Renofix need help choosing right diamond grinding head/disc

[Blahblah]

Hi all I have just removed my fireplace mantle and am planning to plaster over the wall where it was and to floor board where the fireplace floor used to be to basically erase it from existence.

I have managed to remove everything except the concrete on the floor which is too high to put floor boards on. It is up to 1cm that I need to remove. I also planned to remove maybe half a brick from the fireplace so I can reframe the bottom for a baseplate for the plaster to be nailed to but not sure if cutting is better in that case.

I have provided pictures below (happy to take more if it helps!)

I think the best way forward is to somehow grind/sand the concrete down until its level with the joist to use it as the support for the new floorboards. No idea if this practical or a dumb idea. But am considering getting the renofix to test my luck. But I honestly have no idea on what disc to choose that would be best for this type of concrete. Maybe this green one? https://www.festool.com.au/premium-stone-diamond-grinding-disc-130mm-769166.html


I would love any renofix user who has any idea of how long a renofix with the right disc would take to grind this down 1cm as i have never used a concrete grinder before (diyer)

Thanks in advance!

 

[luvmytoolz]

I don't have the renofix but I can say if it's just concrete and not brickwork you need to grind down, the cheapest of the cheap grinding wheels will do it with ease.

I used a generic $15 grinding wheel in my Makita concrete planer to remove 10-15mm thick concrete and another 10mm off the brickwork below. The bricks were a bit tough going but the concrete it just laughed at.

Whatevers economical will do you just fine.

 

[Blahblah]

I don't have the renofix but I can say if it's just concrete and not brickwork you need to grind down, the cheapest of the cheap grinding wheels will do it with ease.

I used a generic $15 grinding wheel in my Makita concrete planer to remove 10-15mm thick concrete and another 10mm off the brickwork below. The bricks were a bit tough going but the concrete it just laughed at.

Whatevers economical will do you just fine.

ah I actually was thinking of removing half a brick back from the fire place but i wasn't sure whether to cut or grind it off haha so i guess i can grind that brick too!

May i ask how the dust was? did you pair it with a festool dust extractor or any dust extractor?

hmmm thanks for the food for thought!

 

[Cheese]

The diamond wheel will grind the concrete down but it will take some time. I'd instead, look at separating the concrete from the surface it sits on with a small/medium SDS hammer. Start at a low angle and aim for the interface of the concrete and the wood(?) that supports it. If you can "peel" the concrete away that'll be considerably faster than grinding with a diamond wheel.

 

[Blahblah]

The diamond wheel will grind the concrete down but it will take some time. I'd instead, look at separating the concrete from the surface it sits on with a small/medium SDS hammer. Start at a low angle and aim for the interface of the concrete and the wood(?) that supports it. If you can "peel" the concrete away that'll be considerably faster than grinding with a diamond wheel.

May I ask (as someone who has never touched a concrete grinder) how long do you think "some time" is? 10minutes? 30? hours? trying to figure out the realities of the job. I did actually use an sds plus rotary hammer to remove the fireplace and did consider chipping away at the floor but thought it would be way too hard to get it level for floorboards that way? or do you mean chip it first with an sds then sand the leftovers maybe?

 

[rst]

I can’t speak to the Remofix, but my Metabo is amazingly fast. I’ve tapered a 12’ wide concrete slab down 3/4” to an exterior drive in less than 20 minutes mostly dust free with a Metabo extractor, The slope was about 10” to enable glass carts to enter smoothly

 

[Blahblah]

I can’t speak to the Remofix, but my Metabo is amazingly fast. I’ve tapered a 12’ wide concrete slab down 3/4” to an exterior drive in less than 20 minutes mostly dust free with a Metabo extractor, The slope was about 10” to enable glass carts to enter smoothly

woah thats really fast. may I ask which disc you used? will have to check out metabo too in that case

 

[luvmytoolz]

@Blahblah Grinding the concrete is really easy and with my Makita I was doing roughly 3mm deep on each pass. It's really pretty easy going. From memory I did probably 2sqm in around a hour or so varying from 1-15mm at spots?

But you MUST use a dust extractor and a grinder with a good shroud. I really can't stress this enough!

It will billow fine concrete dust everywhere like you wouldn't believe. Extremely hazardous with a dust collector, even with a mask. I used my little old Festool DC and there was nothing at all in the air as a result.

This is the one I have, couldn't be happier with the performance and cost: https://makita.com.au/corded/corded...lity-concrete/pc5000c-125mm-5-concrete-planer

 

[Blahblah]

@Blahblah Grinding the concrete is really easy and with my Makita I was doing roughly 3mm deep on each pass. It's really pretty easy going. From memory I did probably 2sqm in around a hour or so varying from 1-15mm at spots?

But you MUST use a dust extractor and a grinder with a good shroud. I really can't stress this enough!

It will billow fine concrete dust everywhere like you wouldn't believe. Extremely hazardous with a dust collector, even with a mask. I used my little old Festool DC and there was nothing at all in the air as a result.

This is the one I have, couldn't be happier with the performance and cost: https://makita.com.au/corded/corded...lity-concrete/pc5000c-125mm-5-concrete-planer

Woah love the advice!

3mm each pass is insane i was expecting it to be a slowwwwww grind down but sounds like its way faster and so fast that i may grind too much accidentally!

I have a festool 36AC vacuum and am hell bent on reducing dust as muchhhhhh as possible, I already have surrounded the fireplace with zipwalls etc hence i was leaning towards the festool renofix since usually festool dust extraction is the best but if makita etc are just as good at dust extraction maybe I can get away with that instead! I do only plan to use it for only this job atm so.....

May I ask which diamond disc you use with the makita?

 

[luvmytoolz]

@Blahblah It was an el cheapo I just wanted to try out and I planned to use the Makita supplied one if it turned out to be garbage, but surprisingly it worked really well and is still in the grinder. I still haven't actually used the Makita supplied one yet, and no doubt it would probably be better, but the cheapo worked so well I didn't bother changing over.

Pretty much like this but maybe a couple dollars more from memory: https://www.ebay.com.au/itm/375703732831

The shroud on the Makita is really superb, and I hooked it up to my 45 year old SR5E "Festo" dusty, and there was zero dust in the air. A good shroud that captures all the dust is probably more important than the type of dust extractor used.

 

[Blahblah]

@Blahblah It was an el cheapo I just wanted to try out and I planned to use the Makita supplied one if it turned out to be garbage, but surprisingly it worked really well and is still in the grinder. I still haven't actually used the Makita supplied one yet, and no doubt it would probably be better, but the cheapo worked so well I didn't bother changing over.

Pretty much like this but maybe a couple dollars more from memory: https://www.ebay.com.au/itm/375703732831

The shroud on the Makita is really superb, and I hooked it up to my 45 year old SR5E "Festo" dusty, and there was zero dust in the air. A good shroud that captures all the dust is probably more important than the type of dust extractor used.

damn maybe i'm overthinking how important the disc type is if they are all overkill even the el cheapo ones!

 

[luvmytoolz]

Not necessarily, there's often a difference in quality/performance/results between cheap and more expensive quality tools, sometimes subtle, sometimes dramatic. A stark example would be the Festool/3M/Mirka sanding discs, considerably more expensive than cheap hardware bought discs, but can last 10 times longer and far outperform them so in the long run they actually work out lots cheaper.

If I was relying on it for a production setting and the more expensive tool offered time/labour savings, that's quite likely the one I'd choose. But for my ad-hoc use the cheaper grinding disc seemed more than adequate, which it turned out to be. Could have gone either way though.

 

[rst]

The disc I used was the one the grinder came with from Metabo. I love my Festool woodworking tools but the Metabo concrete tools are top drawer

 

[Blahblah]

The disc I used was the one the grinder came with from Metabo. I love my Festool woodworking tools but the Metabo concrete tools are top drawer

thanks for confirming! pretty amusing everyone has responded that the default or cheapies have done an amazing job anyway. love to hear it!

Metabo and festool renofix seem pretty close in price. Are metabo known to be the best in the biz? its so hard to see comparisons of concrete grinders

 

[Cheese]

thanks for confirming! pretty amusing everyone has responded that the default or cheapies have done an amazing job anyway. love to hear it!

Metabo and festool renofix seem pretty close in price. Are metabo known to be the best in the biz? its so hard to see comparisons of concrete grinders

Metabo and Fein are probably the best in the business when it comes to grinding steel or concrete. Either one is a dinner winner, nothing bad with either one of them.
However.,..,I'd still purchase a diamond wheel as opposed to an abrasive wheel.

 

[jonnyrocket]

@Blahblah
If you decide to go with the Rennofix, a few tips.
- https://www.festool.com.au/premium-hard-diamond-grinding-disc-130mm-768017.html
This is the disc I would recommend.
- if you use the CT36AC, be sure to use the plastic liners that are used with plaster dust.
- Or, use the pre-separator if you have it. The concrete dust will clog the pores on the standard self-clean filter bags and you will lose suction fast. The Autoclean does a much better job if the “open top” liners are used.
-the “removable adjustable shroud” is great for the finishing pass, but as you get started, remove it and do the majority of the work without it and the re-attach it as you near the end to get a smooth/flat surface.

 

[Blahblah]

Metabo and Fein are probably the best in the business when it comes to grinding steel or concrete. Either one is a dinner winner, nothing bad with either one of them.
However.,..,I'd still purchase a diamond wheel as opposed to an abrasive wheel.

awesome to know thanks! I was initially attracted to the festool since I assumed their dust extraction would be best but is probably the same amongst the top tier anyway

 

[Blahblah]

@Blahblah
If you decide to go with the Rennofix, a few tips.
- https://www.festool.com.au/premium-hard-diamond-grinding-disc-130mm-768017.html
This is the disc I would recommend.
- if you use the CT36AC, be sure to use the plastic liners that are used with plaster dust.
- Or, use the pre-separator if you have it. The concrete dust will clog the pores on the standard self-clean filter bags and you will lose suction fast. The Autoclean does a much better job if the “open top” liners are used.
-the “removable adjustable shroud” is great for the finishing pass, but as you get started, remove it and do the majority of the work without it and the re-attach it as you near the end to get a smooth/flat surface.

thanks for recommending the right disc! I was very confused between your one which is for cured concrete vs the green one which is "very hard concrete" I had no idea what the hell the difference was! (and still dont)

Ahh plastic liners I see, I have admittedly been using the CT36AC with the self clean filter fabric bags for everything including plaster and concrete cutting so far. The festool rep when i bought it said dont ever bother with the plastic open bags and I was confused why. i have both bags so perhaps its time to put it to use!

Ah the shroud I thought would help with dust extraction but its best to remove it? I guess it isn't too essential for dust extraction?

thanks for all the tips its great to hear from someone with experience with the renofix! may i ask if you have used others like the metabo etc and how they compared etc?

 

[Cheese]

awesome to know thanks! I was initially attracted to the festool since I assumed their dust extraction would be best but is probably the same amongst the top tier anyway

FWIW...Fein & Metabo are the only producers, that I know, of RA grinders made specifically for stainless steel work. They limit rpm to the 7000-7500 range while all other RA grinders spin up to 10,000-12,000 rpm.