Home brew concrete and cast-in-place concrete.

[Tscarborough]

Re: Home brew concrete and cast-in-place concrete.

1-1-5 to 6 depending upon the sand. Sharp sand less, round sand more.

[david s]

Re: Home brew concrete and cast-in-place concrete.

As far as I'm aware there is no product readily available in Australia called "masonry cement" either. Bricklayers usually use 5:1 sand, cement and then sometimes use additives I previously mentioned to adjust the brew to their liking and workability.

[mikku]

Re: Home brew concrete and cast-in-place concrete.

You need to be clearer on what you are mortaring. You need a different type for normal bricks to that required for refractory materials. If you want a standard mortar to be more sticky use some mortar plasticiser, lime, bricklayers clay or fireclay added to the mix. Try the search function I'm sure mortar recipes have been discussed ad nauseum.

David s,

I did the search earlier today, the only result I found--referred to standard masonry mortar, no specifications used for a decorative arch. And your reference of 50/50 mix portland and lime with no reference to sand proportions.

There is a lot of chatter about home brew, other refractories, recipe for castable refractory---they seem to go on as you said "ad nauseum". Really not looking for short cuts---but to search everything since 2007 with no good results gets a little tiring! The net version is equally non-productive.

[mikku]

Re: Home brew concrete and cast-in-place concrete.

1-1-5 to 6 depending upon the sand. Sharp sand less, round sand more.

Thank you for the proportions, I will add it to my list of recipe and let you know how the hearth turns out!

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

Here is a link which might help clarify the differences of mortar types.

Mortar

Another link with a ton of useful info.

Mortar & Grout | Portland Cement Association (PCA)

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

portland cement and sand and water... make a lousy mortar, doesn't stick to a trowel--just slips off.

That isn't considered as mortar ( by Masons, anyway ). It is too strong, develops cracks between the stone and bed immediately, and traps moisture behind it..leading to efflorescence, spalling and water damage.

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

If you are going to use a gauged stone like that, why not use an exterior grade modified thin-set instead of mortar. That should be readily available anywhere. I think that is a better option for setting the stone you showed in the picture.

If you do use mortar, make your mix a little on the rich side ( slightly heavier ratio of lime/portland or mortar) and paste the back of the stone with a slurry of your mortar mix ( with no sand added ) and water. Use a heavy brush and apply it to the stone, after you clean off any dust or cutting slurry.

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

The lime is harder on the hands..... I use a barrier cream on my hands prior to handling cement or lime. It helps a bit.

Good idea. Instantly caustic when it contacts water...or blood.

[Tscarborough]

Re: Home brew concrete and cast-in-place concrete.

That looks like cantera stone, limestone with volcanic inclusions, basically. They build fireplaces with it in Mexico.

[brickie in oz]

Re: Home brew concrete and cast-in-place concrete.

Bricklayers usually use 4:1 sand, cement and then sometimes use additives I previously mentioned to adjust the brew to their liking and workability.

Its always, 6:1:1ish

[mikku]

Re: Home brew concrete and cast-in-place concrete.

Here is a link which might help clarify the differences of mortar types.

Mortar

Another link with a ton of useful info.

Mortar & Grout | Portland Cement Association (PCA)

While one side of the world sleeps, the other side responds!

Thank you for the link--I can see by just glancing at it, there is a lot of information included. It is going to take some time to look at.

I have some thinset left over from doing my tilework next to front door. From previous experience.. it works great as long as it is not laid too thick (maybe that is why they call it "thinset") Quick initial set. Thick bed, much longer to obtain a strong bond.

Also have some acrylic bonding liquid (at least I think that's what it is). Since my concrete work was done at a couple of different times.. supplier said to first thoroughly clean, then use a skim coat (portland, bonding agent, micro sand) to coat the concrete and fill in minor voids--then proceed with tile work as if a new build.

Old timer tile guys use a crumbly mud under their tile to create a flat surface, then spread a slurry of water/portland and set the tile directly into the slurry. Sometimes good results, many times -- hollow sounding tile when you tap on it!

Think I will go with the 1-1-(5 to 6) mix, and back butter the stone as mentioned. Makes sense .. the stone is very porous, volcanic in nature--some kind of a zeolite tuff. That way, you have a bonding material on the surface to begin with and do not have to rely on absorption alone!

Do you see any problem with a 3/4" thick mortar bed?

[Tscarborough]

Re: Home brew concrete and cast-in-place concrete.

None at all.

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

3/8" - 3/4" is a standard range for traditional mortar.

[mikku]

Re: Home brew concrete and cast-in-place concrete.

If you are going to use a gauged stone like that, why not use an exterior grade modified thin-set instead of mortar. That should be readily available anywhere. I think that is a better option for setting the stone you showed in the picture.

If you do use mortar, make your mix a little on the rich side ( slightly heavier ratio of lime/portland or mortar) and paste the back of the stone with a slurry of your mortar mix ( with no sand added ) and water. Use a heavy brush and apply it to the stone, after you clean off any dust or cutting slurry.

Hello Stonecutter-
I had some time today to set these gauged stone, did what you said with the mortar style... the results were not satisfactory to me. Actually pasted the stone and the hearth locations with the sandless portland/lime mix--sucked in like painting latex on a hot day. Put down a mortar bed, set the stone --water got sucked out as fast as the stone hit the mortar. Took it up/ thinned the mix and tried twice again. Was not able to get it to settle nicely into the mortar bed even though it was extremely loose.

Looked at it for about 15 minutes and pulled the stones off...cleaned the mortar off anything and disposed of it.

Dug out the bag of thinset and tried to get a proper translation of mixing instructions. I really think that the thinset is going to be the way to go... At least it will be soft enough for the stone to bed down and it is probably a much higher cement ratio with finer sand.

I am starting to appreciate the skills of those who have to do this for a living. At least- when I took the stone off, I could see it had not settled in several locations, just trouble down the road! Thanks for the heads up information!

[stonecutter]

Re: Home brew concrete and cast-in-place concrete.

Hello Stonecutter-
I had some time today to set these gauged stone, did what you said with the mortar style... the results were not satisfactory to me. Actually pasted the stone and the hearth locations with the sandless portland/lime mix--sucked in like painting latex on a hot day. Put down a mortar bed, set the stone --water got sucked out as fast as the stone hit the mortar. Took it up/ thinned the mix and tried twice again. Was not able to get it to settle nicely into the mortar bed even though it was extremely loose.

Looked at it for about 15 minutes and pulled the stones off...cleaned the mortar off anything and disposed of it.

Dug out the bag of thinset and tried to get a proper translation of mixing instructions. I really think that the thinset is going to be the way to go... At least it will be soft enough for the stone to bed down and it is probably a much higher cement ratio with finer sand.

I am starting to appreciate the skills of those who have to do this for a living. At least- when I took the stone off, I could see it had not settled in several locations, just trouble down the road! Thanks for the heads up information!

Here are a few more pointers....

When you set stones in a mortar mix, it won't settle on it's own. You will either have to gently tap or shake the stone down into the mortar bed. Setting stone with ( a correctly mixed ) mortar isn't really as easy as it may seem. That's why I suggested thin-set as the first option, because it's easier for a novice to set stone ( thin gauged ) and get full coverage. And thin-set usually only requires the tile or stone to be gently pressed into it to be bedded firmly...assuming you use the correct notch trowel, burned the back of the stone and then back buttered it...this takes the place of a slurry coat. Furthermore, you can't expect to spread a mortar mix down and just let the stone settle down on it's own...even if the stone is very heavy, it will only settle a little bit, then the mortar compacts under the stone..supporting it solidly.

Also, adding too water to a mix is extremely bad for any mortar or thin-set...and it's a very common mistake that is made by many masons. With a stone setting mortar, only add enough water so that a handful holds it's shape when released, and only make what you can use in 2 hrs or less. Mortar like this is for setting stone...a brick mix will be looser, but it is also richer in portland/lime content than a stone mix...your mix is like a hybrid, between a stone and brick mortar. Within the 2 hr time frame you can re-temper ( add water ) to the mix, but only to bring it back to it's original condition..because (repeat) too much water is bad for mortar. Any mortar that is constantly re-tempered will cure incorrectly, and fail relatively soon. With thin-set, only add the recommended amount when you first mix up the batch, and only stir occasionally...never add water to thin-set.

Hot weather masonry has it's own challenges. You should try to keep your stone cool...either keep it shaded or spray it down with water occasionally...even better, do both. When you applied the paste, (which should have been thick..like a milkshake) and saw that the stone sucked the moisture out, you should have put some water in the rest of the stones before applying the slurry..don't saturate it, but enough to stop your mortar slurry from flash drying. How much water depends on your stone and weather conditions. And the setting surface should be treated the same as the stone..keep it cool.

Traditional mortar takes hours before it sets up..even longer if you made it loose. 15 minutes isn't even long enough for thin-set (other than fast setting ) to achieve a good bond. In hot weather you should keep newly set stone cool for at least 24 hrs. Covering it with a wet drop cloth ( or something else) and plastic will keep the water from evaporating too fast. Sometimes all these steps aren't possible..but do your best to protect the mortar from drying too fast..otherwise the curing process will be compromised.

One thing I noticed that I failed to mention in the original post. When making slurry paste and mortar.... you can use an acrylic admix to make it even more grabby. Polymers and acrylic additives are in modified thin-set and it's fine to use them with traditional mortar, and it makes a superior slurry.

Thin-set is the way to go with the stone you have, but hopefully this info will be of use if you ever set stone again.