Concrete and Wood Slab Table

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First of all, this is my first instructable, so take it easy on this old hillbilly.

This instructable will outline how I made two similar concrete and cedar plank tables. This build probably isn't for the person wanting to try their very first project, but you certainly don't have to be Norm Abram to complete this. This is a fun project that incorporates different materials (wood, concrete, metal), and relatively speaking it can be a pretty quick build. I learned a few things along the way, made a few errors, but overall I'm pretty happy with the end product and hopefully I can help you learn from my mistakes. Let's get started.

Materials needed will vary based on how closely you would like to follow this instructable, but here is what I used:

Log (I used cedar, but any dry wood will work)

Varnish

Concrete mix (type can vary, I'll explain later)

steel rebar

stainless steel bolts

concrete dye and acrylic fortifier

un-sanded grout

wood or steel for legs

Step 1: Roughing Out the Wood Plank

The first step is to get your piece of wood that will go inside the tabletop. Obviously you don't have to include this piece of wood and the rest of the instructions can be used to make just a concrete table, and there are also plenty of other great instructables about concrete tables and countertops.

I used a cedar log that has been laying down in the trees in my back yard for years. You can really use any type of wood as long as it is dry, you could even used milled lumber with squared edges if you want, I just prefer the natural curves and edges of a slab.

I started by just using a chainsaw to cut the log into a couple rough slabs. If you have access to a sawmill or decide to buy a piece of lumber obviously you can skip this step. I got two good sized slabs using my chainsaw that are rough cut to about 3" thick. I want the end thickness to be 2" so I got the surfaces flat and parallel on the planer. I ran the logs through on a plank of sturdy wood so that it wasn't rocking on the planer bed due to my less than perfect freehand chainsaw cut. The nice thing about using cedar is that it smelled amazing when I was planing. I would suggest doing this outside on a nice sunny day because your dog will like to lay in the woodchips and it is friggen adorable, look at that cute little rascal.

Step 2: Finishing the Wood Plank

This step could use some experimenting, and maybe your own experience would lead you down a different path. But I found that it was easier to finish the wood plank prior to pouring the concrete around it so that you aren't screwing up the wood surface as much when you are polishing the concrete surface. The combination of wood and concrete in this table is what makes it a challenging build because the materials are worked so much differently, but this is also what makes it such a unique table.

Once you got your wood plank planed down to the thickness you want (I used 2"), and cut to length you need to prep and finish the surfaces. Don't worry about the underside or even the edges that will be encased in the concrete, you only need to finish on surface and the two end grains. Of course the first step is to sand until you get a good smooth surface, I went to 120 sandpaper on my orbital before filling the knots and holes with epoxy. I used a two part epoxy to fill the knot holes and other spots I wanted to see the character of the wood. If you're not familiar with this epoxy I would suggest experimenting with it a little first, people either love it or they hate it...or they think it's ok (RIP Mitch Hedberg). I used foil tape to plug any holes that went all the way through and to create a dam along some of the rounded edges so that I could pour the epoxy in there to prevent concrete from filling this space. Use a propane torch to remove any air bubbles when you pour the epoxy, just keep the torch moving, you don't want to burn the epoxy.

After letting the epoxy dry for a day or two I sanded everything flat, up to 220 sandpaper, then finished with several coats of polyurethane.

Step 3: Preparing the Concrete Form

The next step is to build a form and prepare to pour concrete.

I used 3/4" melamine to build the forms because the plastic coating of the melamine releases very easily from the concrete without the use of any release agent, and it makes a very smooth surface. I made the sides of my form 2" high, I wouldn't suggest going any thicker than this because holy cats this thing is heavy. As you will see in the pictures I put a dozen 8" stainless steel bolts into the side of the slab, this is to create a good connection between the wood and concrete and keep the two from separating. I suppose this is a good time to point out that I am casting this upside down, the finished part of my wood is laying face down against the form. This allows me to utilize the smooth surface of the melamine to give me an almost finish concrete when I pull it from the form. I then ran some 2x4's across the width and clamped these down to keep the wood plank flat and pressed up tight against the form to keep concrete from oozing in under the wood. The 2x4's also give me a good point to tie off my rebar so that it is hanging in the middle of the concrete. I used two #4 bars on each side running the length of the table. I would also like to point out that I made a sturdy cart with plenty of support to place this form on so I could move it around, make sure you have a sturdy base since this will literally weigh hundreds of pounds and you don't want your form sagging or breaking.

Step 4: Pouring the Concrete

The next step is to actually pour the concrete into the form. Sorry I don't have any good pictures of the actual pouring process, I was doing this as a one man operation and this stage is very time sensitive so I wasn't able to stop and take pictures. I also kinda forgot to because I'm an idiot.

I used a black liquid concrete dye to give it a good dark color, there are other color options and this is totally a personal preference. The concrete mix is the part that can vary the most in this project. You can find countless sources online of what mix to use and different additives. My Menards store actually sells a "countertop" concrete mix, I used this for my parent's coffee table and it turned out great. I used the cheapest concrete mix they had for my dining table, and it turned out great. So take that for what it's worth. I think if I were to make another table I would make my own mix just using portland cement and sand, I like the smooth consistency of the monotone colored areas that don't show any aggregate. I will talk more about the agg later.

Mix up your concrete and color before pouring into the mold. I tried to use as little water as possible to give me a stronger mix, but this was a mistake. Add enough water to make your pour very workable, it will still be plenty strong, I would say you're looking for a runny outmeal texture, not the peanut butter I tried to work into my forms. Work fast, the premix concretes set up quick. When you get it all poured in you will want to vibrate to get out as much air bubbles as you can, and to get the concrete flowing into all the nooks and crannies. I used a vibratory sander without sandpaper on it, runnining it all along the outside of the form. Level it out as best you can, but it doesn't need to be perfect because you can grind it smooth later. Cover it in plastic to keep the moisture from evaporating too quickly and let it sit for a few days, if it is very hot and dry I would suggest dampening the surface with a sponge a couple times a day.

Step 5: Finishing the Concrete

After you have left the concrete to cure at least a few days in the form you can take off the form and start the concrete finishing process. Concrete finishing is another one of those things that can be done a number of different ways, so I would suggest doing a little research online to find a process that seems best for you and the tools you have available.

I started off grinding the bottom to get it smooth. I used an angle grinder with a masonry grinding wheel, if you've never used this setup it is pretty slick, it cuts through concrete like buttah. After grinding the entire bottom surface smooth you will see a lot of small air pockets and voids where some aggregates were ground out, I mixed up some black un-sanded grout with acrylic fortifier to help with adhesion. Work this grout mix into all the voids with a rubber grout float or a good pair rubber gloves by hand to give you the smooth-to-touch surface. You only need to do this on the outside few inches where people would be running their fingers under the table, nobody is going to touch the middle of the underside, and if they do they can just shut up about it...jerks. Let the grout dry for a day then use some masonry polishing pads to wet grind the surface. You will want to get a wet polisher to do this. I just got some polishing pads that fit my orbital sander and held my hose on next to it. That's right, I used an electrical tool not meant to get wet in conjunction with a hose, do not do this, I am an idiot. I was pretty careful and I didn't get shocked, but you may not have the same results. Work your way up through the grits of polishing pads until you are done, then flip that bad boy over and take a look at the top.

Finishing the top is pretty much repeating the last few steps that you just did on the bottom. You will find some small air pinholes that you will fill with the grout mixture, then polish with your pads.

Here's another "issue" I ran into, I don't want to call it a mistake because it looks kind of neat and my wife likes it so that's all that matters. On my dining table I had a couple areas where the wood plank was not completely tight against the form so the concrete was sitting a bit higher than the wood surface. To make the surface smooth between the wood and the concrete I had to grind the concrete down, but this exposed a lot of aggregate in the mix. You will most likely see some agg after polishing, but this was a lot more. My wife said she likes the character of the exposed agg so I left it like that, but if you wanted to you could probably over-grind then backfill with the grout mixture so that you don't see the agg.

During the concrete polishing process you probably scuffed up the finish on the wood, but hopefully you didn't break all the way through the finish. Either way, just fix this with by some light sanding then applying more polyurathane.

Step 6: Table Legs and Benches

I'm not going to go into too much detail about the legs because you can really do this any way you want out of any number of materials. My parent's coffee table I used 2" square steel, welded it together, then applied a blueing finish. This was my first attempt at blueing and I think I still have some experimenting to do with this.

For my dining table I used some Kentucky coffee wood that I milled up from a farm nearby. I cut the metal braces from a long piece of scrap angle iron. The wood on the benches is the same Kentucky coffee wood, and I welded some square steel for those legs then spray painted the steel black.

I also forgot to mention that I used a woodburner to include a small inscription on the coffee table for my parents. This was done before applying polyurathane with the process as follows: Print out your inscription on regular paper in the size and font that you want, tape it to your wood, burn right through the paper into the wood tracing over the letters, sand after you are done to give clean edges to the lettering, then apply your poly finish.

Thanks for following along with my instructable, hopefully it wasn't too wordy. Let me know if you have any questions/comments/suggestions. And if you decide to make something using this as guidance please send me pictures, I would love to see it.

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151 Discussions

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AndrewW417

Question 4 months ago on Introduction

How do you secure the concrete top to the table base if the entire top is made of concrete?

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asammoury

Question 4 months ago on Introduction

Can this table be a patio table? We are worried about the longevity of the wood with the epoxy.

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nyco80

11 months ago

Gorgeous work! I have to ask... has there been any cracking or shifting? We recently built a harvest table and now that it's been in our house for a couple months there has been some shifting and cracking as it acclimates to the house... Has your table done that?

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mdheathnyco80

Reply 11 months ago

I haven't had any cracking in the actual wood, just the epoxy on the top. I finished the two different tables differently. The coffee table, that I think turned out better, I used a standard masonry sealer, like you would use on your patio. The kitchen table I actually put a layer of the epoxy over the entire surface because I still had a bit of a lip that you could feel between the concrete and the wood, so this smoothed that out. The epoxy said it was supposed to remain somewhat flexible, but it did end up cracking at the joint between the concrete and the wood. It still doesn't look terrible, but I notice it and it bugs me.

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revitalm

1 year ago

Gorgeous piece of furniture! Thank you for the great tutorial

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willmotbey

1 year ago

I really like this top, the dark finish on the concrete brings out best of the timber colours. Where I want the aggregate to show, I have used a variety of material in place of the standard aggregate, (shattered safety glass, copper pieces and quartz, pretty much anything that will polish) with good results. A pigment that also gives good results is a dark olive green. I don't have easy access to the slabs that you use, but Camphor Laurel and many of the Australian hardwoods work well.

Very attractive table, excellent notation and photos. Well done.

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shovorka

1 year ago

Wow what a beautiful table top! Im looking into building one of these as a dining room table that gets a lot of use. My question is for sealing the top. Will simply polishing the top be a long durable finish or do you suggest polishing it first then sealing it. I just don't want to expose too much of the aggregate and loosing that smooth black look that you have except for the spots where you said you had to grind down to have it flush? thanks!!!!

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joergosshovorka

Reply 1 year ago

Hello shovorka, If you dont want the aggregates to show you could start with a 400 grit, and you should always put a sealer, because concrete is a reactive surface, and its like a sponge, so all spils from food/oils etc will be sucked up by the concrete and leave stains

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mdheathshovorka

Reply 1 year ago

Thank you. I would add a sealer. If you don't seal you still run the risk of it absorbing some liquids and seeing salt stains and stuff like that. You really won't need to polish much, the sealer actually has a bit of a thickness to it, almost like a varnish.

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WillB109

1 year ago

Amazing project!! I've been trying a similar table but I'm having problems with the wood absorbing some of the concrete moisture. What type of Polyurethane did you use to seal the wood? Thanks!!

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pdeflora

1 year ago

I love this and have been wanting to make something similar for some time. I came across your instructable while gathering reference photos for my project. I was wondering if you could share more info on the dye you used to color the concrete and the process of using the dye? Things such as brand, mixing ratios, liquid or powder? The color is striking and is what drew me to read your post which was very well written and such a cool project.

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mdheathpdeflora

Reply 1 year ago

The color comes from Quikrete liquid pigment, the color is charcoal. Just mix in the amount specified on the bottle. It is a liquid, but it is a pretty thick liquid, so shake it up really well and after you pour it out add some water to the bottle and shake and pour again to make sure you get all the pigment out of the bottle.

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mdougla

1 year ago

Wow this is so inspiring. I have an idea in my head and this brought it to life. You're an incredible artist. I have one concern regarding shrinkage. I'm worried it will separate where the wood meets the concrete.Have you experienced that at all? Again, amazing job!!! Wow.

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DerekA38

1 year ago

Can you clarify the finishing process a little bit? I know you used polyurethane on the slab before you placed in in the form but did you use any masonry or countertop sealer on the concrete? Or did you just use polyurethane over the entire piece?

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mdheathDerekA38

Reply 1 year ago

That is an excellent question. And you are correct, I did forget to mention the finishing of the concrete. I actually did two different finishes on the two different tables. The joint between the concrete and wood on the coffee table turned out really well, so I just used some wax and buffed that into the concrete. This worked well. The dining table had those spots where I had to grind down the concrete, and to make the whole thing flush I put a coat of the epoxy over the entire tabletop and sides. Doing this filled in the low spots and made a smooth surface, but I don't like it as much as the wax finish. It makes the whole thing a little more "fakey" because you can't really feel the concrete, you are feeling the epoxy. I'm not sure if that makes sense or if anyone else even cares, but it's a big downside to me. It will also be much harder to make any repairs should something happen. The epoxy is able to flex with the exp/cont of the wood, but it is already very milky along the wood/concrete joint where it has been expanding, so I may end up sanding all of the epoxy off and going the wax route. Probably not though, I've got too many more projects to do before I ever get to that. So if you can, just go with a wax or concrete sealer on the concrete, don't try to make a single coat of epoxy.

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lexaurnan

1 year ago

Awesome table!!! Just really love it! I have made 2 small concrete tables but now this is next on my project list! Can you tell me is you used and silicone around or under the slab to prevent the concrete from oozing or just clamps? do you think a nursery could cut a slab? thanks for the great ideas!

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mdheathlexaurnan

Reply 1 year ago

Thank you very much. I did not use any silicone to prevent the concrete from oozing onto the wood. There was a small amount of concrete the oozed under onto the wood, but since the wood was already finished with polyurethane the concrete milk couldn't really adhere to it, so I was basically able to just wipe it off. In regards to your question about where to get a slab, I'm not sure where you're from but what we call a "nursery" around my neck of the woods is where they grow trees for transplanting, not milling. If you're referring to a what I would call a lumber mill I would say that is absolutely a great place to get a slab cut.

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PaleoDan

1 year ago

Very Cool and Congrats!