I have a neat little fireplace job right now where I have to rip down some horrendous stone veneer and rebuild the raised hearth. I am building the hearth top with a hand pressed concrete top. I am doing this because the immediate area is completely lacking a good stone source. There is a small supply yard that has some stone (I got my veneer stone there)but no large flat stock. The pressed technique is a nice alternative for now...but I was wondering if anyone else crosses over into doing this kind of work. Also, I am going to seal the concrete and was curious what products you use or can recommend that are specific to GFRC concrete.
On to the second side. The first layer, which ends up being the top, is a drier mix. It is often described as claylike, and is applied first. I work the corners to make sure I get an edge then start pressing handfuls of concrete onto the mold. The more random the size, the more natural looking the voids will be. I have seen pressed counters that look like somebody bounced a tennis ball off the form..the pieces were too uniform.
After covering the surface with the press, a second layer is applied and screeded to fill the mold. This mix is loose, like a regular concrete mix.
Like I said, this is a premixed concrete with pigment added already. It also has nylon fiber...no lath or wire needed. At full cure I will have 6500 PSI. I am very impressed with this product so far. Here we go....
so you actually use your hand to "press" it into the corners etc... (yeah I know what the name is) No vibrating at all? I'm terrible with concrete I always have honeycombing so this is one product that looks great for me. Do you think I could make my own mix? What size is the large aggregate? 3/8ths I'm guessing.
You still want crisp corners and edges, how do you make sure that those areas are full? Would you rub the edges after?
so you actually use your hand to "press" it into the corners etc... (yeah I know what the name is) No vibrating at all? I'm terrible with concrete I always have honeycombing so this is one product that looks great for me. Do you think I could make my own mix? What size is the large aggregate? 3/8ths I'm guessing.
You still want crisp corners and edges, how do you make sure that those areas are full? Would you rub the edges after?
No vibration for hand pressing. It wouldnt do much anyway because the mix is pretty dry and the whole point of this technique is to create voids that simulate veining. You would use vibration when wet casting though...because you DONT want voids.
When doing a handpress mix, typically you dont add aggregate...it is a sand mix. If you do a poured concrete mix it is better to have a variety of size in the aggregate. The same with the sand used for the mix..get one with fines to around 1/8"...concrete sand is better than mason sand for this (I know, duh) A BASIC mix would be 2:1 (sandortland) arylic additive and nylon fiber to help with shrink cracking. For the acrylic, you need to be careful that you get one with a lot of solids or it wont do much good(forton vf 774 is popular). Some of them(acryl 60, 27% solids) create too much air entrainment so you need to add defoamer. With my homemade mix, I used galvanized 1/2" fencing for reinforcement, added after the press layer. Alternatively, you can use a bagged mix like quickcrete 5000, but you should add 1 part portland per bag plus the additives and reinforcment.
Dom, I have only scratched the surface of all the in's and outs of a homemade mix. You should really play around and see how your own mix turns out before commiting to a project. It would be a diaster if your counter started to cup or crack. Make some samples, write down your ratios. One thing you must do when making concrete like this is to carefully measure your additives,cement and sand to create a consistant mix.
All these factors are why I chose to go with a proven, engineered product. Its my first paying job with artisan concrete and I need the control on the quality. It costs more per sqft this way but I have the confidence with this concrete that I dont with mine...I need more time to test my mix before I use it at a customers house..I'm getting there though.
A sand mix, that makes sense since the countertop is only 1.5" Since I'd be doing it for myself I'm not super worried about a potential bad mix but of course I'd rather do it right the first time. I have a friend who did concrete counters for a while but has recently gotten out of the trades to go to school to be an architect. School is on the east coast so I don't see him very often anymore, but he may be able to suggest a mix.
Thanks for answering all my questions. there'll be more to come as this progresses I'm sure. I like this technique (and results) more than other concrete counters I've seen. (PS I know my buddy uses MDF for his forms. Cheap and smooth. Maybe melamine is comparable)
One other thing you could do is a bag mix like I mentioned and dont add any color. After it come out of the mold you can do an acid stain (two or three different colors look cool).
The melamine is $25 a sheet. I like it because it wont absorb any water...MDF, will blow up if it gets wet if I'm not mistaken but I'll look into it.
I was at bLOWES today and saw rigid foam insulation and it only cost $12.50 per 4x8 sheet. I am going to experiment with it because doing a free form mold would be easy being that you could bend the strips very easily.
We use a completely matt, very very expensive, and very worth-while tile sealer for concrete countertops...Tile guard Natural Stone Premium Sealer....
No sheen, but you can spill coffee all over a white counter top and it's a-ok. might not be what you're looking for. I wish I knew how to upload pictures... I'll work on it. Looks great, btw.
Terrible picture, but you can see the mottling. Dry mix, copper pigment...filled the voids with slightly different color. Gave up trying to do a completely cohesive (e.g. vibrated) surface. Too many suprises, too many re-pours. If it's imperfect to start, it's perfecter!
Sorry if I'm hijacking, just finished this installation yesterday. Wet cast concrete top w/ xylexin (sp?) sealer and tiled back splash. The tile in the top is leftovers from the shower floor. I'll show off the whole bath in my one thread. :>)
Yeah, sort of. Not in house....heh...out house? We really struggled with finding a correct sealer...Beeswax and mineral spirits was a lovely idea, but a fail for an undersealer...works nice to buff things out tho. Xylene...I've used it before on a floor. It works, but I hate the way it looks, and I need my last 3 brain cells....So...this counter top, which, I hesitate to even talk about it because it's cursed. BUT it has been used lightly for about a year, and it still looks great, and it still beads water. Silicone magic. I've never used this brand with a sheen.
Did either of you ever try boiled linseed oil? I use it quite a bit on stone and I want to test it out on concrete. I'm not too worried about staining being that this FP is being converted to gas... A soft matte finish is what I'm after.
They have employed the best artisan expert they could find to train people at their classes and IMHO they are head and sholders above any I have seen. Again, just my 2 cents on what's out there and please no offense to anyone's work or opinion.
BTW, there are stone sealers out there that repel water outdoors and also have 0 sheen...some folks want it to look natural and dull. One caution is that you will NOT see 1/2 of potential color.
Tip: Wet the surface with H20 to get a sneak peak for yourself and customer as to how it will look sealed.
Final tip: For the absolute best sealer in terms of durability is a 2 part urethane. It stinks to high heaven and all sources of ignition have to be snuffed out and wear proper masks by 3m ususally so you save your last 3 brain cells...lol It is by far the best in terms of sheen and durability. You can also make it satin or semigloss by adding talc...ask the pro who sells it about the how to.
They have employed the best artisan expert they could find to train people at their classes and IMHO they are head and sholders above any I have seen. Again, just my 2 cents on what's out there and please no offense to anyone's work or opinion.
BTW, there are stone sealers out there that repel water outdoors and also have 0 sheen...some folks want it to look natural and dull. One caution is that you will NOT see 1/2 of potential color.
Tip: Wet the surface with H20 to get a sneak peak for yourself and customer as to how it will look sealed.
Final tip: For the absolute best sealer in terms of durability is a 2 part urethane. It stinks to high heaven and all sources of ignition have to be snuffed out and wear proper masks by 3m ususally so you save your last 3 brain cells...lol It is by far the best in terms of sheen and durability. You can also make it satin or semigloss by adding talc...ask the pro who sells it about the how to.
No offense here. I have been visiting that site for a few years. I never had time for a class but there is one in Chi town that I have been wanting to get to.
Yeah, the water trick is something I have done with my stonework for years..works good.
It means that acetone mucks it up....
Linseed would be fine for vertical surfaces, and if the H.O. neglects to re-do it, it's not like they are leaving spaghetti sauce on it. IMO it would be totally incorrect for a counter-top...it casts a yellowish hue also. Not a problem on black. I encourage a test...cheap cheap...
I'm not using it for a counter top though and my color for the hearth is a dark charcoal. I hear you on the yellowish hue..boiled linseed oil has a honey color to it.
My test sample is close to the hearth so I'll test it out tomorrow.:thumbsup:
I had to work today so I didnt have time to slurry but the profile is done. Really happy with the voids on the second slab so I think the veined effect is going to be cool. Here is tonights pics..tomorrow is slurry time.
I'm pleased so far...this concrete is really hard, almost like real stone.
The other thing that I am happy about is the gentle curve on the front edge...it reminds me of a Katana.
The last pic was taken after using an air hose to remove the water..this matte finish is similar to what the final look will be...maybe a little more shine.
That's going to be a nice piece. I think the curve is what will make the piece when your done.
Curious how long you've had that polisher. I've got the same one and it seems like I have it apart longer than I actually use it. I still have it and figure I'll use it for higher grit wet polishing. But I've switched to a Makita dry polisher for most days.
It's more of a damp polishing, I wet the piece before working it, then rinse and re-wet as I work.
I think you've just convinced me that I need to get a set of edge profilers.So far all of my edging is done in the form.
I have had the Alpha for a little over 2 years now...so far, problem free and it has done a lot of polishing and profiling on stone and concrete. I know about all the other brands, but this was the only one I had used before. I would try another brand though..I love all my Makita grinders (all I buy). Metabo makes nice tools too.
Last fall I had to fabricate large concrete caps for three chimneys. I put this profile on all of them as a test.
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