Rendering onto slate

JimiJames

Please help. Rendering onto slate tiles. I need to make a repair to a wall clad with scantle slate tiles. Quite a few tiles are missing and replacing the tile is not an option. I've searched the internet regarding mix ratios, priming, waterproofing additive etc. and am now very confused. I tried a 3:1 mix of building sand and Mastercrete, with a glug of plasticiser (only an 8lt bucket full). I managed to get it to stick, put a second coat on a few hours later, but the next day it was very powdery and most of it came off very easily. I have Sika MaxMix, enough for 2.5 tonnes of mix, I'm guessing I'll only need a few drops for a bucket full? The wall is in the sun most of the day.
Any advice from someone in the know would be greatly appreciated. A scaffold is required for access, so I want to get it right.

Furts

You will be lucky if your rendering idea does work. The way you have described your proposals, and your reasoning, sound crazy. Step back and consider some fundamentals - slates will have mechanical fixings, some of these may be missing, others corroded. Then there are the battens - ditto - plus rot. To attempt to render over this is pointless.

Also slates are a flexible, moving surface and render is rigid. The two do not mix unless you introduce perhaps galvanised lath sheets. But then these have to be fixed mechanically back past the battens. All round a competent plasterer could do the job. Whether they would want to do the job is up for debate. Then add in the concept of guaranteeing their work and my intuition is the job is a non starter.

Lorian

Furts has summed up the issues nicely - but do post a wide angle and close up photo - perhaps someone will come up with an alternative method of repair when they can see it.

You will need to post the photos on some free photo site and post up broken links to them.

tonyh66

the correct way to do it is to remove the slates and render the wall (properly)

road2manchester

slates move,,,,,, render won't, it will be on the floor within a few weeks.
Remove them all or get it repaired proper like ....
Quick fixes rarely work.

JimiJames

tonyh66 wrote: »

the correct way to do it is to remove the slates and render the wall (properly)

I realize that this has to be done, but financial constraints dictate.

JimiJames

Furts wrote: »

You will be lucky if your rendering idea does work. The way you have described your proposals, and your reasoning, sound crazy. Step back and consider some fundamentals - slates will have mechanical fixings, some of these may be missing, others corroded. Then there are the battens - ditto - plus rot. To attempt to render over this is pointless.

Also slates are a flexible, moving surface and render is rigid. The two do not mix unless you introduce perhaps galvanised lath sheets. But then these have to be fixed mechanically back past the battens. All round a competent plasterer could do the job. Whether they would want to do the job is up for debate. Then add in the concept of guaranteeing their work and my intuition is the job is a non starter.

This is part of an email conversation I had with a local Cornish traditional roofing company.

Hello James,

Thanks for the photos.

The section as a whole does not look to be in a very good condition at all. I'm not sure of your plans with the property but if you are looking to repair and trying and get a few more years out of it, I would render the missing sections with sand/cement mortar. I realise that this sounds like a 'bodge' but it would serve its purpose until you are ready to replace. I presume that you are not a listed building or in an article 4 direction area as the slates on your roof are cement fibre, so when you come to replace you will not have to replace like for like.

If you want the slates repaired properly, you would be looking at an approximate cost of £380.00 + Vat.

Let me know if you have any further questions.

Many Thanks

Damon Wynne | Operations Director
JS Roofing and Building Ltd

JimiJames

Trying to post a link to a photo but as a new member, MSE won't let me. Something about spammers clogging up the site!
I've done it now anyway, the rendering!
Have a look at the results on Facebook 'DIY Top tips on a BUDGET'. If you're interested. I'll let you all know if it all falls off. Lol

Furts

JimiJames wrote: »

Trying to post a link to a photo but as a new member, MSE won't let me. Something about spammers clogging up the site!
I've done it now anyway, the rendering!
Have a look at the results on Facebook 'DIY Top tips on a BUDGET'. If you're interested. I'll let you all know if it all falls off. Lol

Well done, it is always uplifting to get an update on what happens and feedback on info given on the forum. So many thanks for this.

It even gives the forum folks a bit of credit, or kudos. It looks like your email from JS Roofing is saying much along the lines of what was put across to you on the forum.