Router to chase plasterboard?

[John D v2.0]

Hi all, hope everyone is well . Just have a puzzler here for you.
I need to chase around the top edge or thereabouts of the plasterboard in our upstairs bedroom.
(This is because the builders didn't do a full bed for the dot and Dab and the loft is dripping wet, and there's no access above to foam it. Then I will fill the chase with easifill all the way to the blockwork.)

I was looking for easy ways and it seems like there's something that looks like a router

Makita DCO180Z 18V Li-Ion LXT Cordless Drywall Cutter - Bare

Order online at Screwfix.com. Cordless cutting tool ideal for use on drywall. Features ergonomic barrel handle with ribbed soft grip for user comfort and reduced hand fatigue. Easy to operate slide-type on/off switch and shoe plate that can be used as a wrench for bit replacement. FREE next day...

www.screwfix.com

that takes these blades

Makita Drywall Guide Bit 6.35mm (1/4'')

Get it tomorrow: Great Deal on Makita Drywall Guide Bit 6.35mm (1/4'') and on many more Power Tool Accessories . Rated EXCELLENT on TrustPilot

its.co.uk

Is there any reason to buy the proper tool or can I literally just use my trim router?
The collet both are 1/4 inch, and the maximum speed is both 30000rpm.

Thoughts, suggestions and mockery please!

 

[Swwils]

Expand on what the actual issue is..is your loft not ventilated?

 

[John D v2.0]

Expand on what the actual issue is..is your loft not ventilated?

Thanks for your reply,
Yes it's ventilated to the regs but the warm humid air is pouring out behind the plasterboard as the void space connects all the way down to the kitchen, so the ventilation doesn't have much chance in this weather.
But I'm all ears in case there's another solution. As far as I know it's a bypass of the air barrier and the insulation caused by poor detailing.

 

[^woody^]

How have you concluded that the source is the wall void, and not the rest of the ceilings below the loft?

Or that its just normal and the issue is that your membrane is not sufficiently breathable or the ventilation not adequate for extreme cold weather?

 

[cdbe]

Might be better drilling holes and carefully injecting the foam. I think you can get one that doesn't expand massively.

 

[John D v2.0]

How have you concluded that the source is the wall void, and not the rest of the ceilings below the loft?

Or that its just normal and the issue is that your membrane is not sufficiently breathable or the ventilation not adequate for extreme cold weather?

Thanks for the reply.

Basically the only areas with the ridiculously bad condensation are directly above that room especially lower down the roof plane.

The other rooms are original l&p ceiling with solid plastered walls and that's an extension. And I know the builders did dot and Dab and didn't edge fill, I just didn't realise it would cause this or I'd have queried at the time.

The rest of the ceilings I can't see any significant cracks or holes. The loft hatch is a bit leaky and needs attention but nothing too bad.

 

[John D v2.0]

Might be better drilling holes and carefully injecting the foam. I think you can get one that doesn't expand massively.

Thanks for the tip cdbe

I did see people suggesting that online but there was debate about how to make sure it fills adequately from one hole to the next. Also I hate the stuff!

I was thinking of knocking the board to find all the "dots" near the ceiling, cutting between them, and clagging some filler to connect them as they should have been. Then it's done once and for all.

 

[John D v2.0]

Not sure if silence is agreement or just missed the reply, but I popped up and took a photo of the area above the new room and the existing room

Especially over the old external wall is worst, presumably because all the air from the internal plasterboard exits there.

Any further thoughts or ideas I would certainly appreciate! Thanks.