Pral M

Status
Not open for further replies.
S

sedoplastering

Member
Hi, I am looking for some advice based on experience regarding a suitable substrate for mono pral M, I am sure in the coarse they said that light weight blocks (aerated) were suitable but didn't know if anyone had had bad experiences with applying mono to these or cracking afterwards?
 
I would use rendaid before hand with mesh imbedded I would advise you not to go over these with out any prep work before hand to lower suction .
 
Don't render straight onto blocks less than 7nm density,I think Weber are now advising against using their renders on blocks less than 7nm full stop, although I may be wrong Even if the blocks are 7nm expect there is a decent chance of cracking if there are no expansion joints, bed reinforcement and time allowed for the building to settle etc etc.
 
Yeah I would always treat the suction on these blocks but was not sure what the crack was with mono on them. I know what you have suggested is the best way. can mono still crack through the plastic mesh? And do I just bed the mesh into the first coat or do I need a separate product to bed it in with.
 
If it is Weber then rend-aid and be generous with mesh embedded. On the mono coat put in stress patches. I use a 1m2 mesh and cut a .5 x .5 corner out. Not quite to Webers book but near enough. Always advise the customer before hand that the manufacturer specifies 7 newton blocks so even with mesh crack cannot be guaranteed.
 
Porch is being built next week so I am gonna tell them it has to be done in 7N or I won't mono it. Let someone else struggle. Thanks for all your advice, top stuff.
 
spunky said:
Doesn't wetting blocks lead to lime bloom?
Click to expand...

One of our directors has been researching and trying to cure efflorescence (Lime bloom) for over 30 years since he developed the first through coloured renders that were used in the UK, and so far, like everyone else has failed. Wetting blocks does not cause lime bloom, some of the manufacturers actually recommend it and it will help with suction so you can render blocks without having to prep further.
 
How do you know if a block is 7N or not? never rendered on them so my knowledge is minimal
 
wetting the blocks can be a bonus for suction and in dry conditions but if the bottom blocks get wetter than the top blocks you will get uneven drying out so different drying out colours.
 
Rigsby said:
wetting the blocks can be a bonus for suction and in dry conditions but if the bottom blocks get wetter than the top blocks you will get uneven drying out so different drying out colours.
Click to expand...

spot on with that. if in doubt put a primer such as r7 or micro on them.
water will sit on the dpc line and stay in the bottom line of blocks, thus as you say give it a different shade.
 
Rigsby said:
wetting the blocks can be a bonus for suction and in dry conditions but if the bottom blocks get wetter than the top blocks you will get uneven drying out so different drying out colours.
Click to expand...

Try just to damp the blocks if you can as you are spreading, if you finding this to be a consistent problem you may be wetting them too much.
 
Putzmiester said:
Rend aid and mesh is a must
Click to expand...

I wouldn't say so on something like a porch, the shrinkage energies getting distributed around the structure will be nothing like there will be on a full house so shouldn't be a problem for 7NM block as long as the structure gets enough time to dry out before rendering . Blocks tend to crack (Thus cracking the render, render rarely if ever cracks on its own.) when whoever built it did not manage the settling energy with expansion joints and bed reinforcement on a large structure. Some of the worst cracking jobs I've attended have been fully meshed but expansion joints and bed reinforcement was missing. You then get told that the house was built in winter and was only allowed to dry out for 3-7 days or so after the roof went on before the render was done.

Jobs crazy sometimes.
 
RenditLtd said:
I wouldn't say so on something like a porch, the shrinkage energies getting distributed around the structure will be nothing like there will be on a full house so shouldn't be a problem for 7NM block as long as the structure gets enough time to dry out before rendering . Blocks tend to crack (Thus cracking the render, render rarely if ever cracks on its own.) when whoever built it did not manage the settling energy with expansion joints and bed reinforcement on a large structure. Some of the worst cracking jobs I've attended have been fully meshed but expansion joints and bed reinforcement was missing. You then get told that the house was built in winter and was only allowed to dry out for 3-7 days or so after the roof went on before the render was done.

Jobs crazy sometimes.
Click to expand...

On new builds you could get away with stress cracks because of missing reinforcement in the openings. But on a refurb? Yes we know it is a stress crack. WE KNOW! But as far as the customer is concerned we are making it up as we go along! Proving you are right will involve someone with letters after their name like a structural surveyor but who pays to prove your innocence? I had to on that Weber job because their rep was to ignorant to tell the truth and his word was taken as gospel when in fact he was wrong. It just simply cost me £350 to get someone with more degrees than him to prove it. :RpS_cursing:
 
Rigsby said:
On new builds you could get away with stress cracks because of missing reinforcement in the openings. But on a refurb? Yes we know it is a stress crack. WE KNOW! But as far as the customer is concerned we are making it up as we go along! Proving you are right will involve someone with letters after their name like a structural surveyor but who pays to prove your innocence? I had to on that Weber job because their rep was to ignorant to tell the truth and his word was taken as gospel when in fact he was wrong. It just simply cost me £350 to get someone with more degrees than him to prove it. :RpS_cursing:
Click to expand...

You got cracking on a refurb? What was the substrate?
 
RenditLtd said:
You got cracking on a refurb? What was the substrate?
Click to expand...

No it,s Friday and a bank holiday weekend. I am not going through that story again and give myself a headache! Besides I rung you about it in 2011 and told you my story on your phone. You sold me some samples.

Nice lady on the phone by the way.
 
RenditLtd said:
One of our directors has been researching and trying to cure efflorescence (Lime bloom) for over 30 years since he developed the first through coloured renders that were used in the UK, and so far, like everyone else has failed. Wetting blocks does not cause lime bloom, some of the manufacturers actually recommend it and it will help with suction so you can render blocks without having to prep further.
Click to expand...

a good acrylic primer can work a treat on light block also.

can you imagine trying to hack mono off a job from aierated blockwork.....hugh
 
Status
Not open for further replies.

Share this page

Back
Top