Roughcast

[Andy]

Folks,

My boundary wall-building programme has reached the point where I need to think about finishing off. I've rendered the wall with a 1/2" of lime/cement mortar either side, and that is going off e'en as we speak.

As I understand it roughcast involves making up a sort of concrete made with small aggregate (3/8" down to sand size ) and flinging it at the undercoat of render.

Anyone done this? Any tips? I figured on getting a small fire shovel, loading that up and flinging it from a great distance, varying the angles of application to get an even finish, sounds good in theory but what about in practise. I'm worried the roughcast will bounce off*, presumably I may need a thin (1/4"?) topcoat render layer to fling it onto, and I'm going to try and keep that wet by spraying, so the roughcast sticks.

I thought I might try limewash as a finish.

• Which is always what happened when I tried pebbledashing.

Andy.

Andy.

[John Rumm]

How rough do you want your roughcast?

The much of our place is finished with a roughcast / stipple render, and when I was doing the new gable end for my loft conversion I wanted to match it. I found I was able to get an almost perfect match by simply rendering the top coat as normal, then then giving it a firm tamping all over with a stiff dustpan brush.

see bottom two photos on this page:

Anyone done this? Any tips? I figured on getting a small fire shovel,

One thing I found is that new rough render is a PITA to paint!

[Andy]

Thanks for that John, I'm impressed, that looked like a big job! It's not easy to tell how much texture you achieved from your photos, but I'm looking for quite a lot, so I may try the roughcast route and see how it goes.

I've had problems already, listened to a neighbours advice, and left the battens on overnight: of course when it came to pulling them off I pulled off/blew quite a bit of the render undercoat. I had to go around tapping the render with my knuckle to find the detached areas and chop them out and renew. He also said that I didn't need to scratch the undercoat as the texture from using a wooden float on it would be enough to give the topcoat a key, but I'm thinking he speaks with forked tongue now!

I think I will practice roughcast on a piece of plasterboard. For the curious, my wall has exposed red brick-and-a-half piers capped with a thick ( 4.5" ), flat-topped cast concrete coping painted white, blockwork finished ( hopefully ) with roughcast ( limewashed ), and the wall finished with 1.5" Welsh slate coping.

Andy.

[Newshound]

When you say roughcast do you mean tyrollean rendering? This is done by splattering a suitable mix with a hand cranked splattering machine (about £50 from Screwfix).

[Andy]

No no, I've examined the Tyrolean angle but don't find it offers enough texture*. Roughcast is sand and aggregate up to 3/8": thanks for the info anyway.

*Getting all philosophical, I've noticed one of the things in architecture that is usually present in attractive structures is texture: multi-coloured bricks, variation in slates/tiles, rough-rendered walls etc.

Andy

[John Rumm]

Twas about four days to do all the render IIRC (including stuff like buying materials, cadging a cement mixer, and fixing all the corner profiles and drip beads etc).

Probably not as much as it sounds like you want then. The best photo I can find that gives some idea is this one:

> I'm looking for quite a lot, so I may try the roughcast route and see > how it goes.

Sounds like a good plan....

Stick a piccie up somewhere when done so we can all admire!

[legin]

Extremely messy job but can look stunning when done right. For best results it is "thrown" at the scratch coat. If you have already applied

1/2" render both sides then the weight is probably going to pull it off the wall. Jobs I have done have been 3 and 1 scratch coat. Rough cast mix made of 1 cement 2 sand and 2 stone ( last job was cantebury spa, previously have used granno dust but sometimes all dust and no body). The mix needs to be wet, almost runny. If it is too stiff it will stick to the walls like clumps and will be very patchy. Try small areas and scrape off until you get the mix right. If you get a good runny mix then when you fling it at the wall it will splat and even out the surrounding areas that have already been rough cast. Not too runny it will all slide down the wall. Good Luck.

Regards Legin

[The Natural Philosopher]

Surely that is the dreaded pebbledash..?

[legin]

Depends on the region. In the midlands the pebble dash is litterly dry pebble thrown at the wet top coat so that the pebble remains exposed. In Scotland rough cast is termed Harl. I tend to think of rough cast as being the wet mix thrown at the scratch coat. Mind you I have no doubt that regionally the mix will vary as will the technique. I know that you cannot find many people who will carry out such a messy job.

Regards Legin

[Ian White]

Except, perhaps, in Scotland. We had some harl done last year on an upstairs gable wall - lovely job, completely uniform with no patches, and it has set like iron. As Legin says, this is wet-mix, not pebble-dash. The surface finish is the uniform grey mix colour, with no loose pebbles whatever. The rough texture does exactly what it's supposed to, encouraging the water to fall off the wall in drips rather than running down in sheets.

I wasn't here at the time, and have no idea how the builder got it all to stick on the wall, leaving nothing on the window-ledges or the ground beneath.

As John Rumm says, it's a PITA to paint... and a right royal PITA to drill accurately. The only way I've found is to mark the wall, level off the stones very carefully using a small cold chisel, mark again, and "centre-punch" the holes by hand with a small Rawldrill.