What tool to cut a shallow but smooth 150mm slot into concrete?

[PatDIY_Dad]

We want to install some glass sliders doors around our alfresco area

The sun sills need to be level and our slab has a bit of fall

In order to get the sub sills as low as possible for future screeding and tiling the window installer and tiler suggested to cut a slot into the high spots on the concrete do the sub sills get be fitted around half way in. Reducing the required screed thickness 

Of course the tiler and window man aren't keen on cutting the concrete so I can probably do it but finding out how before I will 

I've already got an angel grinder so that's fine to do the cuts which need to be about 30-40mm deep but is there a tool that would be able to cut a flat channel about 150mm wide?

Chiseling or jack hammering it up might be needed first but I wanted to know if there was something else that could do it in one go or after I do the cuts with the angle grinder 

[JacobZ]

Hi @PatDIY_Dad,

The best tool for this job is going to be a wall chaser such as this Full Boar 1500W 125mm Wall Chaser. They are often used in commercial construction to create paths for electrical conduit to be concealed inside concrete walls.

They have two abrasive cutting blades that can be set up to 30mm apart to cut a channel in the concrete. The concrete in between the cuts can then be broken out using an electrician's bolster and a hammer. 

I'd suggest marking out the channel, setting the depth of the cut and running a series of relief cuts along the channel. Once the concrete has been cut, use the electricians bolster to break the concrete, ensuring you angle the bolster inwards to ensure the correct places are fracturing.

Once the bulk of the concrete has been cleared from the channel, you can use your grinder with a DTA 100mm Dual Row Grinding Disc to clean up the channel but be extremely cautious and ensure all the guards are in place.

Please ensure you wear all relevant personal protective equipment including gloves, eye protection, hearing protection, a mask and long protective clothing. If you are not comfortable doing this kind of work, it may be worth contacting a professional concrete cutting service for assistance.

Let me know if you have any further questions.

Jacob

[PatDIY_Dad]

Thanks looks like it would do a more accurate job then just freehanding and a angle grinder 

Bit expensive for just a one time job though but can sell.after

Is there a way to do the cut across but level? As the concrete has some fall so it would start at say 30mm deep then as I go get shallower and shallower until the blade just glides on the top of the concrete then that's when I'd stop

As the sub sills needs to slot into it but level 

[Noyade]

Hi @PatDIY_Dad 

"it would start at say 30mm deep then as I go get shallower and shallower"

Over what distance are we talking about? Is the entire slab tilted? Why would this be the case? 30mm sounds very significant to me.

My only thought is long thin wedges that cover the distance required that will allow the 'chaser' to gradually cut to the deeper side.

But considering the specifications of the Full Boar - maximum cut is 29mm - there may be still more work required and based on it's limited 'shoe' size you will need more more than two wedges - and they would need to be anchored.

Did the tiler and door person offer any thoughts/compromises/solutions?

I have used masonry discs and "ZEC" wheels (requires 9" grinder) with some success but it was only over short distances and 10mm maximum depth.

And it was loud, dirty and incredibly dusty going.

I would like to see some photos of what we're working with and in particular - distances.

Keep us up to date! 👍

10mm depth

[PatDIY_Dad]

Thanks Noyade

I recorded a quick Video  to show you as that would help much more to show the problem 

The tiler suggested to instead of screeding to put treated pine battens all over the concrete and use yellow tongue flooring to make all the floor very flat and even and then tile directly over that. He would use a membrane to on top of the flooring before the tiles go on

But I am not confident with timber as over time any moister from underneath the concrete will evaporate up and damage the timber. Plus if I do get any leakes from rain that will cause issues. ( even though the window installer will fully water proof it. Silicone over time degrades doesnt it?

Ive spoken to other various tradesman and they advise against using timber as a substrate

[MitchellMc]

Pouring a screed/slab of that thickness likely isn't something a tiler would do regularly or if ever @PatDIY_Dad. That's why they are probably not confident in it. I would suggest you speak with a company that pours concrete slabs and get their thoughts. Provided reomesh is used on that corner, I don't see any reason why the height would be of concern.

I like @Noyades' thought of using the timber wedges to achieve smooth cuts out of the concrete.

Mitchell

[PatDIY_Dad]

Yeh when I speak to my tiler ill ask why cant you just use mesh in those lower areas ( thick screed areas) to strengthen it?