Michigan WFO

[Lars]

Re: Michigan WFO

Mike,
I've done many castings and pours...it is usually hard to avoid voids.

A rubber mallet wil do much more than a finish sander. HF makes a cute vibrator for 89 on sale (which is a great price by the way) that would be perfect size for a counter top.

At any rate, it takes a few times more vibrating than most people think while they are placing concrete.

L.

[ThisOldGarageNJ]

Re: Michigan WFO

Lars,
Is there any special technique for countertops ? I have vibrated concrete forms for machinery and we just did it till it bubbled up ...

Mark

[Lars]

Re: Michigan WFO

Mark,
Usually when you vibrate with a vibrator, it bubbles up and puddles at the top, and the overall level drops about a 1/2" ( depending on the shape of the form -- more or less)

There can still be voids, but the majority of them go away at that point.


For pouring there are three main factors. The surface, the seals, and the mix and how it's poured. Usually vaseline makes a good bond breaker for the surfaces. Plain old caulk will seal up most of the leaks in forms, and thick concrete that can be vibrated to a puddling point will maybe still have to be filled with some kind of fine mix after taking off the form.

The guys who do this day in and day out vibrate with concrete vibrators repeatedly all over the form...especially behind the visible front surfaces of the piece.

Oops...long answer again.

L.

[JAG]

Re: Michigan WFO

Hello all,

I have ben following this thread for some time now and I am about to do my first ever counter top pour. It is a pour in place and I have my forms set up for the countertop to come down over the vertical face of my hearth. This vertical face runs aroound the perimeter of the hearth and there is "counter top" around the whole oven.

Are ther any words of wisdom anybody could share before I take on this one time shot at this counter top? Thanks

John

[Lars]

Re: Michigan WFO

John.
If it is poured in place, then get the thing poured, vibrate like heck, and try to make sure you have no 'leaks' in the form work. This will keep the fluid from washing a way the portland around the leak.

Saran wrap or tape will make an almost glasslike surface on the concrete, but the top you will have to go back and trowel after about an hour. Keep it hydrated for a couple of days after you get the top really smooth. Don't forget, the most visible part will be due to your trowelling -- and this happens a hour or two after you are dead tired from the pour. Leave some energy for that crucial step.

Lars.

[mfiore]

Re: Michigan WFO

May sound like a simple thing, but cover the screws that hold the form together with tape or wax of some kind. Concrete spills over the sides of the forms during the pour and screed. A little concrete in the screw head can make it tough to get out.

[JAG]

Re: Michigan WFO

Thanks for the replies. The next few days are slated for rain, so I have time to agonize over the details a little longer.

JG

[Neil2]

Re: Michigan WFO

Are you going to grind the top to expose some of the aggrgate ?

If so, do not float the top any more than necessary to get it level. Floating wet concrete drives the larger aggregate particles down and raises the fines and cement particles.

Ground and polished concrete counter tops (AKA "cultured marble") can look great. If you are going this route I suggest you do a trial run of some sort .

[JAG]

Re: Michigan WFO

Neil2

Thanks for the heads up. I plan on adding small colored glass aggregrate to the top surface and polish. I do plan on making a practice slab to do a couple of practice runs on. I figure at worst the slab could end up being some type of decoration for my landscaping, and if it turns out really bad it can be buried deep in the same landscaping.

I have done quite a bit of reading on the subject but real world and book world sometimes don't jive. Thanks for the insight, it is greatly appreciated.

The biggest problem that I haven't been able to solve is that with the counter being pour in place, and also doing the vertical face of the hearth I see no way of getting the glass aggregrate to be visible on the vert. face, and I have come to terms with that. There may be a way around this but being a first timer I haven't figured it out, so if anybody has experienced this any insight would be of great help. Thanks again.

John

[dmun]

Re: Michigan WFO

The biggest problem that I haven't been able to solve is that with the counter being pour in place, and also doing the vertical face of the hearth I see no way of getting the glass aggregrate to be visible on the vert. face, and I have come to terms with that.

This has been done commercially for years in terazzo floors, where the baseboard goes up from the floor, with a nice radius. I don't know how it's done, but it's surely possible.

As an alternative, there's terazzo tile, which avoids the polishing mess entirely.

[david s]

Re: Michigan WFO

I tried doing some abrasion on concrete and it turned out to be a lot more work than I thought it would be. I cast an arch and then added about an inch in the top of the mould with a mix of black mortar with marble chips as aggregate. The marble being soft is more easily abradable. The bloke I got the marble chips from suggested I wait a week before beginning the abrasion. It was tough as hell. I planned to get stuck into it after two days so it wouldn't be too hard. Anyone had experience with this ?
I imagine the ancient Romans had a team of slaves with big flat rocks to do this job. Italians call it Terrazo. My finished product looked quite good but took way too long to be viable.

[stonylake]

Re: Michigan WFO

hello mike, i am a newby from grand rapids. i poured my slab last week thursday, and bought my block yesterday. i read most of your thread tonite. i am a building materials distributor, Eikenhout : Roofing, Siding and Windows, and have a branch in Saginaw. i can tell you that it caused me pain to see the reference to Wimsatt in your thread. i sell slate, clay tile, metal,synthetic and asphalt roofing, stone veneer, cement fiber siding, copper drip and flashings etc., all of the exterior stuff. i very much appreciate all of the comentary about the chimney flue, i think i will have a steel transition fabricated and use stainless..i hope to have my stand built and hearth poured before snowfall, build my arch in the shop over the winter, and build in earnest come spring..

[ThisOldGarageNJ]

Re: Michigan WFO

To All,,
Can a or should a polishing aggregate be added after the pour, Like glasss or stone and then tamped in beofre the final vibration, ? Would that assure your fancy aggs were all on top to be seen ??
Mark

[mfiore]

Re: Michigan WFO

StonyLake,

Sorry I missed out on your place. I haven't been in this town that long, and was not aware. I'll check it out.

Thanks for all the input about the counter tops. Any thoughts on what to seal it with?

Mark, if you are going to pour in place, than that approach sounds very reasonable.

[mfiore]

Re: Michigan WFO

I used Hardie cement fiber trip board for my trim. That stuff seems very solid and indestructible. Installed, caulked, and painted. I really hate carpentry work, making miter cuts and all. Brick and mortar suits me better.