Resin render

[<cinema]

Hi all

Not posted on here for a couple of years - but had loads of help when I did... so thanks....

I'm here this time to understand 'render'. I ecently had a wall of a barn 'tyrolean' rendered. Seems ok - but got a few hairline cracks - is that to be expected?

I've just had a company out to quote on sorting out the gable ends & chimneys - and they use a product made by Renotex - a breathable resin render.

Has anyone got anything good or bad to say about it?

Thanks in advance

Simon [e-mail]

[roystonallen]

Hi Simon, 'tyrolean' render is old hat now. It has a very bad press. So many cowboys simply hired a gun (a fiver a day or so) and used it to spit a bad mix over untreated walls.

It is essential that all cracks are remidied a week or so before the aplication. If yours has cracks in it then you are in for trouble as the rain will penetrate the affected areas and once under the coating it has nowhere to go other than straight through to the iner walls or straight down, both are not nice.

Good luck, Roy

[mail]

Resin AND "breathable"? Sounds like a contradiction in terms.... What is wrong with a normal lime render? It has been used for some thousands of years...? chris

[Simon Hawthorne]

I thought that a couple of years ago - which is why I went for the traditional tyrolean render on the barn (the cracks are hairline). I've checked out the web pages of the company that makes this resin render - and it would appear to be breathable (it is not resin as used in the construction of canoes). Not being an expert I'd suspect it does the same job as gore-tex does with clothes....

Si

[Merryterry]

It depends on how you define 'breathable' and how you define 'resin'. There are ranges of very successful roof and wall coatings that have a high vapour permeable rate. There are a range of such coatings for roofs, walls etc. A lot of them are based on PU & PVA Resins

[Stuart Noble]

AFAICS what's wrong with it is the rain will come and wash it off if it's not protected with "damp sacking" for several weeks. My plasterer doesn't seem to be interested for some reason

The problem with all coatings is that any gap in the film can admit large amounts of rainwater, which cannot then escape by the same route. However breathable the film is, the imbalance between pouring in and breathing out is too great.

[Merryterry]

There are flexible resin coatings on the market that will withstand some substrate cracking. They do need some care in application and the correct 'bond break' primer, (i.e. a primer whose coating to primer adhesion is less than the tensile strength of the coating) It will then disbond rather than tear in the event of cracks appearing in the substrate. They do not need weeks of damp sacking over them.

Try:

I used to sell this product 15 years ago and it is first class. They no longer use Sales Agents so I lost the agency.

[Stuart Noble]

Looks like it's based on SBR. I don't really trust water based formulations when it comes to water resistance

[Merryterry]

Water Based formulations are perfectly OK for waterproofing. Water is only the carrier for the resin. I can quote hundreds of applications where I got Water Based Coatings specified and still all OK after many years. One that springs to mind is Shelton Water Tower at Shrewsbury. (on the old A5).

[Stuart Noble]

It's the things that have to be added to the resin for water to act as a carrier that are the concern. They end up in the finished film, making it more (if only fractionally) water sensitive. ISTR acrylics are very fussy about temperature and normally require 20 degsC to cure properly. Fine in a controlled environment but a bit hit and miss outdoors I would think. Maybe things have moved on since I last had reason to look at all this.

I can quote hundreds of applications

[Merryterry]

Water based resin coatings will cure at well below 20C but just take longer and need protecting from elements whilst curing. Most will cure down to about 5C.

[Stuart Noble]

The minimum film forming temperature (MFFT) of all but the softest resins is nearer 20, or at least it was last time I looked. The reason most acrylic gloss paint is soft and rubbery is that a harder resin would need a higher temperature to cure properly.