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Discussion Starter · #1 ·
I'm trying to make a concrete table and I've been using Sakrete 5000plus concrete to make little sample blocks to test out the concrete and see how it will come out. A test run if you will. I've been running into a few issues that I can't seem to avoid.

1. In some of my failed attempts, I've been noticing the outline of the stones in the concrete showing through the surface. The stones aren't exposed or anything, I can just barely make out the shape of the stones which is really annoying.

2. I keep getting bugholes and I've been filling them in with portland cement but I can't seem to match the color of the existing concrete. It gives me a very inconsistent look that I don't like.

3. As far as sanding the table down, I've been using diablo sandpaper but I'm not sure if I should be using a special sandpaper for concrete?

4. Sometimes I get this brownish color in the concrete that I can't sand out. And sometimes I'll get these white lines that almost look like water stains.

5. Any suggestions on sealers and waxes? I picked up a concrete sealer and beeswax from home depot but I feel like these are inferior products.

Any help would help thanks!
 

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1. Part of the process of placing concrete is tamping or jitterbugging the concrete. It pushes down the stones into the mix leaving a layer of paste.

2. Sift some of the sand/cement from a bag of the Sakcrete to make a slurry to fill the holes and it will match.

3. You don't normally sand concrete, what are you trying to accomplish.

4. Brown, I don't know, the white is probably efflorescence and is somewhat normal. Leave it alone for a while.

5. Any Good sealer will be fine, the wax will protect it.
 

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Tileguy
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Have no idea how you are "forming" these tests to pour the concrete but if you were to vibrate the casting immediately after pouring you would eliminate a lot of the air holes and the aggregate would also settle below the surface.

The mix must be thoroughly dry before attempting to sand the surface. Using silicone carbide sandpaper would help you a lot. Normal everyday garden variety sand paper is aluminum oxide which doesn't work as well. Your attempts to smooth the surface will improve if you wet sand with silicone carbide paper and sink the aggregate.
 

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Discussion Starter · #4 ·
thanks for the advice guys.

Scarborough I'm trying to get a really smooth finish by sanding the concrete.
Bud I'm going to try a wet sand with the silicone carbide paper.

I'm using melamine to form the concrete. The bottom of the poured concrete is actually the top of the table top. I did this to get a really smooth finish for the table top. So I suppose the stones are settling and showing through the surface. Any way around this?
 

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As to the stone showing through, when the concrete is fully cured you won't see the stone shapes any longer, but the reason you can't get a color match is because the cement used in the bag of mix your using is different from the bag of Portland your making the slurry with, all cement producers have a distinct color depending on what raw ingredients they use.

In regards to sanding forget it ,if you want the floor to look like the floors at the box stores forget that too, as they are ground then polished and you can't reproduce that look.

PS forgot to say use a fine sand like what they use for mixing mortar to mix your grout, the sand in regular concrete mix is too coarse for this purpose.
 

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Most manufactured concrete products use vibration (usually a vibrating of or another type of form that is on a vibrating table to get clean sides and the bottom face(as cast) to get a good distribution of aggregate and eliminate the pin holes.

As far as color, it will change as the concrete cures and you can expect some variation as mother nature cures unless you have closely controlled curing conditions (temperature, humidity and moisture..

If you are looking for a professional smooth, almost glassy surface, you will need to grind the surface with increasingly fine grits of abrasive paper or wheels until you get to something equivalrnt to a 0000 grade.

It can be done to meet your expectations and it limited by your efforts and equipment.

Dick
 

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Tileguy
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thanks for the advice guys.


Bud I'm going to try a wet sand with the silicone carbide paper.

I'm using melamine to form the concrete. The bottom of the poured concrete is actually the top of the table top. I did this to get a really smooth finish for the table top. So I suppose the stones are settling and showing through the surface. Any way around this?
Okay I gotcha but you may be kicking yourself in the shins and don't realize it.

I understand and appreciate why you are using Melamine but if you were to cast your concrete with the top up this would allow you to sink the aggregate and get it out of your way. The aggregate is going to be much harder than the cement matrix and is difficult to grind smoothly while the matrix is softer and grinding away at a different/faster rate.

Even better yet, you may also consider using silica sand mixed with your Portland instead of any of the other mortar or quarry sands available. Silica sand will offer much greater consistency in aggregate size and be more manageable during the grinding stage. At some point you will want some steel reinforcing in the project.

Rig a means of vibrating your cast. This is easily done by attaching and orbital sander to the form-frame. Under the center of the cast is the best location in my opinion.

I have built hundreds of concrete pick-nic tables for the Army Corps of Engineers and everything you are wanting to achieve is certainly do-able. In my case however the Corps furnished steel reusable forms that we bolted together for the purpose.
 

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"I'm using melamine to form the concrete. The bottom of the poured concrete is actually the top of the table top. "
There is the problem right there.You have to finish the top of the slab.All of the agregate is going to go to the bottom no matter what you do.You finish the top and that is your finished product.You don't flip it over.
 

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Discussion Starter · #9 ·
Input from everyone is greatly appreciated.

Any difference from using a cheaper concrete like sakrete 5000 and a more expensive brand?
 

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Tileguy
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Input from everyone is greatly appreciated.

Any difference from using a cheaper concrete like sakrete 5000 and a more expensive brand?
Ya know (?) I tried for years to get someone to tell me the recipe used in bagged concrete and never found an answer, it must be a well guarded secret in the industry. If it were me I wouldn't be using bagged concrete I would use (as I said earlier) Portland cement and silica sand. Get all of that weird unpredictable aggregate out of there. Create your own recipe.
 

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Bud - there is no one "magical" formula since the bagged mixes always use the local aggregates (close to the bagging facility) that can vary regionally. The mixes must meet the ASTM specifications (usually strength) if mixed properly. The common bagged mixes just have to meet the labeled strength levels. The feight of the aggregate(sand and small rock) to the bagging plant is a major production cost item and not the cement cost.

I have a friend that bagged several different brands of concrete/mortar mixes and just switched the bags used. They also bagged kitty litter and sand bags for weight and traction. - They also made custom colored architectural mortar mixes that matched national advertised national samples.

It is not a rustic operation or industry, but is based on controls and conditioning of materials irregardless of the outside weather conditions. After that it is just freight and handling of the bags to the dealer. That is why the formulations and prices vary by region.

Dick
 

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basically you're doing the work right - casting upside down - melamine - etc,,, think the problem's largely w/materials - get ahold of some buddy rhodes mix & figure out how to vibrate your casting table as all the pro's do - that'll solve the bugholes,,, find a pro supply house for the mtls you need - hopefully you'll have a guy in town otherwise start by looking at ' concretenetwork.com '

by & large, you're right about apron/vest stores not having the best mtls :furious: better to shop w/your finners for this job :laughing:
 

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Ya know (?) I tried for years to get someone to tell me the recipe used in bagged concrete and never found an answer, it must be a well guarded secret in the industry. If it were me I wouldn't be using bagged concrete I would use (as I said earlier) Portland cement and silica sand. Get all of that weird unpredictable aggregate out of there. Create your own recipe.

While silica sand has it's use's, using it for concrete is not one of them, silica is best used for foundry casting and making glass ,natural washed sand is still the best for producing concrete.
 

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Tileguy
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While silica sand has it's use's, using it for concrete is not one of them, silica is best used for foundry casting and making glass ,natural washed sand is still the best for producing concrete.
Don't forget it is also used for sand-blast media.

Silica sand is used all the time in casting architectural pieces. We aren't talking about a concrete that will be driven on by eighteen-wheelers. We are talking about a specialized use of a concrete product. I can't disagree with you about the strength of concrete being better served using river sand or quarried washed sand but I can disagree with you about using silica sand for the purpose described in this topic. I have been doing it with great success for decades. I didn't invent the idea, the idea comes from others with much more experience than myself and more know how.
 

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Don't forget it is also used for sand-blast media.

Silica sand is used all the time in casting architectural pieces. We aren't talking about a concrete that will be driven on by eighteen-wheelers. We are talking about a specialized use of a concrete product. I can't disagree with you about the strength of concrete being better served using river sand or quarried washed sand but I can disagree with you about using silica sand for the purpose described in this topic. I have been doing it with great success for decades. I didn't invent the idea, the idea comes from others with much more experience than myself and more know how.

Yes your right about it being used for sand blasting, but those guy's use protective gear so they are probably okay, along with the architectural casting, but you really don't want to get that stuff in your lungs and the worst part of it is the dust created, so I think i'd rather not use it for a table, just as I wouldn't use pressure treated wood for one either, but that's just my opinion.
 

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Yes your right about it being used for sand blasting, but those guy's use protective gear so they are probably okay, along with the architectural casting, but you really don't want to get that stuff in your lungs and the worst part of it is the dust created, so I think i'd rather not use it for a table, just as I wouldn't use pressure treated wood for one either, but that's just my opinion.
Holy Cow!!!

Cow piles are full of nutrition also but I wouldn't run around the pasture eating those things either.

Sands...Canarywood1 is your man, he'll be able to help you from here on in.

I'M OUT!
 

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Discussion Starter · #17 ·
Just looked into the buddy rhodes mix. $46 a bag compared to the sakrete concrete which is around $4. I'm hoping that the quality with the buddy rhodes mix will increase proportionately with the price. I'm going to check it out.
 

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you get what you pay for :thumbsup: you might also try doug bannister's ' thestampstore.com ',,, both doug & buddy's staff's are VERY diy friendly,,, you could, of course, create your own mix design but why bother reinventing the wheel ? since its very unlikely any table caster will share his proprietary design mix, why not buy bagg'd ?

don't forget the $4bag stuff's sold in apron/vest stores which is why we only buy scrub brushes & **** like that :laughing:
 

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There are several "bag" mixes on the market and the costs will vary. You can pay $40 for a 50 lb bag. That can add up for sure, but in the end if your frustrations are gone, it may be worth it. You may look into one of the ad pac outfits. They make your big box mixes like Sakrete into much better mixes. Cheng has one like that. Walttools has their Tru pac. Concrete Countertop Solutions may have the most popular one.
They all do a great job at big cost savings.
Good luck.
 
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