Thread: Fence post crack repair

A lot depends upon what you want the post to look like after the repair.

Assuming that you want the post to look like new.

If you can clamp and close up the crack, using A and B may suffice. But it probably crack again. It might be better to use an epoxy that will fill gaps rather than a waterproof glue but still clamp.

If you use a chisel or router to cut a groove to fit the galvanized strap might be the most aesthetically pleasing solution. Fill around the strap with caulk or plastic wood. Then paint. However I think that the evidence of the split will rear its ugly head eventually.

Another method may be to just replace the entire post and thoroughly seal the end grain after the repair is completed.

Good luck.

Waterproof glue and a couple of bugle head screws wacked in from behind should do the job. If you countersink the head just below the surface a bit of builders bog will cover up the evidence. If its easy just replace the post.

Letaage,

I'm guessing that the timber they used was still a bit green when the fence was built. As the timber continues to season (naturally dry out) the post is probably going to keep cracking. You could try to glue/screw/strap/etc the top of that fence post, but the fact is the timber will continue to loose moisture content until it reaches equilibrium with the atmosphere. When timber looses moisture content as it dries out, the cells in the timber shrink, and incredibly high forces are generated inside the piece of timber as it shrinks - evidenced by the extent of the crack that has appeared so far. Can you image in the force you'd have to apply if you wanted to create that split yourself? Even with all the fastenings and glue, I believe that the crack will probably continue to grow, and may tear the timber at the glue joint, or tear the fastenings out of the timber.

As we can see a gate latch on the side of the post in the photo, it seems that this post is on the end of a fence run at a gate opening. That position makes the prospect of replacing the fence post a relatively easy job - much easier than removing and replacing a post in the middle of the fence run. Due to the paint, we can't tell from the photo what species of timber was used in that post. As it's a fairly new fence, I'd guess it was treated pine, but it could be a hardwood (probably treated, depending on the species). Treated pine is often still has a fairly high moisture content when on the shelves at the suppliers, so can be problematic in use.

When selecting the timber to replace that post, you want to select a well seasoned (dry) piece of timber. Bunnings or similar should have something suitable. If you select treated pine, then unless you've got a moisture meter, you won't be able to tell how dry (well seasoned) the treated pine is - so my recommendation would be to avoid treated pine.

I think that the best choice would be Kiln Dried H4 Treated Hardwood. Because it has been kiln dried, if it's not cracking when you buy it, no new cracks should appear as the timber ages. There may be some old existing cracks in the first 25 mm at each end of the length of timber - those cracks formed during the kiln drying process - just trim off the end 25mm or so untill you expose uncracked timber. The H4 rating means that the chemical treatment makes the timber suitable for outdoor use, in contact with the ground. Use a dust mask when sawing the timber as the chemicals in the saw dust are not healthy. Depending on your region, the locally supplied H4 treated hardwood may also be a termite resistant species (Forest Red Gum, etc).

The hardest part of replacing that fence post will be cutting the two mortices in the side of the post to accommodate the top and bottom fence rails. The H4 treated hardwood will be tough to cut. You'll need a sharp drill to rough out the mortices, and then a sharp chisel to square up the mortices, and you'll need to sharpen the chisel regularly. A sharp hand saw ($20 from a Hardware store) will cut the post to length. In the photo, it's a bit hard to tell whether the top of the post is cut level or not. In any case, it's better practice to cut the top at an angle to help the water run off the end of the post. A flat topped post allows the water to pool on the top and the end grain on top of the post will soak in, which will eventually cause decay etc. Some people cut the top of the post at 45 degrees, other people get fancy and cut a pyramid style top. The style doesn't matter - the goal is to allow the water to run off instead of pooling.

I hope that info helps.

Regards,

RoyG

I don't think you need to replace the post unless you want to as it appears to be in a good condition other than the crack.
If I were you I would inject a pouring type of epoxy into the crack with a syringe. You can get syringes easily on ebay. if the spout of the syringe is too big to fit into the crack, then I would drill holes with the appropriate diameters along the crack from the side pointing downwards and from the top. Lightly clamp the post while the epoxy cures. The crack occurred as the post was trying to relief its internal pressure. Forcing large cracks to close will put the stress back into the timber and may lead to cracking elsewhere.

Go cheap! Pour waterproof glue down it, such as Titebond3 (available Masters). Suck the glue right down/in with a vacuum cleaner nozzle. Clamp it tightly shut for >24 hours. Crush it closed!

Sand and repaint.

Epoxy as recommended above will work too

Plan B. this looks just like the fence I had at a semi-detached in Mosman. It was simply two bits of timber glued together. The railings were notched out and they nailed two bits together over the rebate to make the "post". It was the way back in the days when Mosman was "cheap"

I'd do the glue still, but I'd predrill a hole on both sides for screws. These can be bogged over later.

The trick you want is to ensure the screw acts as a winch to draw/close the gap, so you must follow these instructions precisely....

-- grab some long treated screws from the hardware, such as 60mm (e.g. Buildex Treated Pine NeedlePoints. Size 8, 10x50mm. The thread is aggressive). The thread will be about 4.5mm but the "core" of the screw will be about 2 (or 2.5mm). Drill this small hole right in, but not all the way through, in several neat places.

-- drill another hole the same size as the thread (say 4.5mm) right up to the crack (i.e. half way). This hole size must be goldilocks. If its too big the head of the screw will suck itself down the hole. You don't want that.

-- the head of the screw will act as a lever as its tightened. The larger hole acts as the "washer" and the screws thread wont bite, but the end/rest of the screw engages with the other side of the post and draws them both closed, centering on the gap.

This screw method will apply considerable continuous force on both sides of the post not allowing it to split in the future. Two either side will grip like The Hulk. Still glue it though. It will also need some bog to fill where the heads of the screws are inserted.

Looks like the fence could do with a repaint anyway

post.JPG

Thanks for all the helpful advice everyone!

Sounds like glue and screws might work, I have some Titebond IIII but epoxy might be better, I will have to see if I can find some, I think I will need a lot!

I have no idea how old the fence is or what wood it is, the previous owners would have been the last to touch it. The house is heritage listed and some of the verandah posts look original (or so I have been told by someone in the council) so it could be up to 130 years old.

But I doubt it is that old because it has been concreted in and that looks relatively new, and the concrete is part of the reason I'd rather try and repair than replace.

And yes the whole fence does need a repaint, I want to fix and patch it all before I paint. The prep work is always the worst part of painting!

Assuming that simple replacement isn't an option, I'd go for a more 'mechanical' method to restrain things. Personally, I'd probably use Sikaflex or similar as a sealer, then use a couple of galvanised cup-headed coach bolts to pull it together. One at the top and one around 1/3-1/4 the height of the post down.

Whatever I used to fill it, I'd want it to be pretty much waterproof. ie. not a PVA. I'd just pump it into the crack, tighten the bolts, wipe away the squeeze-out and paint over as soon as practical.

Glue alone will NOT stop further cracking.

Fill gap with sikaflex, cramp up with a strong cramp, purchase a gang nail plate big enough for top of post, you may have to cut to size, use a large block of wood or lump hammer and fix plate to top of post, fill holes in plate with sikaflex and wipe smooth, remove cramp and paint

I've had similar cracks in hardwood gate posts and found the only solution is to use a heavy bolt & nut. About a half inch diameter. Countersink both sides. This should be enough to pull both sides together. Bog both sides and sand smooth. Fill any remaining gaps with bog (I prefer Plastibond) and waterproof with bituminous paint before undercoat & paint.
mick