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Old 03-26-2003, 12:05 AM
Whip
 
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Anyone out there subscribe to the ICPI methodology on
pavers.

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Last edited by Stonehenge; 07-27-2003 at 10:25 PM..
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Old 03-26-2003, 05:30 AM
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I have been certified for a couple of years. The only thing I'm guilty of not following is using screed guides, I prefer strings. When it comes time to re-certify I will do it. The training provided is very comprehensive.
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Old 03-26-2003, 07:35 AM
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Lanelle will become famous soon enough Lanelle will become famous soon enough
I am also certified. Having a standard method cuts out the guess work and simplifies the instructions that the foremen need.
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Old 03-26-2003, 08:15 AM
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I haven't gone through the training but have read some of their materials. They advocate the use of a sand bedding course over the stone base course, and I am as yet unconvinced that this does anything to improve your base prep, from any perspective (drainage, durability, etc). But I'm always willing to listen...

We have found a few applications where sand is necessary, but for the most part we do not use it.

Digin - the screed guides you mention - we use pipe set to the appropriate pitch - is this what you use string for?

Lanelle - I do like the idea of a standard set of procedures for people to follow, so that the job gets done the same way every time.

And speaking of ICPI - how many of you are members, not just certified? I was thinking about joining.


This discussion has been included in the site beginner's brick paving page.

Last edited by Stonehenge; 02-24-2006 at 10:49 AM..
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Old 03-26-2003, 03:29 PM
Whip
 
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Jeff,

ICPI is not about teaching the steps tp laying pavers. They are
about educating contractors as to why problems occur and how to avoid them. They dispell alot of "old wives tales" about installing pavers.

The reason we use a sand bedding course, which by the way is concrete sand as opposed to mason sand, is the sand allows the moisture to drain. The sand has 0% fines passing the #200 sieve. The ASTM for the sand is 133. The more fines you have the more moisture retention will occur. The more mositure equals expansion. Also, when the pavers are conpacted over the sand it will come up between the joints. Certain patterns and pavers can have very small joint lines. If you are using linestone screenings, which are well above 12% fines passing the #200 seive, they are not small enough to come up through the joints.

Our company is a member. I am certified and also teach the class through the ICPI to become certified.

The class is very interesting and worth the investment of time and money.

Peace,
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Old 03-26-2003, 07:50 PM
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Rex, I think I was baited!! That's ok, I'll almost always take this bait....

When using sand, where does that water drain to when it drains? To the stone beneath it. And with a coarse stone, no matter how sloped the pavement, it will be a pretty direct path from the paver to the compacted stone. So better drainage to me is the 'wives tale'. The crushed stone beneath, though thoroughly compacted, is not so dense that there is an absorption rate like a concrete or asphalt - the stone beneath the sand readily absorbs the water. The sand does not create some sort of hollow conduit through which the water passes. And I agree, more fines (meaning more total surface area on which water can sit) means more moisture, whcih can lead to expansion in freeze-thaw. But the stone beneath also has fines (though admittedly not as high a content). So it's a matter of where the expansion will happen, not if. Sand just makes the expansion happen an inch deeper than it would otherwise.

I agree, that the larger stone size of screenings does impede the stone from rising into the paver joints - but as you mentioned, if 0% passes the #200 sieve for the concrete sand and 12% passes for the screenings, then there are screenings that are smaller than the sand, which can and do rise into the joint upon compaction.

I don't know much about what the course offers, other than what I hear from people involved in it...Certification seems to imply teaching a methodology and testing that learning - so I hope there's some teaching going on re: certification.

I would very much like to conduct a test of these two methodologies. Maybe it's something several members can independently verify. If we were to conduct a side-by-side test of these two methods, what would the specs be for your method using sand? Please be specific with pitch (and method to set it), compaction (in a practical sense; I can't afford to have densities tested, but I'll use specific compaction eqpt a specific # of iterations to meet your usual specs), etc, then let's also create a test for the two pavements, and a method for measuring their durabilities. I'll put some specs to paper for my install.

Who knows, this may be fun!
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Old 03-27-2003, 12:10 AM
Whip
 
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Jeff,

Those 12% passing the #200 sieve, which is on the low side, are actually part of the pieces of the screenings. They are like the chocolate on a chocolate covered pretzel. They both "flake" off. Therefore, there is not enough of these fines to help create a lockup effect. The only significant lockup you can achieve is through your joint sand. And, using screenings will deter progressive lockup. The screenings themselves are made up of silt and clay. We all know silt and clay are the worst types of soil to build on. We have all experienced how slippery wet clay can be. Transfer that idea to the screenings. The screenings continue to move and shift when moisture is introduced. And, because they are made up of silt and clay they always hold that moisture. The base stone is best suited at 8% passing the #200, but the ICPI spec ranges from 5 to 12 %. Within these ranges the best compaction can occur. We need moisture for compaction. That is why we need fines-to hold the moisture for this function. With the proper gradation of base material and pitch of the soil we can minimize the moisture content that will be held.

We install pavers just like you do except we use sand as the bedding coarse rather than other materials. We do not precompact the sand. Our base is 95% proctor density as is our soil. Then we screed sand 1" to 1 1/2" then lay pavers. Our tolerance for the base is + or - 3/8" over 10 feet. We want to have a consistent thickness of sand. When I say our sand is 1" to 1 1/2" thick do not become confused. This simply means that the sand can be between this range, but not on the same job. Meaning 1" thick on one job is okay. Then the next week using 1 1/2" on that entire job. I like to use one inch of sand-saves time and money.

I would suggest taking the class to anyone who is serious about installing pavers. More architects, city planners and engineers are specifying ONLY ICPI CERTIFIED CONTRACTORS MAY BID. And, we get allot of work because we have taken the classes.

Peace,
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Old 03-27-2003, 12:15 AM
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Jeff, rather than laying pipes I prefer to string several crossing lines to ensure a very flat surface. I have been using this method for alot of years and it is pure stubbornness that keeps me using it. It probably takes more time and is certainly more difficult. Although, I can spread as fast as 2 guys can barrow material into a back yard. It would certainly be easier to teach screeding than my rake to the string method,followed by smoothing out the sand with a 7' straight edge. This may be the year I pick up some pipes.

I too am firmly on the side of a sand bedding course and was even before the ICPI training. This may be more of a local issue as I have not had the opportunity to see limestone aggregates from other parts of the world but would imagine the following detrimental characteristics to be true of all limestone aggregates. Limestone makes beautiful decorative landscape rocks for one simple reason, limestone dissolves in water. Because of the fines content of screenings it holds water that causes it to dissolve. I have dug up many driveways that are only a few years old where 3/4 crush limestone now resembles and feels very much like saturated clay. Saturated clay as we all know is just about the worst base imaginable. You will not find limestone aggregates on any of my projects ever again.
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Old 03-27-2003, 08:20 AM
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Digin,

I would think you'd need the hands of a surgeon to make pulling a 7' straight edge come out flat and uniform. I recall the first paver project I ever did, which was also the first paver project that company had ever done. We had a 10' board that we pulled across compacted slag sand. Me and the company owner, each with one cheek almost touching the board to eyeball straightness, sawing the board back and forth across the surface to be paved.

I can only imagine what that project looks like now.

Thankfully, about 2 weeks after that project the company hired a top foreman from what was at the time the biggest paver installer in the midwest, and my foundation of paver knowledge came from him. But I'm getting off track.....

Every stone wears down in time - true, some go faster than others. I'm not sure what the limestone looks like near you, but around here it is the base of every pavement made - highways, streets, parking lots, sidewalks and patios. The 3/4- is a lot of 3/4, not much '-'. Makes for a very durable base. If the ones you've seen are coming up mush, I'm betting there was a high fines/dust content to begin with. Digin, what type of stone do you use in your base?

As for the screenings I use for pavers, it may be different than most screenings. Some of the bulk sellers here offer screenings that are very uniform and typically just larger than a coarse sand. I've used that and didn't like it for the occasional 'mushy' reasons you describe. The supplier I use most often has screenings that are quite a bit more robust, larger pieces, fewer fines.

Some of the other things I don't like about using sand:
  • You can't predict the moisture content - bulk sand will have pockets of dry sand, pockets of wet sand. When spread the wet is clingy and the result is less sand in that area, while the sand flows where it's dry. Final result is pavers sitting lower where there was wet sand. Paver compaction will certainly aid in evening out that inconsistency, but it's a (albeit slight) inconsistency nonetheless.
  • It's difficult to lay pavers on sand - not the placing of the pavers, but walking near the edge of the just-layed pavers almost always causes some pavers to be pushed into the sand, altering bond lines. Again compaction mitigates, but can't always completely repair.
  • Most install manuals I've seen that include a sand bedding course always mention using the sand to 'level out the uneven spots.' Gives the impression the function of the sand is more of that of a spackle than anything else, the statements here notwithstanding. Organizations that are proponents of sand should eliminate that wording to remove that impression.

I would also imagine that with the advent of polymeric and organic sand binders (dropping the absorption rate of the paver surface), drainage through materials beneath the paved surface is much less of an issue.

There was something else I wanted to add, but I can't remember it....darn it. I'll add it later if I think of it.

Does anyone know if the National Concrete and Masonry Association (NCMA) has classes as well? I've received a few of their newsletters and they seem pretty informative.

Debate is good - helps ensure we're all doing the best job we can. I hope nobody's toes feel stepped on (Digin, Rex) - I'm enjoying this process.
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Old 03-27-2003, 02:23 PM
Whip
 
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Jeff,

Good point on the sand be thought of as the leveling agent. That is why we promote the + or - 3/8 inch over 10 feet. We used to call the sand the leveling coarse. Not anymore.

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Old 03-27-2003, 03:42 PM
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The method I use to pull a 7' edge is more akin to icing a cake than traditional screeding. As I get older it becomes more and more difficult. Imagine if you will a chubby guy bent over at the waist dragging a level in 1/4 circle patterns at a radius as big as I can reach first to the left and then overlapping to the right. If the area is big enough I will do this first in an east west direction across the patio then in the north south direction. It does produce a very flat surface, but I believe that pipes will do just as good of a job with less time and effort. Now that I have an enclosed trailer carrying and keeping straight a supply of pipes seems like less of a problem, it will become part of my system this year.

Limestone and marble are a bit different than most stone chemically, They will readily dissolve into water, not just erode from constant wear of water running over it. It does require a slightly acidic water but average rainwater fits this bill. The smaller the particle the easier it will go into solution, and hence run away. Around here limestone aggregates are used heavily for pavement bases as well. In my opinion (many other's too) it is poor choice for base material. All of our roads are built on MTO granular 'A' gravel, a sand based aggregate 3/4 minus that complies with ASTM C2940. This is what I use to build pavement bases. Lucky for me it is abundantly available in my area.

I would agree with your theory that the clay like limestone bases I have witnessed had an over abundance of fines. This would be due to poor quality control at the quarry and shipping yards. But there is also another issue with limestone, it has to do with the shape of the fragments, more so in screenings than 3/4 size material. The fragments are often more flat than triangular. Flat fragments are difficult if not impossible to compact to required densities. This is difficult to illustrate with words but I will try a little demonstration. Take the fingers on both hands and interlock them to the first knuckle. You have a 1/3 overlap. Now squeeze down the way a tamper might. You can see how flat particles will have a tendency to leave voids in what may seem like a well compacted base. These voids will fill with water, it's unavoidable. Water dissolves limestone (look it up its scientific fact). Have your supplier provide a sieve analysis of the materials you are using, it won't cost anything. Check to see that they comply with ASTM C2940 for base material and ASTM C33 for bedding sand. I can get the percentages passing each sieve and post them if you like.

Poly sand has been a tremendous benefit in the construction of durable pavements for sure. But I learned yesterday of a new product that I will use instead of poly sand this year. But alas my fingers are turning blue now, I will have to fill ya's in later.

A quick afterthought here.... does everyone realize how small the holes in a No. 200 sieve are? If I remember correctly water won't pass through it.
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Old 03-27-2003, 06:44 PM
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#200 (meaning 200 threads per inch) is the same as a sheet
on your bed. And, you have to go down to a #325 to seperate silt from clay.

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Old 03-27-2003, 10:29 PM
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Digin -

I would be interested to see what info you have about Limestone dissolving in water - there is quarry after quarry around here full of limestone, extending deep into the ground, with a good deal of moisture. When quarried there are seams that have been worn/eroded by the passing of water, but they aren't pits of pudding. I'll see what I can find about it dissolving, but admittedly I'm a bit skeptical. I think we may need to clarify the definition of 'dissolving'. Sodium Chloride dissolves in water, but I have a hard time defining something breaking down over decades as dissolving.

As for it being a poor choice of materials, I guess I have to trust that the civil engineers I went to school with know what they're doing when they engineer a project.

And I agree with you on the compaction of flat particles - didn't even need the example, but appreciate it.

I can relate to the chubby guy not being able to do what he used to do...

But I do think things would go quicker using pipe as a guide. I know Paul likes using heavy (iron ?) pipe as screed guides, I like using very light steel EMT conduit - his are more expensive and heavy, but they won't move as easily and last a long time. Mine are cheap, light and disposable, but they have to be checked for straightness before each use.

Great information here guys. I'll try to dig a little tomorrow to see what I can find.
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Old 03-28-2003, 07:47 AM
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Jeff,

That's just it, it doesn't take decades for smaller particles to dissolve. 8-12% of our base is made up of very small readily soluble particles. For me this seems like too much material to sacrifice. Around here there is an alternative available in huge abundance. I must admit that most of my information has come from conversations like this over many years. I don't have any papers to prove these claims.

When I first started laying pavers they were installed on 6" of screenings as recommended by the manufacturers. I'm sad to say some still use this method. Since then manufacturers have updated their recommended installation methods and more durable pavements have been the result. A number of years ago it was discovered that 'A' gravel results in a more durable base than limestone and the manufacturers again updated their installation guidelines. I chose to follow, not without some skepticism. The information discussed over the years has made sense to me and proved true enough in real world experiences. Limestone bases have far more tendency to rut and distort than sand based aggregate bases. The reasons may well be for other reasons than I believe but my observations do support the theories circulating throughout the industry.
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Old 03-28-2003, 08:46 AM
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Because I believe your hardscape market is more developed than the one I live in, the mfg/sales folks there may well be more knowledgable. In general (there are a couple exceptions I can think of), the people here are mainly just regurgitators of info, and have not independently verified anything they pass along to contractors. Most have at best installed one patio or wall (usually at their own house). So I tend to not believe their info to be very credible.

I have seen rutting in paver pavements of several different bases, sand (bedding course) included, and though I also have no scientific data for this, if you have a small grain (like a coarse sand), with even the most interlocking shape possible in nature, if you have a thickness of that material much more than several grains, it would stand to reason that with the application of pressure it one location, the grains will move away from that pressure.

Put another way, would a base of 8", made totally of a coarse sand, be a feasible base? No way. I'm suggesting that 1" may also be much to much. I'll dig a little on the limestone issue and report back here...
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