Concrete rectangle in first floor bedroom

[IanWood]

Hi all,

I want to lay a wooden floor in the back bedroom.

After taking up the carpet I noticed a concrete rectangle about 143cm * 63cm in one corner against a chimney breast. My plumber says this was probably a fireplace at one point.

The problem is that it isn't level and slopes up into the corner. I used a spirit level and a bit of wood and found its about 35mm higher then the floor boards.

I have taken a picture with a 1m and 30cm rulers on for scale.

Untitled

• IanWood
• 5 Jun 2011
• 1

I want to knock the concrete down so that's its flush with the floorboards so that I can put 6mm ply down and then wooden floors.

I was thinking this may do the trick http://www.hss.com/index.php?g=2151.

My worry it that being on the first floor too much vibration could cause problems downstairs.

What do you think?

Best regards,

Ian

 

[88v8]

Use a breaker upstairs? Caramba....

The hearth slab is cast on noggins attached to the joists, it's going to be a few inches thick. If the downstairs ceiling is lathe & plaster you could well bring the lot down. If it's plasterboard, you might just get away with cracking the joints.
Either way you have no chance of knocking it down. It's old, it will be very hard. It might break up but it certainly won't knock down.
If it were just a few lumps I'd say stitch drill and then use a scutch chisel & a lump hammer to gently knock it back, but the whole thing, no way.

I'd start by taking up a couple more adjacent boards and see if you can get a look how thick it is. You might be able to lever up the whole thing and remove it in a couple of lumps, then replace with new boards.

Unfortunately it's probably cast with joists on three sides, and could be 6" thick, so if you want to get it all out and it won't lever out - as is likely to be the case - chisel at it and break it up from the side so you're knocking it towards the chimney breast. That way, the bounce of the floor won't rob the energy of your blows, and it's less likely you'll damage the the ceiling below. Even so, I'd have someone downstairs watching what happens just in case.

After you've demolished the top couple of inches you can level up with screed.

Or you might just decide that the carpet looked pretty good after all...

Ivor

 

[jc69817]

Hi buddy
If your gonna hire why not buy

http://m.screwfix.com/details.htm?id=55660

Very good for diy and once bought you have it to keep

Hope you don't mind me saying

 

[IanWood]

Thanks for your help Ivor.

I had taken up one board as you can see but I haven't being able to tell how think it is. There are some wires going though the joist about halfway up and it looks like they are in the slab too.

I don't want to remove the slab, "just" reduce its height by 35mm.

I have already used a chisel and lump hammer and taken off some but it was pretty slow going. The material seems like if I took the time it would all come off.

HSS have another tool, the ominously name "Demolition Hammer" with "variable impact control". This looks like it could be used against the wall as you suggest rather than down. This tool seems like it could be used like a mechanical lump hammer and chisel.
http://www.hss.com/index.php?g=2131

What do people think about this tool?

Unfortunately carpets are no longer an option - other half wants wooden floors and that's that!

Regards,

Ian

 

[tim00]

1. The cables from the J/B will not be in the hearth, they will be fixed below it.
2. taking more boards up wont reveal any more information - the joists are double trimmers.
3. where you have the perished hearth corner chip away at it to reveal whats what
4. dont go buying or hiring tools until you know what you are dealing with.
5. using the double joist for a leverage point you and one other might be able to carefully prise the hearth up.
6. reducing or scrabbling off the top surface is feasible
7. go back and re-level and re-level again to determine if you are correct.Is your level true?
8. incidental,but you need a vent in the chimney breast.

 

[JohnD]

an angle grinder will allow you to zip it into manageable chunks that you can lift out. This will not cause impact damage like a hammer would.

there is a fair chance that big nails into the adjacant joists and wall are holding it in place

 

[big-all]

do not under any circumstances treat this like a garden path
you have a bit off concrete in a floor usually the floor is weakend because you have up to 3 timbers onto one often without extra support

you need to go slowly you will likely find the hearth is a bit off cement a layer off crap and wood to support the crap

i had to level a floor in a bathroom last week
it had a 2" drop over 5 ft or should i say 2" after 30" central span

there was a top layer about 1" thick then crud
the central joist was rotten at one end it had been sistered but not level but be3cause it was supporting the other 2 joists towards the wall it sagged a lot lol

if you use anything remotely mechanical you will cause so much damage that you will be laughing at your "embarrassing" mistake

 

[IanWood]

Thanks for all the advice so far guys, really appreciate you all taking the time to help me.

Hi buddy
If your gonna hire why not buy

http://m.screwfix.com/details.htm?id=55660

Very good for diy and once bought you have it to keep

Hope you don't mind me saying

Don't mind you saying at all. Thanks for taking the time to advice.

The more advice the better. To me a drill seems like it would be far more gentle and controllable then the other two tools I have mentioned from HSS.

@tim00

1) Great - that will give me an idea of how thick it is
2) Got that impression myself, glad to know I was right
3) I will give that a go
4) Will do
5) I don't want to remove the heath per se, just reduce its height to be able to put ply on.
6) I hope so!
7) I am pretty sure my level is true
8) There is a vent at the top.

@JondD
Never used or even held an angle grinder but get the idea it would not cause the impact damage. If I am able to grind away bit by bit I think I would be able to reduce its height.

@big-all
I hope my joists aren't rotten. Yesterday I intended to go around the room looking for loose floor boards to screw down prior to plying. To my surprise there only 1 or 2 that were even slightly loose. The whole floors seems very solid indeed.

Also, please excuse my ignorance but what does "sistered" mean in "rotten at one end it had been sistered but not level"

Is it viable to just try to reduce its height or must it be removed? I want to put ply down and then wooden floors. I don't really mind what I do to achieve that. I just don't want to end up with an uneven floor and certainly not a big hole in the downstairs ceiling!

Thanks again,

Ian

 

[RedHerring2]

Use an angle grinder to cut slots, about 25mm apart, about 25mm deep, right across the width. The remaining bits will easily knock out with a bolster chisel, to leave the whole about 25mm lower.
After a couple of bits are knocked out you can angle the chisel towards the wall/breast to knock out the rest.

It'll be a very dusty job so PPE and dust sheet taped over the door aperture, as well as the door shut, obviously.

 

[IanWood]

Thanks RedHerring2, that's exactly the advice I was after.

I like the idea of being able to cut a bit away at a time, rather than use brute force of a hammer/breaker.

What size should I get, 4.5 inch be enough? I don't want to overdo it nor do I want to spend months doing it...

Can these things also be used to chase into walls for adding extra power sockets for instance. When I did this in the kitchen I used a chisel and hammer and it was hard work! I would like in the future to put some extra sockets in the front room...If so I may buy one.

Screwfix have some Makita 4.5inch ones on for around £55 (http://www.screwfix.com/p/makita-9554nb-4-240v-angle-grinder/53964) with a bore depth of 22mm.

Thanks again guys, think I am getting there.

Ian

 

[big-all]

sister means along side attached to to give additional support

sistering a rotten joist is to replace the lost strength where the rot is
this helps to give the strength back without removing all the floor and ceiling connected to it

 

[IanWood]

Thanks for coming back to me.

Sounds a bit like using a split on a broken leg then?

 

[tim00]

Might not seem like it, but it's often simpler to ease and pry the hearth slab up and away, in my limited experience i've only seen them sitting on ledgers. come back here for boarding over, guys with good experience will help.

I'm still not convinced about such out of levelness, was the skirting scribed in in that high corner?

 

[RedHerring2]

What size should I get, 4.5 inch be enough?

Can these things also be used to chase into walls for adding extra power sockets for instance.

Screwfix have some Makita 4.5inch ones on for around £55 (http://www.screwfix.com/p/makita-9554nb-4-240v-angle-grinder/53964) with a bore depth of 22mm.

A 4.5" will do. You might need to give it two goes in the occasional spot.
Otherwise a 9" is a lot more money. And you wouldn't want to use a 9" above chest or shoulder height. They have some serious torque.

Yes it'll do similar grooves in the wall, but you'll still have to chisel out the bit in between the grooves.
The depth of cut depends on how worn the disc is. Obviously, on concrete you'll go through more discs than brick/blocks.

I recently replaced my worn out Bosch with a Makita and I wish I'd gone for the Bosch again. The switch on the Bosch is a lot easier to use than the Makita.

 

[IanWood]

@tim00
Thanks again for coming back.

The corner is definitely that high, the skirting has gone now but I do remember the end of it looking odd, i.e. cut out.

@RedHerring2
Thanks for the advice. I quite like Bosch tools myself.

Again, thanks all for your help on this but I think this may be a bit beyond me, particularly as I would have to use a tool I have never used before.

Before posting I contacted my plumber who has worked in that room installing wall insulation and moving pipes around etc for advice. He has been busy and only replied today. He can arrange for a man of his to to level the rectangle and put self levelling compound down for me.

His plan is for me to ply all the room other than that rectangle and for it to be reduced and then self levelled. I think I trust his staff more than me on this one.

Sorry that I have wasted people's time on this one.