Old timer told me to wet the forms before pouring, I thought he was crazy

When I first started out about 12 years ago in Phoenix, this guy named Walt who had been doing flatwork since the 70s kept telling me to hose down my wood forms before I poured. I figured it was a waste of time and the concrete would just be fine. First big job I skipped it on a 40 yard driveway and the forms sucked all the moisture out of the edges, left me with a bunch of honeycombing and weak spots I had to grind down and patch. Ever had a form dry out on you like that or was I just unlucky that day?

2 comments

2 Comments

abbyc331mo agoTop Commenter

Wait, is that really what happens? I used to think wetting forms was some old-school superstition too until I had a small sidewalk job blow up on me last summer. The wood ended up swelling and my edges looked like crap, had to chip out a whole section. I'm a believer now for sure.

troy_wilson81mo ago

The wood swelling thing is real but it's actually the opposite problem most of the time. You want to wet the forms so they don't suck the water out of the concrete too fast. Dry wood acts like a sponge and pulls moisture from the mix which screws up the hydration near the edges. That gives you weak crumbly concrete right at the surface. The swelling you saw probably happened because the wood was already wet when you poured and it expanded after. Wets forms are good but you gotta be careful not to oversaturate them. A light misting is all you need not a soaking.