Mason Work

cmvargas1

I'm ganna install flagstone treds on top of a concrete stoop at my house with stone risers. What is the best way to adhere these items to existing concrete? Many flagstones are coming loose around here after just 5 years of intallation.

stacker

20 penny nails

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denver 2

We use type M mortar for laying flagstone. Also, a trick we sometimes use on treads is to apply a mortar slurry coat on the backside of stone first and then lay stone stone on your standard mortar bed. This way mortar is sure to bond with stone. Take care when grouting joints with type M to do a clean job because ater drying it does not clean easily.

cmvargas1

thanks but I'm doing stone work!

cmvargas1

Thanks denver, thats what I keep hearing but I just couldnt understand why alot of treds in my area are coming up so soon. Is bonding agent just as good as the slurry?

Captainsls

I would not set flagstone without using an acrylic admixture. Use it as a bonding agent and as an additive for the mortar.

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cmvargas1

Thanks captainsls! How much adative do i put in the mortar, can i mix it with water.

Tscarborough

Type M is not a good choice for setting flatwork. It has poor adhesion, flexability, and flowability. The important thing for flatwork in a freeze thaw environment is to ensure that there are no voids, good adhesion, and then seal the surface to reduce moisture penetration.

Slurrying the backs of the stone is debatable, but if I were going to use Type M mortar, then I would certainly do it.

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RZB

We lay flagstone in type s but we sometimes add an acrylic adhesive to the mix for insurance. We also make sure the bottom of the stone is really clean since they often come with a sort of muddy film on the bottoms, and on dry hot days we wet the bottoms for better bond.

RZB

Stacker's idea will also work you just have to predrill the stones

jomama

Exactly what RZB & TS said. We pick stones up after setting ocaisionally to check for voids. And if you leave any residue on the bottom of the stones you'll never get a complete bond. When it comes to grouting the joints, I use as much Portland as I can, just enough lime to control bleeding. Maybe it's not ideal, but it's worked for us so far with freeze/thaw cycles.

CR2

Type S mortar and thin set the back of the stone, this will guarantee a good bond, doweling the treads will add strenght.
Good Luck!

cmvargas1

good input, thanks that really helps being that a huge part of the problem around here is the winter!

cmvargas1

I was wodering if it were ok to use thinset on exterior applications because it does make a good bond. Thanks for the help!

MasonryPro

Some masons have found that mixing 25% Thinset into their mortar will give them flex and grab at the same time. This allows the mortar to achieve the qualities of the Thinset while not going completely with Thinset.

You'll want to grout your stone with no thinset in that, just regular Type N or S Mortar. Type M mortar is very strong, but can be very brittle too. Strength often comes at the expense of flexibility. Both are necessary in masonry projects.

On an exterior application, it would be wise to apply a Masonry sealer after the 28-30 day mortar cure period.



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cmvargas1

does the sealer leave a smooth or a glaze finsh? Thanks masonpro for your help, this is all new to me.