Hairline cracks in my mortor between Flagstone

by David
(Tucson, Az)


First I want to thank you for taking the time to review this question. Thank you!

I'm finishing up a flagstone project here in Tucson, Arizona. I've laid down flagstone on top of concrete. So I have a great base - also, it's set on the rather hard ground here in Tucson. I'm using premixed mortar to fill the grout lines. I've bought the 'Profinish Quikrete' at Home Depot. I'm having some issues with hairline cracks that will run along the edge of some of the flagstone. I've been spraying a mist of water in the cracks before I up the mortar in. BTW - I have mixed the mortar to a pudding/pancake batter consistancy.

Wondering if I should add something else (some additive) that will help it "not" to crack.

Lastly - temps have been in the 50-60 degree range and 40's at night.

Thanks in advance for any assist you can offer on this.

David Goddard

Comments for Hairline cracks in my mortor between Flagstone

Click here to add your own comments

Sealing a flagstone patio NEW
by: Mark

Would you recommend sealing a wet laid flagstone patio? The patio is in good shape with only a few hairline cracks. We live in the TX panhandle and have periods of freezing/thawing during the winter months. Thank you for your help.

Easy Visitors NEW
by: Anonymous

Thanks for providing recent updates regarding the concern, I look forward to read more
website traffic

Students NEW
by: Mary

When I was a student, went with friends in the evening to a beach and admired fireworks! I can tell, it was impossible to find ready term papers - and now only one click on!

great post NEW
by: Anonymous

this is really great,unique and very informative post, i like it. thanks essay writing uk

rusheessays NEW
by: July

Hello! Got some troubles with study? Get rush essay from our service and forget about any problems. I wish I knew about this service earlier.

Study NEW
by: Tyler

Without education life becomes aimless and tough. So we should understand the importance of the education and you can buy essas on rushessay writing

Advertising on your site NEW
by: Anonymous

You have a great niche site!

I would like to place some ads on your site, is it possible?

My site is essaymaxi I think your blog is an ideal place for advertising.

It will be wonderful to publish banner ads on your site (I will offer more than Adsense does)

Please, answer me and we'll discuss all details, I will pay nice money and really want to be on your site!

Many thanks for answering!

it's common
by: David

Often, the joint between the house and flagstone will crack. You can probably leave it, but make sure you seal your stone and just monitor it.

Many times people will caulk between the house and flagstone. They have gray looking caulking to match the mortar.

Enjoy your patio.


New Flagstone Patio Cracks
by: Steve

I recently had a flagstone patio installed over my existing concrete patio. The work was finished around a week ago. I live in Texas and it has been hot. I went out tonight and noticed a hairline crack in the mortar that basically runs the length of the house where the patio meets the house. There are no other cracks anywhere else on the patio. Is this something that I should worry about or need to fix?

Thanks for the tip
by: David

Dear Marcus,

Thanks for the great tip. I'm going to tell people about that and show your comments to my dad.

That's what this site is all about--helping as many people out as possible.

It's sounds like you know a lot about what you're talking about. If you have any pictures of your work or need any exposure for your business, I'd be happy to help you out in any way I can.

Just let me know!

Take care and thanks again!!!


Hairline cracks
by: Marcus

David: I agree with the last response that true hairline cracks are not always something to worry about.

"Grout" is kind of a funny word in this business since really that is more of a component/method that is employed in the tile business. For flagstone outside, the "cementing" material between the stones is really a "pointing" mortar or "jointing" mortar and to help prevent shrinkage it should be forced into the voids between the edges of the flagstones in a consistency much drier than pudding or "batter"- Any plain Jane inexpensive Type "S" mortar will work. I prefer it only moist enough to barely be formed into a ball when squeezed.(almost crumbly) The method I use to "point" flagstone is to form a fist sized ball in a gloved hand and cut small portions of it away from your palm with a "slicker" and then force it into the joint.(see Marshalltown Tools for an idea of a masonry "slicker") With this type of tool you can "strike" a pretty hard and smooth finish on your flagstone joint. In the 22 years I have been doing this, it seems to help keep the "grain" of the joints closed for a long time (years) and reduce hairline fracturing. This method can be a bit time consuming but I think it is worth the extra trouble. I would not worry too much about installation temperature, but it is a good idea to keep the work moist until the mortar mostly cures (say, overnight) to help it become a more durable joint.....Good Luck!....Marcus

Hairline Cracks
by: David

Thanks for the question David!

Concrete tends to give you hairline cracks. That is something my dad has had on many of his jobs and it is normal. It doesn't have an effect on efflorescence or anything else because the moisture that leaks in evaporates away, especially in Arizona. I recently looked at one of my dad's flagstone patios that he laid 15 years ago and it had some hairline cracks and the patio still looks great.

We have heard of a non shrink grout that some masons use that helps with that. You can read about it here:

(Just copy and paste the above url into your address bar.)

It sounds like your mixing your grout at the right consistency as well.

Great luck with your project!!

Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Flagstone Question.