Waterproof concrete mix

[Darker]

Hi all,

Seems like there are a lot of helpful experts here. So I will pose my question here.

I am looking at making a reinforced form for a pond skimmer. 4' x 3' x 3'. I am looking for a simple waterproof mix for this project. As a somewhat experienced mason I would imagine that a 2:2:1 mix (3/8 aggregate, sand, Portland) with one pound of fiber per yard, would work. I wanted to check with the experts here if there is a better mix that I should be looking at.

Any thoughts?

Thanks.

 

[Ron]

First of all, you are not likely to produce a "waterproof" mix of concrete. The higher the density of the concrete, the more water resistant it is. Secondly, the water cement ratio is extremely important to achieving water resistance.

The aggregates you use in the concrete absorb water and should actually be saturated at the time of mixing. Depending on your aggregates, this can be a small amount of moisture or a lot (1 to 6%, depending on aggregate).

Keep the water cement ratio as low as possible, preferably in the 0.40 to 0.45 range. Use a low absorption coarse aggregate (river rock, granite, etc.). Vibrate the concrete to achieve consolidation.

The ratios you have give should produce a dense concrete, but it will be hard to work with a low water cement ratio (you should not put more than 0.45 parts of water in this mix...if you put 330 lbs of coarse aggregate, 330 lbs of fine aggregate, 197 lbs of cement, 10 gallons of water)

 

[dik]

I've not used them, but there are Stearate additives that can be added to improve water resistance.

Dik

 

[RHTPE]

You may also want to consider a product such as:

http://www.xypex.com/products/product_types.php?pageID=17

Ralph
Structures Consulting
Northeast USA