Do LP SmartSide joints need caulk?

[Brian Elfert]

I just had LP SmartSide installed on my house and I think it looks terrible due to the wide gaps at the joints with no caulk. The general contractor says the joints don't get caulk due to expansion. All of the installation instructions I read say to caulk the joints. The installers did put some flashing or something behind each joint to drain water away.

Should the joints in LP SmartSide have caulk in them?

[Mark Bolton]

They all show caulk as far as Ive ever seen. Print the sheet and make them go back and caulk.

[Brad Adams]

I have smart side on my house. I bought the pre-finished diamond kote smart side. They send matching aluminum covers to go between the joints. It must me caulked if you dont use the covers.

[Tim Offutt]

When we last installed LP smartside we used a plastic joiner tee. Just like what you would use with interior paneling but they were color matched to the siding. This siding was prepainted using the Diamond Coat process so it may have been furnished by the coater. It was easy to work with but I still prefer hardi-plank.

[Brian Elfert]

I have smart side on my house. I bought the pre-finished diamond kote smart side. They send matching aluminum covers to go between the joints. It must me caulked if you dont use the covers.

They did put some sort of matching metal piece behind the joint. I'm not sure if this is why they didn't caulk or not.

[Brad Adams]

No it's not behind. It's an aluminum t type piece that overlaps the joint, and allows the siding to expand and contract. There is a piece of soft flashing behind it to shed any water down above the next course. I'll take a picture in the morning and show what I mean.

[Richard McComas]

There's a bunch of youtube video on installing this siding. Might be worth you time to watch a few of them.

[Brian Elfert]

I am following up on this old thread. I am installing Smartside myself on the garage and I finally found where LP says it is fine to not caulk joints IF the siding is pre-finished at the factory and flashing is used behind the joint.

I am not using factory painted with my garage so I have to decide if I use caulk or the joint covers. I will use flashing behind each joint regardless if the joint is caulked or covered.

[Neil Gaskin]

Whether you use caulk or the joint pieces hit the cut edges with primer before you install. It would be worth a coat of primer on the back side as well prior to isntall. We repalce an awful lot of smart siding due to rot and deterioration.

I would recommend James Hardi cement lap over smart siding. the cost difference is not that much and it will last longer, hold paint better, and require less maintenance over time. It is a tad more expensive and more difficult to work with but a much better product overall.

If you use caulking use a good quality, not the cheap entry level acrylic latex. I would use a 50 year or "lifetime" acrylic latex at a minimum and would prefer OSI Quad or similiar cualking regardless of which siding product you use

[Brian Elfert]

Whether you use caulk or the joint pieces hit the cut edges with primer before you install. It would be worth a coat of primer on the back side as well prior to isntall. We repalce an awful lot of smart siding due to rot and deterioration.


Have you actually replaced any Smartside that was properly installed? Is the reason it was replaced due to lack of maintaining the caulk? If the caulk isn't maintained on cement board the siding may not get wrecked, but moisture intrusion could damage everything underneath.

I already have the Smartside delivered so I am moving forward with it. I may back prime the boards just at places near joints. The house has Smartside already.

[Neil Gaskin]

We have replaced/repaired Smart siding that was properly intalled however it is usually due to a lack of upkeep in painting and cualking. Smart siding is basically OSB with a coating over the face. The most typical problem is at horizontal joints particularly close to the ground or where water can sit.

What I usually see is delamination starting from the bottom of a piece or sheet. Problems at joints, windows, doors, corners, etc can be problems as well. This occurs because the bottom of sheets or laps is porus allowing moisture in, which cause the material to delaminate through swelling and freeze/thaw cycles. Part of this can be contributed to the way the house was paitned. In a lot of cases houses are sprayed, this can cause the paint to be applied well to the face but not to the bottom of the lap, leaving it open to moisture and not sealed. Same can be said for cut edges. If you spray the paint on, that is fine, but at least the first coat should be back-brushed to ensure the paint is worked into these areas.

If you brush out the paint, the same applies, brush the underside of the lap to work the paint in. If the house wrap and flashing is installed properly there is a much less likely chance for water to be a problem. In an ideal world the exterior clading of the building keeps all water out. In reality this does not happen due to lack of upkeep and attention to detail.

Smart Siding is not necessarily a bad product in and of it self, lack of upkeep is where most propblems start. keep up on the painting and caulking it should last fine.

[Alan Bienlein]

It's all in the install. My house has LP smart siding on it and when we did some remodeling this year with new doors and windows the siding I removed looked brand new on the back side. I had one spot that showed water infiltration and that was because they didn't flash the window opening properly.

I also built a small storage shed that's about 12' x 16' back in 2005 using the smart siding. All I did was caulk the joints. Never did paint it and it's still just as solid as day one when it was installed with no signs of deterioration.

I was sold on the product when I tried to knock a hole in it with a hammer to start a cut and couldn't do it. I thought it would have been easy to do since I've done that before on the hardie siding.

[Brian Elfert]

I am going to pre-paint all of my Smartside before I install it. That should ensure that all edges get covered. Sherwin-Williams clerk recommended painting with a 1/2 nap roller instead of a brush. I am using their Duration paint that I just picked up today with their 40% off sale. I plan to take the extra time to paint the back of the bottom row and all cut ends.