Home brew concrete and cast-in-place concrete.

[stonecutter]

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

If you want voids then remember that they weaken the casting. Try making the mix fairly stiff and do a thin layer, then fill the rest with normal consistency. Thanks for the vibrating reciprocating saw idea, I shall try it.

1.Tell me about it. but I use a local company if I use a bagged mix or I just make my own, which is much, much cheaper. When I mix bagged concrete, I only mix what I need.
2.The product I use behaves pretty close to standard concrete. Cold water, yeah..just like making mortar in hot weather too. Clean water is just as important too.
3. SS needles not necessary when I use the bagged mixes...highly engineered with polymers and fibers. When I make my own I used galvanized wire screen and polymer/acrylic additives.
4. This concrete is not for the oven chamber or anywhere near the heat...it is for capping the dry stone base I built.
5. Excess water is bad for any mortar or concrete mix. Only add enough to hydrate the cement or mortar accordingly.
6. Doesn't really apply to this application.
7. Voids are the point with the hand pressed technique, it is how you create the veining effect. Only about a third-half the form is pressed, the rest is filled with a flowable mixture ( at least this is how I have seen it done and the way I have done it myself.)
8. Any concrete should be covered when slow curing is needed or to prevent excessive evaporation of water.
9. I would be interested in doing a cast refractory dome sometime in the future!
10. I always use melemine or pvc trim for my forms and I always use a release agent...though simply cleaning these types of materials is usually enough to prevent sticking.

I think your list was good, but you might be thinking I am talking about cast refractory...I'm not. Pics coming soon.

Voids are fine, check #8 for the method....it's done with success everywhere.

[david s]

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

If you want voids then remember that they weaken the casting. Try making the mix fairly stiff and do a thin layer, then fill the rest with normal consistency. Thanks for the vibrating reciprocating saw idea, I shall try it.

[stonecutter]

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

Forget everything On my list except 7 and 10. If you don't have a vibrator probe an orbital sander without the paper, held to the outside of the mould works reasonably well.

Well... like I said, a release agent applied to my forms, even though it doesn't need it if the form is clean. But you don't vibrate the form when you do this technique. If you did, it would defeat the whole purpose of hand pressing the concrete into the form..and that is to create voids that are later filled with a contrasting colored slurry.

Incidentally, I have tried the orbital sander trick before, but I prefer a sawzall (reciprocating saw) with the blade removed. It is a little more aggressive and did the job better than the sander .( IMO)

[david s]

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

Sorry, when you said you wanted to make a casting for your oven I assumed it was for the hot part. Forget everything On my list except 7 and 10. If you don't have a vibrator probe an orbital sander without the paper, held to the outside of the mould works reasonably well.With normal concrete remove from the mould after 24hrs and keep wet, wrap in plastic for a week.

[stonecutter]

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

There are a few things to consider.
1. The stuff is expensive so you don't want to waste it.

2. It goes off fast (particularly in hot weather- use chilled water) so don't mix up too much in one batch.
3. Add stainless steel needles, at least 2% by weight, for reinforcing.
4. Much stronger and stable under firing if you can fire the casting to 1000 C if practicable.
5. Excess water in the mix weakens it. Water reducers easily create separation.
6.the stuff is very thixotrpic.
7. Use vibration when placing, or mash it in, to reduce voids.
8. Does not require extended curing, should be covered but 24 hrs is sufficient.
9. There are many types of castable refractories available, seek advice from your supplier.
10. Oil your moulds.

1.Tell me about it. but I use a local company if I use a bagged mix or I just make my own, which is much, much cheaper. When I mix bagged concrete, I only mix what I need.
2.The product I use behaves pretty close to standard concrete. Cold water, yeah..just like making mortar in hot weather too. Clean water is just as important too.
3. SS needles not necessary when I use the bagged mixes...highly engineered with polymers and fibers. When I make my own I used galvanized wire screen and polymer/acrylic additives.
4. This concrete is not for the oven chamber or anywhere near the heat...it is for capping the dry stone base I built.
5. Excess water is bad for any mortar or concrete mix. Only add enough to hydrate the cement or mortar accordingly.
6. Doesn't really apply to this application.
7. Voids are the point with the hand pressed technique, it is how you create the veining effect. Only about a third-half the form is pressed, the rest is filled with a flowable mixture ( at least this is how I have seen it done and the way I have done it myself.)
8. Any concrete should be covered when slow curing is needed or to prevent excessive evaporation of water.
9. I would be interested in doing a cast refractory dome sometime in the future!
10. I always use melemine or pvc trim for my forms and I always use a release agent...though simply cleaning these types of materials is usually enough to prevent sticking.

I think your list was good, but you might be thinking I am talking about cast refractory...I'm not. Pics coming soon.

[david s]

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

Let's bring this thread back to concrete.....

Im planning to do some cast pieces on my oven using a hand pressed method. Anyone do this before? I've done a couple pieces, and I'll put some pics up later.

There are a few things to consider.
1. The stuff is expensive so you don't want to waste it.
2. It goes off fast (particularly in hot weather- use chilled water) so don't mix up too much in one batch.
3. Add stainless steel needles, at least 2% by weight, for reinforcing.
4. Much stronger and stable under firing if you can fire the casting to 1000 C if practicable.
5. Excess water in the mix weakens it. Water reducers easily create separation.
6.the stuff is very thixotrpic.
7. Use vibration when placing, or mash it in, to reduce voids.
8. Does not require extended curing, should be covered but 24 hrs is sufficient.
9. There are many types of castable refractories available, seek advice from your supplier.
10. Oil your moulds.

[mikku]

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

I just want to say something about this, because similar expressions have been made on other forums and blogs I have read. Indulge me while I jump on my soapbox.....

You have to realize, guys like me depend on the knowledge we have to earn a living...and not in the obvious sense of that statement either. Not all professionals take the time to learn proper technique or educate themselves in the particular trade or craft they practice. For the ones that do, much of what is learned has come at a cost...not just financially, but mentally and physically. A good tradesman keeps striving to learn, succeeding and failing, while assuming all the responsibility and cost of acquiring this knowledge. Professionals do realize amateurs must learn by experience..that's why some don't want to give away what they had to earn...paying your dues, so to speak.

You have to take this into account. It may be difficult for some to just put hard earned knowledge out there, for anyone to take and get no return on it, other than personal satisfaction that you are helping somebody out. For some, that may be why they only lurk or the comments are limited...and that is not wrong. That doesn't make them bad or selfish. I'm speaking from both sides...I never commented much in the past either, but I have come to enjoy helping out and offering advise if I think I can. Have I benefited financially? Nope...not a cent. But who knows? That's not why I participate anyway. I just really enjoy doing my trade and talking about it with others too.

I don't think pro's hold back so others fail...well, maybe a few of the petty ones do. But then, if that's the case, they aren't much of a pro anyway. And it's up to the amateur to pursue the knowledge they are seeking, not the job of the pro to give it all away. If you want it bad enough, all the information you need is out there.

I'll say this in conclusion...when you are trying to learn about something in masonry, it's no different than anything else in this world. Look for consistency, when in doubt, stick to proven methods and never,ever be afraid to fail..it's the best teacher. And remember that nobody in the trade/craft owes you even one word of information about technique, methods or anything else.

I'm not trying to imply you feel this way, but I guess this was my time to vent this out. It's also my perspective on a point I have seen before, so take it with a grain of salt....it's just my opinion.

Moving on......

I agree, with what you say!
I know where you are coming from! Been there!

[stonecutter]

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

Let's bring this thread back to concrete.....

Im planning to do some cast pieces on my oven using a hand pressed method. Anyone do this before? I've done a couple pieces, and I'll put some pics up later.

[Tscarborough]

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

Secrets don't mean much, none of it is really secret, the difference is manual skill, and the obstacle is repeating the same thing over and over, when a good search will generally suffice.


I answer any question, but do not offer technique.

[david s]

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

I'm too old to benefit from keeping secrets and prefer to share anything I've learned from experience. This oven building thing is fraught with hurdles and pitfalls. Might as well share to help others to the glorious path of a good functioning oven. There are so many ways to get there it makes the subject fascinating. Might not always be right, but if it promotes healthy discussion then surely that advances knowledge.

[stonecutter]

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

Many professionals tend to keep what they have learned by experience as a guarded secret --so amateurs will fail! They don't realize that the amateur must learn by experiencing the same things --and words are only guides, doing is where they learn---and that takes a lot of time!
Being good at it takes a lifetime.

I don't think pro's hold back so others fail...well, maybe a few of the petty ones do. But then, if that's the case, they aren't much of a pro anyway. And it's up to the amateur to pursue the knowledge they are seeking, not the job of the pro to give it all away. If you want it bad enough, all the information you need is out there.

when you are trying to learn about something in masonry, it's no different than anything else in this world. Look for consistency, when in doubt, stick to proven methods and never,ever be afraid to fail..it's the best teacher. And remember that nobody in the trade/craft owes you even one word of information about technique, methods or anything else.

I'm not trying to imply you feel this way, but I guess this was my time to vent this out. It's also my perspective on a point I have seen before, so take it with a grain of salt....it's just my opinion.

Moving on......

[mikku]

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

Stonecutter,
Thank you for the wealth of information. I'm going to print out your post so I don't have to check into the forum to reference the information. I failed to mention that I did use a latex bonding agent on the surface of my concrete base prior to painting the slurry.

The 15 minute wait period was just to look at things, looked under the edge and saw voids in places, actually attempted to force some additional mortar beneath.. I just decided, if I leave this sit too long--I will get an initial bond and make it difficult to remove, longer yet and I would have to destroy the stone to get it off. That is why the operation was aborted.

I will keep in mind all the things you said. I should have considered this stone just a big piece of tile (unglazed) in the first place. It is a challenge working with something as porous as this is. So far no damage done, and some good experience gained.

Thank you for taking the time to explain technique as well as setting conditions for working with this stone. Many professionals tend to keep what they have learned by experience as a guarded secret --so amateurs will fail! They don't realize that the amateur must learn by experiencing the same things --and words are only guides, doing is where they learn---and that takes a lot of time!
Being good at it takes a lifetime.

[stonecutter]

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

Actually pasted the stone and the hearth locations with the sandless portland/lime mix--sucked in like painting latex on a hot day.

Common effect...even if you pre-wet the stone. This will still help with a good bond...you need to make sure that you have enough solids in your slurry though.

[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.

[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!