[MoeMan929]

Hello All,



Next to my house runs a small creek that turns into Class V rapids during big storms. Many years ago someone DIY'ed a very medieval looking stone wall which seems to mostly be comprised of granite rocks and boulders gathered from the land and mortared together. The work looks good and it's held up well over the years. There are a few areas in need of repair and it also needs to be completed at one end. I've always been enamored with stone construction and would love to take on this project.



I've tried placing a few stones with the pre-mix mortars that can be purchased at Lowes and HD, but the adhesion simply is not comparable to the rocks I remove from the old wall. Whatever this mortar is that the guy used, it simply will not let go of the rocks. The stuff I'm using just cracks off, or the best bonds can still be pretty easily chipped off with a chisel.



I've tried varying the amount of water I'm using, making sure the stones are nice and clean. Is there some other product I need to use to get a good bond? A big difference I notice is that the old mortar has pretty large particle sizes, meaning tiny stones 1mm or 2mm in diameter. The pre-mix does not. I'm sure there's more to it than that, but just an observation.


Thank you!

 

[chandler48]

You are using the term "pre mix", indicating a wet product in a bucket. You'll get a few ideas from the guys on this site, so hang on. You may have good luck using Mortar Mix https://www.homedepot.com/p/Quikrete-60-lb-Mortar-Mix-110260/100318487 with a shovel or two of Type S mortar https://www.homedepot.com/p/Quikrete-60-lb-Mortar-Mix-110260/100318487 mixed in and wet to a trowel-able consistency.

 

[MoeMan929]

Right, maybe "pre-blended" is a better descriptor. What I meant is that only water is needed.

 

[Old Thomas]

I would use type S. It has a relatively high compressive strength, good bonding qualities and it is suitable for outdoor and below grade use.

 

[Bondo]

I would use type S. It has a relatively high compressive strength, good bonding qualities and it is suitable for outdoor and below grade use.

Ayuh,.... Type S is the strongest mortar,......

You could also sweeten it abit more by addin' Portland cement, maybe another 10% or 25%,....

 

[MoeMan929]

Yep, type S is what I have right now, but I'm completely unimpressed with its strength and bond, and I can't figure out what I could possibly be doing wrong that's making it perform so poorly. I want something like what the original wall builder used. The bond that the stuff has to the rock is unreal.

 

[JayDoesIt]

Yep, type S is what I have right now, but I'm completely unimpressed with its strength and bond, and I can't figure out what I could possibly be doing wrong that's making it perform so poorly. I want something like what the original wall builder used. The bond that the stuff has to the rock is unreal.

Probably used some type of thinset if it's got better bonding strength then the type s mason mix.

A lot of thin sets have latex and polymer additives in them that increase their bonding strength.

 

[Calson]

It takes 30 days for mortar to reach half strength and it continues to cure and get harder over the years. Don't compare the very old mortar with the new. The 30 days is also based on the ambient temperature. I had a slab done and the temperature did not get above 50 degrees for two months and so I waited for 60 days before driving my truck over it. Below 40 degrees the mortar will stop curing until the temperature rises above that and the joint will be a weak one.

 

[ClarenceBauer]

Add Hydrated Lime to your Portland Cement the Lime will act like a glue.
You can add about 8 lbs. of Lime to a bag of Portland Cement.
Also make sure you keep the new mortar damp while it cures if the humidity is 70% or higher you will not have to moisture cure the mortar.