I have an area of about 9m x 6m and 400mm deep filled to about 275mm with an unbound 2b stone (which is about a 18mm stone) 2b stone has no fines or dust to make it bind together.
If I take the 2b down to 175mm could I then put about 100mm of crusher run or (modified, 2a, or 3/4 quarry blend, as it is called here in the US) on top of the 2b., this would leave 125mm for the sand bed and the pavers.
So I would have 175mm of 2b.
100 mm of Crusher Run.
This would leave about 125mm for the sand bed and the pavers.
I was going by what the contractor who is going to do the pavers said. He wanted to put a 250mm base in and leave 125mm for the pavers and the sand bed.
He was only planning on using the 2b stone for sub-base with "screenings" as the sand bed (he said this is the way he has always put them in).
After doing some reading online and this forum, this does not seem the proper way for it to be done.
Thanks in advance.
PS: I am trying to convert the figures to the Metric, so they may not be exact! If is very difficult.
Also for reference I am in Northeast Pennsylvania.
I really don't see any reason that your contractor would use the 18mm stone for a base and then use the 18mm crusher run on top of that. I would use the crusher run and compact it in 4" lifts with a vibratory plate compactor. Did your contractor give a reason other than he always does it that way? Perhaps there is some unique site condition? You might want to question him as to the specific reason.
As far as the screenings which I assume are stone dust? The paver instructions that I have seen call for sharp sand. I use the stone dust when installing Pa Bluestone. Perhaps Tony knows if the stone dust for pavers is acceptable? I have wondered about that question myself.
Of course the resident experts here may have a reason/idea why this would be done.
I am located in central Maryland (Columbia). I love Pa, what town are you near? I am one of the Ludites that still thinks in inches, but I am tyring to associate the mm thinking.
Hi, Thanks for the quick reply. Since you are from the US maybe I can explain better.
The area is about 30ft x 18ft. It previously had a concrete slab on it. I am remodiling the house and the concrete heaved a little and water was coming in the door. ( This is at ground level.)
So we took the concrete out. The one guy that works with the building contractor worked for a local landscaper for about five years and we decided that after taking out the cement that we would not have enough sub-base to install pavers since it is a poor drainage area.
So...We dug the area down about 16 inches, put drain tile around the perimiter, ran that into another drain tile that takes the water away from the pad.
Thing is I bought 40 ton of 2b and put it in this area we are going to put the pavers in (we didn't use quite 40 ton.)
But Bert the landscaper was telling me that you just put 2b down and then screenings, then the pavers, so I was just listining to him since he said he has done this for years. I had no idea on the proper way to do it. Then I started looking online for pavers and came across this site and here and everywhere else I read says to use like a modified stone for the sub-base( Crusher Run they call it) and concrete sand for the bed. They want something that compacts, 2b does not compact well, but as you probably know is good for drainage.
It rained like heck up here the last 2 days and there was no water setting around the pad, but I am starting to belive that it is not done proper for laying pavers.
I am thinking along the lines of maybe taking about 4-5 inches of the 2b out and maybe put geotextile fabric above the 2b, then modified. I would be afraid to put the modfied on top of the 2b thinking it may eventually choke the 2b and cause drainage problems again.
I don't think you could fill the whole thing up with modified since it is not good for drainage. We are talking 10-12 inches of modified.
Screenings
Screenings is a generic term used to designate the finer fraction of crushed stone that accumulates after primary and secondary crushing and separation on a 4.75 mm (No. 4) sieve. The size distribution, particle shape, and other physical properties can be somewhat different from one quarry location to another, depending on the geological source of the rock quarried, the crushing equipment used, and the method used for coarse aggregate separation. Screenings generally contain freshly fractured faces, have a fairly uniform gradation, and do not usually contain large quantities of plastic fines. ( found this on the net)
Thanks
PS: I am about 50 miles South of Scranton, PA. About 20 Miles from Wilkes-Barre.
"According to the ICPI, coarse concrete sand is recommended for the setting bed. DO NOT USE DUST OR SCREENINGS for the setting bed. These materials do not drain water and become soft over time. Pavers will not seat properly in them when compacted. This will prevent interlock."
I can only offer a European perspective on all this, so bear with me.
The no-fines aggregate would not be acceptable as a sub-base layer, or a capping layer, unless it was covered with a permeable geo-textile to prevent loss of fines from the overlying layers. Each layer should be not more than 225mm deep (verily 9 of thy olde-worlde inches) and compacted thoroughly before placement of subsequent layers. So, a 45mm lift, would be constructed as two layers, each 225mm deep.
The finished sub-base should have a 'tight' finish, with no voids or gaps in the surface, In cases where there are some voids, these should be blinded with grit, grit sand or screening before proceeding.
We would NOT use screenings as a laying course material. Grit or grit sand is used, because it can be shown to perform well over anumber of years. Screenings are rather unspecific and may contain a high proportion of very small particles (less than 0.3mm) which can become 'fluid-like' under pressure. Obviously, some batches of screening would be fine, but as screenings are, by definition, rather unspecific, they are not normally acceptable as a laying course material.
Some stone dusts, though, are suitable, as long as they meet the relevant grading requirements. We have a crushed granite 'dust' in the UK that is actually a sand and does meet the grading requirements for a laying sand, so that is acceptable. However, each products would have to be assessed individually, so, in general stone dusts are not acceptable, either.
Finally, I'm intrigued by the suggestion that you'd allowed 125mm for bed and paver - how deep are these pavers? We'd work on, as I said, 35-50mm for the bed, plus a 50mm paver (for residential driveways) so we'd allow only 85-100mm for bed + paver.
As you have already installed the 40 ton of the 2b. I guess the plan of removing 4-5" and installing the Geo-textile and reinstalling crusher run may work. Again, I am not sure of your specific site situation.
But you did say that:
"So...We dug the area down about 16 inches, put drain tile around the perimiter, ran that into another drain tile that takes the water away from the pad."
I think if doing this job from the start I would have graded the subgrade with a bit of fall to the perimiter and used the 2b stone and drainage work there (as you did). But then I would have used compacted crusher run under the main body of your work.
As far as Tony's question about leaving 125mm for the bedding layer and pavers. I am guessing the EP Henry pavers are 2- 3/8" ? If so Tony is right about the 85mm>100mm.
Thanks for the definitions on the stone dust and screenings questions.
TonyMcC wrote:I can only offer a European perspective on all this, so bear with me.
The no-fines aggregate would not be acceptable as a sub-base layer, or a capping layer, unless it was covered with a permeable geo-textile to prevent loss of fines from the overlying layers. Each layer should be not more than 225mm deep (verily 9 of thy olde-worlde inches) and compacted thoroughly before placement of subsequent layers. So, a 45mm lift, would be constructed as two layers, each 225mm deep.
The finished sub-base should have a 'tight' finish, with no voids or gaps in the surface, In cases where there are some voids, these should be blinded with grit, grit sand or screening before proceeding.
We would NOT use screenings as a laying course material. Grit or grit sand is used, because it can be shown to perform well over anumber of years. Screenings are rather unspecific and may contain a high proportion of very small particles (less than 0.3mm) which can become 'fluid-like' under pressure. Obviously, some batches of screening would be fine, but as screenings are, by definition, rather unspecific, they are not normally acceptable as a laying course material.
Some stone dusts, though, are suitable, as long as they meet the relevant grading requirements. We have a crushed granite 'dust' in the UK that is actually a sand and does meet the grading requirements for a laying sand, so that is acceptable. However, each products would have to be assessed individually, so, in general stone dusts are not acceptable, either.
Finally, I'm intrigued by the suggestion that you'd allowed 125mm for bed and paver - how deep are these pavers? We'd work on, as I said, 35-50mm for the bed, plus a 50mm paver (for residential driveways) so we'd allow only 85-100mm for bed + paver.
Tony,
So you are saying that I could leave the 2b stone in., but lay it in lifts of 225mm x2 (it would be more like 2 lifts of 125mm+) then choke the top layer with like 50mm of sceenings to make it well compacted solid surface (by using a vibrator to compact the screenings into the 2b stone), then lay geotextile on top of that, then grit sand for the laying course, then the pavers?
Tony said:
"The no-fines aggregate would not be acceptable as a sub-base layer" (i.e. the 2b is not acceptable)
LM says:
My read is that you need to follow your own original suggestion as follows:
Twodose said:
"I am thinking along the lines of maybe taking about 4-5 inches of the 2b out and maybe put geotextile fabric above the 2b, then modified. I would be afraid to put the modfied on top of the 2b thinking it may eventually choke the 2b and cause drainage problems again."
LM says:
I would not think that you could succesfully add in stone dust after the fact to "modify" your existing 2B layer. The modified crush and run would need to be installed and compacted in lifts as noted. You are correct to put the geotextile over top of the 2B then add and compact your crush and run lift(s). Then your sand then pavers.
What ever you decide to do, let us know how it is working out.
LM
Thanks LM.
I have talked to 3 different landscapers that do pavers locally. I am going to have them come and look at the job and get a price for them to do it. (Although I do think I can do it myself).
They have all said that it would be ok to leave the 2b in if it is compacted well. They all said that there should be at least 4" (100mm) of Modified ( well compacted bindable material ) on top of the 2b. All but one said to use the geotextile on top of the well compacted 2b stone.
I think I will listen to you and use my own original suggestion:
Good compaction of the 2b stone.
Geotextile.
4" of Modified.
Sand then pavers.
After reading here more I will figure out the correct proportions of bedding sand to use with the pre-compaction method described as being the preferred method.
Another problem I have is that there is a block wall at one end of the patio that I am going to have to run the pavers up to. If it was a flat wall it would be no problem, but these blocks are the type that taper in between the blocks. (If you laid a straight edge on it there would be small V shaped contours between each block. I think it would be very hard to cut the pavers to this coutour..So I am thinking of putting a small concrete pad about 8-10" wide against the wall to make a straight edge to lay the pavers up to. Do you think this is a good Idea?
Thanks Again. I will let you know how things progress.
Hmnn,
I am trying to picture your description of the wall that you are laying against. If you are referring to a V shaped block laid out in a "curved" wall. You are correct that you would have to cut pavers to fit. As far as the concrete pad 8-10" wide. I would question how this would blend in with the overall paving? I think I would first consider cutting in the pavers to keep the surface type consistent. Or am I not understanding your situation correctly?
As far as the sand compaction goes. I understand that the favored method here is the precompaction.
I went to the EP Henry website (FAQ) and they stated:
"Tell me about the sand setting bed...
The material for the bedding layer should be coarse concrete sand. Do not use stone dust or screenings; it does not allow the pavers to seat properly and tends to break down over time. The sand should be an even 1" thick layer. Do not compact the sand setting bed. Do not mix portland cement into the sand used for the setting bed or the joints between pavers. It defeats the flexibility of the system and it cannot be cleaned off the surface of the pavers"
I don't know why they state not to compact the sand?
The wall is a straight wall. The blocks are beveled out, picture like a half circle on each block., if you put a stright edge on it there would be little V's to fill in between each block, I guess you could cut the pavers to fit in the gaps but I think it would be tough.
The wall is a straight wall. The blocks are beveled out, picture like a half circle on each block., if you put a stright edge on it there would be little V's to fill in between each block, I guess you could cut the pavers to fit in the gaps but I think it would be tough.
OK on the straight wall. Perhaps your idea would be workable.
Keep us posted.
