I have done a "CRACKING" job!!!

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richardbrown

richardbrown

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I posted a few days ago about some hairline cracks when topping with CPI GENERAL

Well today we sprayed a panel about 45-50m2 and it went like a dream, sprayed,ruled and cleaned up by 10 then all floated and sponged by about 2. My mate then finds one of these hairline cracks again about 3" across then another and another in the end I bet there were 80-100 that appeared.

I managed to float and sponge them back in but the panel looked sh.ite by then and I was gutted.

again I am looking for SENSIBLE answers as I cant afford for this to happen again.

To re-cap:

The scratch was fully cured, the gear was sprayed using a d-63 and water set to 380, not more than 15mm deep.

HELP GUYS PLEASE :-* :-* :-*
 
f@cked if i know then ???, cpi s got waterproofer in ,i cant see how your finishing it that quick in this weather , should be holding for ages , was it in the sun? was it windy?
 
no one knows more about rendering than me , ive just f**k**g told you what it is , and still you post for help , you lobster eating numb nuts ;D we still alright for next week ?
 
It was an old stone built house. 3 scratch coats of cpi with mesh in the last coat.

It was sunny and the sun was on the panel all day.

It was fully keyed up.

I love you church x
 
rich i sprayed cpi monday over a fully cured scratch in full sun and had the setting a little wet and whole areas were sliding down the wall after ruling so had to be left to pick up....my point is there's next to no suction in the scratch. cant surely be drying too quick? we had a couple of cracks in the part where it was wetest later on. Evaporation/shrinkage? maybe a little too wet being sprayed rich. I think it's more to do with slumpage rather than drying. The cracks are very similar to ecorend/krend that ive experienced in that the product has little integrity within itself to hold itself together butt
 
The last house we did the gear took ages to float up as you say goody so today I sprayed a little dryer at 380 over the 400 i usually do.

The sun was on the entire panel all day with no wind so it was baking.

The top coat was almost hard but you could feel it was wet underneath if you know what I mean
 
Having used parex parmurex I can happily say that CPI is cheap and inferior. It's just a pumpable old fashioned render. Again you getteth what you payeth foruth. Just a comparison but we were spraying with 250 water on a d42 which although slightly slower than yours is still a lot dryer?
 
you never said anything about 3 scratch coats to me , ok basically you have a waterproof base coat , you are appling a top coat to , the water from the top coat can not go anywhere expect downwards (gravity) or forward , a steel trowel or straight edge and lime forms a barrier / a kind of seal to stop moisture evaporating into the atmosphere , the water in the render takes up a space , more water more space it takes up add that to air / lime / plastizers which add tiny bubbles that ar added to the mix can cause a problem in the initial/natural set , weather also has to be taken into the equation
 
Better ask the wider forum rich tbh but the main thing is suitability for floating to a finish. Ironically sas float is no good for floating as a finish too rough but excellent basecoat, parmurex is the best I've used but is 6 odd a bag, that was what we did them quoins in as well as dub out 40mm in one coat!
 
Richard,
There is no suction in your scratch coat because the cpi has been properly blended and had full time to cure.
The final coat was sprayed wetter than you would by hand and was drying from the face back to the scratch coat. The part of the topcoat render next to the wall had no suction and no air to dry it.
You were floating up the face that had been exposed to air and began its setting process and the back was moving slightly because it was wet, then when it settled the cracks appeared to the face.
 
you are better to get all your dubbing and straightness out in one coat with a machine and even finish it if you can, choose the right product for the job. CPI is cheap but may not be the best option. The topcoat if you need one you need to choose something that will be applied at about 5mm. The render will dry quicker and require less work to finish. Me and good used St astier lime topcoat and floated it to a stucco finish. The 5mm will allow 4 mts or more a bag so calculate the cost it will be ok
 
No it doesnt, you just are not aware of products on the market.
Powerwall sell a Base coat which at £6 a bag will cover a meter at 20mm i have used tons of this stuff and believe me when i say you can put it on at 100mm pass over pass wet on wet it never sags, its fibre reinforced and breathable, you can shave it like k rend but you will only use it as a base coat Superb stuff.

You have damn putz which is a 12kg bag the size of a hot air balloon, its sprayable with the g4 you have and can go on at 150mm. It dries like eps polystyrene and then you need to mesh and adhesive and mineral rend it or put a 10mm pass of k rend, weber ocr and rub it up after its set. I have done monocouche over 100mm of it no problems

You can use Primo base coat up to 30mm in one application and up210 after you pre rend and float it off the same time or next day. I found it best to spray to the depth then bed the mesh into the surface. spraying a pass then mesh then another pass makes it sag like tits

All manufacturers have products to be finished in one hit
 
sprayit said:
Richard,
There is no suction in your scratch coat because the cpi has been properly blended and had full time to cure.
The final coat was sprayed wetter than you would by hand and was drying from the face back to the scratch coat. The part of the topcoat render next to the wall had no suction and no air to dry it.
You were floating up the face that had been exposed to air and began its setting process and the back was moving slightly because it was wet, then when it settled the cracks appeared to the face.
Click to expand...

Spot on that mate well done .
 
sprayit said:
Richard,
There is no suction in your scratch coat because the cpi has been properly blended and had full time to cure.
The final coat was sprayed wetter than you would by hand and was drying from the face back to the scratch coat. The part of the topcoat render next to the wall had no suction and no air to dry it.
You were floating up the face that had been exposed to air and began its setting process and the back was moving slightly because it was wet, then when it settled the cracks appeared to the face.
Click to expand...

So what is the solution then Ian ?
 
slightly because it was wet, then when it settled the cracks appeared to the face.
[/quote]

Spot on that mate well done .
church said:
sprayit said:
Richard,
There is no suction in your scratch coat because the cpi has been properly blended and had full time to cure.
The final coat was sprayed wetter than you would by hand and was drying from the face back to the scratch coat. The part of the topcoat render next to the wall had no suction and no air to dry it.
You were floating up the face that had been exposed to air and began its setting process and the back was moving slightly because it was wet, then when it settled the cracks appeared to the face.
Click to expand...

Spot on that mate well done .
Click to expand...

Brown noser!
 
ABSORPTION, the steel trowel over the base coat even though it has been keyed or scratched has formed a skin between scratches which does not allow the subsequent coat to be correctly absorbed, i section the base just to roughen it up a bit, it might not look as perfect as you like but will allow the top coat to merge with the base coat and form a bond. Perhaps.
 
sprayit said:
the solution is to lay the topcoat a bit thinner and spray a bit stiffer
Click to expand...

I normally spray at 400 but sprayed this at 380.

I was thinking maybe after it was sprayed and I was ruling off maybe I trapped air in behind the render some how making it fracture.
 
if you were ruling it then it would have been on quite thick, the last one i rubbed up was sprayed with an 8mm cap and just spatted flat. cement on top of cement is a twatt to spray. it hangs
 
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