James M
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Which material to set flagstone patio? **Special considerati

I've already tamped the 3/4 minus and 1/4 minus bed. I'm now ready to lay the stones but have been reading a lot of conflicting opinions on the material to use.

Special considerations: I'm using thick slabs of granite and marble discards pulled out of dumpsters at local countertop cutting shops. I break them smaller pieces to look make them look more natural, 1-2 sq feet or smaller. So, having laid flagstones a long time ago, this should be much easier as the surface and underside of the stones is flat, making leveling much less tedios. I'm not sure if I should put a layer of material under the stones or just lay them directly on tamped 1/4 minus surface and worry about filling the gaps between the slabs.

Concerns: Drainage. This is a low spot on a two-tiered yard and anything that considerably inhibits drainage could cause a temporary pond as the water has to go straight down as there's no where else to go. The tamped gravel bed is draining pretty wall, as is. I'm in Portland, Oregon so rain is frequent but no "flash floods" usually.

Sand: good drainage, but I'm worried about ants. We already have an ant problem in the summer and I figure they'd love the sand option.

Polymeric sand: From what I read it inhibits drainage considerably. Also, not crazy about acrylic/plastic in my yard

1/4 minus: One local landscaper suggested this and the only downside I can think of is the gravel would end up on the slabs themselves and I might be constantly sweeping it back into the cracks.

Rock dust/screening: One opinion I read is that it inhibits drainage. Also, not sure where I can find it out here. I've already called a couple of landscaping outfits and they weren't sure where I could find it.

Soil: Moss grows very very easily out here. It would look great to have moss between the slabs, but I'm not sure what the downside would be. Weeds? Chunks of moss breaking off with foot traffic?

I may be overthinking this option but would appreciate someone with experience to share their opinions.

Posts: 11595
Joined: Tue Jan 01, 2013 1:32 pm
Location: hawaii, zone 12a 587 ft elev.

Re: Which material to set flagstone patio? **Special conside

I still would go with sand. Ants don't particularly like sand, they like moisture and a food source nearby. They probably like any food you drop on the patio or access to the house if the patio is connected to the house where the food is stored.

Low spot in the yard will mean it will collect water and ants like water, but not drowning they will come up to look for a dry spot when it rains.

Best option for low spots is proper grading to keep water running away from the foundation and into the swale to the street. Don't fill the swale. To keep the patio from flooding make sure it is also filled so it is not the low point in the yard and that water can be directed away. You could use drain pipes under the patio if the area is large.

In areas that get a lot of rainfall, new houses are usually graded with a swale. The first thing homeowners like to do is level the lawn and put up a solid wall around their property. This usually ends with a lake in the back yard when there is torrential rain.
My neighbor did that at my former house and everytime it rained heavily there were literally fountains of water shooting 10 ft in the air through the holes in their walls into our property. Their back yard was a lake. They also damaged the swale on my side when they built their wall and so we had to re dig the swale so the water could move toward the street. My current house has some issues with heavy rain, the lanai will flood because the grass and the drainage can't move it out fast enough. It recedes after the rain stops. I probably have to make the swale a little deeper and the patio end a little higher.

Happy gardening in Hawaii. Gardens are where people grow.

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Joined: Fri Apr 14, 2017 6:34 pm
Location: Nebraska

Re: Which material to set flagstone patio? **Special conside

I agree with implementing a swale. I designed and built a flagstone patio with a 1% slope. I wanted the finished flagstone patio to be environmentally friendly. I chose to lay and fill the gaps with Envirobond. After reading the reviews, I thought the self sealing aspects of the product combined with the lower end slope percentage to mitigate water would sufice. I was wrong. The patio did not receive enough sun and the product did not properly bond post wet periods, Therefore, I was left with runoff and gaping after only one season. Eventually, I ripped it out, installed a French drain And because by that point i was out of money I finished the patio with a pretty pea gravel.

I had to lean my lesson the hard way. I would work work on drainage and then, if it were up to me I would go for the moss! How fun would that be?!

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