[drive surgeon]

was cleaning two clay block paving drives today, came up well but there where black marks all over which i think is lichen, it wont shift with cold turbo.  wonder if hot turbo would shift it?  or do i need chemicals.  also the joints are wider on clay blocks so you get more sludge and use more sand when re sanding the joints!

[trevor perry]

hot does move them but it is still very slow , much easier to use chemical first.

[drive surgeon]

what you use trevor for lichen?

[Griffus]

Clay blocks are always a pain when resanding. Be careful not to use too much sand as it blows around for weeks. I use a blower and a top quality brush and still go over a good few times!

As for the black marks; I assume the blocks are the light coloured (yellowy orange) cheap and nasty ones? If so I have done a good few of these and I have come to the conclusion that it is not always possible to remove this type of mark completely.

I confess to only using cold water. I am convinced that due to the porosity of the clay that the lichen are absorbed in to the block itself. In my experience this only happens with the cheap and nasty light coloured clay blocks.

I have a few before and after pic's if you are interested.

Regards

[BDCS]

I thought clay pavers were cheap til I had to buy a pack - they cost the customer £400 !

[steve_doyle]

How come you needed to buy some for a customer?

[BDCS]

I cleaned her drive then she got out of her car onto the mud and walked it across the drive, then asked if I could pave the area for her so that went on the winter list

[trevor perry]

what you use trevor for lichen?

bleach moves it but beware anyone walking it into house as it will bleach their carpets so i only use this occasionally, the best method i have found is to treat areas with neat algon 2 days before doing the job then when you come to wash area it does come off.
  a chemical called chloras works really well but once again it is a bleach so you must beware people walking it into their properties.

[drive surgeon]

yes its that cheap and nasty orange clay pavers! 

[mark.laycock1@ntlw]

i had this trouble with clay blocks but found out later on that there garden put iron lawn killer on to kill the moss.

am interested in those photos.

[Griffus]

This was as good as this part of this job got and is the best example I have of lichen being absorbed into the clay. I only see this with these cheap clay blocks.

For the record Clay blocks tend to me more expensive to buy than concrete and more of a pain when resanding.

One important point to note. The customer was delighted with these results, along with the rest of the job which comprised of concrete blocks. He was going to have these clay blocks replaced but after the clean decided to keep them.

[mark.laycock1@ntlw]

they look great .can you use hot water on clay blocks? did you use any chemcials.

[Griffus]

We use only cold water and rarely use any chemicals.

We also clean new build exteriors using cold water and brick acid with great success.

I can't see any real need for hot water unless you are involved in the pressure washing of commercial premises and maybe graffiti removal or similar.

[Chris Galloway]

that looks great! I wouldn;t have cared about the small black dots, its add a bit of character, dont want it looking too new.