Stone Floors

Jose Garcia has been a landscape contractor for 24 years and has gravitated to doing a lot of rock work. He has built innumerable retaining walls of timbers, boulders, drystacked and mortared stone. He has built foundations out of stone and mortar and put rock veneer around the base of a straw bale building to raise the level of waterproofing. He lays about 20 tons of flagstone a year in patios and walkways. Over the last couple of years he has built a half dozen mortared flagstone staircases. In Colorado we are blessed with a wonderful red flagstone with great tensile strength that he uses to make benches. He tries to work with the stone's shape as it comes, and can generally lay out a patio with a minimal amount of cutting or chipping, and the benches are free form and distinctly shaped. Mostly he's out rolling boulders and flipping flagstone on a daily basis.

Questions and Answers

Q: Have you every heard of someone using natural rock (like the ones you pick up yourself out of your own field) for an interior floor? Do you know of any websites I could check this out at? I would like to see some photos & know of what type of finish to use. I know the rocks won't be level if I do this, but I'm inquiring for that reason to see if anyone has ever attempted it before.

A: (Kelly) Well I have a substantial portion of my floor composed of rock. I chose flagstone, because it is available locally and is nearly perfectly flat, being a sedimentary stone that separates along the striation lines. I would recommend using this type of stone, if it can be found in your area, as it greatly simplifies the laying of a reasonably flat floor. Otherwise, it is a matter of scouring the countryside (where you legally can) for natural stones that are flat enough...this can be an arduous task. My dad made a rock floor in an area near the fireplace that was composed of flattish rocks, but you had to watch you step or you might stumble. Towards the bottom of the earthbag page is a picture of our dog at the window. He is standing on our flagstone floor. It has been lightly oiled with linseed oil to protect the stone from spills and to bring out the color.

Q: I am trying to lay a flagstone floor in my kitchen/den. The area is 600 sq. feet. I am having a lot of problems getting someone to give me a reasonable quote to lay the pattern flagstone I have chosen ( last quote was $4,500). My partner and I are pretty 'handy', is it so very
difficult to lay flagstone if you are a novice? I do not mind irregularities, the only thing I want to avoid is 'lipping' so that we don't trip over edges. Any advice you'd care to offer would be greatly appreciated. I just cannot live with ceramic tile, the stone/slate flagstones bring something with them into my home that I can't describe.

A: (Kelly) I love flagstone, and laid quite a bit of it in my living room, mud room and greenhouse floor. I actually tried three different techniques, and they all have worked fairly well. In my living room, which is mostly an adobe floor, I arranged the flagstone in the pattern that I wanted down on a bed of a few inches of sand, then pushed and settled the stones until they were as level as I wanted, leaving an average of 1 1/2 inches of space around the stones. This space I filled in with the same adobe material that I had used elsewhere. Because the adobe shrinks as it dries, I had to do a second application. The only problem I have had with this approach is that the adobe is a bit fragile and chips up occasionally and I have to repair these places periodically.

In the greenhouse area, I did exactly the same thing, but used ordinary cement mortar between the stone, and this has stood up to the test of time and traffic much better, since the cement is harder and more durable.

In the mudroom I tried an entirely different approach: I roughly arranged the flagstone in the pattern that I wanted, and then set it aside in such a way that I could reconstruct the pattern. Then I poured several inches of a papercrete/sand mix over part of the area I wanted to cover, in such a way that I could drop the flagstones into the wet mix and settle them so that they were level, even, and the mortar spaces were filled. Then I would proceed pouring and arranging the stones until the entire floor was covered. This was a bit tricky to accomplish, but the end result has worked out well, and in some ways it was easier than the other method. I used the papercrete mix, but ordinary concrete could also be used.

Q: I just finished building a flagstone patio. In the spaces between rocks I put small decorative river rock...but the pebbles knock easily all over the place..is there some sort of sealant I can use to keep the pebbles in place...something that doesn't look plastic-y?

A: Its tough to keep any gravel in the spaces between flagstone. I generally use a crushed rock that is 3/8 minus with fines, it generally stays in place. To keep the river rock in place keep it well below the flagstone height. I wouldn't try to treat or seal the rock in as this might create other problems The best fix to tighten the gaps between the flagstone and skip the river rock all together. I know there is some artistic merit to the river rock but function and form don't always mesh.

Q: I live in east TN. I have a large concrete slab that serves as the front porch for my red brick house. I would like to cover the concrete slab with slate flagstones. Will this choice look good with my brick house? If not, can you suggest an alternative? If so, is there any advantage to using larger stones (say, 24" x 24" versus 12" by 12")? Any other advice is appreciated.

A: It's a little hard for me to comment on how the stone will look in front of your house without seeing them both. My guess is that there isn't a flagstone that will look bad compared to concrete. If you have a choice I might pick a stone that contrasts with the red brick rather than try to match the colors.The main advantage to using larger stone is that the area of patio that is grout joints is reduced. You will have to try and find some flagstone that is relatively similar in thickness and thin, try 1/2", or 3/4". Set the stone on a thinset concrete being careful to match the height of the stone to avoid trippers. This is in many ways harder to do than setting thick stone in sand.

Q: I'm looking at a tobacco barn for a retail store. It has a brick floor that is simply on top of crushed gravel (dust)....over the natural ground. I'm concerned about cleaning....water would just soak in....and concerned about moisture in the building, etc. Wondering what a solution would be. Is it possible to mortar and seal the bricks in this type of scenario?

A: I don't think you should have too much problem sealing the brick from the top. I have used a clear sealer over brick with success and would think that you can use linseed oil as well. This should allow you to mop the floor easily and keep spills from soaking in. Test either application in an out of the way spot for discoloration. I would be more concerned about ground water seeping up through the subfloor especially if it is sealed. Crushed rock with a lot of fines can wick ground water up. Without a generous capillary break you may have to pay special attention to drainage on the outside of the building. Having said all that I think you have to consider that using the floor as it is may be the best solution. It has obviously worked for some time so why mess with success.

Q: I am building a flagstone patio at my home in Colorado and am torn as to what is the best material to place in the flagstone joints? (Sand, if so what type of sand, Polymetric sand, or concert).

A: I like to have a little contrast between the joints and the flagstone itself. I am in the process of installing a patio using red Lyons flagstone and a dark gray breeze in the joints. Sand tends to move around too much for my liking. The crushed rock, 3/8" minus, with fines called breeze tends to stay in place better. I actually use the breeze as a base to lay the stone too. You will always have some material make it's way to the top of the flags but the breeze is a better option.

Q: I want to lay a flagstone floor that will be a permanent fixture in my den. Since I have a basement, will I need more support for this amount of weight? Also, when laying flagstone, how deep should the mortar be, before laying the flagstone on top of it?

A: Laying flagstone on a wood floor can add weight that your floor joists are not sized to handle. A one inch stone can add 2000 lbs. to a 10 by 12 foot room plus the weight of the mortar. If you can get a thin stone I think you should consider laying the flagstone like tile. Regular concrete mortar will crack with the movement of the wood floor and adds considerable weight. If you can find a flagstone that is about 1/4" thick lay it on a mastic and grout it as you would a tile floor. The mastic will have to be thick enough to account for the difference in the thickness of the stone so try and get closely matched stone. If you can't get thin flags in your area this may be the wrong solution for your floor.

Q: I was just wondering what is the best type of stone or brick to use for building a patio? This info is for a project that I am doing myself ,so I want something that is easy to work with and inexpensive.

A (Kelly): Flagstone is commonly used for patios because it is nice and flat. If you use brick, it should be well fired so that it isn't too soft. Manufactured pavers are another option.

Q: We have collected many beautiful flat beach stones, and we want to embed them in concrete to cover the existing concrete pad under our outdoor hot tub. Probably 2 feet wide on all sides. We thought of doing a 1 foot square test patch, laying the stones first to get an idea of the pattern, then pouring the concrete, laying the stones in the prescribed pattern, then using a 1 foot square piece of plywood, to press the stones in evenly to make a reasonably flat, comfortable walking surface. The stones are all 3 inches or less in length/width. Does this sound do-able to you? Do we need to use a special type of concrete for this? Obviously not the kind with gravel in it, but what kind?

A (Kelly): What you describe will probably work. You might try out the concept with a trial patch and stones that aren't important to see how well it works. I would suggest using ordinary concrete with gravel in it, because this will be stronger and less likely to crack over time. You can use a little pointing tool (like a bent kitchen knife) to smooth out the cement surrounding your stones.

Q: We have a 12'x12' concrete slab in our backyard. We would like to extend our patio on the side by an additional 15' making it a total of 12' x 27' - however the area off to the left is nothing more than a grassy area at the moment. Our question is that we would like to do some sort of slate patio - but would like to know if it is possible to cover that entire area without having to pour an additional concrete slab. We were at Home Depot and one of the workers there said we could just use crushed rock and compact it down with one of those gas plate compactors. Afterwards we could then use mortar in order to keep the slate tiles affixed to the surface of the compacted rock as well as the existing concrete slab. We would like to try and use some of the square slate tiles they carry at Home Depot, however they are not 2" thick. Is it critical that any slate tile (or similar rock tiles) be at least 2" thick if not placed on top of a solid base as a concrete slab? And is pouring a concrete slab a necessary step, or would that person's suggestion of compacting the rock and using mortar be a viable alternative?

A: (Kelly) It is quite possible that you could use crushed rock as a base, especially if you use a small enough aggregate (no greater than 3/4" minus) that the the tiles are well supported from below. Without knowing how thick the tiles are and how brittle they might be, I would say that placing them on solid concrete is a safer solution. If you do go with the gravel, I would suggest that you create a perimeter of concrete around the area to contain the gravel and keep the edges from slumping.

Q: How can I, or is it even worth the effort to, remove flagstone from mortar? I had an offer that I could take the flagstone to use elsewhere if I could remove it from a 250sq porch.

A: (Kelly) It really depends on how well the flags are cemented in place, how easy it would be to remove them. If they are just set on sand and mortared in between them, then they should lift out pretty easily. If they have been set into a cement base, then the job could be very difficult indeed. I would start on one edge with a crowbar and gently pry one up to see which is the case.

Q: We just moved into a house that has flagstone steps on the interior staircase. The top step is lose and needs to be resecured. While we are at it we want to raise it about 3/8 inch so that it will transition smoothly to the hardwood floor (without a lip). It is approximately 48 inches wide, 14 inches deep, and 3 inches thick. Can you please tell us how to reset this step properly so that it is solid and stable and does not end up cracking eventually?

A: You should be able to reset the top step very easily. First pull off the flag and make sure the mortar bed is solid. If it is you can use a thinset mortar on top and set the flagstone 3/8 inch higher to match the wood floor. If you do this and the rest of the staircase has even spacing on the risers you may tend to notice that last step. If the mortar bed has degraded any, just take a chisel and pull the old mortar off or at least deep enough to get an inch or so of new mortar. Clean and wet the area well and put masonry cement that allows the top of the stone to match the hardwood floor. Make sure to wet the bottom of the flagstone as well.

Q: I am building an apartment in Southern India, where the climate is primarily dry and very hot. What kind of stone flooring should I go for to keep the house cool? Alternatively, is stone flooring a good idea in the first place?

A: (Kelly) Almost any local stone that is commonly used for flooring should work, the denser the better. The more thermal mass (such as stone) you have inside the house the better in a situation like this. I would try to have the stone floor coupled directly to the earth beneath it if possible. If the stone is set in or on concrete, that works fine. Then the stone floor can transmit the cool from the ground under your house.

Q: I live in Canada and I would like to lay a flagstone down in the interior entrance of my cottage. The sub floor is currently hardwood and I would only like to do a small section inside the entrance. As this is an interior application that is exposed to very large temperature swings I'm nervous about cracking in the joints. What is the best thing for me to put down before laying the flagstone? mastic? Concrete? mortar? etc.. will I be required to grout as well? I have the stones and they are small.. I'm just nervous to set them in the wrong thing and the resulting cracking that may occur.

A: I'd lay your small flagstone as if they were tile with a mastic base and grout. Spend some time laying and try and keep the joints a consistent width. Get a diamond blade for your skillsaw and cut to fit.

Q: My landlord has a stonewall, dirt floor basement. She wants a perimeter drain system (which is done) with a flagstone floor with hydronic heat, without a concrete slab. What procedure would you suggest? Level dirt floor to subgrade elevation, then vapor barrier, then tamped sand, then set tubing, then set stone on a mortar bed and grout the joints?

A: I just set a radiant hot water heat system in my floor last winter. This is how I did it. I leveled the dirt to about 6" below the finished floor grade, then put in about 3" of small gravel to create a capillary break, no vapor barrier. I put a thin layer of insulation under the flagstone portion of the floor. I tried to insulate the earthen floor but ended up taking it out. Immediately over the insulation I put a welded wire grid and tied the hot water pipe to the grid. I covered everything with a couple of inches of sand, crusher fines also work well. I set stone on the sand and grouted the joints. I used a thick flagstone, inch and a half to two inches, so no mortar bed was necessary, a thinner stone might need a mortar bed. You should keep the hot water pipe within 3 inches or so of the surface. I have a friend who calculated how long the heat should take to go from the pipe during the day to the floor at night and put the pipe 9 inches deep. His floor never heats up.

Q: I am a stone mason in Southwestern Colorado and am in the planning stages of building a house. I would like to do the second story floors out of flagstone but am concerned about the extra weight this would put on my floor joists/garage ceiling. What is your recommendation? Are there extra strong floor joists I should use?

A: You are right to be concerned about the extra weight. Builders will sometimes put cement floors in upper stories but will use lightweight concrete or thinset. Engineered joists, or I joists, can give you a stiffer floor and hold more weight than standard joists but flagstone can be very heavy and you will have to put a base of some sort down to allow you to make the floor flat on top. I think this would be possible with a plywood floor on I joists using a thin flagstone on thinset concrete. I would be somewhat concerned about your grout joints showing stress from the joists flexing so beef them up and block them well. All in all this may be a better question for an engineer but I sure wish you luck with your project.

Q: My husband and I are preparing to build a river rock patio in our backyard and we are disagreeing on whether or not we need to set the rocks in sand or a cement mortar. Can you provide some insight as to the pros/cons of doing this? Is this really a necessary step?

A: I assume that you are using the river rock as the floor of the patio. I guess river rock comes in all shapes and sizes but this sounds like a challenge to get flat. If the stone are large and flat you might be able to lay a surface that no one will trip on but the rounded nature of river rock will leave a lot of space between stones. I guess I would recommend mortaring the stone in place if you must use the river rock.

Q: We live in the Houston, Texas area and would like to lay flagstone (any type of flat stone) on our existing covered concrete patio. We would like to be able to remove the stone if we ever want a different look or if needed for foundation leveling. Is it possible to use sand or another base on top of the concrete that would allow us to remove the stones? We would like a stone that is approximate. 1 inch thick and fairly consistent in thickness to minimize the thickness of he base. Any recommendations?

A: I think you can pull this off if you install a good border around the patio to hold the sand in. I usually hammer the sand under the stone to level but you won't have that luxury. I wish I could tell you where to get a consistently thick stone but you will have to research that yourself.

Q: I purchased an old 1920's stone home with a stone floor. The stone appears to be actually laying on top of sand. It also appears to have been painted. We scraped as much of the paint off the stone as we could without doing damage to the stone. When we purchased the home it had indoor/outdoor carpet on the basement floor so we weren't really sure what we were dealing with. I am interested in putting an office in my basement but don't want to put a ton of expense in the flooring and I like the stone look. Do you have suggestions as to what and how to complete the project.

A: I doubt that you would have to do much based on what you described. Too bad about the paint but your real concern is ground water and unless the carpet was rotten it sounds like that may have been addressed in the original construction. A sand base that the stone sits on is appropriate. I would imagine that you might have to repoint the grout after so many years. I use a type n masonry cement with a cement adhesive in the mix.

Q: We are building an Earthship type home with a flagstone floor. We want to seal the floor with linseed oil and wax. Would the process be the same for porous stone as it is for adobe floor? Or would you recommend something else?

A{ (Kelly) I once used flagstone for a floor and put linseed oil on as a finish, and this worked well. I did not wax mine because I didn't think it was necessary. If you don't wax it you can later refinish with more oil easily if necessary.

Q: We are wondering if its possible to lay flagstone directly on an earth and gravel sub-floor in a cob home we are building.

A: (Kelly) You should be able to do that. I have used a bed of sand for that purpose, which allows the flagstone to be seated solidly and level.

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