Repairing cracked render on marine ply substrate

Hello all,
3 years ago we had our hip roofed bungalow converted to a gable end with 4 rooms in dormer. The initial builder didn't complete on budget and walked off the job but before he disappeared his plasterer dis re-plaster all internal rooms to a good standard as well as the rendering of the gable end and rear dormer. These were done as wooden frame with marine ply rather than block (don't need to discuss that on here but am wishing we'd insisted on block now).

Problem: A number of cracks have appeared in render on gable end. It does not seem to have blown (consistent sound when tapped all over the gable and ground level). I think it is most likely due to thermal expansion an

Question: What should I repair the cracks with? If I use hard/rigid mix involving sand cement/Toupret or similar on marine ply will that just crack as the frame expands in summer & contracts in winter? Should I be using some sort of flexible filler, if so what? How should I finish? complete repaint job? Any suggestions?

Hopeful someone out there might be able to guide me
 

satan

Active Member
Today there is marine ply and there is marine ply.

Marine ply used to be a ply that people made boats out of and I think it may have had a 20 year life span possibly guaranteed?

To my great expense I purchased marine ply believing it would last 20 years. Cost me about 45.00 15 years ago. After less than 12 months the ply failed and was told the 'other proper' marine ply would have cost me 75.00 per sheet.

Apparently what I had been given was the marine ply that the builder use for making dormer windows and then plastering over it with expanded metal covering the ply first.

Sorry for all this but you may want to find out why your render/plaster has suddenly started cracking.

Plywood will not usually expand and contract.
 
Today there is marine ply and there is marine ply.

Marine ply used to be a ply that people made boats out of and I think it may have had a 20 year life span possibly guaranteed?

To my great expense I purchased marine ply believing it would last 20 years. Cost me about 45.00 15 years ago. After less than 12 months the ply failed and was told the 'other proper' marine ply would have cost me 75.00 per sheet.

Apparently what I had been given was the marine ply that the builder use for making dormer windows and then plastering over it with expanded metal covering the ply first.

Sorry for all this but you may want to find out why your render/plaster has suddenly started cracking.

Plywood will not usually expand and contract.
Thanks Satan
I'm thinking (hoping?!) we have the correct marine ply. Building control were very attentive (read picky) and saved us from a couple of issues that had not been complied with by the builder; not sure sub standard material would have got passed.

Good to know that ply won't expand/contract. Some of the cracks stem from from drilled holes. Others could possibly be attributable to impact of internal work when fitting carcasses for built in wardrobes & drawers?
 
BDEC exterior paint for cracked render. have a look at their web page.
Thanks Malc.
Looks like just the thing! Looks like I'll wait for warmer weather and repaint the entire Gable & dormer. I do have one crack about 3m long that I think I will need to rake out and fill. I'm conscious the repair might show through the paint job. Any thoughts on whether Toupret or flexible filler is the best way to go?
 

satan

Active Member
The way I have seen plywood or board rendered is by covering it in expanded metal then plastering it or rendering it. Expanded metal is put over cracks in block work and then plastered/rendered so that the crack does not transfer through into the plaster/render. If it does it is only like a hair line crack.

I have see a passive house made out of board and rendered and there is no cracks.

What are your cracks. Hairline pencil cracks or bigger or is the render lifting?
 

malc

TPF Special Forces
Thanks Malc.
Looks like just the thing! Looks like I'll wait for warmer weather and repaint the entire Gable & dormer. I do have one crack about 3m long that I think I will need to rake out and fill. I'm conscious the repair might show through the paint job. Any thoughts on whether Toupret or flexible filler is the best way to go?

it does state on the bdec can do not fill the cracks just paint over them.
one of my pals painted his render and the only crack that reappeared was the one that he had filled.
 
The way I have seen plywood or board rendered is by covering it in expanded metal then plastering it or rendering it. Expanded metal is put over cracks in block work and then plastered/rendered so that the crack does not transfer through into the plaster/render. If it does it is only like a hair line crack.

I have see a passive house made out of board and rendered and there is no cracks.

What are your cracks. Hairline pencil cracks or bigger or is the render lifting?
They're hairline/pencil for the most part. one slightly larger one (perhaps 2mm) stemming from a drill hole where a security light was retrofitted but it doesn't seem like the render is lifting.
 

satan

Active Member
If done correctly it would be unlikely that the plywood would move and cause cracking. As you say you were banging around inside and fitted other things to this wall?...........if so that may have done some damage as the render does not have any strength. You dont see the cracks straight away, they always appear later.

It sounds not much to worry about and only cosmetic at present.

Worse thing that can happen is in future it needs replacing.
 
If done correctly it would be unlikely that the plywood would move and cause cracking. As you say you were banging around inside and fitted other things to this wall?...........if so that may have done some damage as the render does not have any strength. You dont see the cracks straight away, they always appear later.

It sounds not much to worry about and only cosmetic at present.

Worse thing that can happen is in future it needs replacing.
Thanks for your insight Satan. Reassuring, the good lady of the house is more likely to be convinced if she reads this!
Cheers:maraca:
 
D

Deleted member 32554

Guest
Make sure your wife's favorite plant pots not underneath
 

Gibbo

Well-Known Member
The way I have seen plywood or board rendered is by covering it in expanded metal then plastering it or rendering it. Expanded metal is put over cracks in block work and then plastered/rendered so that the crack does not transfer through into the plaster/render. If it does it is only like a hair line crack.

I have see a passive house made out of board and rendered and there is no cracks.

What are your cracks. Hairline pencil cracks or bigger or is the render lifting?
Should be riblath with building paper behind no wonder its cracked
 
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