Repairing damaged blockwork

[stevrosflatley]

Hello all. At the weekend I stripped the garage of a load of units the previous owner left behind. Behind some of them, I found a load of the thermalite type blocks had been hacked/ chipped away, this wall backs directly onto the kitchen and the damage is pretty extensive. Could this be fixed with a load of mortar repair type stuff slapped into the section or does it need something more extensive? Any advice greatly appreciated, thanks.

 

[RandomGrinch]

Blimey, it looks like they were attacking those blocks with spade bits...
....I would hide that by fitting some new units!

 

[conny]

I presume those bits of wood sticking through are your kitchen floor joists?
You need to make sure you don't potentially bridge any damp proof course so my actions would be as follows;

Fix a batten with the top edge level with the top edge of the lowest blocks, (i.e. the top edge of the dark ones). The batten needs to be such a thickness that, when you hold a vertical batten/spirit level across the gap, they are flush.
Mix up a mortar & cement mix, (4 mortar : 1 cement should be adequate), and fill up the gap with the mix.
Using a straight edge board/batten slide it up and down whilst working across from left to right, (or right to left which ever suits you), levelling off the filler. Allow to dry for a few days then remove the support batten fitted to the lower blocks.
If you are not putting anything against that wall you could always fit a bit of skirting to hide the lower blocks or just leave them and paint over when you re-paint the rest of the walls.
If that dark strip across the floor is damp proof membrane, then you can take the filler down to floor level. Just set the support batten on the floor, do the above and then remove the batten and fill in the slot left by the batten.

 

[stevrosflatley]

I presume those bits of wood sticking through are your kitchen floor joists?
You need to make sure you don't potentially bridge any damp proof course so my actions would be as follows;

Fix a batten with the top edge level with the top edge of the lowest blocks, (i.e. the top edge of the dark ones). The batten needs to be such a thickness that, when you hold a vertical batten/spirit level across the gap, they are flush.
Mix up a mortar & cement mix, (4 mortar : 1 cement should be adequate), and fill up the gap with the mix.
Using a straight edge board/batten slide it up and down whilst working across from left to right, (or right to left which ever suits you), levelling off the filler. Allow to dry for a few days then remove the support batten fitted to the lower blocks.
If you are not putting anything against that wall you could always fit a bit of skirting to hide the lower blocks or just leave them and paint over when you re-paint the rest of the walls.
If that dark strip across the floor is damp proof membrane, then you can take the filler down to floor level. Just set the support batten on the floor, do the above and then remove the batten and fill in the slot left by the batten.

Wonderful, clear concise advice. Very much appreciated, thank you!

 

[cdbe]

1. Unless it's shallower than it looks, you'll need to build up the render in thin layers over a few days or it'll slump off.

2. If they're lightweight (breeze blocks) you'll need to prime them with a few coats of PVA or they'll suck the water out of the render and it won't stick.

 

[stevrosflatley]

1. Unless it's shallower than it looks, you'll need to build up the render in thin layers over a few days or it'll slump off.

2. If they're lightweight (breeze blocks) you'll need to prime them with a few coats of PVA or they'll suck the water out of the render and it won't stick.

Thanks cdbe. I did wonder if adhesion would be a problem as the blocks are still quite crumbly if you get what I mean. Found out from the neighbour that the previous owner did this so he could fit his car in the garage!

 

[JohnD]

I found that plaster or render tends to crack over joist ends. They will expand when wet with the fresh mix and contract as they dry out. You can reduce moisture absorbency with a coat of oil-based gloss paint on the timber, and some expanded metal or small mesh nailed to the wall before rendering will reduce cracking.

Usually you can wrap joist ends with DPC or similar tacked on before building into a wall, but yours might be difficult to get at.

You can brush over the blocks with a wet slurry of PVA, water, cement and sand to bind the crumbly surface and improve adhesion. I'd do a couple of coats. Cement products need to stay damp for at least a couple of days to gain strength so you can spray with water first (this will also wash away some of the loose dust)

 

[RandomGrinch]

...I would be tempted to avoid the wet work and just attach some cement boards to neaten it up.

 

[stevrosflatley]

I found that plaster or render tends to crack over joist ends. They will expand when wet with the fresh mix and contract as they dry out. You can reduce moisture absorbency with a coat of oil-based gloss paint on the timber, and some expanded metal or small mesh nailed to the wall before rendering will reduce cracking.

Usually you can wrap joist ends with DPC or similar tacked on before building into a wall, but yours might be difficult to get at.

You can brush over the blocks with a wet slurry of PVA, water, cement and sand to bind the crumbly surface and improve adhesion. I'd do a couple of coats. Cement products need to stay damp for at least a couple of days to gain strength so you can spray with water first (this will also wash away some of the loose dust)

Thank you JohnD. Really appreciate you all taking time to reply and I think I am pretty clear about what the best plan of action is now. I should be able to get the the joists with a bit of dpc and I suppose if I cant get a tight wrap then it wont hurt having a go at it.

 

[stevrosflatley]

...I would be tempted to avoid the wet work and just attach some cement boards to neaten it up.

I did consider this but the width of the damage is probably about 4 or 5 ft so I was a bit concerned that it would affect the structural integrity somewhere over time, I am probably over thinking it but better to be safe than sorry I suppose.