I want to make some exposed aggregate finished concrete blocks to
repair an existing garden wall. They're about 9"x8"x8", tapered
slightly so that they interlock each other a bit like lego.

Is there a book I can buy, or a website that explains a good step by
step procedure?

I've had some success by trial and error, but I'm not getting it quite
right.
I've made formwork out of wood
I'm using a mix 2 sand 2 cement 4 gravel,
Once its in the mould, I screw a lid on, turn the mold on its side,
take off the side and pour extra gravel on the face. Ditto the other
side.
I can get it almost right, but parts will be pitted where the
additional gravel has been too thick.



Here's a pic of an original http://homepage.ntlworld.com/tony.jeffs/block.jpg
(this may stop working as I'm changing isp)

tony

On 14 Apr, 14:23, "tonyjeffs" wrote:

I want to make some exposed aggregate finished concrete blocks to
repair an existing garden wall. They're about 9"x8"x8", tapered
slightly so that they interlock each other a bit like lego.

Is there a book I can buy, or a website that explains a good step by
step procedure?

I've had some success by trial and error, but I'm not getting it quite
right.
I've made formwork out of wood
I'm using a mix 2 sand 2 cement 4 gravel,
Once its in the mould, I screw a lid on, turn the mold on its side,
take off the side and pour extra gravel on the face. Ditto the other
side.
I can get it almost right, but parts will be pitted where the
additional gravel has been too thick.

Here's a pic of an originalhttp://homepage.ntlworld.com/tony.jeffs/block.jpg
(this may stop working as I'm changing isp)

tony

http://wiki.diyfaq.org.uk/index.php?...oncrete_Blocks
explains why that mix isnt recommended. Cant answer your q though.


NT

On Apr 14, 11:19 am, wrote:
On 14 Apr, 14:23, "tonyjeffs" wrote:



I want to make someexposed aggregatefinished concrete blocks to
repair an existing garden wall. They're about 9"x8"x8", tapered
slightly so that they interlock each other a bit like lego.

Is there a book I can buy, or a website that explains a good step by
step procedure?

I've had some success by trial and error, but I'm not getting it quite
right.
I've made formwork out of wood
I'm using a mix 2 sand 2 cement 4 gravel,
Once its in the mould, I screw a lid on, turn the mold on its side,
take off the side and pour extra gravel on the face. Ditto the other
side.
I can get it almost right, but parts will be pitted where the
additional gravel has been too thick.

Here's a pic of an originalhttp://homepage.ntlworld.com/tony.jeffs/block.jpg
(this may stop working as I'm changing isp)

tony

http://wiki.diyfaq.org.uk/index.php?...oncrete_Blocks
explains why that mix isnt recommended. Cant answer your q though.

NT

I think you can improve the quality of your seeded exposed aggregate
in one or both of two ways.
First, make sure the substrate has had time to settle, and allow te
cream to rise to the surface. At this point, the top surface will be
quite moist, and any aggregate that is seeded in should be easily
worked into the top surface. It is possible to seed too early, and
this will result in the aggregate sinking out of sight. It is a good
idea to use some method such a pressing, tapping, or rolling the
seeded aggregate inot the surface, in order to work it inot the
concreate fines, and produce a solid bond to the substrate.
Second, you may find it better to pour you molds to about 2 or 3 cm
from the top, using your regular concrete mix. Then, use a sand/cement
'mortar' mix to complete the fill, and seed the aggregate into that.
Allow the normal mixture to begin to just harden before adding the
mortar topping. This will allow the base to support the topping
mixture, but still provide a good bond between the layers. I have used
this method to create large stepping stones, as well as stair treads
and landings. Normally, I use a roller to press the aggregate into the
base substrate, but on these kinds of surfaces, it was not possible,
so I came up with this method as an alternative.
I have a couple of web pages that show some of these techniques:

http://members.shaw.ca/bomr/ExposedAgg.html
http://members.shaw.ca/bomr/Building_a_patio_bench.html

--- rod.

I think you can improve the quality of your seeded exposed aggregate
in one or both of two ways.
First, make sure the substrate has had time to settle, and allow te
cream to rise to the surface. At this point, the top surface will be
quite moist, and any aggregate that is seeded in should be easily
worked into the top surface. It is possible to seed too early, and
this will result in the aggregate sinking out of sight. It is a good
idea to use some method such a pressing, tapping, or rolling the
seeded aggregate inot the surface, in order to work it inot the
concreate fines, and produce a solid bond to the substrate.
Second, you may find it better to pour you molds to about 2 or 3 cm
from the top, using your regular concrete mix. Then, use a sand/cement
'mortar' mix to complete the fill, and seed the aggregate into that.
Allow the normal mixture to begin to just harden before adding the
mortar topping. This will allow the base to support the topping
mixture, but still provide a good bond between the layers. I have used
this method to create large stepping stones, as well as stair treads
and landings. Normally, I use a roller to press the aggregate into the
base substrate, but on these kinds of surfaces, it was not possible,
so I came up with this method as an alternative.
I have a couple of web pages that show some of these techniques:

http://members.shaw.ca/bomr/ExposedAgg.html
http://members.shaw.ca/bomr/Building_a_patio_bench.html

--- rod.

Thanks NT, I'll use that mix as described on website.

Rod,
the problem is I have to seed two opposite sides, the front and back
vertical sides of the block, which I do by turning each side upwards
in turn, but in doing this at least one of the sides tends to go
wrong. Maybe I need to be more careful about putting a single layer
of aggregate on what is effectively the bottom side?

I was thinking of trying it a different way, painting retarder on the
outsides of the block as soon as it is stable enough to loosen the
mold; then hosing it down after 24 hours to expose the surface
aggregate that is already in the mix. would this be a better approach?

Tony

Rod,
Is that your site? I read it already & found it v helpful. Having
read it, I don't think I'd have a problem with a flat surface such as
a patio or a driveway. It's the two sided aspect of my block.....

Tony

Rod
Is that your site. I already read it recently. It's v helpful and I
would have no probem I think following your advice on creating rough
driveway. The big problem is how to deal with the two opposing sides
of my block...

Tony

On Apr 15, 3:36 pm, "tonyjeffs" wrote:
Rod
Is that your site. I already read it recently. It's v helpful and I
would have no probem I think following your advice on creating rough
driveway. The big problem is how to deal with the two opposing sides
of my block...

Tony

I believe the method that you need to use is to apply a retardent gell
to the inside of the mold before you fill it. After the piece is de-
molded, the retardent will have left the surfaces uncured, and the
*integral* aggregate can be exposed by washing/brushing. This is the
method used to create exposed aggregate finishes on vertical surfaces
such as retaining walls. I have never done this, and as you know from
reading my web site, I am no expert, just a homeowner do-it-
yourselfer. A company (N.American) that supplies this stuff sent me a
link to their web sight. I don't know anything about them, or have any
connection to them whatsoever.
http://www.exposedaggregateconcrete.com/retarder.htm
Hope this helps.
--- rod.

On 15 Apr, 23:59, wrote:
On Apr 15, 3:36 pm, "tonyjeffs" wrote:

Rod
Is that your site. I already read it recently. It's v helpful and I
would have no probem I think following your advice on creating rough
driveway. The big problem is how to deal with the two opposing sides
of my block...

Tony

I believe the method that you need to use is to apply a retardent gell
to the inside of the mold before you fill it. After the piece is de-
molded, the retardent will have left the surfaces uncured, and the
*integral* aggregate can be exposed by washing/brushing. This is the
method used to create exposed aggregate finishes on vertical surfaces
such as retaining walls. I have never done this, and as you know from
reading my web site, I am no expert, just a homeowner do-it-
yourselfer. A company (N.American) that supplies this stuff sent me a
link to their web sight. I don't know anything about them, or have any
connection to them whatsoever.
http://www.exposedaggregateconcrete.com/retarder.htm
Hope this helps.
--- rod.

Yes that makes sense. I'll ask at the local builders yard.
I think I'll try lining my wooden formwork with polythene too, so that
it comes away from the block more easily.
It's a darn slow process trying to get it right - 2 days per block
during the trial-and error experimentation, so I hope to get it right
before I lose heart. I'll keep you informed, and when I get there ,
I'll make a web page on how to do it.

Thanks again
Tony

On 16 Apr, 08:41, "tonyjeffs" wrote:
On 15 Apr, 23:59, wrote:
On Apr 15, 3:36 pm, "tonyjeffs" wrote:

Rod
Is that your site. I already read it recently. It's v helpful and I
would have no probem I think following your advice on creating rough
driveway. The big problem is how to deal with the two opposing sides
of my block...

Tony

I believe the method that you need to use is to apply a retardent gell
to the inside of the mold before you fill it. After the piece is de-
molded, the retardent will have left the surfaces uncured, and the
*integral* aggregate can be exposed by washing/brushing. This is the
method used to create exposed aggregate finishes on vertical surfaces
such as retaining walls. I have never done this, and as you know from
reading my web site, I am no expert, just a homeowner do-it-
yourselfer. A company (N.American) that supplies this stuff sent me a
link to their web sight. I don't know anything about them, or have any
connection to them whatsoever.
http://www.exposedaggregateconcrete.com/retarder.htm
Hope this helps.
--- rod.

Yes that makes sense. I'll ask at the local builders yard.
I think I'll try lining my wooden formwork with polythene too, so that
it comes away from the block more easily.
It's a darn slow process trying to get it right - 2 days per block
during the trial-and error experimentation, so I hope to get it right
before I lose heart. I'll keep you informed, and when I get there ,
I'll make a web page on how to do it.

Thanks again
Tony

I'd try that too, brushing & hosing to expose aggregate. But I dont
think you need any retarder for that, concrete has very little
strength when first set, it takes a few days to have serious strength,
so you could do it after 24 hours or sooner.


NT

I'd try that too, brushing & hosing to exposeaggregate. But I dont
think you need any retarder for that, concrete has very little
strength when first set, it takes a few days to have serious strength,
so you could do it after 24 hours or sooner.

NT

I have created bricks by casting concrete in wooden forms/molds, and I
found that 24 hours was too soon to de-mold them. The edges and
corners were still too fragile, and ended up chipping off during the
extraction from the mold. At that point, there is no way at all that I
could have exposed any of the aggregate without extremely vigorous
brushing and spraying. I think people use the retardent for a reason.
I have never seen the stuff for sale at any home centre style of
retailer. I think you would have to go to a wholesaler that
specializes in serving the concrete contracting industry.
--- rod.

I actually bought 5l of retarder in a local builder's yard (Beesley
and Fildes). It is a combined plasticiser/retarder and is liquid
rather than gell. I think it will help because I've found it tricky to
judge the best time to spray without it. Too soon, and I wash holes
into the surface. And too late is too late.

Another unavoidable problem is that granite chippings are different
every time I buy a bag. I could do with adapting the technique so that
I save the 'best finish' chippings for the outer coat, maybe add
timber slips to the front and back of my mould so that I can make an
undersize block, then add the last half inch either side as soon as it
is strong enough to sustain its shape.

An idea that I thought of is to retard one side, just the back face.
This means I can have the front face upwards, seed it etc as per Rod's
patio, wait till it is setting, then flip it over and work on the
retarded back face later.


I could do with a small manual cement mixer rather than mixing a
small amount in a bucket for my trial blocks. Save my back!
And an old pan for measuring quantities.

tonyjeffs wrote:
I actually bought 5l of retarder in a local builder's yard (Beesley
and Fildes). It is a combined plasticiser/retarder and is liquid
rather than gell. I think it will help because I've found it tricky to
judge the best time to spray without it. Too soon, and I wash holes
into the surface. And too late is too late.

Another unavoidable problem is that granite chippings are different
every time I buy a bag. I could do with adapting the technique so that
I save the 'best finish' chippings for the outer coat, maybe add
timber slips to the front and back of my mould so that I can make an
undersize block, then add the last half inch either side as soon as it
is strong enough to sustain its shape.

An idea that I thought of is to retard one side, just the back face.
This means I can have the front face upwards, seed it etc as per Rod's
patio, wait till it is setting, then flip it over and work on the
retarded back face later.


I could do with a small manual cement mixer rather than mixing a
small amount in a bucket for my trial blocks. Save my back!
And an old pan for measuring quantities.



Sounds like the problems you get making a fruitcake i.e. getting the
ingredients to stay where you put them.
I'm always amazed how little plasticiser it takes to replace most of the
water you would normally have to use but I don't know if that makes for
a better end product in your case.

On 16 Apr, 20:40, wrote:

I'd try that too, brushing & hosing to exposeaggregate. But I dont
think you need any retarder for that, concrete has very little
strength when first set, it takes a few days to have serious strength,
so you could do it after 24 hours or sooner.

NT

I have created bricks by casting concrete in wooden forms/molds, and I
found that 24 hours was too soon to de-mold them. The edges and
corners were still too fragile, and ended up chipping off during the
extraction from the mold. At that point, there is no way at all that I
could have exposed any of the aggregate without extremely vigorous
brushing and spraying. I think people use the retardent for a reason.
I have never seen the stuff for sale at any home centre style of
retailer. I think you would have to go to a wholesaler that
specializes in serving the concrete contracting industry.


Interesting. Last time I did concrete work I did most of the brushing
after 1 day, and a bit after 2 days, and it came away easily.


NT