render and set celcon blocks

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richardbrown

richardbrown

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Hello guys,

I have a job coming up that is all render and set celcon/lightweight blocks which I hate with a passion because I have had problems in the past with the render failing in places.... and they just give me the S hits in general.

What do you think is the best solution so I know I wont have any problems.

Wet walls first ?
PVA walls then apply when tacky ?
etc etc .

Thanks
Rich
 
are you hardwalling or sand and cement? either way run a hose over them if possible, never failed me before.

however, as said in a previous thread, if soaking them is an issue, i don't see why pva shoul be a problem.
 
I am doing this one myself napper got the other boys elsewhere at the mo.

well thats what I usually do pug wet them down with a hose but I have just finished doing a block of flats here and the outside rendering was over lightweight blocks, I subbed it out to a local gang who followed the architects spec to the letter. I was leaning out one of the windows a few days ago and gave the wall a tap and it was hollow ..... only found one spot like it so kept my mouth shut.
 
I have never had a problem with celcons internally but i wouldn't touch an external with lightweights. I think Rb if you keep the thicknesses down use a 5-1 or 6-1 mix, dont over plastisize the muck ,give the wall a light spray not a soak and your going to love this bit...... use the two coat method and screeds,perhaps id use matercreate which mixes a bit better with less water and has a higher lime content and i dont see you having a problem mate .
 
Out of interest why wouldnt you touch an external built from celcon church ???

The spec was 3 coats of render 5-1 sand/limelite and only use waterproofer in the mix.

Rich
 
richardbrown said:
Out of interest why wouldnt you touch an external built from celcon church ???

The spec was 3 coats of render 5-1 sand/limelite and only use waterproofer in the mix.

Rich
[/quote

had problems years back with them , done about six houses with a dyed render (pink and yellow ) they went hollow and cracked before i had finished the site , the builders got all the reps from blue circle , sovereign and celcon involed.... they all blamed each other
Click to expand...
 
I have had similar problems ... so whats gonna stop that happening on the inside ???

Rend aid is out as its far to expensive.

The problem is everyone has a different idea, I just want to know the best way of doing it !! ???

Rich
 
Dont worry to much Rich ive never had any problems with them inside ..... its only one coat and its not directlly affected by the weather mate , on outsides ive noticed that the scratch coat never fails ....untill you put the top coat on ??? perhaps its a weight to key thing im not sure.One thing the celcon rep did say was not to soak the block
 
I have never been that impressed with the blocks and I think they need to provide more of a mechanical key on the block it's self not just a few wavey lines.

If its only a small wall I usually get the lab when he is quiet to spend 10 minutes with a brick hammer just to try and key them up a bit more.

Its interesting why celcon say dont soak them.... thats what I usually do ! soak them have snack then go for it.
 
He said a light spray was sufficient, soaking the block will cause the block to expand and then contract when dry .....made sense at the time to me . Just remembered he said that a soaked block had a different shrinkage rate to render especially with waterproofer in it ( he didn't like the sovereign rep or waterproofer in general .
 
does anybody else knock their scratch up like pee in these situations? jsut get it on real quick (messy like) and go over a quick 2nd coat then scratch it?
i find ive a bit more confidence doing that on high suction but its all psycological..
 
You say Rendaid is out the question , pity , cos there really is no come back if you use it , What a bout a SBR,slurry ,sort out your wetting problems , and with sharp sand will give more key.Ive done it that way on a recomend from my old faithfull oldtime spread mate .
 
Sorry to bring up an old thread guys, but having similar problem myself, rendering is fine on anything but thermalites and celcons, slight different problem of scratch drying way to fast and drying weak, how on earth do you combat this?! I stood there with the hose for a good couple of minutes soaking said area (obviously a few minutes on each section), the wall was soaked through, but still, come scratch time it still didnt save it!

How long exactly do you stand there soaking the wall for? or as said above, celcon say dont do this?! I wouldnt dare try render over the blocks if they had just a light wetting down! **** me, the render would go off before I could even lay a metre on!

Help apreciated cheers guys! rattling my brain this one and has put me off rendering over the ******* things ever again!
 
Soak it with the hose, splatter it with a slurry coat with loads of freeflo in it and soak it again when the splatter has set. Then soak it again - and again:RpS_thumbup:
 
So basically, just soak the **** out of them for ages? I tell ya what, next time Ill tell the customer someone else can do it! ******* not worth the hassle!
 
if its internal you need to get on it early with your devil float- it brings the moisture in the render back to the surface and stops rapid drying out. If its external I'd use an umbrella
 
Sorry for sounding like a dick, but what do you mean by scud coat?

Just one coat of an sbr slurry? then lay on when tacky? or one to seal wall first?
 
Does the throwing it at the wall give the render the key you need then? so no need to lay on when tacky? 3:1 sand and cement and sbr, bit like an internal bonding agent? cheers matey

Sorry, also, do you not prep the block work at all before the sbr coat? surely the blocks would still suck the life out of the sbr and cause a dusty slurry coat?
 
naughty boy kebab king. this thread is 2 yrs old :RpS_laugh:

Wet the blocks down as normal. MIX S/C at about 3/1with water and some sbr to a sloppy consistency and throw it at the wall with ur trowel. The wall will suck in a bit but the slurry with sbr in will stick like sh1t 2 a blanket by blocking the pores in the blocks. When dry it forms a mechanical key :RpS_thumbup:
 
Beddy - never used tyrolean or a gun before, are they easy to use? make a mess of everything near what your spraying I presume? so all windows and walls would need covering up? When you say mix it like tyrolean, what sort of consistancy is that? fairly runny render mix?
 
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