How To Clean Old Flagstones

Devin Devine, flagstone contractor, mason and sculptor

based out of the Poconos, Pennsylvania

devin@devineescapes.com

DIY hardscape consultation services available

Flagstone Repair Explained: wet laid flagstone

This article shall go into some detail, explaining how to repair flagstone, how to assess flagstone damage and maybe some ideas about flagstone repair cost

Flagstone repair can be a tricky matter, and confusing for the home-owner. Especially in the case of wet-laid flagstone, flagstone patios and walkways that have been laid in a bed or mortar. This article shall hopefully explain the issues at play and make it easier for home owners to find the right contractor for the job.

Flagstones that are set in cement can be vulnerable to heaving due to freeze-thaw conditions. Here in Pennsylvania we have serious winters, leading to serious winter damage to masonry. (HINT if you're having a new patio installed go dry-laid. repairs for dry laid will be much simpler.)

broken Flagstone repair

flagstone repair: BEFORE

Flagstone repair

flagstone repair: AFTER

Some important questions:

how old is the patio or walkway?
how long have the flagstones been showing damage–cracked mortar joints, loose flagstones?
have you, the home owner observed these conditions worsening over the years?
if there are major cracks present, how wide are they–and have they gotten wider over the years?
Check references and ask to see a portfolio of completed works

That last question is one you should ask the contractor. The rest are questions that your contractor should probably be asking YOU.

flagstone repair

For this flagstone repair job every single stone was taken up. Foundation was repaired and stones re-set. Many of the original stones were deemed too thin/not likely to last too many Pennsylvania winters–and so they were replaced with thicker stones.

The last couple of questions relate to trying to discern if the problems at play involve and serious foundational issues or not. That question is best answered by having a professional mason pull up a couple stones and have a look. Still, I'll always ask, as it's good to know how the patio or walkway has behaved over the past few years.

I used to do these types of jobs for an hourly rate, since you can't accurately predict exactly what a repair job will take. Not so, anymore! I find that I can look at a damaged or aged patio, judge fairly well what the job will take, and just give a full quote for the entire job. I used to bill 90 an hour for me, 40 an hour for a helper–now I just decide that the job will take 3 days and xxx amount of material, and quote you at that number.

General plan of action for Flagstone repair | how-to repair wet-laid flagstone patio:

I'll now describe a hypothetical flagstone patio which is in need of repair and then I shall outline the proper means of repairing said damage. Problems–failing mortar joints between flagstones on many or most flagstones. Some of the flagstones are lose. A long crack exists on one section of the patio, running over ten feet long which is fairly clear indication that the foundation itself has some serious cracking.

Solution:

Loose flagstones shall be removed. Old cement from underneath these flagstones shall likewise be removed.

Any crack in the foundation itself shall be widened to a full inch in width. Widened crack shall be coated with a masonry adhesive agent, this shall be given proper time to set up. The crack should then be filled with proper mortar mix with bonding agent added to this mortar mix as well.

New steel* reinforcements may be added as well, along the crack area.

*or basalt

Often flagstones that have come loose have a) to deep of a mortar bed and/or a very thin flagstone was used to begin with. If such is the case…and in my experience it often is, then I will a) use a thicker flagstone thus ensuring a smaller mortar bed and/or b) fiber additives will be added to the mortar mix. These are 1″ fiberglass strips, they look kind of like shredded up cigarette filters and are sold as a stucco additive. Mortar has a low structural integrity. Concrete is stronger, by comparison, because it has gravel added to it. The addition of the fibers will strengthen the mortar, making it less likely to crack.

This video will hopefully be of some help, to illustrate some of what I'm talking about:

Many masons will build patios with thinner stones and thicker mortar beds, because it saves them money, gets the job done quicker, is much easier, and is likely to last very well….for a few years or so. A proper mortar bed for flagstone should be about one inch in depth, say half an inch to one and a half inches. Very often, more often that not, really, when doing flagstone repairs, I find flagstones that were laid in a solid two inches, or even three inches of mortar. Yikes, not good. Mortar is the weak link, and should be kept to a minimum. Irregular (natural shaped) flagstone is sold by weight, thus it is much cheaper to use thinner pieces. Being lighter in weight, it is also easier and faster to install thinner flagstone. Furthermore, a two inch thick bed of mortar is a faster installation technique–you can just slop a whole bunch or mortar down and then take your individual flagstones and smoosh them down to the proper level. Your individual flagstones are of various thickness, thus having a deeper mortar bed will make it easier to get them all down to the same level.

The above paragraph merely describes one of the common cut-corners in flagstone installation. Stuff that I see all the time. Masons and landscapers follow such practices because a) the home owners do not know any better and b) sometimes the workers do not know any better. I hope this article serves to educate both my fellow stone masons as well as to better arm the savvy home owner and protect them from unscrupulous or unskilled contractors.

I prefer thicker flagstones. They have more mass and thus are less easy to disturb, to come loose, or to heave from the freeze-thaw. It's harder to dislodge something that is heavier. Common-sense, right? Seriously, there are masons out there who have not figured this out yet. What? Masons everywhere–read Devin's blog, and take notes.

Thicker flagstones are also more well-rooted. A two inch flagstone will have 2 inches of mortar along it's sides, wedging it down in better. Commonly, masons and hardscapers will recommend thicker flagstone for dry-laid work and will proclaim that the thinner stuff is fine for cemented-in work. In the short term, yes. Mortar however is not infinitely tough stuff and it is weaker than stone. Have more stone down there, less cement. Okay? My approach to wet-laid work is informed by 17 years experience in this trade and by many years experience performing repairs and many years doing dry laid work. Grade-level )ground level) masonry is vulnerable. My wet-laid work is informed by my knowledge of dry stone work. Thicker flagstones are more steady for dry stone….that means they'll be more steady for wet-laid work too.

In summary:

Find and repair the foundational cracks
re-set flagstones in no more than one and a half inches of mortar mix
don't use too-wet of a mix.hire someone who you believe will take their time and will pay attention. This stuff is not rocket science…paying full attention, having many years experience and actually caring about the work they do–these are the qualities to look for when hiring a masonry repair service.
More how-to articles related to flagstone work: patio and weeds and what to use, sand cement or gravel? Also, for those of you interested polymeric sand, I've written up an article weighing the pros and cons of polymeric sand as compared to stone dust.

Also, please check out the gallery pages for more examples of my landscape/hardscape work, patio ideas and dry stone sculpture….in fact, if you find my advice helpful, you should say thank by sharing some of my artistic dry stone work on whatever social media you use.

I now offer phone consultation services. Devin Devine, your Hardscape Helper.

DIY Flagstone and Hardscape help

My rates for DIY consultations are as follows:

$80.00 for a half hour consultation

$115.00 for a full hour

Monies are payable via paypal or Zelle.

I love to be helpful. Now please help support my more artistic stone aspirations by sharing this website, and/or by sharing photos of my sculptural work. Thank you.