Trapout advice

[Black Comb]

I'm doing a trapout in a larder wall - they are entering and leaving via the air grid.

I've made a box similar to the one shown recently in a Beecraft article and also Muswell's post a while ago using a foam pad (with hole) pushed against the wall. Problem is they are still getting in and out of the nest as the wall is an old one made of rough slate so it's difficult to seal. Additionally there is a creeper growing up the wall and duck tape has proved useless in this constant torrential rain.

Any suggestions?

 

[Rosti]

Expanding foam with a bin liner placed over the top and gaffa taped until dry. The risk is the residue left on the wall afterwards, it will wire brush off but with some effort and some risk of residual surface damage to the wall.

Property owners call I guess.

 

[Viddy Green]

To avoid any staining on the wall try spraying the expanding foam into a plastic bag or bin liner. As long as it has the right shape it should hold.
For horizontal surfaces I use plastic bags half filled with water to plug up any gaps.

 

[Rosti]

spraying the expanding foam into a plastic bag or bin liner. As long as it has the right shape it should hold.

Yeah! I was going to say that!

Viddy has been my KISS 'general construction skills' mentor for sometime, I am clearly not quite ready for the exams yet

 

[Black Comb]

Thanks.
Will give this a try.