Re: vapor barrier between a slab and tile with Portland Cement

[Guest guest]

Don,

I suggest that you have a concrete moisture emission test completed to help

determine the best flooring choice. There are very good epoxy slab sealants that

we use to seal against moisture emission.

A physical vapor retarder with a skim coat applied will not last, and probably

won't perform as desired.

You shouldn't normally install tile without grout because even the smallest gaps

will collect dirt and debris. You can usually install tile on slabs with higher

emission rates because the moisture evaporates at the grout line. If the

moisture emission is too high you will sometimes see efflorescence along the

grout lines.

I hope this helps.

>

> Hello,

> I have a question about preventing wicking of moisture under a slab. I have

removed the carpets in my home and want to put either a green guard laminate or

ceramic tile. Ceramic tile would be more inert but I think I need a vapor 10 mil

barrier over the slab. Is it possible to lay Portland cement on a vapor barrier

to prevent wicking from the slab? Will mold be an issue? The slab my house is on

is a floating slab (probably sand, then kraft paper and tar over fiberglass

insulation, and finally a cement slab on top). This house was built in 1960.

There appears to be gutters drained to a storm sewer. The house does has a

strange odor and mold in the kitchen and bathroom that may have had leaks in the

past.

>

> Also, is it possible to place the tile close without grout or will this cause

problems in the future?

>

> Any suggestions to improve IEQ would be greatly appreciated. Thanks,

> Don Paladin WSMCSN owner

>

> http://wsmcsn.s5.com

>

[Guest guest]

There are special products used to block moisture (and negate the effects of

slab cracks) when tile will be laid over a slab. Sixteen years ago our tile guy

used one which looked like a vinyl floor in a strange color (only thicker) over

a slab which water was coming up through, before laying tile.

However

I now believe that blocking the water in the parts of the floor we could get to

simply concentrated it coming up through the walls and under the cabinets

(including around plumbing). Fixing the drainage problem, including wicking

from perched water (meaning the french drains should be deeper than the wicking

height of the soil below the base of the slab), should be your top priority.

Good luck,

Steve

stevec@...

>

> Hello,

> I have a question about preventing wicking of moisture under a slab. I have

removed the carpets in my home and want to put either a green guard laminate or

ceramic tile. Ceramic tile would be more inert but I think I need a vapor 10 mil

barrier over the slab. Is it possible to lay Portland cement on a vapor barrier

to prevent wicking from the slab? Will mold be an issue? The slab my house is on

is a floating slab (probably sand, then kraft paper and tar over fiberglass

insulation, and finally a cement slab on top). This house was built in 1960.

There appears to be gutters drained to a storm sewer. The house does has a

strange odor and mold in the kitchen and bathroom that may have had leaks in the

past.

>

> Also, is it possible to place the tile close without grout or will this cause

problems in the future?

>

> Any suggestions to improve IEQ would be greatly appreciated. Thanks,

> Don Paladin WSMCSN owner

>

> http://wsmcsn.s5.com

>

[Guest guest]

Short strokes:

Presuming you have inconsequential ground water problems a multi function

product equivalent to the Schluter-DITRA mat would serve your needs.

Discussion:

It's highly unlikely that you have " kraft paper and tar over fiberglass

insulation " underneath a floating slab unless the slab has been poured as a

topping onto a wood subfloor in which case you would likely have a crawl space

if so then this conversation needs to take a different path. It wouldn't change

what you do on top but it will change what you have to do underneath.

If it is a true floating slab and it's on grade - it is very likely that there

is sand…unlikely there is insulation or a vapour barrier…and well none of the

above is particularly useful for a top surface solution.

Simply taping a 1m x 1m sheet of clear poly over a cleaned section of the slab

can serve as a low cost indicator of slab moisture problems. In a house that old

- if you do have a problem (under the poly sheet it will show up as condensate

or a slab darkening) then you have/had ground water problems at the time of the

test…if so then this adds another dimension to your project. If not then it only

means there wasn't likely a moisture problem at the time of the test and then

you would have to do long term testing or assess the risk of ground water

problems based on a number of climatology, geological and topography

considerations. As per the crawl space scenario - it wouldn't change what you do

on top but it will change what you have to do underneath.

>

> >

> > Hello,

> > I have a question about preventing wicking of moisture under a slab. I have

removed the carpets in my home and want to put either a green guard laminate or

ceramic tile. Ceramic tile would be more inert but I think I need a vapor 10 mil

barrier over the slab. Is it possible to lay Portland cement on a vapor barrier

to prevent wicking from the slab? Will mold be an issue? The slab my house is on

is a floating slab (probably sand, then kraft paper and tar over fiberglass

insulation, and finally a cement slab on top). This house was built in 1960.

There appears to be gutters drained to a storm sewer. The house does has a

strange odor and mold in the kitchen and bathroom that may have had leaks in the

past.

> >

> > Also, is it possible to place the tile close without grout or will this

cause problems in the future?

> >

> > Any suggestions to improve IEQ would be greatly appreciated. Thanks,

> > Don Paladin WSMCSN owner

> >

> > http://wsmcsn.s5.com

> >

>

[Guest guest]

Don:

Vapor barriers under 1960's era slabs were rudimentary at best. In addition,

capillary breaks and/or foundation drainage was not code in many areas of the

country in the 60's.

There are a couple of things you can do to mitigate slab vapor intrusion. (This

is assuming you do not have a cracked foundation and that your slab is of proper

thickness for your soil conditions.)

First is to direct all water away from the foundation. Second is to install a

new french drain around your slab to mitigate capillary water intrusion. This

may include a sump pump if your slab sits in a depression.

There are products which will vapor seal concrete flooring. In addition to this

I would check your HVAC system to ensure there are no plenum leaks. A negative

pressured structure will pull moisture through the slab. In this instance, you

can typically find moisture and mold under kitchen cabinets that sit directly on

top of the slab.

In extreme cases, it is advisable to have an engineering company core your

foundation to validate thickness, moisture content and soil conditions. Most of

the time however, remedial moisture mitigation steps solve the problem.

Will

>

> Hello,

> I have a question about preventing wicking of moisture under a slab. I have

removed the carpets in my home and want to put either a green guard laminate or

ceramic tile. Ceramic tile would be more inert but I think I need a vapor 10 mil

barrier over the slab. Is it possible to lay Portland cement on a vapor barrier

to prevent wicking from the slab? Will mold be an issue? The slab my house is on

is a floating slab (probably sand, then kraft paper and tar over fiberglass

insulation, and finally a cement slab on top). This house was built in 1960.

There appears to be gutters drained to a storm sewer. The house does has a

strange odor and mold in the kitchen and bathroom that may have had leaks in the

past.

>

> Also, is it possible to place the tile close without grout or will this cause

problems in the future?

>

> Any suggestions to improve IEQ would be greatly appreciated. Thanks,

> Don Paladin WSMCSN owner

>

> http://wsmcsn.s5.com

>