Is cement waterproof ?

[63t-cab]

or is it close to being so ?

[BobGlasscock]

Concrete is not waterproof, as in repelling water. It is very porous and acts like a sponge. It will become saturated with water depending on its' thickness and will no longer absorb enough water for the water to soak to the opposite side of that thickness.

In my business, it always surprises people when I explain this to them when they are thinking of draining the water out of their plaster-coated, gunnite (concrete) swimming pools. The approximately foot thick gunnite will absorb water for a few inches before becoming saturated, and thus holds water without 'leaking' it through to the surrounding ground. The plaster is also not waterproof. Both substances are porous and absorb water.

[jclary]

Early in my industrial sales career, I had a plant engineer request that I sell him a floor coating for a newly constructed Plant. When I asked if the concrete was poured over a moisture barrier, he acted insulted and insisted that this was a new "state of the art" facility. In the quote I prepared, I specifically stated in bold print that for the coating to adhere and perform, there must be a moisture barrier. Even in the early '80's fifty five gallon drums of Rustoleum floor coating was expensive. In less than a month, the stuff was bubbling up and pealing off the floor. I was called into a meeting that included the plant manager, chief of purchasing, and the plant engineer. During the meeting, I handed all a copy of the original quote and had marked the moisture barrier statement with a highlighter.

The engineer insisted there was a moisture barrier. I requested that they accompany me out to a maintenance shop in the plant where I knew they had not coated the floor. I turned over a rubber work mat. Underneath the rubber mat...the floor was wet where ground moisture had wicked up from underneath. I explained that, "this is what happens when there is no moisture barrier."

I left the meeting without having to issue a huge credit (nor suffer lost commissions), a good relationship and respect of the plant manager and chief purchasing agent. That plant engineer didn't stay much longer.

Your post brought back this memory...and no! Concrete (if that is what you mean by "cement") is not waterproof!

[63t-cab]

Well I guess I though that cement was part of what makes concrete,and cement (I was told is waterproof) and (concrete is not waterproof).

Early in my industrial sales career, I had a plant engineer request that I sell him a floor coating for a newly constructed Plant. When I asked if the concrete was poured over a moisture barrier, he acted insulted and insisted that this was a new "state of the art" facility. In the quote I prepared, I specifically stated in bold print that for the coating to adhere and perform, there must be a moisture barrier. Even in the early '80's fifty five gallon drums of Rustoleum floor coating was expensive. In less than a month, the stuff was bubbling up and pealing off the floor. I was called into a meeting that included the plant manager, chief of purchasing, and the plant engineer. During the meeting, I handed all a copy of the original quote and had marked the moisture barrier statement with a highlighter.

The engineer insisted there was a moisture barrier. I requested that they accompany me out to a maintenance shop in the plant where I knew they had not coated the floor. I turned over a rubber work mat. Underneath the rubber mat...the floor was wet where ground moisture had wicked up from underneath. I explained that, "this is what happens when there is no moisture barrier."

I left the meeting without having to issue a huge credit (nor suffer lost commissions), a good relationship and respect of the plant manager and chief purchasing agent. That plant engineer didn't stay much longer.

Your post brought back this memory...and no! Concrete (if that is what you mean by "cement") is not waterproof!

[rockne10]

Referring to concrete as cement seems to be a geographic thing. Where I grew up, concrete was called cement.
Cement is actually the "glue" that binds concrete together; Portland cement itself, once mixed with water and cured, is a water-resistant product. Mix it with aggregate and sand to make concrete and it's porous.

[jclary]

Well I guess I though that cement was part of what makes concrete,and cement (I was told is waterproof) and (concrete is not waterproof).

Please don't take it that I was demeaning your knowledge. Although cement and concrete are often treated as interchangeable terms, they are not.(and your comment shows that you knew this.) Cement IS one of the ingredients that make up concrete. The way I was taught, cement is the binder that holds everything together. I am not going to take it any further than that. The only D I made in college was chemistry. Being the first of my family to go to college, I foolishly majored in psychology. However, it did help me in my daily dealings with crazy engineers!

[rockinhawk]

Masonry Cement commonly known as Mortar is not water proof either. If it is compressed tightly between bricks it becomes water resistant but will still absorb water, as will the brick.

[63t-cab]

None taken John <G>. no it's this,my Daughter is doing a project in school.her Teacher told her that cement is waterproof,and concrete is not.(my Daughter was a bit confused,actually I also)but did tell her that cement was one portion of concrete,though I did'nt know for sure as to it being waterproof ?so I learned something tonight.

Please don't take it that I was demeaning your knowledge. Although cement and concrete are often treated as interchangeable terms, they are not.(and your comment shows that you knew this.) Cement IS one of the ingredients that make up concrete. The way I was taught, cement is the binder that holds everything together. I am not going to take it any further than that. The only D I made in college was chemistry. Being the first of my family to go to college, I foolishly majored in psychology. However, it did help me in my daily dealings with crazy engineers!

[rockne10]

In post #5 I called it water-resistant. Neil echoed that in post #6.

[8E45E]

One of the VERY FIRST things they teach you in a welding class (oxy-acetylene) is to never cut or weld with the open flame directly on a concrete floor! Any moisture trapped within the pores turns to steam, expands, and chunks of concrete will literally explode from the hot spots. On another note, a few years ago, a guy I worked with assembled one of those DIY barbeques from curved concrete block on top of his concrete patio, and built a fire directly on the concrete. About an hour after it smouldering, the concrete below suddenly exploded with the hot cinders and pieces of concrete landing on the roof of the house and neighbors garage. The round steel grille was found in a neighbor's backyard two houses away. Lucky for him~less than a minute before that happened, he bent forward from his chair and looked over top of it to see how the fire was 'doing'....

Craig

[bob40]

Early Spring weather can cause conctete to "sweat". Have seen many old cars that were sitting in garages unmoving for years where the floors,suspension,even brake lines rusted away.

[hausdok]

Hi,

I thought I'd answered this first but apparently forgot to save my post.

Typical construction 3500 to 4000 psi concreteis not considered waterproof and you need to use some type of coating - asphalt or butylene - a vapor barrier or use a crystaline waterproofing material (CWM) - a catalyst that causes crystals to form in the body of the concrete and block the pores - if you want to prevent moisture passing through it.

On the other hand, 5000 psi concrete is considered to be waterproof. As an example Superior precast uses 5,000 psi concrete in the precast foundation walls that they manufacture and those foundations are placed in the ground without exterior coatings. They remain dry on the interior surfaces even in the worst climates.

5000 psi conrete is also what they used for the floating concrete highway bridges we have out here on Lake Washington and what's used for the concrete pontoons/basements used under floating homes out here..

Mike O'Handley
Kenmore, Washington
hausdok@msn.com

[avantilover]

I see our concrete floors being poured over the top of an orange colored moisture-proof barrier plastic, seems that old customer of John Clary's need to use that.

[jnormanh]

There are lots of ferrocement boats floating just fine, some of them for as much as a hundred years.

[BShaw]

Interesting. I just had a new 24 x 36 garage built and I'm pretty sure no moisture barrier was used beneath it. On Mrs. Bob's 2/3 it's 4000 psi and my modest 1/3 "Studebaker side" it's 5000 psi. I've been told I need to put a sealer on the floor. True? If so, what type/brand is recommended? I'm not interested in those Epoxy coatings as I've yet to see one last for more than a year here in Minne-snow-tah, land o' 10,000 MinnDot salt piles.