Pumping Cavity Walls

mise_mise

Hi. I'm hoping someone can help/advise on the following.

My house has been built five years this month. The wall construction consists of 100mm outer leaf, 60mm kingspan cavity insulation, 50mm cavity, 100mm inner leaf block and 50mm insulated plaster board on the inside walls.

When the builders attached the insulated plasterboard, they drilled the plug holes through the plasterboard and inner leaf block. My problem is, where the aluminium plugs are attaching the board to the wall, I have pale black spots coming through my paint. I presume it's from the cold air in the cavity hitting the aluminium plugs creating a cold bridge, or is it something else? The problem does get worse in the winter.

Would pumping the cavity stop this? Would pumping the cavity help retain heat or is it worthwhile with what I've already done??

Your help would be much appreciated. Thanks

BryanF

Is it an exposed site ?
How is the houses ventilated?
To answer your question pumping would worth looking in to. But If this much thought was put into the wall insulation where will the next cold spots appear? Around windows/ floor level/ ceiling wall junctions/corners ?

cyfac

The problem with the plugs is a cosmetic one prior to skimming they should have been sprayed with what is called BPM spray costs about 14euros a can a whole house would need about 6 cans. I know this because it hapened to myself on my first house but not on the second Bryan F is right if u think its mould u would have it around the window opes unless you applied air tightness here on ur build

MicktheMan

mise_mise wrote: »

1.Would pumping the cavity stop this?
2.Would pumping the cavity help retain heat or is it worthwhile with what I've already done??

1. Imo. no. You already have insulation boards in the cavity.
2. Depends on the primary heat loss mechanism but probably not.

The discolored spots on the walls is a sign of an in-balance in the heating/ventilation/moisture load of the house. You need to address this to solve this problem.

mise_mise

Thanks for the information lads.

Byran F - I've seen mould between my oak window boards and the window in the bedrooms. One of the boards get a bad hit every winter. I thought it was the cold air in the cavity hitting warmer material.

cyfac - You managed to get it right the second time! I doubt I'll go that far. A lot of improvement on site in five years! A painter I got after one year in the house told me he could sort it with some oil based paint over the spots. We did see an improvement at the beginning, but, they did return!

How would I go about fixing the in-balance? Would there be any benefit in pumping cavity to keep heat in house or would I get my value out of it?

Thanks again.

tedimc

A family member has had the same problem and his painter tried stain block over the dark spots. It has worked so far, but I believe the problem will return.

My understanding is that you have 2 possible courses of action which you could do one or both.

Pump the remaining space in the cavity - however I don't think bead is an option for you as it's impact will be limited with the existing insulation. I've got mine pumped with walltite and am very happy with it. This may also help around the windows.

The other option is to fit a heat recovery ventilation unit of some type to reduce the amount of condensation hitting the cold spots. This is the approach my relative is taking as his cavity is fully pumped with bead.

I believe this is a common problem and that the thermally broken plastic fixings are better at avoiding this issue.