How to repair crack in staircase wood

[John Neel]

In my staircase in a 3 inch wide board leading up and away from the newel post, there was a 4 inch crack maybe three times wider than what I would term a hairline crack. There is no strain on this wood, only normal expansion and contraction. This is essentially molding, but would take a lot of work to replace. The wood is painted white, I am repainting. When I examined the crack, I found it had been filled with calk. Removing the calk left a crack about 1/16 inch wide that appears to extend through the board, but is only visible to a depth of about 1/8 inch. The crack has been evident for years so the calk fix hasn't been 100% effective. In similar situations, I have used plastic wood and found it to last at least 6 years without the crack reappearing. I am hoping this painting will be the last I ever need to do here. I would appreciate any comments on the situation and any advice regarding the repair before painting.

[Malcolm Schweizer]

In my staircase in a 3 inch wide board leading up and away from the newel post, there was a 4 inch crack maybe three times wider than what I would term a hairline crack. There is no strain on this wood, only normal expansion and contraction. This is essentially molding, but would take a lot of work to replace. The wood is painted white, I am repainting. When I examined the crack, I found it had been filled with calk. Removing the calk left a crack about 1/16 inch wide that appears to extend through the board, but is only visible to a depth of about 1/8 inch. The crack has been evident for years so the calk fix hasn't been 100% effective. In similar situations, I have used plastic wood and found it to last at least 6 years without the crack reappearing. I am hoping this painting will be the last I ever need to do here. I would appreciate any comments on the situation and any advice regarding the repair before painting.

Use epoxy mixed with micro balloons as a filler. You can find micro balloons online or at any good boatyard, but I see you're in Atlanta- try a body shop supply. They make the epoxy thick like peanut butter and you spread it into the gap and then you can easily sand it after it cures. Add a bit of sawdust if you want a stronger joint. Other fillers like colloidal silica don't sand very well.

This will fix the crack and will help keep it from spreading.

[Doug Garson]

What is the advantage of micro balloons over plain old sander dust?

[Malcolm Schweizer]

What is the advantage of micro balloons over plain old sander dust?

Much easier to sand. Sometimes it is sold as "fairing filler." When you add sawdust to epoxy it can be very difficult to sand, but fairing filler/micro balloons are much easier.

[Doug Garson]

Good to know, thanks for the info. I've just used sander dust in the past, if the balloons make sanding easier I'll have to try them.

[Malcolm Schweizer]

Good to know, thanks for the info. I've just used sander dust in the past, if the balloons make sanding easier I'll have to try them.

It makes the mix turn a very unnatural brown. Although it does kind of match mahogany, this is more for areas where you plan to paint. Mix it to the consistency of creamy peanut butter. It will drip and sag when fresh. I mix small batches and let it cure ever so slightly before applying if putting it on a vertical surface. It's a combo of science and gut instinct as to how long to wait before applying. For flat surfaces it doesn't matter. If the crack goes all the way through then tape the bottom with plastic packing tape and then fill it with the mix. Epoxy won't stick to it. I have a glue-up curing right now and the sawhorses are covered in packing tape so they don't get stuck to the epoxy.

I use wood flour (sanding dust) as well. I keep it in separate containers by color. Different dust makes different colors. Teak turns almost black. Pine turns mahogany/aged cherry color. I do use wood flour sometimes to fill small gaps that are going to be visible.

For a structural joint, use colloidal silica and/or glass fibers. Don't use it where you might want to sand. It's good for reinforcing joints like a butt join. I use this mainly for repairing fiberglass boats.

[Charles Lent]

You might also consider Bondo, since it will be painted over. I have fixed weather cracks in window sills with Bondo. As long as the paing keeps the moisture out of the wood, Bondo has held up very well.

Charley

[John Neel]

I had the epoxy and dust, so I did that. It worked very well. Now I just need to wait 20 years to see how it holds up.

Thanks to all how commented and advised.

[Charles Lent]

I frequently use Bondo to fill screw countersinks and voids in cabinets that will be covered with high pressure laminate. I make exhibits for science museums, and if a void is left under the laminate, eventually some kid will find it and punch a hole through the laminate. The Bondo prevents this, and it's easy to sand and flexible enough to move with the wood. I know you have fixed your crack with epoxy and sawdust, which should also work well if the epoxy choice remains flexible after it cures, but next time consider using Bondo. It's been my number one choice for crack and hole filling in any project that will be painted or covered with laminate.

Charley