Concrete grinding

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lemuzz

70 posts

Master Geek

#223339 24-Sep-2017 13:45

Hi I want to overlay a stamped concrete area with tiles. The area is 12sq metre and other than wanting to get rid of the stamped and coloured concrete is in good condition BUT one edge of the slab must match an adjoining path after tiling. This means I need to grind at least the thickness of the tile perhaps 12mm. Is this practical, or should I replace the slab with new concrete instead

elpenguino

3427 posts

Uber Geek

#1872181 24-Sep-2017 20:41

it wouldn't be too hard to remove some thickness, especially if surface condition is unimportant. Ideas.....

1 - concrete drill with spade bit. Apply at an oblique angle and chip off carefully.

2-skill saw with diamond blade - set to desired shallow thickness and make a series of parallel cuts 5 mm apart, then chisel off.

Bearing in mind the hard work this involves, is it easier to pack the other side up? Or just remove a 2-3 tile's material at the joint rather than the whole slab's surface?

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neb

11294 posts

Uber Geek

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Lifetime subscriber

#1872242 25-Sep-2017 06:49

I wouldn't just attack it with a spade bit, you're going to end up with very uneven concrete. Better would be a variant of option #2, hire a concrete saw (e.g. this sort of thing) and make the cuts at the right depth, then use that to guide the bit/chisel/whatever.

However, as you point out, this is going to be an awful lot of work. It'd probably be easier to break up the concrete and relay at the right thickness, or as you suggest pack the other side up, or whatever.

mcdongle

16 posts

Geek

#1872298 25-Sep-2017 09:45

Get a decent tiler to look at it,

If you are going to tile it will need to be a flat surface..

lemuzz

70 posts

Master Geek

#1872299 25-Sep-2017 09:45

Yes a saw might work but a shallow depth of cut would allow the concrete to break along the least resistance which maybe the 12mm then would probably mean a lot of work and I would be better with complete replacement. But thanks anyway.

lemuzz

70 posts

Master Geek

#1872300 25-Sep-2017 09:49

Yes. That maybe the way to go. But we need to get the surface lower than the path anyway so there will be no edge to trip on.

timmmay

20587 posts

Uber Geek

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Lifetime subscriber

#1872303 25-Sep-2017 09:52

We had some concrete cut last week. It was an area about 30cm by 2m. The cuts were easy, but it took a guy six hours with a jackhammer to chip the rest of the concrete out. I tell you this to point out how hard concrete can be. The concrete in question was laid by a commercial concrete guy who probably specified a pretty high grade.

lemuzz

70 posts

Master Geek

#1872311 25-Sep-2017 10:03

Yes That could be a problem especially if it is reinforced. I dont think ours will be reinforced, so removal may not be such a problem after cutting into manageable pieces. Though access is not easy, so no digger. But as I said earlier grinding is my first thought and is 12mm too much to expect for a grinder to remove. The finish will not matter as long as I can cut below the tile thickness plus the adhesive plus the levelling compound.

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BlueShift

1692 posts

Uber Geek

#1872314 25-Sep-2017 10:12

lemuzz: Hi I want to overlay a stamped concrete area with tiles. The area is 12sq metre and other than wanting to get rid of the stamped and coloured concrete is in good condition BUT one edge of the slab must match an adjoining path after tiling. This means I need to grind at least the thickness of the tile perhaps 12mm. Is this practical, or should I replace the slab with new concrete instead

Maybe grind on an angle along the adjoining edge for a slope from tiles down to path? Much less grinding involved then.

lemuzz

70 posts

Master Geek

#1872316 25-Sep-2017 10:22

Yes that has been considered as an option. Though if I get that far I wonder if I would always be happy with only a part slab flat. I may regret not doing the full slab or even grinding from zero to 12mm

jpoc

1043 posts

Uber Geek

#1873633 27-Sep-2017 13:28

How thick is the existing concrete and will the thickness of what is left be adequate after you have removed the top 12mm?

It would be a shame if your existing layer was only just thick enough for purpose and after cutting it down, it started to fracture after a couple of years.

MikeAqua

7785 posts

Uber Geek

#1873655 27-Sep-2017 14:17

You can get large push-along machines designed to grind concrete floors (e.g. polished floors with visible aggregate) I'm not sure how deep they grind. But I suspect 1mm or 2mm per pass.

https://www.hirepool.co.nz/concrete-floor-grinder-6-stone-electric/concrete-grinders

Mike

BruceHamilton

77 posts

Master Geek

#1873698 27-Sep-2017 16:22

There are specialist firms around NZ that use various machines to remove concrete surfaces. Grinding and shot blasting will remove small amounts and leave a smooth surface, but scarifiers and scabblers will cut several mm each pass. They are used on paths, airport runways, removing trip hazards, etc. Oversized lawn mower units about 30 -40 cm wide are common, and a Google search should locate local concrete removal firms with scarifiers and scabblers. We had 200 m2 of concrete floor reduced by 5 - 10 mm, and it only took a day. Noisy, but not as dusty as I expected.

lemuzz

70 posts

Master Geek

#1873700 27-Sep-2017 16:31

Yes that is what I am looking for Bruce Hopefully I can get one to where I need it. Would need to be mower size

lemuzz

70 posts

Master Geek

#1873706 27-Sep-2017 16:45

Yes Mike thats the grinder I was thinking With a 2mm cut each pass I would like to know roughly how long to grind a sqm each pass. 12 or 14 mm would take 6 or 7 passes. I guess the slab will be 100mm. As it is only carrying foot traffic that depth should be ok'. Cutting the slab into squares and removing by hand then wheeling them out to where they can be put into a skip, then cartage to the hard fill area, then a concrete truck and pump will amount to a considerable cost, for a relatively small area. The only costs to grind it flat other than labour, are the hire cost and removal of the dust

lemuzz

70 posts

Master Geek

#1873728 27-Sep-2017 17:11

Looks like 35 to 50 sq m at 1 or 2 mm depth per hour. This is the info I need. Thanks everyone