float and set - around corners

[NickB_99]

Hello all,

Next part of house project due at the weekend - dining room needs a lot of plaster attention..... Can't wait!

Back of the chimney stack is in the corner and has cracked badly, so I suspect I'll need to take it all back to brick/block (at least here).
It has an external angle on the corner.
I would like to continue with the float & set, but have not had to handle an external corner before.

What's the recommended course of action with the external corner bead when floating and skimming later?

I can see there maybe two solutions -
a) get one of the thicker float beads and float level with this and then stick a thin coat bead over the top when skimming
b) just use the thicker float bead and remove a couple of mm depth to about 1ft away from the bead

Can see there would be pros and cons with each. Or of course maybe something else?

TIA

 

[roughcaster]

Use the thicker expamet float bead. Fix it on using dabs of multi finish, put it on with a guager, making sure you keep the dabs below the finish level.Put the dabs on the brick/block corner, one at the top/bottom,, with 3 or 4 in between. Level/plumb the bead (carefully) using a long straight edge/spirit level. When you have it "set plumb", leave the multi finish dabs to harden,, don't fiddle with it You can then float the wall, using the angle bead as the guide,, and you "don't" need to use a thin coat bead on top of the bead before you put on the finish,,,,, just use the original bead you put on earlier

 

[NickB_99]

Use the thicker expamet float bead....... just use the original bead you put on earlier

Hi Roughcaster - thanks for the prompt reply.

Ok, will go for the single bead approach.
But not quite sure how to leave things after floating.
Do I float flush with the corner bead or do I need to take some back before it sets?

 

[roughcaster]

I never scrape it back. The finishing will feather away to the edge of the bead.
I've just been thinking Newbee, what are you using to float coat the wall with, hardwall, bonding or sand and cement?

 

[trowelmonkey1]

have to admit to cutting back my float coat a little along the bead, gives me a squarer finish, sure this is down to my inferior floating skills though RC!

 

[roughcaster]

I don't, and never have scraped back along the spine of any metal bead. Even a thin coat coat bead, with a tight coat of bonding + 2 coats of multi, will still give you a good enough square finish down the corner.

 

[trowelmonkey1]

when i last did a chimney breast with render angle beads and ruled it off and skimmed it, i found because the float coat was flush out to the very corner of the beads when i skimmed it i ended up with ever so slightly 'over-filled' beads making the corners ever so slightly rounder than i would have liked, so ever since have been just cutting back slightly which sorts my problem out, never really gone back to thinking about what exactly i did or didn't do to trip me up like that.

would like to know though RC, can see this being a tricky one to talk through though.

having said all this, i've seen the chimney breast in question now it's painted and it looks fine, just not as sharp a corner as skimming using thincoat beads would be, maybe expecting a corner this sharp when using render angle beads is where i'm going wrong...

 

[roughcaster]

Maybe TM,,, each to their own, but i prefer not to scrape. There's not much in it either way really.

 

[trowelmonkey1]

i would prefer not too mate, just wondered if i'm expecting too sharp a corner from using render angle beads, am i you think?

 

[roughcaster]

Try one and see. To scrape or not to scrape,,, as i say,, there's not much in it. Different if it's around patch in a wall,, unless you're going to plaster over the whole wall afterwards.

 

[NickB_99]

I never scrape it back. The finishing will feather away to the edge of the bead.
I've just been thinking Newbee, what are you using to float coat the wall with, hardwall, bonding or sand and cement?

Will give it a go to not scrape back.

Was planning on using bonding. I have used hardwall now, but found bonding a little easier to work with.
Sand & cement I've never used before, so my initial thoughts I should stick with tried & tested.
Or run the risk of the wrath of the good lady of the house if it all goes wrong!
But as keen to learn, you've got me thinking......

The chimney in the dining room is actually the back - there is no opening I'm going into. The opening is in the lounge.

If you had a choice, which would you go for?
(Are hygroscopic salts an issue to work through even on the back of a chimney stack?)

 

[trowelmonkey1]

hiya newb!

getting out of my depth now here

but if i'm understanding it correctly, salts shouldn't be a problem but i could well be wrong, both sides of the stack are inside the house just not in the same room? as far as i know you need damp to get salts, not sure how damp would be getting into that level of the stack unless it's coming in from underneath.

i wait to be corrected though.

 

[NickB_99]

if i'm understanding it correctly, salts shouldn't be a problem but i could well be wrong, both sides of the stack are inside the house just not in the same room? as far as i know you need damp to get salts, not sure how damp would be getting into that level of the stack unless it's coming in from underneath.

i wait to be corrected though.

Hi TM1.

Yes, you are understanding correctly as regards stack - inside house but shared between the two rooms.

I had just assumed when the subject of render was mentioned by R/C in the context of a chimney stack, that it was to avoid possible salts coming through.

I had thought that after fossil fuels have been burnt up a chimney for a long time, this causes problems when gypsum plastering over the bricks... this could have been due to the moisture in the hot gases as much as the fuel itself....now confusing myself
Either way, wondered if it was possible for them to get through the brickwork at the back of a stack.

 

[trowelmonkey1]

ah i see...well as far as i understand it, if there is no longer any burning going on then you needn't worry about the by products of burning stuff, it's possible that RC was talking render when you mentioned a fire place/chimney breast/stack etc because of the heat resistance of gypsum, or lack of it to be precise.