Thin coat System

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JohnDoe

JohnDoe

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Went to look at some internal work for a guy, who then asked me about his external render. He had a thin coat system done 3 1/2 years ago and from what i could see the top coat was coming away from the basecoat, it had been meshed as i could see it. They used Weber.plast TF .... I told him it very unlikely to be able to patch it up, but it old him i will see what i can find out and do.

Thoughts on why top coat would come away? And what can be done?

Thanks
 
@owls is it commen for the top coat to come away from basecoat? The basecoat, mesh, insulation seemed pretty sound.
 
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what substrate is it over, is it phenolic insulation, wool, eps etc?

ive never seen it delaminate like that, doesn't mean it doesn't happen like, but I cant see it being the product failing more like another source.
 
Couldn't tell you mate, i didn't do it and customer don't know and different .... A couple of the main places were around beads coming off in like hand size sheets.

Would you say remove loose and thin coat it?
 
most of the time it is down to damp base. either not fully dried or getting damp through the layer somewhere and then trying to escape
 
JohnDoe said:
@owls is it commen for the top coat to come away from basecoat? The basecoat, mesh, insulation seemed pretty sound.
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very common

especially on the schemes where peiple cant afford to wait for the base to dry and more often than not coat it over after its primed but you cant always see damp with the primer on.
Weber LAC base should be left for a week to dry

I seen a wall that was allowed to dry fully, it was then primered but the day after it rained all day and got wet in parts, the following morning all looked good and well so it was textured off but low and behold 5 months later the acrylic shelled off because the damp was trapped in by the acrylic
 
Not sure that's correct John as all the systems are supposed to be fully breathable so any moisture should evaporate through the top coat
 
Thin coat System

Here is a remedial job I looked at for refurb, the coping was a cheap and porous stone with a weak and failed bed joint also there was no dpc membrane only engineering brick as a base but the rain was striking through the mortar and into the block also from the coping. it had then saturated the render base until it tried to escape through the surface. the effect is delamination.
 
plasterjfe said:
View attachment 3416

Here is a remedial job I looked at for refurb, the coping was a cheap and porous stone with a weak and failed bed joint also there was no dpc membrane only engineering brick as a base but the rain was striking through the mortar and into the block also from the coping. it had then saturated the render base until it tried to escape through the surface. the effect is delamination.
Click to expand...

See this all the time...bad practice with copings keep us in business.
 
richardbrown said:
Not sure that's correct John as all the systems are supposed to be fully breathable so any moisture should evaporate through the top coat
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its true friend. moisture permeability is very very low even though it is breathable. but how breathable, is another question.
vapour permiability is high - totally different things but all in all it means they are breathable.

Got whole tower blocks in glasgow being refit because of this problem onto wool insulation that got wet on install.

Because moisture permiability is so low it keeps dangerous levels of moisture out, if that moisture is already in there (or finds a way such as the image above) it will also mean it cant escape quick enough.

I seen it happen in the lab under a microscope video reconstruction in italy. ask Ade he will tell you the difference between moisture permeability and vapour permeability
 
you can install noblo or equal mineral textures over slightly damp base and it will dry through but bucket coat mixed in paint and silicone will dry faster on the surface than the trapped moisture under the surface and will in most cases suffer delamination over time

that pic I posted is conni s
 
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Morning all...
Without sniffing it I would assume an acrylic topcoat.
Each component of the system has different vapour resistivity, and as above it really needs to dry thoroughly, otherwise trapped vapour can de-laminate topcoat.
Acrylic is vapour permeable, but at the bottom range...go for silicon or a mineral topcoat with an equaliser.

A very large project went tits up with an acrylic system over mineral wool...
 
Breathable they are but were talking very low levels of moisture. If huge or excessive levels of moisture get in behind or are present from undried base work then it can't handle it and will not expell it before it pushes the finish off so in effect it will trap moisture at those levels.

It is essential that all works are 100 percent dry before texture is applied. And as Ade has hinted. Acrylic can often be worse than silicone texture for this.

Think about it. Its not rocket science texture finish stays better longer why - its more resistant to the elements. If it were so breathable it would also allow water into the background as well as out making it useless on a thin coat system over a substrate such as board/timber or insulation.

Look at mono now that it really is breathable but will absorb and release moisture at will.

Remember guys were talking about higher levels of moisture not just what is in the air - that the render can handle

Stay safe stay dry.

:thumbup:
 
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