Restoration of Stonework

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: I intend to renovate a stone barn in France and would welcome the names of any books that you could recommend that would help with methods of forming new window & door openings in existing walls, also re-pointing of walls.

A: (Kelly) I suggest that you check out this title: The Art of the Stonemason by Ian Cramb. He comes from many generations of stonemasons has a particular interest in restoration.

Q: I have a river rock home in Southern California surrounded by a river rock retaining wall. I notice that cracks are developing in the mortar and I wondered if there was a method that you could recommend that I can re-mortar the walls.

A: The method you need to use is called tuck pointing. First you will have to chip out the old mortar. Use a hammer and chisel or an air hammer works well if you have the capabilities. Really old mortar comes out relatively easy but sometimes you can have cracks in a hard mortar that will take a lot of effort to get out. Mix your replacement mortar pretty dry, as you trowel it into the cracks you may be surprised at how moist it becomes. Make sure to wet down the cracks to be mortared as well as the rock that will receive the mortar. I have used masonry glue in the mortar as well as painting the cracks with the glue but in most cases this isn't necessary. The hardest part of the process is keeping the rock from getting stained from the new mortar, so use a dry mix and spend some time every evening with a stiff brush and soapy water after the days mortar has set up.

Q: We have a slightly elevated front porch with crawlspace underneath and would like to create a river rock facade to cover the space underneath. There are currently some rotting/warped boards underneath. I was thinking we could replace those boards with cement board cut-to-size, then trowel on mortar, chicken wire, more mortar, and finally place the river rocks over the mortar. We could create the facade boards flat on the ground, then lift and install.

My questions are:
1. Does this approach make sense?
2. We have whole river rocks (1.5"-6"), but plan on using the smaller ones if we have enough. Do we need to split the rocks so there's a flatter surface to adhere to the mortar? If so, how do I split the rocks?
3. What kind of mortar should I use?
4. Do I need to vent the space, and if so, how? (I doubt I'll get it completely air-tight, as that's not the goal.)

A:I am not sure that your approach makes sense. First the cement board will need some sort of backing as it has no structural capabilities itself. So I guess you should replace at least some of the rotten boards to support the cement board. I don't think you need the two layers of mortar or the chicken wire. You should be able to get by with one layer of thinset as if you were laying tiles. I don't know about installing the boards after you have laid up the stone either, you will have to screw the cement board to the framing and the seams will be evident so I might think about troweling on the thinset and the river rock after the boards are up. I have never tried what you are attempting so I will qualify my advise and recommend that you try a sample board to see how it all works out. I can't imagine how you would split a river rock so if the thinset doesn't work use a type N masonry cement.

1. Assuming a 4-6 foot spread between the vertical supports, do you think it would be sufficient to mount the cement board directly to the vertical supports, or should I build some extra supports?
2. Does it make sense to use cement board at all, or should I use MDF, plywood, or something else entirely?
3. If I use something else instead of cement board, does this change my tactics in terms of adhering the river rock to it? Would I have to weatherproof the surface before adhering the rock?

A: If you go with cement board you will definitely need additional support than the verticals. If plywood use tar paper and expanded metal lath. I don't know MDF plywood's characteristics but best to keep any wood off the ground.

Q: I have a 5 step staircase that leads up to the front of my house. It is cement, with flagstone on top, and stucco on the sides. I had a rail installed by way of core drilling. The drilling caused cracks on the flagstone and on the stucco sides. The drillers tried to fix the flagstone cracks with some sort of sealant for the flagstone, and re-stuccoed the sides. The stucco has since re-cracked, and the flagstone, too. I live in Southern California, so I'm not concerned about freezing water expanding the cracks any more than they already are, but I am convinced that there is no bonding material that will keep the flagstone from further cracking, due to weathering and just the sheer nature of flagstone (or any natural material). Should I just go ahead and replace the flagstone piece altogether, and re-do the cement underneath it, or is there truly a substance that will create a bond and stop further cracking?

A (Kelly): I think that you are right that there is no bonding material that will keep the flagstone from cracking at this point. If the steps are still solid and secure, I would be tempted to live with the cracks as a natural event...or replace the whole piece if that suits your aesthetics better.

Q: I had arizona flagstone placed around the top and side of my gunite pool three years ago. The flagstone (coping) which sits about 8 inches above the water line and also the flagstone all around the outside of my spa is flaking off - it becomes very moist and then falls into the pool after it dries or on the concrete patio. The water has been tested regularly and is always within limits. The outside of the spa and the top of the spa never come in contact with the pool water. I have freezer bags with the flagstone flakes - no one wants to take responsibility or even look to help. They say the warranty was for one year and I must have done something with the chemicals. I think I have a bad batch of flagstone, which was not sealed properly as not every piece has flaked apart. How do I go about proving this and what can be done to rectify the situation.

A (Kelly): It is not uncommon for flagstone to periodically flake off, since it is formed in sedimentary layers. Each piece of flagstone has its own history and tendency to separate over time, so it may be that the only way to rectify this is to remove the original stone and replace it with some that has been selected as more solid. Proving culpability in this situation would be quite difficult.

Q: I purchase a "rock" house that was built in 1933. It is, to my knowledge, the only one in the city in which I live in. My problem, or question is: What is the best way to repair what appears to be a crack from ground movement, that now has created the ceiling to crack? Do I just chip out old mortar, and repair? Any advice?

A: Repairing the crack is the way to go. This procedure is called tuck pointing. Chisel out the old mortar as deep as you can comfortably get at and fill with new mortar. Use masonry cement with sand mixed to a fairly dry consistency. Wet the rocks and old mortar that you will be repairing and use a thin pointing trowel. I use a spray bottle to clean and moisten the rock and old mortar. A dry mix will keep you from having to do a lot of clean up. The underlying weakness of the wall is probably in the foundation and this repair won't address that of course, but with any luck it should last another 70 years.

Q: We purchased a stone house build in 1942 and the hardwood floors in the living room continue to show water leakage in the seams and more when it rains. Can find no leaks and think the water must seep in the walls and between the sub-floor and the hardwood. What would be the best way to seal the outside walls in this area.

A: (Kelly) There is a commercial product called "Thompson's Water Seal" that is clear and intended to seal masonry materials, like concrete. A few coats of this might do the trick. At least it should help you eliminate seepage through the wall as the problem, and it won't radically affect the appearance of the exterior. I would carefully examine the wall in that area for cracks or stones that might be loose, or are somehow funneling water through the wall during heavy rain. If you find anything suspect of this sort, you can use some common silicone caulk to seal the area.

Q: I need to rebuild a 4 foot tall mortared flagstone wall that is about 8 feet long. It was built in 1958 and is falling down. Can the mortar be cleaned off the stone allowing the stone to be reused?

A: You can surely clean the flagstone. Start with a chisel to knock the big pieces off and then with a wire brush. You may have to use a masonry glue in the new mortar if you are building to an old structure. A vertical wall could use the help of glue in any case.

Q: We are busy restoring a stone cottage in the Karoo which is in the dry centre of South Africa, with hot summers and cool winters, not a lot of rain but when it does come it can be heavy. We rebuilt the walls using a mixture of cement and mud and river rock and "plastered"with the same. Now we want to seal the surface to reduce the amount of sand falling out of the walls and are thinking of using a standard water based stone tile sealer. We have decided we must spray it on as any attempt to paint it just spreads the mud and we want clean stone in between. Do you think that would work - just wondering whether it will be sticky enough to bind anything.

A: Sorry I am no expert on sealers. I guess it's too late to mention that mud and cement are not that great a combination for a finished surface. You may as well try the sealer though, I haven't had great luck with water based products but there are so many. Try a small area first and be careful spraying as some sealers are flammable.

Q: I have a rock building, built in 1949, that needs some mortar replaced. A repairman wants to use a silicone grout. He also wants to pressure wash the rock and use a sealant over all of it since we are having leaking inside the building when it rains. What are your recommendation for maintenance?

A: You can easily replace the mortar by "tuck pointing". Chip out any soft or cracked mortar as far back into the stone as you can. Some rocks may fall out but no worries, just mortar them back in later. I like a type N masonry cement with a small coarse sand, you can use portland cement with lime if the masonry cement isn't available. Mix the sand 3 to 1 with the cement keeping it pretty stiff, not too wet. Make sure the stone are clean and wet with a sprayer. I use a pointing trowel to repack the joints pretty flush with the outside of the rock. Start at the top and work down so the finished work doesn't get dirty. I like to cut back the mortar joints with the pointing trowel after they have set up a bit, an hour or two, this shows off more of the stone. I have used this technique on buildings that were much older than yours with good waterproof results. All this talk of silicone, pressure washing and sealants seem expensive and superfluous. Find a stone mason if you don't want to try it yourself and call the repairman when your washing machine need fixing.


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I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks LLC.