Plastering Internal : External Wall.

[Greg20]

Hi guys , (again, sorry for all the posts i always ask loads of questions),

My question is this :

Having looked at a job, i need to knock of various hollow/blown bits off 6 walls in a 12'x12' room(all above the skirting aswell, right around the room, as was ruined when skirting was removed), sort out, prep and re skim all the walls and the ceiling, the rest of which is sound.

Easy enough job, i think we'd all agree.

My only query is : One of the walls where ill need to knock off various bits and re undercoat before skimming, is an internal - external wall.

Im sure you understand . The house is quite old, and has 2 skins of brickwork, with a cavity, though more likely 50mm rather then 100mm.

There are no signs of damp or anything, but the brickwork is like i said quite old. And past its best in a few places. Dusty, wonky ect.

On all the other walls i will prep, (dust down, pva, key, ect) the bits and then apply hardwall, in two coats as the plaster is certainly thicker then 11 mm.

On the internal - external wall though, who reckons i would be better and safer off, sorting out the patches which are down to brickwork, with a 4:1 sand and cement morter mix, rather then hardwall? Due to the fact it is old, and external.

Or do you think hardwall would be fine? (after correct prep work of course).

The brickwork is old commons, not engineering bricks or anything, so hardwall is the correct choice.

Thanks again for your patience everyone. I look forward to your intelligent replies.

Greg.

 

[stevethespreader]

i would patch it all in with thistle bonding greg

 

[Greg20]

What makes you say bonding Steve?

The bricks are quite high suction and ive made the mistake of using bonding instead of hardwall before at college once during an assesment and i tell you ill never make that mistake again. Bonded yes, very well infact. But looked like a map!

The whole lot cracked.

I would never use bonding unless i was going onto something like dense concrete blocks or something with very little suction.

Thanks for the reply though Steve.

 

[Alastairreid]

whats the rest of the wall done in greg?

i dont see the point using sand/cement to patch in a wall which has a plaster basecoat, bonding would be fine if the suction was dealt with 1st.

 

[Greg20]

The rest of of the wall is done in bonding alistair, - (this is why i think its in such a bad state, as bonding clearly shudnt have been used as its a high suction wall )parts of it are fine but alot of it is cracked and coming down, obviosly hasnt taken to the wall very well.

Im sure an undercoat plaster would be fine , though under the window, the brickwork is very bad.

Its old, got some nasty holes in it, a couple of them fist size, this seems to be where someone has been abit heavy handed in the past as theres not alot of weight above the window and the window is only several years old. Cracks, very dusty morter, falling apart basicly.

So i was just thinking it may be a good idea to give it a morter coat first in the most offending areas, to hold the whole lot together and give it some serious strength?

Then skim the wall afterwards.

Or do you reckon undercoating onto such shabby brickwork wont cause a problem?

Thanks guys.

 

[Richard C]

If the wall is basically sound, I’d probably fill any large holes/mortar joints with sand/cement render & then Bonding coat over that. If there are any signs of cracking, reinforce with metal lath or it’ll come through; I always use render over such repairs.

Bonding is quiet good for binding together crappy old walls & I even use it on blocks; it’ll be fine as long as you PVA seal it the day before to control the suction; then PVA again before plastering as normal. Use two coats to bring it out flush regardless & watch carefully as it starts to go off, particularly the 1st coat, you may need to dampen it down a little & go over it again to prevent crazing but don’t over do the water; I always use an old kitchen spray bottle. I tape around the join lines as well before skimming, just to be sure.

 

[Alastairreid]

if i considered the brickwork to be as bad as you suggest i would remove all the plaster and then render, i can understand your reasoning though greg.

 

[Greg20]

If the wall is basically sound, I’d probably fill any large holes/mortar joints with sand/cement render & then Bonding coat over that. If there are any signs of cracking, reinforce with metal lath or it’ll come through; I always use render over such repairs.

Thanks Richard, thats what i was thinking. Render, then undercoat.

 

[Greg20]

if i considered the brickwork to be as bad as you suggest i would remove all the plaster and then render, i can understand your reasoning though greg.

The brickwork is only bad in a couple of places allistair and where it is, the whole lots coming off. (under the window mainly and then above the skirting in one or two places) The rest of the wall is sweet. If it wasnt then the rest of it would be on the floor aswell.

I dont see the reason for taking off the parts that are fine and are bonded to the wall very well.

Sorry if i caused any confusion.

Thanks for the replies.

 

[stevethespreader]

What makes you say bonding Steve?

The bricks are quite high suction and ive made the mistake of using bonding instead of hardwall before at college once during an assesment and i tell you ill never make that mistake again. Bonded yes, very well infact. But looked like a map!

The whole lot cracked.

I would never use bonding unless i was going onto something like dense concrete blocks or something with very little suction.

Thanks for the reply though Steve.

if it all cracked up and looked like a map you dident control the suction, bonding is the pefered material for many a spread when patching dont forget you are also patching in to existing render and plaster, bonding will adhere to all of that, i have been on large refubs of hospitals and healthcenters and on those jobs we always used bonding not hardwall but if you dont want to listen to my advice thats up to you, hardwall was not made for patching it was made for brick and block not to bind with other plasters like bonding, and if you are just ever going to use bonding on just dense blocks i cant see you getting very far in the plastering trade at all

 

[Richard C]

Thanks Richard, thats what i was thinking. Render, then undercoat.

Just to be clear; unless repairing cracks/lath is involved, I would only fill the holes & patch up any craggy mortar joints with render & then fill out with Bonding, not render over the whole area & then Bonding; if you’re going to apply an initial rended coat over the lot, you might as well fill out with a render base as well.

 

[Greg20]

but if you dont want to listen to my advice thats up to you, hardwall was not made for patching it was made for brick and block not to bind with other plasters like bonding, and if you are just ever going to use bonding on just dense blocks i cant see you getting very far in the plastering trade at all

I wasnt not listening to your advice Steve.

Am i wrong in saying that bonding is for low suction backrounds?

You see that ive always been taught bonding was for low suction backrounds ONLY.

Ive never seen or even been told you can use bonding on high suction backrounds, even if you control the suction. Why would you when theres another gypsum based plaster designed to do this? Enlighten me as your obviously more experienced then me.

I mean surely its quicker and easier to use browning or hardwall on high suction backrounds instead of bonding? If not why did they invent it if you can just use bonding? Or am i just being irrational?


And thanks Richard C - I was clear with what you said , i was thinking the same. Otherwise i may aswell just bring it out in render and then skim the render.

 

[stevethespreader]

but if you dont want to listen to my advice thats up to you, hardwall was not made for patching it was made for brick and block not to bind with other plasters like bonding, and if you are just ever going to use bonding on just dense blocks i cant see you getting very far in the plastering trade at all

I wasnt not listening to your advice Steve.

Am i wrong in saying that bonding is for low suction backrounds?

You see that ive always been taught bonding was for low suction backrounds ONLY.

Ive never seen or even been told you can use bonding on high suction backrounds, even if you control the suction. Why would you when theres another gypsum based plaster designed to do this? Enlighten me as your obviously more experienced then me.

I mean surely its quicker and easier to use browning or hardwall on high suction backrounds instead of bonding? If not why did they invent it if you can just use bonding? Or am i just being irrational?


And thanks Richard C - I was clear with what you said , i was thinking the same. Otherwise i may aswell just bring it out in render and then skim the render.

since when have bricks become high suction? lets recall now if i can remember rightly breeze blocks high suction, brick medium, and concrete and concrete blocks low suction now if you damp that MEDIUM suction brick down what do you have? you have a low suction background to apply the bonding to and why is it quicker to use browning and hardwall? if you went out onsite and used hardwall for patching you would soon get a pull from the site agent

 

[NickB_99]

Am i wrong in saying that bonding is for low suction backrounds?

You see that ive always been taught bonding was for low suction backrounds ONLY.

Ive never seen or even been told you can use bonding on high suction backrounds, even if you control the suction. Why would you when theres another gypsum based plaster designed to do this? Enlighten me as your obviously more experienced then me.

I mean surely its quicker and easier to use browning or hardwall on high suction backrounds instead of bonding? If not why did they invent it if you can just use bonding? Or am i just being irrational?

I asked a similar question about plaster undercoats recently.
Trowelmonkey1 put up a very useful link on the post:

http://www.british-gypsum.com/products/thistle_plaster_products.aspx

Cheers TM1

 

[Richard C]

I asked a similar question about plaster undercoats recently.
Trowelmonkey1 put up a very useful link on the post:
http://www.british-gypsum.com/products/thistle_plaster_products.aspx

It’s wise to remember that manufacturers like to have lots of lovely products to fill lots of different niches. I don’t advise completely ignoring their recommendations as that would be foolish but, sometimes, you can use a particular product with special prep or allowances to very good effect for something other than the manufacturer would recommend or would have you believe it’s suitable for, especially if they also make a bespoke product that is more expensive!