I have a project coming up that will be cast on site. It's essentially 3/4" thick tops with a roughly 3" drop edge. I want to do this cast face up, so foam knockouts underneath everywhere except where the drop edge will be. I'm going to be using a wetcast GFRC using Trinic's admix, probably on the lower end of fiber loading (2.5%).
My question is am I going to be ok lightly troweling the top after it sets a bit without pulling up the glass fibers? I plan on processing anyway slightly to a hone, 200 to 400 grit, staining then sealing. Has anyone had any luck with this type of pour/situation?
Thanks much, JB
This could work, I would not suggest going to the lower end of the fiber load. Keep in the 3% range. GFRC is notorious for shrinkage and a CIP project is not a place you want shrinkage without control joints to absorb potential shrinkage cracking over long spans and around knock outs for sinks or stoves. I would also suggest adding some acrylic fibers or PVA fibers to your face to help control shrinkage and impact strength if this is the way you are sure you want to go.
This is one of those situations where the adage is true, because it can be done doesn't mean it should.
There are mixes that are designed for these types of situations and would be the preferred method for a thin CIP project, or any cast project that wants strength over long spans without shrinkage or curl. Take a look an an ECC mix also referred to as an RPC mix. These mixes are designed to be cast thin and processed in which ever manner you choose, without the worry about fiber showing. The fibers used are stealth. This way no matter how much you process, grind, or cut away you have a consistency of color from the top to the bottom of the cast.
These mixes can be easily mixed and placed on site with a large mixer or hand mixer. ECC is all we use for thin cast situations, especially if it needs a good trowel for different finishes. The beauty of an ECC mix is that you can control what type of consistency you want with the mix by simply controlling the fiber loading and plasticizer being used. This can give you everything from a clay like consistency to a SCC type of consistency.
For CIP projects we use the Clay consistency, just a little loose not a full clay. This allows us to place a large amount of mix pretty quickly, level it off, and give a nice trowel to an entire surface no matter how much square footage we are covering for the project. Our last CIP kitchen had 1 sections that was 85 sqft from peninsula, around sink, to around the stove area, with a few turns and 90's along the way.
Take a look at the Evolution addmixture from Buddy Rhodes. There is an ECC Addmixture that you can use your sands and cement.
If you are more comfortable using a spread sheet for this type of situation PM me and I will give you a copy of my spread sheet that we use every day.
Jon, thanks so much for the help! I know you have some experience with this, at that thickness with no glass fibers what PVA fiber loading are you comfortable with? What dosage of PVA 100's is going to give me the strength I need compared to glass? Also, how do I lightly trowel this mix (wait til it sets, etc.)?
Thanks again, JB
With an ECC mix that we are using the 100's we are running about 1.3% loading. I like to add a bit of the 7's into the mix, the smaller fibers bond quicker than the larger 100's you just can't load them too high without choking out the mix.
IMO I would not use the 100's for this situation, I would use an ECC clay mix using the 15's (.6-.7% loading) and the acrylic fibers (.17% loading). Maybe add some scrim as your comfort level suggests around knock outs or think sections around 90's). We use the clay consistency which can be leveled and trowed much earlier and more efficiently than using a more flowable mix and 100's.
The more clay like consistency with the combination of fibers is pretty easy to use for this situation, compared to the 100's which are a bear to trowel with any good consistency.
If you a going to do any sanding or light grinding the fiber combo is the way to go as well. We have found the 100's can pop up later after light grinding, so we don't use them in hand placed mixes that are going to have the tops sanded or exposed in any way. I now reserve them for flowable mixes which don't have the same issue with the 100's popping up later.