I have to remove the existing crushed granite gravel from some walkways, and then pour concrete and add the gravel back on top.
the idea is to keep kids from scattering the stone all over the place.
my questions relate to timing and application…. I’m guessing that screeding will suffice, but how long afterward should I be broadcasting my surface aggregate? should I then tamp or trowel it in? what is my window of opportunity?
thanks,
pete
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Replies
I am curious Pete, where you got the idea this will do you any good?
Exposed aggregate work is specialized and not done this way - for good reasons. First, if the gravel is not washed it is unlikely to"stick" at all. More oten exposed aggregate surface is done by washing the surface at the right time to expose aggregate that is part of the original mix.
Next concern is what your climate is. If in any frost zone, the base under the cocrete is critical to success. You might only have a thi gravel surface over native soils...who knows until you find out...
Living in Jacksonville, I suspect that frost is not a concern for him. But for others it's worth noting that exposed aggegate sidewalks create a number of problems in frost/snow areas. They're hard to clear, and, unless done perfectly, the aggregate tends to be popped loose by frost.
Piffin. I agree that your agg. needs to be clean and requires special skills, but we often use what I call seeding in exp. agg. applications. First, around here our mix agg. is crushed stone which is not very attractive and has sharp edges making for a poor finished surface. Also when using expensive decorative agg. it is too costly to use as the basic mix. agg.
I don't know about granite as exposed agg. We don't have such a critter around here, but I would think that it would pose the same problem that our crushed stone does. Also we don't have much of a freeze/thaw problem.
By the way, it's good to see your name pop up here now and then. It seems that a lot of the old timers have moved on. I don't like the new forum, but I have not found anything any better. I'm not much of a computer guru and I go nuts trying to figure out how to do anything. oops
Piffin. I agree that your agg. needs to be clean and requires special skills, but we often use what I call seeding in exp. agg. applications. First, around here our mix agg. is crushed stone which is not very attractive and has sharp edges making for a poor finished surface. Also when using expensive decorative agg. it is too costly to use as the basic mix. agg.
I don't know about granite as exposed agg. We don't have such a critter around here, but I would think that it would pose the same problem that our crushed stone does. Also we don't have much of a freeze/thaw problem.
By the way, it's good to see your name pop up here now and then. It seems that a lot of the old timers have moved on. I don't like the new forum, but I have not found anything any better. I'm not much of a computer guru and I go nuts trying to figure out how to do anything. oops
Piffin. I agree that your agg. needs to be clean and requires special skills, but we often use what I call seeding in exp. agg. applications. First, around here our mix agg. is crushed stone which is not very attractive and has sharp edges making for a poor finished surface. Also when using expensive decorative agg. it is too costly to use as the basic mix. agg.
I don't know about granite as exposed agg. We don't have such a critter around here, but I would think that it would pose the same problem that our crushed stone does. Also we don't have much of a freeze/thaw problem.
By the way, it's good to see your name pop up here now and then. It seems that a lot of the old timers have moved on. I don't like the new forum, but I have not found anything any better. I'm not much of a computer guru and I go nuts trying to figure out how to do anything. oops
I C U have had one of the same problems that has frustrated me with trying to post in this new "Improved" format! LOL
I did an exposed aggregate deck some years ago. The trick is really when to expose the aggregate.
I salted the concrete with the washed gravel (bagged) right after it was screeded and I floated the aggregate in lightly so it was even with or right under the cream. When the concrete had hardened to the point when you would normally start hard trowelling it I squirted it with a hose, nozzle set to a soft spray, working the top layer of cream off the stone. If it starts eating into the concrete too much you are too soon. That is the main trick, figuring out the right time. Don't go crazy washing this off yet. Get the top layer off just to the point that the top of the stones show and wait a while. When this dries and sets up a little more you can use a soft brush or grout sponge to get the stones clean. If you still have some haze or small bits of concrete,don't worry about it, it will come off with time. Bear in mind, you can always take some more away but you can't put it back.
I have done exposed ag slabs using the "top seeded" method, and also just by ordering the crete mix from the batch plant with the gravel I want for aggregate.
The gravel pits we had in northeast Indiana had perfect stuff for exposed ag slabs, due to the pits all being in the glacial moraine we had there. Here, there is no gravel like that, and for "pea gravel," the batch plants all use crushed granite.
Since crushed granite would not do the look I wanted, I used washed screened river stone I got from a landscape supply outfit, and seeded it into the wet tops of just-screeded slabs, then refloated. Seeding requires complete cover, and you'll be mashing it in with the screed boards, but you'll want to fully bed your seeded ag into the creamy top.
The trick is to use a retardant, and to do the wash at just the right time.
My method is to make small 12x12 forms of 2x6 or 2x4, and pour those little test slabs at the same time as the main work. Do four or five of these.
There are retardants you can buy and have added to the mix, but I just use molasses or sugar, dissolved in water, and spray it on with a garden sprayer. This, right after you screed and float.
With your spray, wash off the cream of a test slab at, say, 30 minutes time. More or less. Your first wash-off of a test should be a little early. Wait 15 minutes and do another. You'll know when it is right, and time to do the whole thing.
Best of luck!