Ooooh, dry pour update :3 Very excited structural engineer here. So wall of text incoming. You have been warned. First of all I see nothing wrong with your testing job with the concrete-strength-testing thingy (which is called a Schmidt hammer by the way). All in all I'm pleasantly surprised and also glad for having been more or less able to predict the results; and also the pitfalls of dry pouring. Pleasant surprise comes from your results. Which I could interpret right away as a European (SI ftw). One thing I feel the need to add: this hammer method tests surface hardness which directly correlates with concrete strength... in wet poured stuff. As you said the method can be ver unpredictable. The smallest inconsistencies in pouring, compacting, and wetting the slab have major effects on its final strength. Also in a lot of cases the inner part of the slab does not get properly hydrated. This means there will be uncured cement remaining in the slab reducing strength. All these results align with my opinion I established last year about dry pouring. Great for horizontal slabs without reinforcement and highly not recommended when: a) working with rebars - proper hydration across the slab is critical for the rebars to properly adhere b) building actual load bearing structure - we want the least amount of uncontrolled variables c) being prone to rush / half-*ss a job :) One more thing to keep in mind: cement content and proper hydration makes or breaks the concrete's resistance to freezing. Overhydration leaves a lot of pores / air pockets after drying. The top surface is the most critical in this regard both because water sitting there when done and because that's the surface you wet your dry pour through. If you work at a location that sees freezing temps be extra careful not to overwater your dry pour.
@@Fonok87 Awesome comment! I didn’t know about the over wetting leaving more pockets/pores. As a structural engineer, do you know anything about the closed cell expanding foam called Secure Set? It claims that concrete has approximately 6,000+ psi after 30 days and their foam has approximately 10,000+ psi after 30 minutes. I haven’t seen anything about it being used in load bearing or structural work but if that psi is correct, why not? I did find (on RU-vid) a couple in Arizona that built a geodesic dome house and covered it with a closed cell foam. They built the house in only 4 days. If this stuff is as strong as they claim, I’m thinking it could be an awesome material to use after disasters to quickly build structures for people who have lost their homes. Do you have any insight into this product?
I haven't heard of Secure Set but I'm in Europe so that might be the reason (I checked their site, they have no presence outside the US). The thing with these materials is that they tend to be waay more expensive than concrete which is the case here. Their 4 gal kit says it can be used to set 20 posts in a 8"x24" hole at a price of $132. Even if I omit the volume of the post (which is not insignificant) cost comes out to about $190 per cubic foot. Other materials might be cheaper but they all come with enormous R&D costs. Also concrete mixed at a plant can easily reach 9000 psi strength. When using literal tons of concrete to build a structure it means millions of dollars in cost difference. On the other hand, concrete needs at least a week before it can safely take a load. So it comes down to what you're willing to pay for the massive reduction in building time. Disaster recovery and critical structure repairs are good examples where getting results quickly is a priority above all else.
"proper hydration makes or breaks the concrete's resistance to freezing." So, is it possible to dry pour a base, leave 1/2 inch at the top of the form, then finish the job with a traditional mixture, for the remainder of the project. I'm thinking, if cement adheres to older cement, this method might prove to be a solution for the cracking and flaking. I'm not pouring any cement slab, nor have I ever done any cement projects. Just curious as to what your opinion might be.
Have you seen the video with the 86 year-old man mixing concrete quickly using only a tarp? The technique was amazing and easy. You should look it up... very impressive. Do a video for it, many will watch.
Love the fact that you went through all the different dry pours and tests. I was thinking, dry pour a base, leave 1/2 inch at the top of the form, then finish the job with a traditional mixture, for the remainder of the project. If cement adheres to older cement, this method might prove to be a solution for the cracking and flaking.
Hey, I worked as a concrete QC tester for 5 years. I've never seen this rebound test before, so I looked it up real quick. Unfortunately, it is not an accepted method for strength testing. It looks could be within 25% of the real strength. The best way, would be to drill out a 4 in diameter cylinder, or cut a 2x2x2 cube, and break it in a machine with a load cell. You probably won't want to damage your concrete though. As for the delamination. Usually, I would see this if the finishers sprayed water on top after the concrete was mostly set up. Which is not allowed on civil projects.
It is interesting to see the resulting psi on those dry pours. By your own words the unpredictability of the final appearance would be the exact reason I would never do a dry pour. Everyone has their own preference on aesthetics but I look at it from a standpoint that if you already paid for the concrete mix it proper and get a predictable result. I know some people love Jackson Pollock artwork but I don't want my concrete projects ending up like that. 🤣😂🤣 Good on you for doing the testing because it seems everyone else who promotes a dry pour never comes back later to show any real world updates.
Funny all of these imperfect surface issues in appearance..... I see in commercial wet concrete pours ... especially on side walks at new truck stops. Less than a year old .... lots of "deamination " and cracked broken corners
This is really good to know. I stayed to watch the math makes a good argument for dry pour. I have a chicken house I plan on cleaning out with drain lines so every so. Often I clean the floors and hide it out. Thanks for the exoeriment
CORRECTION for those who think they learned something physics-y. A "Newton" measures force, not pressure. That device he's using measures Newtons per square millimeter, not Newtons. It's right at the top of the chart he shows. 1 Newton per square millimeter ~= 145 PSI. Those extra digits past the decimal point given for the conversion don't mean much IF... IF... IF... the way that device obtains its result is affected by the local value of gravitational acceleration (e.g. ball drop), which can be +/- 0.2 PS1 between Seattle and Los Angeles due to the "centrifugal" affect of the rotation of the earth. (This is why you were tortured with "significant figures" in science class).
New Video 💡 : I have been building an off grid cabin & found secure set expanding foam for setting fence posts. (My back is loving NOT dragging heavy bags of concrete). The product website states that normal concrete has a 6,000 psi after 30 days and their foam has a 10,000 psi after 30 minutes. I don’t think my posts will ever move! It would be a very cool thing to check with your new toy. I love concrete but this stuff is only slightly more expensive (actually may be a bit less $ if you buy in bulk) and as we get older, those bags just keep getting heavier 😂. If this stuff is all it says, why aren’t we using it for foundations, etc? You have so much experience with concrete, I would love to see your input on this stuff! ♥️🕊
As a professional user of the rebound hammer, you did pretty well, but you didn't keep it perfectly at 90° at least on the first one. It probably wouldn't affect the results much. Great job!!!
Looks great. I like the "decayed" look too, especially in older-home landscapes. I'd love to see you try some "Portland cement paint" and coat some concrete areas with that. Maybe it will help fill those peeling areas and cracks.
It would seem as if the dry pours that remained in contact with the ground, and therefore soaked up more water, where stronger. So I wonder if that would be an additional variable to consider.
QUESTION???? What are the results on the the one that are delaminating?? Is there a possibility that the one you tested in the middle was able to get more water so the outside ones may be lower?? Just wondering I love doing these types of tests so I would have don’t multiple tests around the patio “slab”
PSI strength will depend on the concrete mix that you used, do you remember what you used? That would tell us more about what the manufacture expected it to be in normal use as opposed to dry pour.
I think the reason you get the flaky surface on the concrete dry poor is because of the initial misting before soaking. I’m curious if that would still happen if you did an extended initial misting that really really saturated the top layer so that the thickness was closer to a quarter of an inch or even half inch instead of a 16th or an 8th of an inch.
not sure if this will help or hurt but i live in florida and there is a road from naples fl. to ft. lauderdale called alligator alley and when it was built back in the early 60s all the bridges and there were many!! had bagged sakcrete used at the ends of each . they were laid att approx. 45deree angle up on the dirt . they were still there in the 70s when I75 replaced them .!!!!!
They lasted better than the road did, that's for sure. You would think with no frost heave or freeze cycles the roads would be better here, but nope. Cape Coral especially, the roads here are trash for how much they tax us here.
Awesome vid, so interesting. I have been doing a bunch of dry pours using 24/6 rapid set. Says 6000 psi on the bag. I wonder how much a difference this makes as opposed to the normal concrete mix. I think you used the 24/6 rapid set for one of your dry pours, but I cant remember which one.
I had concrete steps in a house poured the "right way" and the top started flaking off too, so Concrete is never 100% consistent regardless on how you pour it.
The top chipping off the concrete is caused by the inside of the concrete drying slower than the top. This is why people use spray on cure or do a wet cure. It essentially slows the curing process on the surface so the concrete dries more evenly. Since a dry pour doesn’t have the water evenly distributed through the concrete it isn’t activating the lye equally and that’s what’s causing most of these problems.
I need to fill in a large area that had large raised planters for40 years , and had to be torn down because they were no longer structurally sound, aggregate cement was poured around that. I’ve pondered anything from brick pavers to artificial turf. I wonder if this is the solution? And what would be the best way to do a dry poor inset the empty space?
I can imagine dry pour being great for a walkway like on the side of a house, where people don't care how it looks as much. I think the compression test might be flawed, but I'm not professional. The only reason I say that is because you're testing the top of the dry pour and that's the main part that got water. As we saw in some other dry pour videos, the bottom doesn't get nearly as saturated and I don't know if the improper saturation makes it worse or not.
I worry about the methodology here. AFAIK that type of tester can only measure the compressive strength of a shallow layer. If the top layer is fully cured (exposed to enough moisture to do that) but an inch below the surface is still dry, all you have is a hard layer on top of basically dust. It might be fine for patio furniture but if you used this method on anything that actually requires a certain thickness (e.g. 4", 6", a footing, etc...) you could have a dangerously weak core under a thin, hard shell on top. It would be interesting to see you use this same tool on a test pour or two, say 1'x1'x4" and maybe 1'x1'x6", then cut the test piece with a disc and test the sides/bottom. I would bet if you tested enough thicknesses, you'd probably find some maximum that can be used as a rule of thumb between "just DYI it with a dry pour" (pavers) and "that really does need a wet mix" (garage slab). If the center isn't going to cure past, say, 3" thickness, you might as well just lay down a (cheaper) bed of sand and do a thinner layer of concrete over that...
Thanks for revisiting these dry pours. I think the delamination is a result of your dry pour technique. I went back to watch the video of you dry pouring the blocks, I think when you misted, you put way too much water on the concrete, and the after the mistings, it's supposed to be a shower not just pouring out of the hose. Also, I don't think you watered them enough, supposed to be 2 showers per inch, 1 every hour. So 8 showers since you have a 4" thick block, 8 hours of showering.
So it has been 39 months since you quit your job and become a full time RU-vidr. In that time, I have seen, I believe, 68 videos. Are you still happy? Does it pay enough with putting out almost 2 videos a month? I know it helped that you had a decently large audience before quiting. Any advice for someone considering the same?
OK ok ok So, what would happen if you did a dry pour in lifts. Like 2 inch lifts minutes a parts. So just my brain rattling around. Keep up the great work.
Your conversion of Newton to PSI is dubious. PSI essentially maps to Newton/unit area. So, in order to do this conversion, you need to have some kind of surface area term you divide by. You cant just say 1 Newton = this many PSI because these are not the same kind of quantity. Namely, a Newton is not a unit of pressure, but a N/m^2 is. Can you give more details?
I mean, my take-away from this video is that dry pouring can work, but it's unreliable, and typically results in much weaker (and uglier) results, so, outside of some niche circumstances, you should basically always do a traditional pour.
Dry pour is just unpredictable.. inconsistent. As shown rapidly by the surface defects in the patio. Sure. you can get places that work well. But you get too much that goes wrong. Just too easy to use a Harbor Freight mixer and do it right.
These numbers are garbage without correlation to core sample test. It is extremely important to note that the hammer must not be regarded as a substitute for standard compression tests but rather as a method for determining the uniformity of concrete in the structures, comparing one concrete against another, and reducing the number of core samples. You also have too much scatter in your data and thus the data should be collected again. Additionally, a newton is a unit of force and not pressure, so you need an area to be able to convert to PSI (Pounds per Sqaure Inch). I assume your measurements are Newton per sqaure millimeter, but not sure since you didn't mention it.