Render help please

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sandyblocks

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Need help have a roughcast house (with largish pebbles) unpainted render in poor state, it is cracked and hollow to the knock in places. Would knock it all off and get redone but the cement blocks underneath don't like to be disturbed. They are made of a high proportion of aggregate. (just had to rebuild rear elevation as block was disturbed!) The cement block is stable unless drilled with SDS or hit hard when it is friable and just crumbles away. Have had a few suggestions, use really light hand tools to remove very loose and then trying to go over the rest.

Is this okay to do and if so how? Have had various suggestions including attaching a mesh (but worried may struggle to get a fixing without disturbing cement block). Or rendaid then scratch coat before top coat.

Can't afford to take risk with knocking off as if this disturbs block no money to rebuild other eleveation, and don't fancy the house falling down!

Any products, suggestions, experience would be really greatly appreciated.
 
Wonder if you could just dab insulation boards and thin coat, no fixings in the insulation and it would be lighter than traditional render
 
I'm no expert mind you might still have to mechanical fix, adhesive coat for eifs systems like sm700 or maite
 
sandyblocks said:
Need help have a roughcast house (with largish pebbles) unpainted render in poor state, it is cracked and hollow to the knock in places. Would knock it all off and get redone but the cement blocks underneath don't like to be disturbed. They are made of a high proportion of aggregate. (just had to rebuild rear elevation as block was disturbed!) The cement block is stable unless drilled with SDS or hit hard when it is friable and just crumbles away. Have had a few suggestions, use really light hand tools to remove very loose and then trying to go over the rest.

You need carefully considered advice from people experienced in solving this type of problem. The danger is that you throw time, effort and money into temporary expedients that don't offer worthwhile solutions. Any coating that might allow water behind it, for example, with the possibility of subsequent frost damage is likely to make the situation worse. You might be best waiting until you have enough money to rebuild. Get the advice of a practical, structural engineer or building surveyor. By practical I mean someone used to solving day to day building problems in an economic rather than academic manner.
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You could ring up a manufacturer like Weber (yuk) or Marmorit. They would advise on what materials to use and how.

Otherwise invent your own. Algicide, pressure wash, sbr and slurry coat. Scratch coat with 8mm mesh and any subsequent scratch coats with glass fibre strands.
 
If it were mine mate just hand tools chopping off then see why some areas are hollow it could just be bad block work in odd area's. Find out when property was built and match the blocks to this period and find out what is suitable to use on these blocks. Are they them blocks which are use more in france and Spain light and hollow ,come across them a lot over the years.
 
Can't be that bad, if most of its blown anyway. If it were me i'd stop being a p***y and hack it off, do any repairs to the blockwork required and then render it to spec as supplied by manu. weber etc.

Or you could sand blast it off.
 
Thank you so much for all your advice. Don't think will ever have the money to rebuild and can't just leave it. Will try structural engineers and manufacturers and anyone else who has a suggestion. If you think of anything else or hear of any other products would really appreciate any pointers at all.
 
If the substrate is not stble enough to have render removed then its not going to be stable enough to be re rendered. Do what has to be done, not half a job.
 
sandyblocks said:
Thank you so much for all your advice. Don't think will ever have the money to rebuild and can't just leave it. Will try structural engineers and manufacturers and anyone else who has a suggestion. If you think of anything else or hear of any other products would really appreciate any pointers at all.
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To save money. Does any of yoru neighbours have the problem? have you asked buildimng control whether the problem exists elsewhere in the localit/ Where abouts in the country .. like nearest vown are you?
 
sliemasteve said:
To save money. Does any of yoru neighbours have the problem? have you asked buildimng control whether the problem exists elsewhere in the localit/ Where abouts in the country .. like nearest vown are you?
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Have you been watching your drink tonight, if not either go to your room and lock your door or lube up well. Those Londeners cant be trusted.
 
Rigsby said:
You could ring up a manufacturer like Weber (yuk) or Marmorit. They would advise on what materials to use and how.

Otherwise invent your own. Algicide, pressure wash, sbr and slurry coat. Scratch coat with 8mm mesh and any subsequent scratch coats with glass fibre strands.
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Do you use fibre strands in most of your render rigsby?? av never used them and im curious. Not Bi-curious just curious.......:RpS_wink:
 
Art I use fibres in all my S&C rendering, have done for many years it just wouldn't feel right not to now. It's almost like having a mesh right through the finished render.
 
essexandy said:
Art I use fibres in all my S&C rendering, have done for many years it just wouldn't feel right not to now. It's almost like having a mesh right through the finished render.
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Do you use them in your top coat Andy?

I've never used them, how much do you put into each mix?
 
I don't usually use them, but did on my last job as Andy says handful in the mix...on the packet it said add fibres to dry mix first which I did...but found clumps of fibres in the top coat as I was floating up. I stopped adding to dry mix as soon as I noticed this added them to the water first before adding sand/cement let the mixer spin for a min then adding the materials...that seemed to work.
 
essexandy said:
Art I use fibres in all my S&C rendering, have done for many years it just wouldn't feel right not to now. It's almost like having a mesh right through the finished render.
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So do you use them to prevent cracking and crazing?? Like danny said i would have thought they would show through when your sponging up. take it you just buy them at builders merchants??
 
DannyMac said:
Do they come to the surface when you float and sponge?

Heavier grade in the scratch?
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Yeah heavier grade in scratch and no they don't rise to the surface you just get the ones that are already at the surface showing but they are finer than a human hair and you just can't see them.

Artisan998 said:
So do you use them to prevent cracking and crazing?? Like danny said i would have thought they would show through when your sponging up. take it you just buy them at builders merchants??
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More as a precaution than anything else as I never really suffered from cracking/crazing to any great degree before using them.
I buy in bulk (about 70 bags at a time) direct from a manufacturer.
 
essexandy said:
Yeah heavier grade in scratch and no they don't rise to the surface you just get the ones that are already at the surface showing but they are finer than a human hair and you just can't see them.



More as a precaution than anything else as I never really suffered from cracking/crazing to any great degree before using them.
I buy in bulk (about 70 bags at a time) direct from a manufacturer.
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so how do u gauge how much to put in the mix??
 
sandyblocks said:
Need help have a roughcast house (with largish pebbles) unpainted render in poor state, it is cracked and hollow to the knock in places. Would knock it all off and get redone but the cement blocks underneath don't like to be disturbed. They are made of a high proportion of aggregate. (just had to rebuild rear elevation as block was disturbed!) The cement block is stable unless drilled with SDS or hit hard when it is friable and just crumbles away. Have had a few suggestions, use really light hand tools to remove very loose and then trying to go over the rest.

Is this okay to do and if so how? Have had various suggestions including attaching a mesh (but worried may struggle to get a fixing without disturbing cement block). Or rendaid then scratch coat before top coat.

Can't afford to take risk with knocking off as if this disturbs block no money to rebuild other eleveation, and don't fancy the house falling down!

Any products, suggestions, experience would be really greatly appreciated.
Click to expand...

a tough one,

if your going down the insulation route youd need mechancal fixings as the insulation would want to be around 100mm to meet current u values.
The rule of thumb with rendering is your only as good as your substrate, so if your going over loose rendering your asking for problems, and not only that you are putting additional weight on already weak blocks.
possibly you could go directly over it with parinter with a small 5mm guage mesh and an acrylic,
but for me your storing up problems.As said is not knocking it off with a bolster not an option?
ive seen most types of substrates over the years and theres always an option, but with out seeing the job or any pictures its just speculaton.
 
I use 12mm fibres in the backing coats and 6mm in the top coat if its going to have silicone trowel or tyrolean and the like. Sometimes do get the odd bit of hair sticking out so I dont bother if its going to be painted.

I only use it on a dodgy background where there might be a risk of a comeback.
 
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