Why is this happening?

[Plaster Guy]

Hello, well down here in little New Zealand we repeated the same mistake you guys were in not that long ago. There's close to a 5 Billion dollar repair problem when it come leaky homes over here now. However the building industry has made us install a 20mm cavity to deal with any possible leaks behind the cladding. This is not the silver bullet but it's gone a long way. NOW here's our latest problem.... homes that we have plastered with EIFS are showing stress lines right around the perimeter of the 40mm sheets only three months after completion. Large walls look like a patchwork quilt. The shrinkage lines are very straight and are only 5-7 mm wide but can be up to 6mm deep. It only seems to be on the studs and nogs but not in the center of the sheet. This is a HUGE problem but no one has taken the suppliers to task YET. What's making this happen ???

Cheers, Plaster Guy.

[kurt]

Well, moisture in some form. I'd be looking very hard at vapor retarders and vapor drive possiblities. Given the minimal description, it's kind of hard for me to wing anything accurately. Got any picturs?

How do you imagine water is getting into these assemblie?

[Jim Katen]

Hello, well down here in little New Zealand we repeated the same mistake you guys were in not that long ago. There's close to a 5 Billion dollar repair problem when it come leaky homes over here now. However the building industry has made us install a 20mm cavity to deal with any possible leaks behind the cladding. This is not the silver bullet but it's gone a long way. NOW here's our latest problem.... homes that we have plastered with EIFS are showing stress lines right around the perimeter of the 40mm sheets only three months after completion. Large walls look like a patchwork quilt. The shrinkage lines are very straight and are only 5-7 mm wide but can be up to 6mm deep. It only seems to be on the studs and nogs but not in the center of the sheet. This is a HUGE problem but no one has taken the suppliers to task YET. What's making this happen ???

Cheers, Plaster Guy.

I'm not sure that I understand how you're installing the EIFS from your description but it seems like you're installing 40mm thick sheets of foam over 20mm thick battens. How far apart are the battens? If they're far apart, maybe the foam sheets are simply tin-canning in & out and the joints crack in response to the stress. A 40-mm thick sheet of foam needs nearly continuous backing to prevent it from flexing.

- Jim Katen, Oregon

[kurt]

True. What's the specific foam substrate? EPS? If so, it could be flexing. When I look at that stuff, I tend to knee jerk to water........

40mm is a little over 1 1/2"; if it was XPS foam, it would be pretty stiff, though.

[RobC]

Hello, well down here in little New Zealand

Large walls look like a patchwork quilt. The shrinkage lines are very straight and are only 5-7 mm wide but can be up to 6mm deep.

It only seems to be on the studs and nogs but not in the center of the sheet. This is a HUGE problem but no one has taken the suppliers to task YET. What's making this happen ???

Cheers, Plaster Guy.

If I understand this correctly, you're building EIFS cladding over a rain screen system and three months later, ONLY 6mm deep cracks [:-bigeyes have appeared at the perimeter of the plastic insulation.

If your base/finish coats are 6mm thick then a 6 mil deep crack (1/4") would be considered a failure. If I had to guess, I'd blame thermal expansion and contraction of the underlying plastic insulation.

Also, the 6mm x 6mm cracks in the cladding will expose the plastic insulation to sunlight and eventually destroy the board. In short, the cladding is 'toast' and the recommended plan would be to start over and do it right the second time. Although I've never liked the EIFS concept, perhaps you might consider second generation EIFS.

Questions:

Are the cracks of similar size around the building or do they differ in size from one elevation to another?

Is a nog a furring strip?

[Plaster Guy]

Thanks guys for your answers, OK I'll try to describe how the system is put together. You have the studs at 600mm centers and nogs at 800mm centers. I've seen pics of the US framing and they tend to use full sheets of ply to cover the whole building. Not sure if you use the same method ? Anyway our framing ( apart from bracing sheets) does not use any ply at all. You install the building wrap and run 20mm x 50mm polystyrene battens down the 2 x 4 stud over the building wrap , thus creating that 20mm cavity. You then install one 100mm long batten on the nog either side of studs and along the bottom plate. Then fix a 40mm EPS sheet (1200mm x 2400mm) to the battens using a 22mm washer at 300mm centres. Then plaster away..... Since I wrote the last post we went over to a house I did 2 years ago and ,armed with a level, put it on the wall horizontally across the sheet join. In the middle there was a 15mm gap, decreasing to nothing 300mm either side of the join, ie: the join is dishing in 15 mm but as yet has not cracked the surface. The mystery is why is this only happening around the perimeter and not on the center studs or nogs ? We are heading back today to see if we can cut a sample out of the wall to see what's going on. The trade off is that the home owner gets his walls fixed up. We are even looking at the type of building wrap used. We have moved away from the old type of tar paper in 2002 and moved into wraps like tyvek. Is this part of the problem ? Who knows. I'll let you know is a couple of weeks what we find. Thanks to those who replied.

[Jim Katen]

Thanks guys for your answers, OK I'll try to describe how the system is put together. You have the studs at 600mm centers and nogs at 800mm centers. I've seen pics of the US framing and they tend to use full sheets of ply to cover the whole building. Not sure if you use the same method ? Anyway our framing ( apart from bracing sheets) does not use any ply at all. You install the building wrap and run 20mm x 50mm polystyrene battens down the 2 x 4 stud over the building wrap , thus creating that 20mm cavity. You then install one 100mm long batten on the nog either side of studs and along the bottom plate. Then fix a 40mm EPS sheet (1200mm x 2400mm) to the battens using a 22mm washer at 300mm centres. Then plaster away.....

It's like you're speaking in Greek.

As far as I can tell, a "nog" is the same as what we in the US call "blocking." It's a horizontal member that fits between the studs and is flush with their outer surface. Yes?

So, to translate into language that I can understand:

You've got 2x4 studs placed on 24" centers with horizontal blocking every 30". You've got what we call "brace panels" at certain locations but otherwise you have no sheathing on top of the studs. (In the US, we generally sheath the entire wall. Yet, we do occasionally do the brace panel thing and its very similar to what you seem to do.)

You cover the whole frame with paper and apply plastic furring strips over each stud and additional furring strips halfway between each stud, over the blocking. You run yet more furring strips around the perimeter.

You then install your 1-1/2" EPS and attach it on one-foot centers.

Since I wrote the last post we went over to a house I did 2 years ago and ,armed with a level, put it on the wall horizontally across the sheet join. In the middle there was a 15mm gap, decreasing to nothing 300mm either side of the join, ie: the join is dishing in 15 mm but as yet has not cracked the surface. The mystery is why is this only happening around the perimeter and not on the center studs or nogs ?

So, at the seams, your foam is deflecting inward about 1/2" over a 24" span. That's crazy. It's as if your studs are bowing as they dry. Do you used wet lumber or dry lumber?

- Jim Katen, Oregon

[Plaster Guy]

Thanks Jim , you are on the ball. Nogs = blocking , Battens = furring , however you use plastic and what we are using is polystyrene 50mm x 20mm strips. I was on the phone today to the ploy supply company and he made a good point. Since we only drive home the nail heads or washers down 5-10mm below the surface of the ploy any shrinkage in the ploy of 15mm would make the heads of the washers poke out of the fibreglass mesh coat , BUT there is nothing at all showing in the join , just the dishing. SO knowing this one would think that it must be in the framing. We will need to ask the owner if we can put a straight edge on the wall inside to see if there is any plaster board cracking....

Not sure what you mean by dry Lumber and wet ? Is this kiln dried and tanalized ? Thanks Jim good answer.

[kurt]

Sounds messy. EPS is pretty floppy. Could it be oil canning somehow?

I'd also be thinking of lumber moisture content. Tree farm lumber moves around a lot. Do you use tree farm SPF type material, or is it old growth stuff?

[hausdok]

Hi Guys,

If it will help, you'll find that about a year and a half ago I downloaded a number of different New Zealand Department of Building and Housing documents into TIJ's resource library.

Here are three that might help you understand what Plaster Guy is talking about more clearly.

Construction Cavities For Wall Cladding

Exterior Moisture Design Principles

Exterior Moisture Guide

If you guys are interested in exploring some interesting construction-related documents, visit the New Zealand Department of Building and Housing site and the BRANZ Ltd. sites. You can also obtain from Standards New Zealand a copy of the New Zealand Property Inspection Standard (SNZ 4306) that was first published in 2005 here; but it's pretty expensive.

ONE TEAM - ONE FIGHT!!!

Mike

[Jim Katen]

. . . Not sure what you mean by dry Lumber and wet ? Is this kiln dried and tanalized ? Thanks Jim good answer.

Well, if the lumber is green -- you cut down the tree, mill the wood, build a house with it and *then* allow it to dry -- then, as it dries, it distorts. Some studs bow in and others bow out.

On the other hand, if you dry the lumber before building the house, movement and shrinkage is much less likely.

- Jim Katen, Oregon