I've got a rear extension built of thermalite blocks which have been
rendered. I want to fix some trellis to it for some climbing plants,
and also an outside light. I've just been reading some archived posts
about the problems of getting a good fixing in this stuff - obviously
some trellis with a bit of clematis on it doesn't present the same
problem as putting up kitchen cabinets containing the family silver, so
I reckon I should be OK with some long plugs and screws.

What's bothering me more is that I do remember being told about
penetrating damp problems being created by puncturing the render with
screws in situations like this. Anyone have any experience of this?

The message .com
from "Martin Pentreath" contains these words:

I reckon I should be OK with some long plugs and screws.

I use polyurethane foaming glue on thermalite blocks. Wash the hole out
with a water pistol and dip the wallplug in the glue and shove it in the
damp hole. It'll never come out.

I'd definitely use stainless screws.

--
Skipweasel
Pay no attention to that man behind the curtain.

Guy King wrote:

I use polyurethane foaming glue on thermalite blocks. Wash the hole out
with a water pistol and dip the wallplug in the glue and shove it in the
damp hole. It'll never come out.

I'd definitely use stainless screws.

Thanks for the tip. I'm worried about this issue of puncturing the
render though, and letting dampness through into the blocks. Anyone
have any thoughts, or am I being paranoid?

"Martin Pentreath" wrote in message
oups.com...
Guy King wrote:

I use polyurethane foaming glue on thermalite blocks. Wash the hole out
with a water pistol and dip the wallplug in the glue and shove it in the
damp hole. It'll never come out.

I'd definitely use stainless screws.

Thanks for the tip. I'm worried about this issue of puncturing the
render though, and letting dampness through into the blocks. Anyone
have any thoughts, or am I being paranoid?


The issue is not letting damp into the blocks, they have a closed cell
structure and will not transmit damp through to the internal wall. You need
to be concerned (in the long term) about allowing moisture behind the
render, which might make the render 'blow' over a few winter cycles.

I would seal the hole through the render with silicon to ensure that the
water does not get behind the render

SalesGuy

salesguy wrote:
"Martin Pentreath" wrote in message
oups.com...
Guy King wrote:

I use polyurethane foaming glue on thermalite blocks. Wash the hole
out with a water pistol and dip the wallplug in the glue and shove
it in the damp hole. It'll never come out.

I'd definitely use stainless screws.

Thanks for the tip. I'm worried about this issue of puncturing the
render though, and letting dampness through into the blocks. Anyone
have any thoughts, or am I being paranoid?


The issue is not letting damp into the blocks, they have a closed cell
structure and will not transmit damp through to the internal wall. You need to be concerned (in
the long term) about allowing moisture
behind the render, which might make the render 'blow' over a few
winter cycles.
I would seal the hole through the render with silicon to ensure that
the water does not get behind the render

SalesGuy

all good advice from the others, and you are right to be concerned about
the render blowing. do you have enough floor space to build some planters
with 2" x 2" x 8' uprights fixed to the back of them which the clematis can
grow up ? you could plant the clematis in the planters and infill with herbs
and the like which you can eat and will smell really nice.

anyway, that's what I'm planning to do in a similar situation, hth :-)

In article ,
"salesguy" writes:

The issue is not letting damp into the blocks, they have a closed cell
structure and will not transmit damp through to the internal wall. You need

What? I guess you never got one wet. They act like a giant sponge.

Incidently, I read the recomendations on one of the manufacturer's
web sites recently. One surprising thing, initially at least, is
that they say never use a masonary drill. Use a HSS drill bit (no
hammer action) to create a clean parallel sided hole to take rawl
plugs. I used that tip recently, and got an excellent grip for a
reasonably heavy air conditioner (indoor half).

--
Andrew Gabriel

The issue is not letting damp into the blocks, they have a closed cell
structure and will not transmit damp through to the internal wall.

What? I guess you never got one wet. They act like a giant sponge.


Several times actually - I used to sell Thermalite. The outer surfaces do
take on water, through the exposed cells. Cut the block in half and the
water penetration is no more than 25-30mm.

We used to do a demo with two 'cups', one made from Thermalite and one from
a lightweight agg block - fill them with water and the Thermalite one would
not leak, whereas the l/w agg one....!

Also, the team at the Newbury factory once used an uncut cake of material
(roughly 2.5m x 1.5m x 1m) to make a raft for the local raft race - and it
floated!!!!


SalesGuy

salesguy wrote:

I used to sell Thermalite. The outer surfaces do
take on water, through the exposed cells. Cut the block in half and the
water penetration is no more than 25-30mm.

Thanks Salesguy, you've put my mind at rest about the internal wall.
Point taken about the render blowing, I hadn't considered that.

replying to Andrew Gabriel, skillbuilder.uk wrote:
Everyone assumes that aircrete is a sponge but at Celcon HQ they have an
office built of 9inch solid blocks with no render on it and the damp never
penetrates more than an inch or two. The face of the blocks has a kind of
weathered skin and they are fine.

--
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