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Need help with laying flagstone over gravel and concrete

Need help with laying flagstone over gravel and concrete

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  #1  
Old 08-02-06, 10:50 AM
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Join Date: Aug 2006
Posts: 2
Need help with laying flagstone over gravel and concrete

I would love some recommendations to a tricky situation with a new house I've just bought in Denver. It's an old Victorian that's been vertically split into three units (basement, 1st floor, 2nd floor). Two of the units have side entrances, and I'd like to spruce up the area on the side with the entrances.

Right now, there is a very narrow walk that leads from the sidewalk, up two steps, then along the side of the house to the back. Next to the walk is several feet of pea gravel (I presume for drainage), 3-4 inches deep. The top of the pea gravel is about 2 in. below the surface of the walk. Where the walk goes up two steps, the pea gravel is held in place by some small pieces of stone laid on an angle. In places, the concrete walk goes right to the house and in other places there is 3-4 inches of dirt between the house and the walk.

My problem is this - I'd like to lay flagstone along the entire side of the house without having to break up the walk or remove all the pea gravel and pour a new walk. So I'm thinking I could compact the gravel, then compact about 2 in. of sand on top of the gravel, and then lay the entire area with a wet base. However, I've never heard of anyone using wet base over sand, so I don't know if that will work.

Also, I'd like my steps to be flagstone and not concrete, so I'm planning on covering the existing steps with flagstone. They're low so it won't create a high stepp. However, next to the concrete steps, it's basically a dirt slope with some stones loosely laid on a steep slope, so I am totally lost as to how to create the flagstone steps where I don't have pre-made concrete steps.

All advice, commentary is welcome, but I'd especially like tips and comments on:
1) wet install over adjacent concrete/sand bases; and
2) flagstone steps in dirt next to existing concrete steps.

Thanks all!!!

p.s., I'll try to post photos before Friday to better explain the situation.
 
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  #2  
Old 08-04-06, 01:13 AM
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Join Date: May 2002
Location: Maryland zone 7
Posts: 1,716
Hi DenverHiker,

I have been thinking about your questions since you posted them and here's what I've learned from men that do that sort of work.

My problem is this - I'd like to lay flagstone along the entire side of the house without having to break up the walk or remove all the pea gravel and pour a new walk. So I'm thinking I could compact the gravel, then compact about 2 in. of sand on top of the gravel, and then lay the entire area with a wet base. However, I've never heard of anyone using wet base over sand, so I don't know if that will work.
From JdN:
"Pea gravel is a clean product where the individual stones are rounded and basically the same size. Pea gravel never packs down. It will always move when concentrated weight is applied.

For the base for your flagstone you need a crushed stone product that is a designed mixture of a range of partical sizes ranging from powder to the nominal size of the product. Typically you will use 3/4" minus. It has different names in various locations. In this area it is called 3/4" minus road stone. It is also called engineered stone and a couple of other names I've seen but can't remember. Crushed rock will have angular pieces with rough surfaces. This creates a lot of friction between the pieces. Then the voids are filled by a mixture of finer and finer particles so that the whole mass will pack and settle into a fairly stable layer. The little round clean rocks in pea gravel don't do that sort of thing."

Rick M added:
"You will generally find a graded stone mixed to state specifications and a product called "crusher run." Crusher run has a mixture of stone sizes, but no particular ratio of sizes. Crusher run will be cheaper and good enough for your job."

As to the flagstone steps, there are preformed concrete steps. Not sure they will have the same rise as what is there now though. I also have some concerns about applying flagstone in mortar to the existing steps in your climate with reference to freeze and thaw and the chemicals applied to melt ice. I think you will find that the mortar will fail over time. Consider stamped concrete with a flagstone look. A good contractor can do an incredible job.

I'd love to see pictures.
Newt
 
  #3  
Old 03-12-07, 09:55 AM
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Join Date: Mar 2007
Posts: 2
DenverHiker- I read this and have a similar question. I want to lay a wet flagstone installation over a crushed stone base and I am looking for some useful tips and strategy. The base is there already. I am told you can lay the stone in a form fit and then sprinkle cement over the base, lay a mortar bed, butter the stone, and press into place. Then, use a mortar grout. I am in the snow belt. Do you have any more information?

Jhobstetter/ohio
 

Last edited by DIYaddict; 03-12-07 at 10:44 AM. Reason: Unnecessary quote removed
  #4  
Old 03-12-07, 10:23 AM
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Join Date: Mar 2007
Posts: 2
laying flagstone in a wet application over gravel

I am hoping someone can help me with a strategy to lay a flagstone patio in the snow belt over a crushed stone base. I am thinking about wet mortar installation. My stategy is to get a nice tamped flat bed of crushed sone 5-8" deep. Then to form fit the stones. I was thinking of sprinkling a thin layer of dry cement then lay a mortar bed and or butter the back of the stone in an exterior thinset, then place the stone and use a mortar grout. Can anyone shed a little light on this. I see lots of information on installation but can't seem to find much on wet installation over a stone base.

Hob
 
  #5  
Old 03-12-07, 10:35 AM
Join Date: Mar 2005
Location: USA
Posts: 6,126
Need help with laying flagstone over gravel and concrete

The cement and mortar will be ineffective after a short period of time.

The mortar will crack since you are trying to put a rigid surface over a surface that is not rigid. No mater how much you compact "crushed stone", it will not be strong enough and it will deflect enough to crack the thin morat joints.

If you can tolerate some cracks and movement, it might be adequate for a couple of years if everything is done right.

Dick
 
  #6  
Old 04-24-07, 08:52 AM
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Join Date: Aug 2006
Posts: 2
Job's Finished

Well, I never did post photos (sorry!) but did finish the project, and thought I'd post the results now that the work has made it through the winter. We had massive blizzards and snowstorms in Denver this year, with lots of freezing and thawing, and despite my best efforts, the new flagstone walk had some freezing/thawing water on it - and it held up beautifully.

I opted to invest the time now to hopefully save time in the future - I poured additional concrete so that I'd have a solid concrete bed for the entire length and width of the walk. Then I "glued" the flagstone to the concrete with a portland cement mixture as mortar, and filled in the gaps with the same material. I basically followed rules for the concrete and mortar that you'd find in any masonry guide, be it online or in print. I won't go into details here because there are many other great posts that do a much better job than I would here. Pouring the additional concrete took extra time, but I thoroughly believe that it was worth it. I think it's the best way to go unless you are looking for a much more "natural" look (e.g. moss growing in between stones) and don't mind some shifting and unevenness of the walk.

A word to the wise, be prepared to spend a lot of time on hands and knees, and for a nice clean look, a large bucket, a ready supply of clean water, a place to dump dirty water, a wide horsehair brush, and a large sponge are all necessary to get a clean look for the mortar. Otherwise be prepared to have mortar stuck to the flags for a long time - until it wears off through weather and walking. Fill the mortar in starting up slope and wipe the excess off with the brush, dipping in the water often, working the excess water down slope. I eventually found a rythym and this went pretty quickly.

The stones haven't moved or cracked and neither has the mortar, and it's been a brutal winter and spring for masonry to live through. The streets are full of pot holes but my flag walk is pristine!

Thanks for all the suggestions everyone.
 
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