Super Plastisizer in GFRC countertop mix

[Chip Turner]

Does anyone use a super plastisizer in their GFRC countertop mix? We are experiencing a much longer curing time (48-72 hours) before we can pull a piece, still somewhat crumbly, and are questioning if our SP is causing a retarded set time? Weather has chilled some, but usually doesn't affect this much. Any ideas appreciated!!

[AndyUK]

We all use a Super Plasticiser in our mixes, it's essential to GFRC. Glenium is highly recommended, I have fantastic results with Sikament (which is lucky as I had to buy a 25 litre barrel, I think I've used about 100ml so far...). With the addition of Polyplex, mine sets up and is ready to be de-molded in about 20 hours (in an unheated room, about 16 deg C)

[Jeff Osborne]

hey Chip, I have been using OPTIMUM 380 Premium Superplasticizer, from tom at fishstone. pretty powerful stuff. demold in 20 hr. no problem. that is with fortons and covered with plastic and foamboard. kinda cooks the concrete. Tell Rex I said hi will ya. nice to meet you, later.

[Chip Turner]

Actually AndyUK, a Super Plasticiser is not essential to GFRC in fact it could well be contraindicated in certain situations. Many people subscribe to the idea that because you need an SP in a Wet Cast project to increase flowability that also need it in a GFRC project. This presumption is not always correct in a GFRC spray-up situation, especially if you are working with vertical surfaces.
Our question was in regard to the retarding properties of the SP not whether or not is was required. We are currently using ADVA 100 which is a high range SP by WR Grace.

Thanks for your input.

AndyUK said:

We all use a Super Plasticiser in our mixes, it's essential to GFRC. Glenium is highly recommended, I have fantastic results with Sikament (which is lucky as I had to buy a 25 litre barrel, I think I've used about 100ml so far...). With the addition of Polyplex, mine sets up and is ready to be de-molded in about 20 hours (in an unheated room, about 16 deg C)

[jschuler]

Looking at the ADVA 100 super, yes it would retard set. Take a look at the data sheet, any super that says....neutral set....usually means they have the potential to increase set.

If you are happy other wise with the ADVA, try adding 5-10% Qwix to compensate for the slower set with the ADVA....this would take care of the long set time and lower strength.

[Alla Linetsky]

No experience with Adva, but Glenium has been most successful for us so far. Of course you can make gfrc without any super-p, but you'll end up using too much water. If you approach it as a construction-grade product, for cladding buildings, for example, then you will make good enough panels that won't cost too much to make. But if you can reduce your water to below 0.3 and make concrete that is way stronger and harder than the construction-grade panels, why not?

I use Qwix in my concrete, and any retarding of the set is a good thing.

[Mark Celebuski]

There are mid-range and high-range water reducers.

If you used an older generation mid-range water reducer at a high range it would begin to retard the set, more so as you used more of it.

Some high range water reducers where designed for ready mix applications and contain retarder (to hold slump on the way to the job and during unloading).

Mark C

[Chip Turner]

Thanks for all the responses, guys! They were a help. Another few questions:

1.) How many folks using GFRC are casting on a steel table? Versus plexi or acrylic or melamine.

2.) Has anyone tried building a double sink for a kitchen counter-top?

Thanks, again.

Chip Turner
S.B. Grace
www.sbgrace.com

[Alla Linetsky]

I cast on stainless steel-covered tables, and I've done a wet-cast gfrc double sink. Photo attached.

[James Catabia]

Alla,

That is an awesome looking counter and sink.

What did you use to to form the curves?

I also cast on steel. My steel tops are just plain hot rolled steel 3/16" thick. I wax the surface then apply 880 VOC form release before casting. I spray my face coat, wets cast and hand pack on the surfaces. No problems at all. I currently have 2 tables 1 5'x12' and 1 5'x 8'.

[John Cardwell(www.crete-unique.com)]

Looks like abs plastic rips to me. I also cast on steel and use the same basic methods you do James.

[Alla Linetsky]

Thanks James.

Actually, it's HDPE plastic, gloss surface. Very tough, you can tie it in knots and it won't break. I get it custom-cut by a local plastics supplier, and it's available in all kinds of thicknesses, from 1/16" to 1.5". I do curves with 3/16" or 1/4" strips, and straight sides with 3/4". Very easy to rip it on a table saw.

I splurged on stainless for my tables. It actually didn't cost much more than hot rolled because it's so much thinner. I believe mine are 11 gauge sheets; it's what the plant had available in 5x12 and 5x10 when I called them. I tried getting hot rolled steel, but when I saw the surfaces, I just sent them back. I glue the plastic strips and backer blocks directly onto the surface. We use mostly No More Nails (since it replaced PowerGrab) and some hot glue, although the hot glue sucks in the winter.

[Dana Andrews]

Alla,

How did you attach the SS to your table? Is it a 300 or 400 series SS? I'm starting the thinking process so when it's time I can move on it.

Alla Linetsky said:

Thanks James.

Actually, it's HDPE plastic, gloss surface. Very tough, you can tie it in knots and it won't break. I get it custom-cut by a local plastics supplier, and it's available in all kinds of thicknesses, from 1/16" to 1.5". I do curves with 3/16" or 1/4" strips, and straight sides with 3/4". Very easy to rip it on a table saw.

I splurged on stainless for my tables. It actually didn't cost much more than hot rolled because it's so much thinner. I believe mine are 11 gauge sheets; it's what the plant had available in 5x12 and 5x10 when I called them. I tried getting hot rolled steel, but when I saw the surfaces, I just sent them back. I glue the plastic strips and backer blocks directly onto the surface. We use mostly No More Nails (since it replaced PowerGrab) and some hot glue, although the hot glue sucks in the winter.