Coloring and stamping or patterning concrete

[DennisCA]

Wondering if one should reinforce when making slabs that are 1x1m or not.. Very hard to decide how it should be. Those ready-made casting nets seem interesting as well:

http://www.wsochcompany.se/gjutform...attor-marksten/gjutnat-rektangulart-60x50-cm/

 

[0lle]

Finja no longer recommends countertops longer than 2.5 meters due to the risk of cracks, especially not with cutouts for sinks, etc.

With expanding concrete, you get an almost pore-free concrete without vibrating. However, the open time is short with that concrete, so it's difficult to get a good surface if you're working alone. If you cast and turn, you get a very fine surface, but the slightest distortion in the form naturally means that the countertop doesn't quite align with the substrate.

I have very good experience with mixing in fibers in the concrete to prevent cracking. I have used this
http://www.danishfibres.dk/en/concrete--wiking-18-micron.aspx

It has worked well for longer thin slabs but has also worked well in rendering mortar when applying thicker coatings than recommended. I remember buying a bag from eBay, and it has lasted for several projects and is still available.

 

[mexitegel]

Interesting! Isn't there ready-made mix with fibers in it? Fiber cement? But one would want the properties of expansive concrete and maybe there's no fiber expansive concrete available?

Do you have a link to eBay for the fibers?

 

[0lle]

http://www.ebay.de/itm/PP-FASER-fur...587572?hash=item232c4531b4:g:ERwAAOSwaNBUiL1w

That corresponds to what I have used.
I haven't tried mixing it into expanding concrete, maybe someone else can comment on that.

I know that when I bought the fibers, I initially considered buying ready-made fiber concrete but couldn't find anyone selling it by the bag and no hardware store selling what I link to. I find that a bit strange.

 

[DennisCA]

Is it possible to use regular cement + fiber, I wonder. I would like to manage with regular cement that I mix

Masonry is done otherwise, so once the form is fixed (it's not just a quick fix either), you can start casting. Then plaster the leca blocks. Then the woodworking itself (doors, etc.). I think I will be busy with this project for quite a while ... everything takes so much longer than you think.

 

[mexitegel]

If I am not misunderstanding 0lle's post above, it was just regular concrete (cement) that he used.

 

[DennisCA]

Yes, I think so, but I'm that kind of person who can't handle even the slightest ambiguities...

 

[mexitegel]

I have similar tendencies

 

[DennisCA]

On Saturday, I poured half of the concrete countertop for the outdoor kitchen! Unfortunately, the result wasn't as good as I had hoped.

It's incredibly difficult to get it even and I couldn't reach one spot with the smoothing trowel, now I hope it can be straightened out with a concrete grinder of some sort, take down the high spots, maybe use self-leveling compound on the low spots, or perhaps it can be filled with pure cement without sand/rock where it's too small.

I plan to continue hopefully next Saturday with the other part of the countertop, hopefully it goes better there as there isn't a wall on one side preventing you from easily leveling the countertop.

I understand the appeal of casting upside down and then moving the countertop into place but don't see how it would have been possible with such a large countertop as I'm making...

 

[mexitegel]

Boring, what concrete did you end up using?

Casting upside-down and flipping in place is impossible with such a large slab, it would need to be divided into sections.

 

[DennisCA]

What we discussed above, regular cement, gravel, sand and that kind of fiber. But hopefully, it will be good after sanding, I'll see if there is a suitable machine to rent.

 

[DennisCA]

Jesus called and asked what is available to rent for concrete grinding and besides floor grinders or belt sanders, there was a 125mm angle grinder with a diamond blade for 350/day + wear on the diamond blade....

Then one might consider this
http://www.biltema.fi/sv-fi/Verktyg/Slip-och-Kap/Diamantkapklinga/Diamantslipskiva-2000019635/

Seen on this forum those who have built their own dust collection also with something like microwave covers:
https://www.byggahus.se/forum/threads/fattigmansbetongfraes.87023/

Otherwise, I have a real polishing machine that probably works better than the angle grinder...

 

[DennisCA]

Anyone know how well these diamond blades remove material?

 

[mexitegel]

A few millimeters are not a major problem to grind down with such grinding discs. However, you won't get a nice and smooth surface. For that, floor sanders are probably the only option.

 

[DennisCA]

Maybe I'll rent one of those and lift it onto the board after I've gnawed down the worst. Removed parts of the form today and there are many air bubbles unfortunately, what's the best way to fill them in?

Also tried using a steel brush on an angle grinder and it exposed the aggregate, and I actually thought it looked quite nice, the whole board is a bit "rough" and I'm almost starting to like the look.