Rendering underside of concrete lintel s/c

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PotatoSack

New Member
Hi Guys,

There are many ways of tackling this issue. I've heard gripfilling plasterboard, coat PVA onto lintel, mix PVA into s/c, meshing into scratch. I will be doing some s/c rendering onto an exterior wall with a garage lintel that will need to be rendered on the underside, and I've always felt a bit iffy about it due to its positioning, and having had bad experiences with them in the past. So rather than staying in the dark about it, I'd like to know what's worked for you guys, and whether there is a consensus amongst the more experienced renderers out there as to best practices.
 
That's a brill idea mate. Have you tried rend aid?

P.S. how would you scud with a harling trowel? since it's underside, I would imagine a lot of it would fall off - troweling it would be better, but then the finish would be smoother - although I could just scratch it once I've laid it with the trowel.
 
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PotatoSack said:
That's a brill idea mate. Have you tried rend aid?

P.S. how would you scud with a harling trowel? since it's underside, I would imagine a lot of it would fall off - troweling it would be better, but then the finish would be smoother - although I could just scratch it once I've laid it with the trowel.
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I've never seen rendaid in Ireland.As regards using a Harling trowel it's not that difficult to do underneath.Just make sure and cover anything that needs it.
 
Thanks. What do you think I should do with the top coat? I would imagine that once I've laid on the top coat, and begin to flatten/darby it to remove excess, that large chunks will fall off (as was the case with the scratch coats, and I wasn't doing anything to them!).
The mix was 4:1 plastering-sand : opc and a dash of freeflo.
 
If your unsure best get a good local plasterer to do it.If it's your own property them fair enough you'll be the one looking at it, but don't chance it for a paying customer.As for chunks falling off I don't like the sound of that.How long are you plastering?.
 
It's a self build. I've got a few years of skimming under my belt, still quite new to rendering though. Although I've done most of the rendering and it's looking good, it's just the lintels that are giving me issues.

With that said, what I mean is a s/c mix doesn't have much suction, so it can fall off quite easily if it's not got enough water or a plasticier. But since this is on the underside and I'm fighting gravity, I suspect that once I've thrown the top coat on, and start removing excess with my darby that chunks of it might fall off. I just want to know how I could mitigate that.
I could apply some SBR onto the final scratch coat, or I could mix some SBR into the top coat? So a 5:1 sand:cement and and a dash of SBR is what I'm thinking for the topcoat, but not sure if this is the best way to go.
 
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How did you resolve this in the end?

I have a similar job.

1.I will probably scud with a cement and SBR mix
2.Then paint undiluted SBR onto the scud.
3.Apply a thin Scratch Coat 1 (5mm max) before SBR dries
4.Then paint undiluted SBR onto Scratch 1.
5.Apply a thin Scratch Coat 2 (5mm max) before SBR dries
6.Paint undiluted SBR onto Scratch 2
7.Apply a thin finish coat (5mm max)

Thin coats = Less weight = less of a battle against Gravity
 
Self Build said:
How did you resolve this in the end?

I have a similar job.

1.I will probably scud with a cement and SBR mix
2.Then paint undiluted SBR onto the scud.
3.Apply a thin Scratch Coat 1 (5mm max) before SBR dries
4.Then paint undiluted SBR onto Scratch 1.
5.Apply a thin Scratch Coat 2 (5mm max) before SBR dries
6.Paint undiluted SBR onto Scratch 2
7.Apply a thin finish coat (5mm max)

Thin coats = Less weight = less of a battle against Gravity
Click to expand...

What a load of fecking about. A plasterer would give it a coat of rend aid.
 
Self Build said:
How did you resolve this in the end?

I have a similar job.

1.I will probably scud with a cement and SBR mix
2.Then paint undiluted SBR onto the scud.
3.Apply a thin Scratch Coat 1 (5mm max) before SBR dries
4.Then paint undiluted SBR onto Scratch 1.
5.Apply a thin Scratch Coat 2 (5mm max) before SBR dries
6.Paint undiluted SBR onto Scratch 2
7.Apply a thin finish coat (5mm max)

Thin coats = Less weight = less of a battle against Gravity
Click to expand...
I think abit more sbr will do the trick
 
Self Build said:
How did you resolve this in the end?

I have a similar job.

1.I will probably scud with a cement and SBR mix
2.Then paint undiluted SBR onto the scud.
3.Apply a thin Scratch Coat 1 (5mm max) before SBR dries
4.Then paint undiluted SBR onto Scratch 1.
5.Apply a thin Scratch Coat 2 (5mm max) before SBR dries
6.Paint undiluted SBR onto Scratch 2
7.Apply a thin finish coat (5mm max)

Thin coats = Less weight = less of a battle against Gravity
Click to expand...
God that’s a long process so long as the scratch coat is stuck to lintel and you top the next day never had an issue. I’ve double bubble them before
 
devneydutch said:
God that’s a long process so long as the scratch coat is stuck to lintel and you top the next day never had an issue. I’ve double bubble them before
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f**k SBR I won’t use it as it’s too messy and gets everywhere. I would just use pva on the scratch coat then wet down for topping. I know I will have everyone back up about using pva outside but what do u think the old boys of done?
 
Self Build said:
How did you resolve this in the end?

I have a similar job.

1.I will probably scud with a cement and SBR mix
2.Then paint undiluted SBR onto the scud.
3.Apply a thin Scratch Coat 1 (5mm max) before SBR dries
4.Then paint undiluted SBR onto Scratch 1.
5.Apply a thin Scratch Coat 2 (5mm max) before SBR dries
6.Paint undiluted SBR onto Scratch 2
7.Apply a thin finish coat (5mm max)

Thin coats = Less weight = less of a battle against Gravity
Click to expand...
There’s no such thing as gravity @Dollar will tell you that!!!
 
devneydutch said:
God that’s a long process so long as the scratch coat is stuck to lintel and you top the next day never had an issue. I’ve double bubble them before
Click to expand...
Got the job done in two passes. Painted on some undiluted SBR with a paintbrush. Brilliant stuff but you need to apply the scratch coat really quickly.

Once the scratch coat is stuck, finish coat is not an issue.
 
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