Cracking plaster

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Gromit1

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Hi all. My 1985 house is constructed of thermalite block with browning and multifinish. Problem is whenever I've had plasterers re-do walls in my house hairline cracks have always appeared after some weeks/months. The plasterers have knocked off any loose plaster and re-plastered in bonding or hardwall.

One plasterer recently advised the use of this stuff - please see below.
Fibrego Oy
https://www.google.co.uk/imgres?img...=en&sa=N&tbs=isch:1&ei=x301TcWuNsiKhQedueyeCw
Do you think it'd help?

Cheers


https://www.google.co.uk/imgres?img...=en&sa=N&tbs=isch:1&ei=x301TcWuNsiKhQedueyeCw
 
The mesh may make a difference but its not guaranteed. Most backing coats will crack with movement in the building etc especially around weak points windows/doors.

Why don't you plasterboard the walls instead of using a backing coat. Make sure you use scrim tape to cover all joints and at wall/ceiling line. Should stop the cracks coming back.
 
Thank you both very much. I reckon it's got more to do with the existing browning plaster because when the garage was plastered (it's not been plastered previously) not a crack in sight, but when walls that had been previously plastered were patched up that's when I had problems. It seems a pity to knock all the old plaster off, even the stuff that's not blown so I don't think boarding is an option. I'll give the mesh a go. And one more thing - substrate being thermalite blocks and existing plaster probably browning, is it better to use bonding or hardwall?
 
usually happens over doors and windows at each end of the lintel, any movement on such a big piece of concrete will crack.

its happened on my own living room after i skimmed it, and i always skrim about 4-5 times diagonal from top left & right of doors and windows up to the ceiling, whether its cracked or not.

obviously its not worked on my own living room, like said the only ways to get rid i think would be to dot and dab the reason being the boards are flexible enough to take slight movement, where as browning/hardwall dries solid and and movement behind will affect the finish skim.
 
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I reskimmed a lounge on a house last year which had the same problems. I worked on this house from new nearly 3o yrs ago when browing was been used more on new builds. I think over the years it becomes so dry the skim coat just becomes brittle and cracks and also with the event of plastic windows and central
heating, houses cannot retain moisture in the walls there just bone dry.
 
browning - bonding or hardwall

if your going over blocks i use hardwall, but i only do so on new builds, i was taught to use browning over older brickwork which is how i do things and never had anytrouble.

if your just pacthing then bonding is what you want, i wouldn't use bonding to float a full wall though i find it easier with the former 2. seems not to pull in as quick with hardwall or browning, or blister come to think of it.
 
Forgot to say thanks for the link. Also on the link Installing Instructions useing a hot air gun to bend a bead may come in handy some day. If it was me mate I would 2 coat with plasprime then skim.
 
with the backing plasters its easy to catogorise them depending on backgrounds...
Bonding - Low Suction
Browning - Moderate Suction
Hardwall - High Suction

thing about the blistering in bonding when skimming is down to spashing too much water and over trowelling
 
Cracking is a common problem ive tried every thing over the years and one of the best solutions have been the rolls of mesh they use for external thin coat renders i think weber make it as well a bit expensive though and we only used it on problem areas. I was always sceptical about sand and cement but did a job last year onto thermalites with a ratio of 8:1:1 and we had no cracks what so ever, well so far that is, it could crack a year later or 6 months later i suppose thats why alot of builders stop retention.
 
bodplasterer said:
Cracking is a common problem ive tried every thing over the years and one of the best solutions have been the rolls of mesh they use for external thin coat renders i think weber make it as well a bit expensive though and we only used it on problem areas. I was always sceptical about sand and cement but did a job last year onto thermalites with a ratio of 8:1:1 and we had no cracks what so ever, well so far that is, it could crack a year later or 6 months later i suppose thats why alot of builders stop retention.
Click to expand...

8:1:1 on therms? Was that scratch or top coat? I take it was top coat as you have lime in that mix (8.1.1)? it just shows the weak mix you have to use, is this whats recommended on therms?
 
you dont need to use mesh i cant do links but there is a reinforcing fibre you put in to skim only the first coat and it cures the problem nice and easy no need to mesh the whole wall
 
Yeah 1 coat on internal same as you would do with hardwall i personally freehand and the 8:1:1 is sand, cement and lime no waterproofer just a dash of plasticiser. supprisingly it was a lovely mix to use but it might have just been down to my labourer getting better at mixing.
 
rockhardsolidplastering said:
you dont need to use mesh i cant do links but there is a reinforcing fibre you put in to skim only the first coat and it cures the problem nice and easy no need to mesh the whole wall
Click to expand...

I know the stuff its the same fibres they use in screed you can buy it from most builders merchants i think you can buy it in different grades, i tried it on a bathroom a few weeks ago and found you get the odd fibre sticking out had to keep picking em out luckily it was being tiled so didnt have to worry to much.
 
I would be careful one coating high suction backgrounds or walls that are very uneven, in this case better to do 2 coats, scratch then top.
 
FreeD said:
I would be careful one coating high suction backgrounds or walls that are very uneven, in this case better to do 2 coats, scratch then top.
Click to expand...

Thats how I was taught as well... On a high suction background you will need to 2 coat hardwall. First you scratch coat, then second build screeds and fill in. I know on insurance work such as rising damp - you have to use 2 coats of hardwall where sand and cememt is not specified..

On internal rendering is it 1 coat or 2 coat?
 
Depends on your thickness whether 2 coats are applicable or not if you can get away with 1 then use 1 i am still putting it on 15mm and covering all the electrical conduits, i would only use more than 1 coat if it was on refurb and the walls were all over the place but on new work 1 coat suffices.
 
Thanks very much - I did attach a link but for some reason it doesn't look like one. Please click below. I met a plasterer who swears by this. By the way where can I buy fibres to put in the mix?

Fibrego Oy
 
I tried all the usual suspects Jewson, Wickes etc but no one's heard of fibres to go in plaster. Anyone know where I can buy them?
 
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