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hallsy86

Cement Pots Cracking

8 years ago

Hey guys,

This isn't necessarily a hypertufa issue as I've been using straight portland cement instead of a hypertufa mix but I don't know where else to post it.
I recently started making pots out of cement and have been happy with the results but I'm having an issue with cracks as soon as I put soil into the pots. Several cracks usually appear about 24 hours after placing soil and plants in the pots. I'm waiting a few days after making them to place the soil in the pots. I live in a desert environment and the temps regularly get 100+ degrees and stays hot at night. Is the soil taking moisture from the cement causing them to crack? Should I submerge them in water for some time after taking them out of the mold?
Thanks for any help!
Eric

Comments (50)

  • 8 years ago

    Hey Mike,
    Thanks for the reply. I'll pick up some sand and give it a try.
    I haven't been curing the pots and that sounds like the problem. What do you recommend for keeping them wet? I've read about putting them in garbage bags or into a tub of water. What do you prefer?
    Thanks again!

    Eric

  • 8 years ago

    Hi:

    I have found, for some reason, that putting pots in a tub of water after they have cured enough to handle without breaking (24-36 hours, usually) works better than keeping them in a bag. Also, are you letting them cure in that hot sun? That will damage them as that temperature is way too hot for a good cure.

    hallsy86 thanked club53
  • 8 years ago

    I'm glad I found this forum. Sounds like I've been doing everything wrong, lol. I have been leaving them in the heat. Time to start soaking them and bringing them inside. How long do you leave them in water for?

    Thanks!

  • 8 years ago

    No problem! Concrete cures between 50 - 90 degrees F and hydration is important or it shrinks. It doesn't have much tensile strength at best, so keep it moist. Two or three weeks in the water bath is what I use for hypertufa; some do it shorter, but that is what works for me for best strength.

  • 8 years ago

    Sorry for the delay. This is the curing process I use for making Hypertufa and for making cement cast leaves. Both have portland cement in the mix, so the curing process is the same.

    After I remove from the mold ( about 24 hrs after I mix the ingredients) I rinse with water, then I place the pot or leaf in a garbage bag and secure the open end. Every day or so I open the bag and rinse. I keep them moist for 7 - 14 days. After that ritual, The pot or leaf should be properly cured. Larger items I try to go the 14 days or more. To get ready for planting, I will rinse several time more or soak for a day or two. The soaking typically done to remove the residue for the Hypertufa pots. Or you can leave outside for a period of time and let the rain rinse. ( I cant wait that long) The cement leaves I never soak. There is no need unless I plan to use as a bird bath. Cement cures best over 50 degrees F. There are many methods to cure - the important step is that you do go through some type of curing process.

    All the Hypertufa container on my site, I made. There are many photos to enjoy. Mike

    My Blog

  • 8 years ago

    OK, after reading this I think I should mention that my leaves are not the huge ones some are making. I used my neighbor's large squash leaves they are about 1' x 2'. So if I understand correctly, smaller pieces need less time? At thickest in the center thy are maybe 2" thick, narrowing to about 1/4 to 1/2 at the edges. I took the leaves off today and am very pleased with the results. That said... Do you think a week? Or two? Thanks again

  • 8 years ago

    Two weeks, would be better; put them in a tub of water. The size doesn't make a whole lot of difference in the cure time, it is just that I've found that the smaller pots are not subject to as much pressure from soil volume, weight, etc. The leaves are not going to have any kind of stress on them, but you still would like to have them as strong as possible.

  • 8 years ago

    Mike, Thank you so much for the help. I will get a tub that will fit them and put them in water for the two weeks you recommend. thanks again :)

  • 6 years ago

    I tried straight cement and put in water bath for 15 days .... all cracked within 24hr of planting going to try sand I think

  • 6 years ago

    describe how you are mixing, how cold in your area,

  • 6 years ago

    I have the same problem, some of my pots develop hairline cracks on opposite sides soon after planting them. I have made a few hundred pots all sizes, and I reckon about 10 procent develop cracks. I am quite sure its not the recepe nor the curing, because I follow all the rules, nor thw freezing. It s something else, and I can not figure it out. Please advise. I attach some photos. The pots never develop cracks if empty, only planted.




  • 6 years ago

    I use this type of portland cement


  • 6 years ago

  • 6 years ago

    Anyone knows if it's the right type?


  • PRO
    6 years ago

    Cement cracks when it dries out too fast. i would use the water technique described above. I just made some with sand and perlite and the came out OK. You are in the desert and they are probably drying out too fast.

  • 6 years ago

    Thanks for your comment. I agree that usually the main reason for cracking is the curing, but I keep my pots in plastic bags for 3 weeks. I water them thoroughly when I bag them, and it's true that I do not spray them anymore, but inside the bag I see water drops all the time, so it's not a dry environment. I cure them in shade, and we have max. 30 degress celsius.

    And my pots never crack if empty. I have empty ones out for two years in -20 celcius, and they are ok, some only crack soon after putting soil in it.

  • 5 years ago

    old question, I know, but I have recently found out that there is a type of fibre you can buy to re-inforce your concrete pieces... it just goes in the mix. I found this out when we had a concrete outdoor kitchen made - doors, splashback, and all. I couldn't believe how thin the pieces are! The craftsman told me about the fibre, and I've seen people using small amounts online - however I'm in Australia, and I don't know where I'd get a small amount from, let alone Rest Of World.

  • 5 years ago

    I am in also in Australia I have been making small rectangle pots and have the same problem with cracking after I fill will soul and succulents. I use a white concrete (no sand) pots set well in 24hrs and I’ve never used the water cure but do seal my pots with Boncrete and they are still cracking. Slightly annoying so close to Christmas and I have 30 corporate orders for gifts that I have to have finished in two weeks!!! Help!!! So does the water curing work in Australia and hex I don’t have the lead time


  • 5 years ago

    HU - I use a white concrete, ( conrete is a mixute of portland cement and agregate )

    I assume that you are making concrete pots ?

    Are these pots to allowed to cure ? Sitting for 24 hrs is not curing. If cement ( or hypertufa ) dries quickly instead or curing slowing - it will crack ! Curing minimally takes 7-14 days. the longer the better. They must be damp for the entire time. Also for curing to be sucessful ( if making outside) The outdoor temps should be warm. 50 degrees farenheight or higher. see my post above. Curing should work in Australia

  • 5 years ago

    I’m in Australia too and mine keep cracking, I’m going to try the water too and would you recommend adding something to the cement to strengthen it too? Or what about concrete sealant

  • 5 years ago

    Thanks mike I currently have my remaining rectangle white cement pots soaking in a bath of water, I intend to leave them in the water for 7 days, I had used bincrete sealer on the sides and inside of the pots, two coasts so I’m relying on the water penetrating from the base of the pots, I feel as though the sealer is coming off, kinda think that’s a bonus?? As I can now resell after the curing process(I’ll leave them to slowly dry over the Christmas new year period - yep the almost bloody hottest time of our year,, hahah! Should I keep them in a bag so they don’t dry out too quickly- I live in the Gold Coast so it’s rather humid here. Perhaps they will be ok on a shelf in the garage?? What are your thoughts mike?? I’ll also be chasing down some finer mesh- which my “boral concrete“ mate has recommended is the best plan of attack for adding tensile strength to the pots.

  • 5 years ago
    last modified: 5 years ago

    Do you use straight portland cement? Did your mix include sand with the portland cement?

    becasue -----

    Sand is an agregate, it will mix with the cement to create a stronger pot. No agregate and your pot will not be as strong. For example when we make hypertufa, we add peatmoss and perlite to the portland cement. When you make concrete you add sand and gravel to the portland cement.


    Curing plays an important role on strength development and durability of concrete., it is a reaction that allows the cement mix to grain strenght. The pot must be damp to cure. Minimally It needs to be damp 7 - 14 days . Temperature is also important to curing process, It should be over 50 degrees farenheight. Proper curing will result in strenght.


    A water bath is typically done to remove some of the cemicals from the fresh cement. It is called leaching. The leaching or bath helps to rinse away the alkalinity from the cement. Many people do this before they plant in their pots. I have read that you can also cure in a water bath, ( I have not). Keeping the pot damp in a garbage bag works great. The garage is bloody fine. ( just wanted to try bloody in a sentance lol !)

    IMPORTANT- If you allow it to dry (before it has cured) most likely will crack. If you use too much water it is more likely to crack.

    Please google search "curing cement" Learn about this process.

    Humidity may also impact the cure time. Maybe slow it down. I am not sure if it impacts the overall strenght or if it causes cracking.


    Also why are you sealing? and why are you sealing early? there are different types of sealers. for some sealers the cement must be fully cured before application. I am not sure if using the selaer too early would impact the curing procees. Please check the instructions on the sealer. Or ask where you purchase.

    Fiber mesh - IMHO it is overkill for small pots. Good for LARGE pots.

    I typically make hypertufa and only use fibers when my pots are very large, maybe 3ft by 3ft.

    Fibers add one more step to the process. The fibers will stick out the sides of the pot, and you will need to burn them off. Unless you want a fuzzy pot!

    My blog - with photos

  • 5 years ago
    last modified: 5 years ago

    How do I prevent bubbles ..upon taking the dried pot or bird bath out of the mould I have bubble holes...I use a shaker to shake the concrete...but still have bubbles.

  • 4 years ago

    I have the same problem. I mix white Portland cement with sand, 1:1. And all pot are

  • 4 years ago

    . Can I mix white cement with ordinary grey

  • 4 years ago

    Hi there,


    My daughter and I decided to diy a cemented vase using cloth as seen on youtube. We followed all the steps, cured it for 3 days and spray painted it. The problem after 2 weeks the paint is flaking off and you can see cement chippings on the floor.


    Could someone advise us what the problem is? could it be in the mixing? is it possible to fix this problems with a concrete sealer for future reference? and what can we do now when creating a second pot to avoid this mistakes?


    I live in Kenya.

  • 4 years ago

    Can someone advise me of a way to leave my heavy Pottery Barn Fluted Concrete planters out in winter? I live in Washington State and we get cold temps and snow however these will be up against the house. https://www.potterybarn.com/products/concrete-fluted-planters/?pkey=s%7Cfluted%20concrete%7C2

    I'd like to put Holiday decor in these during the season.

  • 4 years ago

    Stack some straw bales around them? That'll stop them freezing... but I don't know if that's a fire danger against the house... I live in extreme heat, not snow, though we get down to freezing sometimes.

    If the straw bales worked, then you'd have some lovely mulch ready come the warmer weather.

  • 4 years ago

    Can you guys please help me.. i started making my own cement pots bout 4 says ago.. so the first time if used a thin fabric see threw annd dipped it in cement mixed with water let it dry but it is so brittle i can take it of with my fingers.. first atempt.. second one i used the bucket one also only cement and water left it for about a day try to take out the bucket and it break... so i thought maby the cement and water alone is not strong enough so i mixed in a rocky sand mix used to built with and still in the containers for the second day going to make sure they are dry but it seemed as i it is also going to break if i take it apart... i love in south africa and am currently using cement cant remember name but 42 neutins...


    Is cement and water alone strong enough for planters alone or what woeks best... im struggling and could use some experienced advice please

  • 3 years ago

    Been making bonsai pots and I find 3 parts sand one part cement a cup of hydrated lime or say 1 part hydrated lime . I let them dry in shed in Australia any month and they come out fine few cracks if I take them outside to sit on sun but I don’t do that any more . I don’t know if it does anything but I add colour dye cement powder to my mix for making my pots brown and black . keeping damp is a good idea over curing process but not a must I have found and I pot soil in bonsai pots up to 2 ft bt 1ft and smaller.

    at


  • 3 years ago

    One with inner mould removed

  • 3 years ago

    Little olive in a cement pot with black dye powder added to cement

  • 3 years ago

    Clients want their pots as soon as they decide on their design. As such, I use Fibre Reinforcement to prevent cracks even before full curing occurs. Follow on Insta @Muchcrafts for detailed description.

  • 3 years ago

    https://youtu.be/JYuF2TqsRFE. Check out how I make mine and they are pretty

  • 3 years ago

    Hi guys, your help is needed here - I have a problem with curing my concrete items.


    I use the ratio 1 :1 in order to make my mixture (1 cement : 1 sand), pour it to a silicone mold, cover it with a plastic bag, and after 24 hours I take it out from the mold - until this stage everything is great.


    In order to have a good curing process, I put the item in a bucket with cold water and wait 14 days. Then, when I take out the item from the water there is a white "powdery" layer / stains on it.


    In addition, after several hours in the water, I can see this "powder" at the top layer of the water.



    I have tried to change water every day, I even tried mineral water, I tried to take out the item after one day... everything leads to the same result - a powdery layer that damage the item.

  • 3 years ago

    Use sand paper sand the white powder

  • 3 years ago

    Unfortunately it damage the texture of the casting.


    I attached 2 photos, the first one is without curing under water, and therefore I didn't sand it.


    And the second one, is curing under water + sanding (paper 180).





  • 3 years ago

    Great read, have gathered plenty of info from this thread.

    One question still. What kind of sand are you using for your pots (grain size). I want smooth surface but i don't want to get cracks or loose the strength of the concrete.

    I am in the process of making concrete bonsai pots and i want to research as much as i can.

  • 3 years ago

    I am not making cement pots but have 6 large

    cement pots from Pottery Barn. Would like to leave them out this winter. Is their steps I can take to ensure they don't crack? I have heard to remove half of the dirt so it has room to expand. Any other advice?

  • 3 years ago
    last modified: 3 years ago

    This has been a great conversation. I create cement sculptures and am having troubles with small cracks. My sculptures are over 3' tall so I'm not able to emerge them in water. These sculptures can take many weeks to finish because of their size. I use a scratch coat first and let that dry for about a week. I then apply a slurry of just cement as I apply the second coat of cement. When I'm not working on it I cover and seal with a plastic sheet. But those pesky cracks show up. Could it be I'm applying the second coat too thin? I apply the cement with a small trowel.

    PS. I tried to attach a photo of the sculptures, but it won't take it.

  • 3 years ago

    So I have been trying to make a concrete planter for months at this point. I have been following this forum as well as a few others also experimenting with various methods by myself and I still failed. The problem is my planter cracks when I put soil and plant in. my mixture is good ( i use all cement ). I let it harden at room temperature for 24h before de-mold. I cured it for 7 days at room temperature bath. I sealed it with a water-based sealer for 2 layers ( letting it dry 24h between each layer) and it still cracks. At this point, I am running out of methods to try.

    Does anyone have any suggestions?

  • 3 years ago

    I've seen where people put straw in the mix to give it more substance... Also I've seen where they make the shape of chicken wire and put the concrete on that.

  • 3 years ago
    last modified: 3 years ago

    I am making small pots using white cement, coarse sand and aggregate. But I get “runs” in the finish that look like the sand has settled to the outside, even though I make sure I mix very well. What am I doing wrong?


  • 3 years ago

    Any advice/experience for cement candle vessels?

    Ive tried multiple type of cement and the moment i demolded them they cracked.

  • 3 years ago
    last modified: 3 years ago

    Hi guys, we are making concrete pots with the mix of white and grey cement, 1:2 with sand, and aditives, Sika Plastocrete and Sika Viscocrete. Our pots doesnt crack, but they has these imperfections, mostly on inners side, but sometimes also on outer side. Does someone know what could be the reason


  • 3 years ago

    Hi there..im from South Africa. My cement pots are also cracking as soon as I put soil and succulents in them..when I water the plants the pots crack. I use a 32.5 concrete cement and mix sand.. the ratio I usually work with is 2 cement and 1 sand.. I've tried curing it in water but only for about 4 days... when leaving the pots to dry they are standing in the sun.. I have read some of the comments above, and see that the pots shoul rather not be left in the sun? And i woul also like to know what ratio is the best to use?


  • 3 years ago

    I would use a standard hypertufa mix or use premixed concrete (don’t try to make your own unless you are familiar with the chemistry and points of making a good strong mix). Do not get quick Crete like they use for post holes. That works well because it’s in the ground and rain and water keep it damp as it cures. Remember first, concrete never stops curing. It sets up etc and can be used like driveways after at least a week two weeks better. But even then you keep it covered and misted each day — the longer it stays damp (damp not wet in the beginning) the stronger it will be. But the faster you try to dry and cure it, the more cracks, and more brittle it will be. I see people out there doing DIY walks etc and they got fans going cause they want to use that day or the next — and they wonder why it’s cracked, chipping up on the edges, and spalling in a few months. The way I use to do hypertufa (for lightness of weight) or regular concrete if I needed it to stay in place ie wildlife not messing with them - was to make them up, unmold, and then immediately mist, wrap in double layers of heavy plastic and leave sitting in the shade (no sun) for a few days, check it each day and mist it down daily and cover it back up. Do this for 4-5 days. Uncover and let sit in the shade for 6-8 months and mist it down daily .when it rains obviously no need like in the winter. By following spring or summer - put in big tub etc of water and let soak. Change the water every day x 3 or more if you can. Check water with a pH meter. When it reaches around 6-7 you can plant anything you want except for blueberries they want pH around 4-5 I believe. You are trying to neutralize the lime or the pH out of the pot. Concrete is around12-13 (highly alkaline). Even hypertufa is high because it’s peat and concrete but not quite as bad as straight concrete. Peat Moss is about 3-4 pH (very acidic) and it will bring down the concrete some. And this is how we do hypertufa too. But if the pH is still around 8 then you will need to make sure what you put in it can stand that high a pH - not a lot of choices. Remember 7 is neutral, under is acidic, over is alkaline. Roses like 6-6.5, tomatoes 5.5-6, beans like snaps like 6.5-7+ a little. Asparagus like 7 maybe +. Lilacs like higher 6.5-7.5, Cactus can take higher 7+, but there are lots of pH plant charts. Your potting mixes will be acidic based (peat Moss, and bark) but they initially charge all potting mixes with lime to bring them to a general pH. You can contact whoever’s brand you use (look the manufacturer on the internet, they all have customer service)call them up and ask. They will all be different and different mixes within the same manufacturer line may be different if made for different types of plants. A general mix would be 6-6.5 or 5.5-6.5. You can do a media pour-through test - search “media pour thru pH testing) so you know for sure. But the initial lime charge only lasts about 4-6 months depending on how often you water or it rains. You need to resweeten the soil each year — it depends on the size of the pot. Or you can retest with pour through technique to know what the level is. Regular Lime adds calcium, dolomite lime adds magnesium and calcium. If the pH is okay and you want to add calcium - use gypsum. I just know that mine will need it so I add a tablespoons every 6 months for pots 6-10” and up it for larger. If the pot is deep, you will need more or less. For things like tomatoes I add gypsum because they like calcium and you won’t get cat faced or blossom end rot. But back to the pots. I wouldn’t plant in them for at least 6-8 months or at least through your rainy season, and 3-5 days soaking and changing the water daily. If you don’t change the water, you aren’t getting rid of the lime. Check the pH and dilute with water til it reaches 7-7.3 and sprinkle your lawn with the soaking water — it will like the higher pH.

  • 3 years ago

    Okay! Great news. The pots I purchased from Pottery Barn made it through a PNW winter. I emptied probably 4-6 of dirt, added foam blocks sold by florists to soak up water in case any got into the pots, then bubble wrap, then covered with decorator spanish moss as these are next to my front door (held down with slate landscaping rocks and not one crack. I did cover them up with a blanket for a few days when our temps got down to single digits, but this beats hauling very heavy decorator cement pots in and out in the fall and spring. Thanks for all of your suggestions, as you can tell I used a lot of them!

  • 2 years ago
    last modified: 2 years ago

    i have the same issue as some folks above where the pots crack after being planted in (after a day or so of holding soil and being watered). my process was pure portland cement with water, sometimes i soaked them in a tub for a couple days but mostly i would hose them down a couple times a day until they were super smooth.

    ive tried a couple different sealants. the ones ive sealed with Drylok (which has a rough, stubbly finish, its meant for pools) have never cracked! Also ones ive painted dont seem to crack but they could be cracking underneath the paint and just not showing.

    I switched off drylok for a clear, gloss finish concrete sealant off amazon (brand is Kilz), and if i leave the pot naturally finished with triple layer of glossy sealant on the concrete, all of them crack, and crack pretty badly but ONLY WHEN PLANTED WITH SOIL.

    still have not seen a good answer here for why it only happens when they get planted in... is it something with the pressure of the dirt interacting with temperature and moisture changes? is the sealant not strong enough? i have a feeling that even if i let it cure longer, it will still be like others here with the cracking.

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