# Forum Home Renovation Roofing  Lichen on terra-cotta roofing tiles

## opalmagic

What is the best way to remove lichen on terra-cotta roof tiles, please? The house is about 35 to 40 years old, a three bedroom, brick veneer, just recently rendered. The roof lichen is very obvious since having the rendering done.  
Has anyone used the product called "Wet  and Forget"? 
Apparently it takes up to 12 months to completely work. 
Would really appreciate any advice or help on this problem, the house is in the Cranbourne area. 
Thanks in anticipation.

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## johnc

Had a very heavy build up of moss on glazed terra-cotta, wet and forget upset it but didn't kill it so we had it water blasted, we intend to give wet and forget a go again this year to attack the bits that are beginning to come back.

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## phild01

Pressure spray was what I did recently, though I think you will still be left with staining.  Mine was polycarbonate roofing and it didn't want to leave in any hurry.

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## justonething

Had water blasted my roof back in the 90s but I remember water got in the ceiling space and the roof insulation got all wet in some places. I understand a mixture of hot water and steam is much better. Not sure if it is allowed anymore, but a solution of copper sulphate seemed to do the trick.

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## Oldsaltoz

I have used the Wet and forget product with very good results, the trick seems to be to wet the area to the point the product starts run off. Then you need some rain to wash the dead material away. 
Areas like your roof tiles seem to benefit by a second coat when the first one has done most of the work, and again wait for rain. 
No good at all in areas that rain will not fall on it though. 
Also works well on concrete, did the gutters a few years ago and still the cleanest in the street. 
I suspect high pressure blasting leaves a surface more suitable for more growth. 
Have also used it external brick walls that were damp because the original sealant was not correctly applied. waited a few moths and re sealed it for the client. 
Good luck and fair winds.   :Smilie:

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## DuckCommander

I pressure blasted what I could do safely on my 30 degree terracotta roof. The bits I didn't do I used 30 seconds roof cleaner. I mixed up 100L in a wheelbarrow and used a 12V pump to spray from a ladder at the eaves. Got it all done in under half an hour.
I was initially quite annoyed with seemingly little effect over 6 months until we had the big rain last weekend. I noticed bits of moss and lichen around on the ground which have come off the roof. It appears it relies heavily on weathering to work.
I experimented with roundup on one small area that was the worst of the roof about 12 months ago. 90% of the mould/lichen has come off. Roundup is certainly a lot cheaper...

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## phild01

> I experimented with roundup on one small area that was the worst of the roof about 12 months ago. 90% of the mould/lichen has come off. Roundup is certainly a lot cheaper...

  Gotta try this idea, wet and forget has a ridiculous price tag.

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## Ozcar

> Gotta try this idea, wet and forget has a ridiculous price tag.

  Our local hardware store had Wet and Forget, but also something similar branded "30 Seconds" which was a lot cheaper, and which, according to the label has the same concentration of the same active ingredient. I got some of the "30 Seconds" stuff, but I have not got around to trying it yet.

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## opalmagic

Thanks, johns, for your helpful response. Yes, I gathered that the product takes a fairly long time to work, therefore wondering if it was going to work at all.

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## opalmagic

Thanks very much for all this info!

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## opalmagic

Thanks, and I agree about the high price of the product in question!

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## opalmagic

Did think about using a pressure hose, but I was worried about the probable (?) water damage! Thanks for your response.

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## opalmagic

A few years ago  I used "30 Seconds" with very good results on a mossy, slippery fernery path! Good idea to use it on the tiles, thanks!

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## justonething

> I experimented with roundup on one small area that was the worst of the roof about 12 months ago. 90% of the mould/lichen has come off. Roundup is certainly a lot cheaper...

  Does it really work on the black mould?

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## jamestaylorad

If we are going to professionaly then Wet and Forge is the best product with very good results. But if the problem is big and then you have to contact any roofing expert, they give you helpful advice and a quote.

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## Ozcar

> A few years ago  I used "30 Seconds" with very good results on a mossy, slippery fernery path! Good idea to use it on the tiles, thanks!

  I think there is more than one "30 Seconds" product. The one I got is called "Roof Treatment", but I'm pretty sure the place I got it also had some other stuff which was more for garden paths or something. 
  If I look at the "30 Seconds" web site now, for some reason I don't see "Roof Treatment", but there is "Outdoor Cleaner" and "Spray & Walk Away", with the latter being promoted for use on roofs.  
I did however also pick up several places, including Bunnings and Masters, selling the 30 Seconds "Roof Treatment" product (it is around $36 for 5l compared to $100 or more for "Wet and Forget").

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## DuckCommander

> Does it really work on the black mould?

  The area had a lot of lichen and there was black mould and it has stripped most of it. I will see if I can conjure up some before and afters when I get some time. I should have some before and afters with the 30 Seconds treatment as well. 
When I was pressure cleaning I was concerned about water getting in the roof cavity but I experimented in one area with my 4300psi, 15 litre/min petrol powered washer trying various angles etc then checked the roof cavity. It was all good inside, even when attacking the toe of the tiles. I was a bit surprised, but then again they're at 30 degree pitch! 
With the pressure washer, forget the electric junk. They do not have the grunt to remove lichen, unless you work on a 5cm x 5cm area for 3-5 min. It's all about the flow rate not psi. The cheap electric ones claim high psi but flow less than 5 l/min. You want a petrol one capable of at least 12 l/min.  
I highly recommend a 12V sprayer if going to the 30 second, wet and forget, roundup route. I went el cheapo and bought a 12V diaphragm pump and 240-12V transformer from ebay, used some garden hose lying around, a 40 cent tap and the straight spray bit from my pressure washer. Of course I made a enclosure waterproofing the elektrikkity from the pump. I was able to spray up to the apex from the eaves and saturated the whole roof in under 30min. It would be crazy to do it with a backpack sprayer. 
Oh yeah, I know a former "roof restorer", they only used roundup on roofs prior to painting. On a side note it is ridiculous how much they earn and charge.

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