Exterior fixing into thermalite blocks - dampness?

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?

Reply to
Martin Pentreath
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The message from "Martin Pentreath" contains these words:

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.

Reply to
Guy King

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?

Reply to
Martin Pentreath

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

Reply to
salesguy

be concerned (in

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 :-)

Reply to
.

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).

Reply to
Andrew Gabriel

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

Reply to
salesguy

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

Reply to
Martin Pentreath

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.

Reply to
skillbuilder.uk

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