is a must, although the builder doesn't normally do it. I found 'Asphalt Impregnated Kraft Moisture Barrier' for the right price and am wondering if I can use that?

Also, any other recommendations prior to pour? I considered the fiber reinforcement, but then would have to burn off the fibers for the Epoxy Coat I'll apply. So I'm tempted to NOT use the fiber.


Thanks!

 

[red]

Most people I know use 6mm plastic as a vapor barrier. Covered it with 1/4" of sand for the water in the concrete. I would use wire mesh if your considering epoxy. If you use fibers you'll have "hair" showing after grinding which can be burned off. Being in Canada, you may want to consider foam under the concrete Good Luck!

 

[darkk]

I did a 30'x30'x6" pour. I used 6 mil plastic, 6"x6" steel mesh and fiber mesh hairs in 3500 psi concrete. I kept it soaking wet for 7 solid days. It has cured beautifully.

 

[Justanoldguy]

more info here

http://www.garagejournal.com/forum/showthread.php?t=110525

 

[ConCretin]

Lots of threads on this subject but almost as many opinions. Since you asked, here's mine;

Use a 6 or 10 mil poly vapor barrier laid directly on subgrade. If you are going to coat your floor, upgrade to a 35 mil product.

Fibermesh controls early plastic shrinkage cracks giving you time to saw cut some control joints then ceases to be of much value.

Properly supported wire mesh helps control shrinkage and thermal cracks but has the added benefit of keeping cracks from opening up.

If you can afford it and cannot live with a random shrinkage crack, use both. If you can't afford both, I'd opt for wire and cut the slab asap.

I'm sure this will make perfect sense until the next post with an entirely different take.

 

[gabeancounter]

I found 'Asphalt Impregnated Kraft Moisture Barrier' for the right price and am wondering if I can use that?

Roofing paper? You don't want to use that. Get the 10 mil plastic and a good roll of duct tape to seal the seams.

 

[xrdad]

Thanks guys..

I posted in the other forum my concern about the plastic and the possibility of freezing issues. I am going to Epoxy Coat, so the fiber 'hairs' aren't wanted and everything I read so far says that the fiber is only useful while the concrete sets up.

There will be mesh and saw cuts to control cracking. I don't know if there will be water available though to keep it wet. So the vapor barrier is still the best bet, isn't it?

I don't understand why I'd need the 35mil poly because of the Epoxy though?

 

[darkk]

Thanks guys..

I posted in the other forum my concern about the plastic and the possibility of freezing issues. I am going to Epoxy Coat, so the fiber 'hairs' aren't wanted and everything I read so far says that the fiber is only useful while the concrete sets up.

There will be mesh and saw cuts to control cracking. I don't know if there will be water available though to keep it wet. So the vapor barrier is still the best bet, isn't it?

I don't understand why I'd need the 35mil poly because of the Epoxy though?

The hairs can be burned off without any problems with one of those weed burning attachments for a propane can, the plastic under the slab...6 mil minimum.....35 mil???

 

[jonesy16]

Take it from someone like me that is extremely sorry I allowed a contracter to talk me into not using a vapor barrier. Sure it takes a little more time to do the finish work with it there the day they pour, but you will save yourself tremendous grief later by doing it now. If you ever go watch a commercial pour where they plan to put tiles, etc., you will find that they always use a vapor barrier. DO IT!! DON'T BE SORRY LATER!!

 

[ConCretin]

I don't understand why I'd need the 35mil poly because of the Epoxy though?

The 35 mil products are more resistant to damage during placement and are designed to virtually eliminate vapor transmission. If I was going to invest big bucks on an epoxy floor, I'd consider spending the extra money to ensure it stays put. 6 mil poly is hardly ever used in commercial construction anymore.

 

[rburke65]

What about using multi layers of 6mil plastic/Visqueen. I have lots of pieces of plastic that I've accumulated over the years. They are big pieces. And is it really neccesary to tape the seams? Would the moister travel back and forth over the undersides of the layers and travel to the bottom surface of the concrete? I would think the moisture would be trapped in the multi layers? Comments from any gurus out there....please. Thanks.

 

[MScott]

I posted this request in the other VB thread, but never received an answer so I will try again here. I will be having a floor poured soon and will be installing pex for infloor heating as well as foam for insulation. What is the the correct order to install these items? Is it gravel, foam, plastic, mesh or rebar, and then pex, or should the order be different?

 

[ConCretin]

I posted this request in the other VB thread, but never received an answer so I will try again here. I will be having a floor poured soon and will be installing pex for infloor heating as well as foam for insulation. What is the the correct order to install these items? Is it gravel, foam, plastic, mesh or rebar, and then pex, or should the order be different?

I'd put the vapor barrier directly on the sub grade followed by the insulation. I'd use screw in plastic clips or something similar to secure the tubing. Place your supports around the pex and lay your mesh over the top.

I know a lot of people use the mesh to secure the pex but it inevitably ends up putting the mesh too low or the tubing too high.

If you are going to sawcut control joints, pay extra attention to securing the tubing and try to be there during the placement to keep an eye on it.

Hope this helps.

 

[ConCretin]

What about using multi layers of 6mil plastic/Visqueen. I have lots of pieces of plastic that I've accumulated over the years. They are big pieces. And is it really neccesary to tape the seams? Would the moister travel back and forth over the undersides of the layers and travel to the bottom surface of the concrete? I would think the moisture would be trapped in the multi layers? Comments from any gurus out there....please. Thanks.

Not claiming guru status but I'd spring for a roll of 10 mil poly. The goal is to stop the transmission of vapor, which can be persistent. It really depends on if you think you might apply some kind of floor covering. If you don't you can probably get away with something less but if you might I'd recommend a continuous membrane with taped seams and penetrations.

 

[MScott]

Thanks LLWillysfan, that makes a lot of sense. It also reduces the chance of having the pex cut when sawcutting the control joints, something I had been concerned about.

 

[xrdad]

****.. I started out thinking I only needed the poly in the shop, but with plans to tile the basement floor, looks like I'm doing that floor too!??

Will a heavier poly still need a sand cushion or can I lay it on the gravel base?

 

[Kevin54]

On Kijiji http://toronto.kijiji.ca/c-buy-and-...ted-Kraft-Moisture-Barrier-W0QQAdIdZ290309758 It states that it is puncture proof. And it is up your way, just not sure how far from you though.

 

[gabeancounter]

What about using multi layers of 6mil plastic/Visqueen. I have lots of pieces of plastic that I've accumulated over the years. They are big pieces. And is it really neccesary to tape the seams? Would the moister travel back and forth over the undersides of the layers and travel to the bottom surface of the concrete? I would think the moisture would be trapped in the multi layers? Comments from any gurus out there....please. Thanks.

One of the major reasons to tape the plastic is to keep it from moving. Somebody steps on it and moves it back during the pour etc. Yes, it completes the seal as well.

I purchased two rolls of 20x100 -10 mil from HD for around $75 each. This meant I only had 4 seams. Less than 15 min to tape.

I understand trying to save $ etc, but I would not piece together the vapor barrier. For most garages this cost is less than $100. If things are this tight before you even pour concrete, probably going to have a hard time finishing the build.

 

[xrdad]

On Kijiji http://toronto.kijiji.ca/c-buy-and-...ted-Kraft-Moisture-Barrier-W0QQAdIdZ290309758 It states that it is puncture proof. And it is up your way, just not sure how far from you though.

This is the stuff I mentioned earlier.. spoke to the guy and he has lots left! But from the replies, I was under the impression this would not be adequate?

Price is right, but I can't change it once the pour starts. I need to be sure this will be as good/better than poly!!

HELP!

 

[ConCretin]

****.. I started out thinking I only needed the poly in the shop, but with plans to tile the basement floor, looks like I'm doing that floor too!??

Will a heavier poly still need a sand cushion or can I lay it on the gravel base?

Standard poly won't stand up to sharp aggregate very well should be Ok on a compacted gravel sub base.

If you are asking about a sand course over the vapor barrier, that practice has largely fallen out of favor. Engineers were designing floor systems with a sand 'blotter course' of sand over the vapor barrier to give bleed water a place to go but they found out it was expensive and a lot of rain water ended up in there too.

 

[Wastedwagesracing]

Little bit of a hijack but... What are the thoughts on using re-ground black top under a slab.

 

[ConCretin]

Up here we call it 'reclaim'. It would probably work fine but it would be more expensive than gravel.

 

[Justanoldguy]

This is the stuff I mentioned earlier.. spoke to the guy and he has lots left! But from the replies, I was under the impression this would not be adequate?

Price is right, but I can't change it once the pour starts. I need to be sure this will be as good/better than poly!!

HELP!

"Will a heavier poly still need a sand cushion or can I lay it on the gravel base?"

Pretty SURE he means Under the poly not on top.
And yes, I always use sand base under the poly.

 

[Eric Commarato]

Poly goes on over the gravel or sand sub-base. Its there to keep the ground from wicking water out of the concrete during the curing process when a sub-base isn't used. It also does the reverse and prevents moisture from telegraphing up to the top of the slab in high humidity environments. Make sure you tape the laps in the poly as well, they make a special tape product for this.

 

[rburke65]

LLWillysfan.....thanks for the reply. Maybe what I will do is place the pieces, to get rid of them, buy the roll of 10 mil and put that on top, tape and then I'll be covered. Thanks again.