Reducing small[ish] hump in concrete

red_imps_2003

As some of you will know, I have recently had a chimney breast removed from my living room and plan to lay 1.5cm thick 'Phonestar' soundboards over the flooring before fitting carpet. Most of the room is traditional floorboards but there is an area of concrete where the fire and hearth used to be. A small portion of this concrete (perhaps 1.5sqft) forms a bump that rises about 1.5cm proud of the rest (including the floorboards). This will mess up the installation of the Phonestar flooring so I need to remove the hump somehow. Can anybody advise the most practical way of achieving this please?

Many suggest grinding down with a grinder (and vacuum attachment). I am aware this will generate a lot of dust but this isn't an insurmountable problem. I am just wondering whether such a tool (e.g. https://diy.hirestation.co.uk/basket/add-items/hire/210110/) would be capable of taking such a bump down by roughly 15mm or is there a better way?

spadoosh

i always go the easy route so would look at making the rest of the floor level with the raised bit. A bit of ply would do the job. It'd cost more but i wouldnt spend a week grinding out concrete.

Looking at the price of the tool hire, probably wouldnt be that much more expensive.

Youll have issues with the door thresholds this way though.

pmartin86

Jack hammer it down to just below the level of the floorboards, then fill back up top correct level would be my thoughts.

red_imps_2003

Jack hammering down the offending section seems sensible (and quicker/cheaper) and I could easily raise and level using sand. My concern with the jack hammer is that I have never used one before and I am anxious about potential collateral damage. Is there a risk the adjoining load-bearing wall could crack, for instance? The bump is very close to it. How much control would I have over chipping away at the area concerned?

dominoman

Any angle grinder will easily do it - though it will cause masses of dust.

Screwfix sells angle grinders for around 40 quid that will be more than adequate. Just use a mask and take care.

red_imps_2003

I've seen a few people mention the Screwfix one elsewhere, dominoman. Can you clarify how I would use it please (sorry, total angle grinder newbie)? Would it be to slice into the mound at an angle and 'scoop' it out or push down vertically with the full face of the disc like a sander?

dominoman

red_imps_2003 wrote: »

I've seen a few people mention the Screwfix one elsewhere, dominoman. Can you clarify how I would use it please (sorry, total angle grinder newbie)? Would it be to slice into the mound at an angle and 'scoop' it out or push down vertically with the full face of the disc like a sander?

No, not the full face.

You'd basically cut lots of little vertical slices into the mound and then if there are remaining bits they will just break off. It will leave an uneven surface so you'd then put a thin layer of concrete over it to smooth it.

Angle grinders are easy to use but they can be dangerous so read the instructions, hold it the right way - and keep fingers and kids well away

dominoman

These are the discs I used to grind concrete when I accidentally put down too much while building a wall. They would do your job perfectly - and much cheaper than hiring a machine

http://www.screwfix.com/p/erbauer-grinding-discs-115-x-6-x-22-23mm-5-pack/61431

red_imps_2003

Thank you, dominoman. As luck would have it, these are the ones the nice man at Screwfix sold to me when I picked up this grinder last night. I bought one pack (of five) but would you recommend getting another pack or two? I am also considering purchasing one of these blades to slice the edge off that touches the skirting and perhaps to take the top off some of the smaller (pea-sized) bumps in the area.

EssexExile

I would use that diamond blade in preference to the others mentioned. It will cut quicker & last longer.

red_imps_2003

EssexExile wrote: »

I would use that diamond blade in preference to the others mentioned. It will cut quicker & last longer.

Thank you. I intend to purchase both, as my understanding is that they work in different ways. Am I right in thinking that the diamond blade is designed to 'slice' through concrete (and similar materials) whereas the grinding blades are designed to 'sand' an area down? I suspect I may need to do both to get the area flat enough to lay soundboards over the top. Am off to buy dust mask, ear defenders and goggle snow too. And a massive dust sheet!