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Concrete Countertop Series #6: Concrete Curing

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Blog entry by Siegel_KenEvil posted 12-05-2010 04:21 PM 2267 reads 1 time favorited 9 comments Add to Favorites Watch
« Part 5: The Big Pour Part 6 of Concrete Countertop Series series Part 7: Be Carefull, Cement Burns! »

It’s been two days since the first pour. When I pulled off the top form, I discovered that the concrete didn’t fill completely. I also had the back-splash forms to fill so I mixed up a sand/cement mix. To this, I added acrylic fortifier and liquid charcoal dye. I filled the back-splash forms and troweled in the voids on the sink.

I’m learning about curing. My approach is to spray with water every couple hours and cover with plastic trash bags. The concrete mix was warm for the first 24 hours but isn’t warm now. I was surprised that the sand mix never warmed up like the concrete did.

I’m not sure if this is an indication curing is complete. Until I understand this better, I’m going to keep it wet and covered.

-- Scott



9 comments so far

View JJohnston's profile

JJohnston

1578 posts in 1948 days


#1 posted 12-05-2010 05:01 PM

The rate of cure has peaked, but concrete curing is never really “complete” – the hydration process can continue for years, even decades in massive structures. You should be able to handle your countertop safely in about a week, and shoud expect to get the advertised strength in about 4. Keeping it wet and covered is right.

-- "Sorry I'm late. Somebody tampered with my brakes." "You should have been early, then."

View dakremer's profile

dakremer

2455 posts in 1748 days


#2 posted 12-05-2010 06:34 PM

looking good so far! i’m excited to see the finished project. I’ve always wanted to make a countertop/table top/bench top…..or SOMETHING out of concrete! cool blog, very informative

-- Hey you dang woodchucks, quit chucking my wood!!!!

View smartlikestick's profile

smartlikestick

52 posts in 2235 days


#3 posted 12-05-2010 07:15 PM

Hey Scott

The heat you felt after introducing the cement / water is a result of a chemical reaction of the materials. Depending on the cement you used, I would leave the sink at least 3-5 days before I tried handling it, to allow it to come up to strength. Keeping it covered and moist will help to strengthen it and make it a more robust product. All in all it looks good!

Mike

-- -- Mike Beauvais

View Siegel_KenEvil's profile

Siegel_KenEvil

114 posts in 1495 days


#4 posted 12-05-2010 07:26 PM

Thanks, I needed some reassurance.

I should mention something else I heard. Concrete won’t stick to concrete without a bonding agent. I didn’t use concrete or a bonding agent. As mentioned, I used a sand/cement mix. According to Sunset’s Decorative Concrete book, sand mix is good for contertops less than two inches thick (my back-splashes) and as a 1/2-inch or thicker coating on old concrete (filling in voids on the sink).

Non-shrink precision grout was recommended as an alternative but I couldn’t find a large bag of it. I did buy a 25 pound bag of white grout that I will use on the top side to fill in those voids. I anticipate the contrasting color to look like natural marbling.

-- Scott

View childress's profile

childress

841 posts in 2198 days


#5 posted 12-06-2010 11:26 PM

Sorry, I haven’t checked all your blogs yet, but did you use a vibrating wand when pouring? This would ensure the mix gets set into all the little crevices and what not.

Also, my brother used to be a mason and has done quite a few poured concrete counters. Mainly for outdoor kitchens. He did use concrete (basically mortor with rocks in it) but would get the really small rocks that were smooth and a high tensile strength cement. I know it doesn’t matter now, but it’s always good to “hear” stuff from as many people as possible…

Are you going to sand and polish the top surface???

-- Childress Woodworks

View Siegel_KenEvil's profile

Siegel_KenEvil

114 posts in 1495 days


#6 posted 12-07-2010 02:40 PM

For vibrating, I used a cordless drill with a bold inserted. I also heard of using a sander. The truth is that I was so panicked that I didn’t spend a lot of time vibrating. The mix was not stiff enough to stay in place and too stiff to flow nicely. Discovering this, I had to quickly improvise and add to my form and I forgot about everything else.

I am going to do whatever is necessary to get a good top surface. By the time it’s exposed, I don’t think sanding will work but I’ll try. If need be, I’ll rent a wet polisher. Maybe I’ll start looking for a used one on e-bay or craigslist today.

-- Scott

View Siegel_KenEvil's profile

Siegel_KenEvil

114 posts in 1495 days


#7 posted 12-07-2010 02:48 PM

I thought it would be a good idea to start using water on the mdf since I had to spray the concrete frequently. Im using chisels and paddle bits in my 12v Dewalt to create cavities in the form. One minute I feel like a crazed dentist drilling a tooth, the next like Bob Ross watering flowers. The ancient canister vacuum cleaner I inherited works perfect for keeping things tidy.

-- Scott

View childress's profile

childress

841 posts in 2198 days


#8 posted 12-07-2010 06:51 PM

Yeah, I guess I should have been more clear. I didn’t mean sand like you would with wood. You will need some sorta diamond coated sandpaper like this

They work good on a 7” angle grinder. You should look for a granite supply store in your area that sells tools and stuff for working with stone. They will have something for you.

Right on! I’m looking forward to the finished product

-- Childress Woodworks

View flowchart_jockey's profile

flowchart_jockey

37 posts in 1733 days


#9 posted 12-09-2010 11:06 PM

I love this series, and the detail you are putting in to the blog posts. I am looking forward to the next installment. Thanks for sharing this with us!

-- Why make it easy when you can make it difficult?

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