Jump to content

External Rendering


ryder72

Recommended Posts

Our house is being partially rendered on the outside and it is out intention to use a thin coat render system on render board. Having done some research here are my findings-

 

There appear to be broadly 2 options, Acrylic and Silicone.

Silicone is dearer but meant to be breathable and more flexible

Additives are available to inhibit algae build up

Silicone is meant to be better to washdown with a low pressure jet

Some of the higher end (dearer) brands like Sto insist on using their own branded renderboard, mesh and stopbeads etc but claim to offer better warranties and product suppport

Others more mainstream brands like Weber, Parex, Mapei dont offer such comprehensive support and are less prescriptive for the application. The product is freely available through builders merchants, so works out a little bit cheaper. There is a school of thought that these products are cheaper for a reason, but the reasons seem to be more subjective.

 

I am totally confused and while the render system itself is proprietary and will inevitably have minor differences, I cannot see how a product that has been around for nearly 40-50 years can have massive differences. I cannot understand how a Sto renderboard can be any different to any other. A good established brand like Knauf should be as good as any and probably offer a good saving too.

 

Does anyone have experiences/opinions on these types of systems, products and recommended applicators?

Link to comment
Share on other sites

I am going through the same thing at present. A company  that has a lot of followers on a plasterers forum is ProRend although I have yet to get quotes  from the three recommend installers 

Link to comment
Share on other sites

Our architect recommended STO, he said it is better than others (not sure of the basis for that claim - e.g. said Parex gives a more chalky finish).

 

I looked at a number of other options like Wetherby, Knauf, Brillux (via Greenspan, mentioned by MBC), but in the end the price of the finished system was not very different so I went with the STO. Do not understimate the cost of these, by the time you have added battens and got them aligned, boarded etc it adds up to a big number - very labour intensive and time consuming, the cost of the materials is a smaller portion. If I were to do it again I would try to focus on finding a more efficient system to apply (if such a thing even exists).

 

One of the issues we kept coming up with, but did not get a definitive answer to, was that TRADA recommend a ventilation gap behind the render for a timber frame house, hence a non-compliant system might void any future warranty claim.

 

STO did insist on their own complete system and an approved installer for the warranty to be effective. My builder installed the battens as per their spec.

 

We fell out with our applicator big time - that is a different story - quality and pricing issues, even though the references were good.

Link to comment
Share on other sites

I found that to get the 10yr warranty you  had to use the full system with ProRend it looks good from the made up samples.  I have priced up boards etc to see if they are loading the quotes.  Knauff were very good helping with the design 

Link to comment
Share on other sites

Ours is rendered using the Baumit.com render system. I will warn you their website is next to useless to find anything. We used the MC55W base coat which is a lime based render mixed from a powder, and their Silicon Top top coat that is available in a range of colours and textures, that comes ready mixed in a tub.  A fibrerglass mesh is applied from a roll into the base coat for extra strength.

Link to comment
Share on other sites

  • 2 weeks later...

Thanks for all your replies guys.

 

I am looking at multiple systems but getting quotes is  proving difficult. Lots of local chaps willing to buy some off the shelf product like Johnstones, Weber etc and put it on but completely clueless in working through the merits and demerits of the various available options, cost/benefit ratios etc.

 

I have a rather unrelated query.

 

We have render on the lower level and cladding on the upper.

 

Render is to be applied on a render carrier board and the board or render system itself doesnt require a ventilated cavity. However, the frame will require ventilation achieved with treated battens with cavities closed off with insect mesh, top and bottom. The only recommendation I can see is from TRADA stating that the batten must be a minimum of 6 times screw diameter and the screws for 12.5mm renderboard need to be 4mm making it a minimum vent cavity of 24mm. The obvious solution is a 25*38mm treated batten.


The cladding needs to overhang the render and the render system build up is 12.5mm render board and 6mm render making its 18.5mm, say 20mm plus batten thickness = 45mm. The cladding is going to be board on board using 18mm boards and the renderers  recommend that the inner boards are ideally 30mm past the render (more is better) to minimise any render staining risk. This makes the need for the battens for cladding a minimum 75mm so making 47 * 75 battens the obvious choice. This is obviously going to be both expensive and heavy. TO make things a bit more complicated, the battens are to be horizontally fitted with a taper to angle any water that gets on it to run down the taper and flow away. I cant get my head round what this tapering will do to the treatment.

 

Does anyone have any thoughts on-

1. The battening solution proposed

2. The 25mm cavity and whether this is adequate?

3. The taper required on the cladding battens

 

Thanks

 

 

Link to comment
Share on other sites

I have been looking in to this exact detail myself with vertical cladding. You can buy pre-treated cant rails @ 47x75 off the shelf. A bit over-engineered but designed for fencing and i cant find anything smaller. 25mm cavity should be fine provided sufficient ventilation grilles/gaps left at openings and top and bottom of cladding.

Link to comment
Share on other sites

Our specification is an aluminium capping at the top and open below. At the top, the coping will overhang the render or cladding by a minimum of 35mm and both will stop 20mm shy of the capping to allow ventilation.

 

I like your idea of using cant rails.

Link to comment
Share on other sites

I'm not sure you need the tapered horizontal batten for vertical cladding if its board on board.

 

That is exactly what I have and think somewhere on the TRADA guidance it says the taper is only needed if there is a chance water can get through, like if there is a gap in the cladding between the boards, but if it's board on board on water can get through.

 

Can you post a link to the guidence saying you need to have tapered rails.

 

Link to comment
Share on other sites

36 minutes ago, JSHarris said:

I'd avoid the insect mech, as it's a pain to position top and bottom, plus it's expensive.  Commercial kitchen stainless steel pan scourers are both cheaper and easier to use.

Jeremy, did you stretch the scourer mesh. Its generally pretty tightly packed isnt it?

 

I have seen the quantity I need for under £50.

 

38 minutes ago, Calvinmiddle said:

I'm not sure you need the tapered horizontal batten for vertical cladding if its board on board.

 

That is exactly what I have and think somewhere on the TRADA guidance it says the taper is only needed if there is a chance water can get through, like if there is a gap in the cladding between the boards, but if it's board on board on water can get through.

 

Can you post a link to the guidence saying you need to have tapered rails.

 

I havent seen that guidance specifically but all detailing for board on board batten shows this type of battening. I suppose you are right in that the change of water getting in with board  on board detail is very small but there is the possibility that the boards arent perfectly straight and prone to come degree of warping opening up gaps for water ingress.

Link to comment
Share on other sites

19 minutes ago, ryder72 said:

Jeremy, did you stretch the scourer mesh. Its generally pretty tightly packed isnt it?

 

I have seen the quantity I need for under £50.

 

I havent seen that guidance specifically but all detailing for board on board batten shows this type of battening. I suppose you are right in that the change of water getting in with board  on board detail is very small but there is the possibility that the boards arent perfectly straight and prone to come degree of warping opening up gaps for water ingress.

 

Thats the thing about water, it is both canny and incredibly patient - it will find its way in eventually! 

Link to comment
Share on other sites

Instead of the one thick batten can you not use a vertical counter batten and then your horizontal. To make up the 75mm

 

should you not have a counter batten any way, what way is the slope on the battens going to go ? 

If you slope it inwards water could run towards the house, if you slope it out it will run to the back of the cladding. Surely with a counter batten you provide a gap for it to run off and drop out of the vent gap at the bottom. 

Link to comment
Share on other sites

The slope is meant to be away from the house.

 

I still think the slope is still required and I am not sure battening and counterbattening is going to help.  If anything, it would probably be more expensive on labour.

Link to comment
Share on other sites

1 hour ago, ryder72 said:

Jeremy, did you stretch the scourer mesh. Its generally pretty tightly packed isnt it?

 

I have seen the quantity I need for under £50.

 

 

Yes you can unravel them to form linear rolls of the stainless stuff that fits snugly in a 25mm batten space.

Link to comment
Share on other sites

We have vertical half lap boards for cladding in one area. The detail we have is vertical batten over the membrane, screwed into the board, with horizontal cross battens on which the cladding is nailed. The cross battens are tapered so water can run off towards the wall.

 

In our case counter battening is needed for effective run off of water or condensation.

Link to comment
Share on other sites

10 hours ago, JSHarris said:

 

 

Yes you can unravel them to form linear rolls of the stainless stuff that fits snugly in a 25mm batten space.

Thank you. Will look into this.

 

8 hours ago, ragg987 said:

We have vertical half lap boards for cladding in one area. The detail we have is vertical batten over the membrane, screwed into the board, with horizontal cross battens on which the cladding is nailed. The cross battens are tapered so water can run off towards the wall.

 

In our case counter battening is needed for effective run off of water or condensation.

Any chance you can post a photo?

Link to comment
Share on other sites

10 hours ago, JSHarris said:

 

 

Yes you can unravel them to form linear rolls of the stainless stuff that fits snugly in a 25mm batten space.

 

I used stainless steel wire wool. It's used in exhaust systems, I've still got a roll left over somewhere.

Link to comment
Share on other sites

Re the battens. I have been in contact with a couple of the technical departments for the different boards.

They all ask that the timber is at least 75mm face and kiln dried and treated. I think it is to stop movement. They also only specify vertical battens with gaps rather than counter battened.

Link to comment
Share on other sites

1 hour ago, ragg987 said:

We used 80x35 batten at 600mm centres as specified by STO. Detail of batten and board showing expansion joint.

rendercarrier.jpg

 

What is the detail above windows and door for the above?

 

I really would like to get away from a block outer leaf but the traditionalists keep giving me the fear about resale value and also mortgage availability :( 

Link to comment
Share on other sites

40 minutes ago, Rossek9 said:

I really would like to get away from a block outer leaf but the traditionalists keep giving me the fear about resale value and also mortgage availability :( 

 

+1. 

We were also very very strongly advised against anything other than cavity and block/render* due to our exposed location. 

 

*brick is a no go on our national park. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...