I bought some navvy jack from a cement company. It's 50/50 sand and gravel. What is the best amount of cement to add to this to pour piers? I have read the 123 method using 2 sand and 3 gravel. Is the 50/50 mix not a good idea? Will it be weaker? Thanks for any help.
Quote from: busted knuckles on May 12, 2016, 09:55:59 AM
I bought some navvy jack from a cement company. It's 50/50 sand and gravel. What is the best amount of cement to add to this to pour piers? I have read the 123 method using 2 sand and 3 gravel. Is the 50/50 mix not a good idea? Will it be weaker? Thanks for any help.
Did you inquire of them what concrete ratio should be added to make it "321". You could purchase extra gravel/sand to get the right ratio and add cement to that corrected ratio. They deal with this on a daily basis. Maybe a call back will give you some guidance.
I did call them. They said they mix by weight not volume. He said if I was measuring by shovel then just make sure I had enough cement that I could not see the colour of the aggregate. I realize I could add one more shovel full of gravel to get the right ratio, and I will if I can find out if it matters. Or I suppose if I can't find out if it matters. 😀
The 3:2:1 shovel ratio comes out to about equal weights of sand and gravel. You can get a lot more sand in a shovel full than you can gravel. If the pre-mixed sand/aggregate is the same I've played with, 4 1/2 :1 comes out about right. (5 not quite full shovels in real practice) Add just enough water so it looks like oatmeal. I like to use the plastic cement, it seems to work better with less water
Here's another way to look at it. I start with a yard of gravel, a yard of sand, and 14 bags of plastic cement. (A yard of sand weighs 2,600-3,000 #, and 3/4" gravel is supposed to weigh 2,835 #) I think the huge range for sand has to do with how dry and/or fine it is. In any event they essentially weigh the same.
So my sand and gravel start out same weight, same volume. I do the 3:2:1 measuring with my shovel. I run out of all three materials at the same time.
Thank you for the responses. I am going to remove the guessing and anxiety and add another scoop of gravel. Then I can get the 123 ratio.
Cold joint prep? I have a footing poured and it has set up for the last 5 days. I am ready to pour piers on it. I have 3 pieces of rebar sticking out of the footing for each pier. Is there any prep I should do to the footing before pouring piers?
I will start a build thread soon. A slowly progressing build.
Quote from: busted knuckles on May 12, 2016, 10:11:00 PM
Cold joint prep? I have a footing poured and it has set up for the last 5 days. I am ready to pour piers on it. I have 3 pieces of rebar sticking out of the footing for each pier. Is there any prep I should do to the footing before pouring piers?
I will start a build thread soon. A slowly progressing build.
They do make a bonding agent but general it is not frequently used in pier construction. Just make sure that it is clean and free of dirt or any contaminates that could have washed into/onto the pad.
When doing my own home concrete or mortar mixing, I always keep a bit of extra Portland cement around. Its the primary bonding agent and easy to "cheap out" if one is not cautious. Not matter what mix is I'm after, I always employ a final visual check just for reference: Using a pointed, clean and polished trowel, and making a trough in the mix by dragging the trowel through ... the trough should stay in-place and not "slump", showing good definition. Also, for mortar especially, one should be able to scoop up some of the mix on the trowel and the mix should stay in-place on the trowel, even if the trowel is inverted. I'm no expert and this may result in a mix that is too rich and rigid for some.
Quote from: flyingvan on May 12, 2016, 03:04:16 PM
Here's another way to look at it. I start with a yard of gravel, a yard of sand, and 14 bags of plastic cement. (A yard of sand weighs 2,600-3,000 #, and 3/4" gravel is supposed to weigh 2,835 #) I think the huge range for sand has to do with how dry and/or fine it is. In any event they essentially weigh the same.
So my sand and gravel start out same weight, same volume. I do the 3:2:1 measuring with my shovel. I run out of all three materials at the same time.
Plastic cement is primarily used in "plastering" and the sand that they recommend is "plaster sand" for bonding. It is a lot finer than regular sand. I not sure I would consider it in your application. Regular cement would do a lot better job of bonding the heavier sand and larger aggregate.