No shellac will hold up to direct water for any length of time. I have no idea what Mike adds to his but I have found that the dewaxed flakes make a good sealer under Chambers Traditional Oil Finish. reduces hunitity exchange rate and therefor swellin and shrinking and the oil varnish protects from the rain etc."Dewaxed Shellac is necessary if the shellac will be used as a primer/sealer, undercoater or transitional coating.A Shellac seal coat (made with dewaxed shellac) may be topcoated by almost any other clear coating or with paint.(always test materials for compatibility in you application"I used the orange dewaxed shellac as a sealer in a highly diluted form.You don't want shellac on the surface of the wood. Only in the wood.I also used to use a hard steel burning tool after the last coat of shellac sealer. The pressure of the burnishing tools causes the shellac to melt and quickly solidify again. Smooth finish results.Shellac first came into Europe as a "gum resin" in the late 1600's. In India they had never used shellac as a spirit varnish. The shellac had always been applied on round things in a lathe. As the piece would spin they would hold a stick of shellac against the part. The frictional heating melted the shellac. This was then smoothed with scouring rush and then polished.So with the burning tool I was simply melting the shellac. This was a way of dewiskering a finish.A boiled oil or boiled oil varnish will not have good adhesion to shellac. Why it is used as a highly diiluted sealer. In the wood but not on the wood.The top finish of boiled oil or boiled oil varnish will resist liquid water. But water in the molecular form (humidity) will pass through it fairly easily. Fairly permeable. The shellac will transmit some moisture through the film of sealer. As moisture enters into the shellac film it causes it to swell. A point is reached in the selling where all of the pores are effectively closed off and no additional moisture will be transmitted through the film.So a combination finish of shellac under a boiled oil or boiled oil varnish limits stock moisture changes on a daily basis. NO finish can limit the seasonal changes in wood moisture content. But it is the rapid, and sometimes extreme, changes in relative humidity that can cause stresses in the wood that then cause the wood to crack.Shellac was used alone indoors. As a floor finish and on some furniture. It was easy toi refinish but would water or alcohol mark on furniture. On floors it would crack and chip if something heavy was dropped on it.E. Ogre