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Anyone else having issues with end-checking on KD Cumaru?

Tyler Morrison Aug 4, 2026 at 10:34 PM

I am currently wrapping up a 600sqft Cumaru deck in the desert heat of Arizona, and I am noticing some aggressive end-checking on a fresh batch of 5/4x6 KD boards. I am using Anchorseal immediately after every cut, but these boards seem to be splitting within 48 hours regardless. The moisture content is testing at 12 percent, which is standard, but the thermal cycling out here is brutal. I have never seen it this bad with this supplier before. Are you guys bumping up the wax treatment, or is it time to switch to a different sealant for these high-exposure installs? I have about 200 linear feet left and I don't want to deal with callbacks in six months because the ends look like a broom. Any advice on managing the expansion gaps or sealants would be appreciated.

2 Replies

Marcus WebbAug 16, 2026 at 10:34 AM

Marcus Webb here. AZ heat is brutal on Cumaru; 12% MC is tricky because it’s still aggressive. When you're dealing with that extreme thermal cycling, Anchorseal is fine, but you need to double-coat those ends. I usually wait 15 minutes after the first coat so it soaks in, then hit it again. Also, are you mitering or butting? I’ve found that transitioning to a loose butt joint with a 'spacer' board between ends helps manage that movement better than tight miters that just rip apart. If you have 200 feet left, shade the deck area with tarps during install if possible. It’ll slow down the shock and save your callback sanity.

Dana KowalskiAug 17, 2026 at 10:34 AM

Dana Kowalski here. I've been battling the same desert conditions, and honestly, Anchorseal can struggle with the rapid moisture flash-off in AZ. Try switching to a heavy-duty end grain sealer like Ipe Seal; it has a slightly higher solid content that seems to hold up better under that intense solar gain. Also, make sure you aren't installing boards that have been sitting in direct sun for hours before securing them. Keep your remaining stock under shade and mist them down slightly if the ambient humidity drops into the single digits. It sounds overkill, but it keeps the grain stable long enough for your fasteners to lock everything in.